D2.1 - REQUIREMENTS BASELINE - UV - Uni Stuttgart...2018/05/31 · Del. No D2.1 Part 1 Title Requirements Baseline - UV Lead Beneficiary “MPG” Nature “Report” Short Description

D2.1 - REQUIREMENTS BASELINE - UV

Version 1.0

31.05.2018

Status: Released

ESBO DS Requirements Baseline - UV Version: 1.0

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Deliverable

H2020 INFRADEV-01-2017 project "European

Stratospheric Balloon Observatory Design Study"

Topic: INFRADEV-01-2017 Design Studies

Project Title: European Stratospheric Balloon Observatory Design Study –

ESBO DS

Proposal No: 777516 – ESBO DS

Duration: Mar 1, 2018 - Feb 28, 2021

WP WP 2 Del. No D2.1 Part 1 Title Requirements Baseline - UV Lead Beneficiary “MPG”

Nature “Report”

Short Description This document contains the top-level user requirements that

shall be fulfilled by the infrastructure.

Dissemination Level “Public”

Est. Del. Date 31/05/2018

Version 1.0

Date 31.05.2018

Status Released

Authors T. Müller, [email protected], MPG-MPE

P. Maier, [email protected], USTUTT

B. Stelzer, [email protected], EKUT

K. Werner, [email protected], EKUT

L. Hanke, [email protected], EKUT

Approved by P. Maier, [email protected], USTUTT


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TABLE OF CONTENTS

LIST OF ABBREVIATIONS AND DEFINITIONS ................................................................. 3

REFERENCE DOCUMENTS ..................................................................................................... 3

1 INTRODUCTION .................................................................................................................... 5

2 SCOPE ...................................................................................................................................... 5

2.1 Scope of the Requirements Baseline ......................................................................... 5

2.2 Scope of this Document ............................................................................................ 6

3 NEEDS AND REQUIREMENTS LOGIC ............................................................................ 6

3.1 General Needs and Requirements Logic ................................................................... 6

3.2 Needs and Requirements Levels covered in this document ...................................... 8

4 SCIENCE CASES AND NEEDS ............................................................................................ 8

4.1 Science Goals / Objectives ........................................................................................ 8

4.1.1 Search for variable hot compact stars .................................................................. 8

4.1.2 Detection of flares from cool dwarf stars ............................................................ 9

4.2 STUDIO Mission Statement ................................................................................... 10

4.3 Scientific Needs ....................................................................................................... 10

5 STUDIO REQUIREMENTS ................................................................................................ 10

5.1 Terms and Categories .............................................................................................. 10

5.2 STUDIO Scientific Requirements ........................................................................... 12

5.3 STUDIO Functional Requirements ......................................................................... 13

5.4 STUDIO Operational Requirements ....................................................................... 14

5.5 Studio Interface Requirements ................................................................................ 15

5.6 Studio Environmental Requirements ...................................................................... 16

5.7 STUDIO Physical Requirements ............................................................................ 17

6 ADD-ON SCIENCE NEEDS AND REQUIREMENTS ..................................................... 17

6.1 Add-On Mission Statement ..................................................................................... 18

6.2 Add-On Instruments Requirements ......................................................................... 18

7 PRELIMINARY TECHNOLOGY DEMONSTRATION PROTOTYPE NEEDS ......... 18

7.1 Precise Image Stabilisation System ......................................................................... 19

7.2 Soft Landing Technology ........................................................................................ 19

7.3 Modular and Scalable Gondola and Subsystems .................................................... 20


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LIST OF ABBREVIATIONS AND DEFINITIONS

Abbreviation Definition

AO Adaptive optics

BLAST Balloon-borne Large Aperture Submillimeter

Telescope

CBE Current Best Estimate

DH Detector Head

DLR German Aerospace Center

ESA European Space Agency

ESBO DS European Stratospheric Balloon Observatory

Design Study

FEE Front-End-Electronics

FIR Far-Infrared

FWHM Full Width Half Maximum

HV / HVPS High-Voltage Power Supply

(Hochspannungsversorgung)

PDR Preliminary Design Review

NASA National Aeronautics and Space Administration

NIR Near Infrared

SOFIA Stratospheric Observatory for Infrared

Astronomy

STUDIO Stratospheric Ultraviolet Demonstrator of an

Imaging Observatory

TBC To be confirmed

TBD To be determined

TDR Telescope Design Review

UV Ultraviolet

WD White Dwarf

REFERENCE DOCUMENTS

[RD1] ORISON - innOvative Research Infrastructure based on Stratospheric

balloONs. Technical and Functional Report. 30 November 2016.

[RD2] ORISON - innOvative Research Infrastructure based on Stratospheric

balloONs. State of the Art and Market Offer Report. Version 1.2. 29

January 2018.


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[RD3] Fuhrmeister et al. (2011). Multi-wavelength observations of Proxima

Centauri. Astronomy & Astrophysics, Volume 534, id. A133.

[RD4] Berkefeld, T. et al. (2011). The Wave-Front Correction System for the

Sunrise Balloon-Borne Solar Observatory. Solar Phys, 268, 103-123.

[RD5] Shariff, J.A. et al. (2014). Pointing control for the SPIDER balloon-borne

telescope. Proc. SPIE, 9145, id. 91450U.

[RD6] Pascale,E. et al. (2008). The Balloon-borne Large Aperture Submillimeter

Telescope: BLAST. Astrophys. J. 681 400.


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1 INTRODUCTION

The Requirements Baseline contains the top-level user needs and requirements as defined

for the infrastructure to be developed, upon which all subsequent development within ESBO

DS will be based. It thereby summarizes and documents the work performed under WP2,

“Detailed Science Case Analysis”.

2 SCOPE

2.1 SCOPE OF THE REQUIREMENTS BASELINE

The purpose of the Requirements Baseline is to document the needs and requirements of

scientific users with regard to the ESBO infrastructure, i.e. the first / second level of the

requirements hierarchy as also further described in chapter 3 of this document. Detailed

technical requirements on the system level and below are foreseen to be documented in

further Technical Requirements Specification documents.

User needs and requirements have been defined with regard to four aspects of the ESBO

DS project, and mirroring the four tasks within WP2:

o User needs and requirements for UV science, i.e. already relevant for the prototype

development within ESBO DS;

o User needs and requirements for near infrared (NIR) science, including exoplanet

science, i.e. relevant for the mid-term platform of ESBO;

o User needs and requirements for far infrared (FIR) science, i.e. relevant for the long-

term platform of ESBO;

o User needs in terms of operation.

The structure of the Requirements Baseline follows these four categories of needs and

requirements. As there are significant differences in the degrees of detail to which needs and

requirements of these four categories are known at this time (e.g. for UV science, system

level technical requirements have been identified already), the requirements baseline is

implemented as a series of three documents:

o D2.1-1 Requirements Baseline – UV

Contains detailed scientific user requirements as well as system level technical

requirements already identified and relevant for the prototype development within

ESBO DS;

o D2.1-2 Requirements Baseline – NIR & FIR

Contains descriptions of the driving science and scientific needs as well as

requirements to the degree known at this point for the two mid- and long-term

platforms currently envisioned for ESBO;

o D2.1-3 Requirements Baseline – Common Operational Needs

Contains user needs of the scientific community regarding the infrastructure’s

operational concept beyond the scientific needs of each science case and applicable

to all three scientific areas / envisioned flight platforms.

Particularly parts 2 and 3 of the Requirements Baseline are, to large extents, based on

findings of the ORISON H2020 project.


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2.2 SCOPE OF THIS DOCUMENT

This document – the Requirements Baseline – UV – covers the user needs and requirements

for UV science, which will be relevant for the prototype development within ESBO DS. As

the UV science cases are already well defined, the document includes

o A description of the UV science cases and their scientific needs;

o The detailed scientific user requirements of the UV science cases;

o The technical requirements on system level.

In addition to the requirements related to the UV science cases, this document also includes

other user requirements relevant to the prototype development, particularly those derived

from the concept of add-on platform science opportunities and those for the proof-of-concept

function of the prototype as far as they have already been identified.

A further description of the different hierarchical levels of needs / requirements covered in

this document is included in chapter 3.

The prototype mission was assigned the mission name “STUDIO” (Stratospheric Ultraviolet

Demonstrator of an Imaging Observatory) so that the mission name will be used

synonymously throughout the rest of this document.

3 NEEDS AND REQUIREMENTS LOGIC

3.1 GENERAL NEEDS AND REQUIREMENTS LOGIC

Figure 1 shows the general flowdown of needs and requirements within the ESBO

DS project, limited to the highest levels as relevant for this report. For further details on the

requirements flowdown, please consult the System Engineering Plan (D1.4).

Definition of “user”

As ESBO is envisioned as an infrastructure primarily for astronomical (and via the add-on

platform instruments also others) scientific observations, the “user” in the case of ESBO /

ESBO DS is always the scientist who will exploit the infrastructure for scientific research.

As ESBO foresees different kinds of usage, however, a distinction of different types of

scientific users needs to be made as they are understood within this document:

o The most general interpretation of “user”, mostly relevant to parts 1 and 2 of the

Requirements Baseline is the astronomical community (or parts thereof) that requires

or desires certain observational capabilities / means to further scientific research.

This interpretation of “user” underlies the identification of the driving science;

o More specifically and particular to the kinds of usage foreseen for ESBO, the user

can be a scientist / scientific group that wants to fly an own instrument on ESBO, or,

o A scientist / scientific group that wants to use an existing instrument on ESBO for

an observation.

General Needs and Requirements Logic

The following graph and paragraphs describe the general hierarchical logic of needs and

requirements. The general description is followed by an indication as to which elements of

the hierarchy are covered in this particular part of the Requirements Baseline. This indication

is included in each part of the Requirements Baseline.


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Figure 1: General flowdown of needs and requirements

User Needs

The User Needs describe in general terms what is needed or desired by the user. In the scope

of parts 1 (UV) and 2 (NIR and FIR) of this document, scientific user needs are described as

science cases / scientific applications to be coverable. In Part 3 (Common Operational

Needs), they are represented as general descriptions of operational concepts and details that

are important for the usability and suitability of an observatory infrastructure for the

scientific user.

The User Needs answer the question “What does the user need?” with a general, verbal

description, including the necessary context.

User Requirements

The User Requirements are a specification of the User Needs into concrete, preferably

quantified pieces of information.

They answer the question “What does the user need?” with concrete, quantified

requirements.

Technical Requirements

The technical requirements on the system level are derived from the User Requirements and

describe the top-level technical (functional, operational,…) requirements that the

infrastructure needs to meet in order to fulfill the user requirements. The answer the question

“What is needed form the infrastructure perspective to fulfill the User Needs and User

Requirements?

User Needs

User Requirements

Technical Requirements (System Level)

Lower Level Technical Requirements

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The lower level requirements are requirements on subsystems or components, derived from

the technical requirements on the next higher level. The Technical Requirements on System

Level represent the highest level.

3.2 NEEDS AND REQUIREMENTS LEVELS COVERED IN THIS DOCUMENT

Figure 2: Elements of the needs and requirements hierarchy covered in this part of the Requirements

Baseline

4 SCIENCE CASES AND NEEDS

4.1 SCIENCE GOALS / OBJECTIVES

4.1.1 Search for variable hot compact stars

Hot and compact stars are the rather short-lived

end stages of stellar evolution. They comprise the

hottest white dwarfs (WDs) and hot subdwarfs. A

significant fraction of them show light variations

with periods ranging from seconds to hours.

Among them are diverse types of pulsators, which

are important to improve asteroseismic models.

Others are members of ultracompact binaries (e.g.,

WD+WD pairs) and are strong sources of

gravitational wave radiation and crucial calibrators

for the future space mission eLISA. They are also

User Needs

User Requirements



Figure 3: Left: The globular cluster 47 Tuc as

seen by the Hubble Space Telescope. Right:

Faint, hot white dwarfs in this dense field are

identified by comparing visible light and UV

images (image credit: NASA).

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regarded as good candidates for the progenitors of thermonuclear supernovae. Furthermore,

compact binaries are formed via common envelope evolution and are important to study this

poorly understood phase of binary evolution.

Hot compact stars have so far been studied predominantly at high Galactic latitudes. Due to

their very blue colours they stick out in old stellar populations like the Galactic halo.

However, the density of stars at high Galactic latitudes is rather small and those objects

therefore very rare. Due to the 1000-times higher stellar density, the disc should contain

many more of those objects. Searches in the Galactic plane are desirable but the

identification of these faint stars is hampered by the dense, crowded fields. But not so in the

UV band. The hot stars are much easier to detect there, because their emitted flux is

increasing towards the UV, while the flux of the majority of other stars decreases because

of their lower temperatures. Surveying the Galactic plane with a UV imaging telescope will

uncover many new variable hot stars.

4.1.2 Detection of flares from cool dwarf stars

Red dwarf stars (spectral type M) are hydrogen-

burning main sequence stars like our Sun, but less

massive, cooler and less luminous. The large

majority of the stars in our Milky Way belong to

this group. Red dwarfs emit most of their radiation

in the visible and near-infrared wavelength

regions. Their UV and X-ray emission, despite

being energetically a minor contribution to the

overall radiation budget, ionizes material

surrounding the stars and is, therefore, of central

interest for the evolution of planets and other

circumstellar matter. This high-energy emission of red dwarf stars is highly dynamic.

One characteristic phenomenon are flares that

are stochastic brightness outbursts resulting

from reconfigura-tions of the stellar magnetic

field. During such flares, these normally faint

stars become much brighter for the duration of

minutes. A strong emission line of ionized

magnesium (Mg II) at 280 nm, covered by the

STUDIO instrument, can carry up to 50% of

the near-UV flux during flares. Up to now, no

systematic monitoring of “flare stars” exists.

Consequently, the flare occurrence rate is

unknown as well as the flare energy number

distribution. Particularly interesting for the

study of the physics of flares is their multi-wavelength behaviour (time lags, relative energy

in different bands). However, only a few simultaneous UV and optical observations of flares

exist. STUDIO enables such observations by monitoring (continuous over hours or multi-

epoch) of stars across the field or of individual prominent objects.

Figure 4: Relative size of a low-mass flare

star (image credit: NASA).

Figure 5: A flare observed from our nearest-

neighbour star Proxima Centauri. Green: optical

light, red: X-rays (from Fuhrmeister et al. 2011;

A&A 534, A133 [RD3]).


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4.2 STUDIO MISSION STATEMENT

The ESBO DS prototype mission, whose scientific component will be to study the

abovementioned science cases, will have the mission name STUDIO (Stratospheric

Ultraviolet Demonstrator of an Imaging Observatory). Its scientific mission statement is as

follows:

We will study the brightness variability of low-mass stars in two different stages of their

evolution. We aim to understand (i) their interior structure during the final evolutionary

stage (hot white dwarfs and subdwarfs) as well as their interaction with binary companions,

and (ii) the atmospheric dynamics driven by magnetic fields during the main-sequence stage

(M dwarf stars).

4.3 SCIENTIFIC NEEDS

We aim to detect variability of hot compact stars (white dwarfs and subdwarfs) as well as of

cool main-sequence stars in the ultraviolet band. We need a moderate field-of-view (30'x30'),

large enough to achieve a useful detection probability but not too large in order to avoid

source confusion. A number of about 15 fields shall be observed for ~2 hours each. We

estimate to find about 20 variable hot stars. About 1000 M dwarf stars out to 300pc are

located in 15 fields but their flare rate is rather uncertain and subject of the proposed study.

5 STUDIO REQUIREMENTS

5.1 TERMS AND CATEGORIES

Numbering of Requirements

The requirements are named according to the following scheme:

R-UV-SCI-XX

Where the first element indicates the type of requirement, the second element indicates the

science case it refers to, the third element indicates the topical area covered, and XX is a

running number. Tables 1 to 3 list the applied implementations of the first three elements.

Table 1: Abbreviations used for types of requirements

Abbreviation Meaning

R Scientific Requirement

RF Functional Requirement

RO Operational Requirement

RI Interface Requirement

RE Environmental Requirement

RP Physical Requirement


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Table 2: Abbreviations used for the originating science case


UV Original (variable hot compact stars) UV science case

FL Additional requirements from the flare-stars UV science case

Table 3: Abbreviations used for the topical area


SCI Scientific

POI Pointing

TEL Telescope

FLI Flight conditions

COM Communication

POW Power supply

DH Detector head

FEE Front-end-electronics

HV High-voltage power supply

Requirements and Goals

Requirements that will not be treated as design drivers are indicated as “Goals”, with the

first letter “R” in their designation being replaced by “G”.

Distinction of image acquisition modes

Additionally, in some cases a distinction is made between Mode 1 and Mode 2, referring to

different image acquisition modes of the UV instrument. These are:

o Mode 1

Events are integrated to images in the front-end electronics and sent to the payload

computer as complete images.

o Mode 2

Single photons are registered with a time stamp, integration to images is performed

on the ground.

Status and time of definition of requirements

The requirements table also indicates the current status of each requirement and, if

applicable, the time of final / next definition for the requirement (abbreviated as “Def.”).

The status indicators used are:

o Final

o TBC – to be confirmed

o TBD – to be determined

o CBE – current best estimate of an underlying property, i.e. final value TBD


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The time of definition either quotes a specific time or one of the following reviews:

o TDR – Telescope Design Review (August 2018)

o PDR – Preliminary Design Review (November 2018)

5.2 STUDIO SCIENTIFIC REQUIREMENTS

Wavelength and Colour Status Def.

R-UV-

SCI-01

Wavelength coverage

The primary UV payload shall provide imaging capabilities in the

wavelength band 180 to 330 nm

Final -

R-UV-

SCI-02

UV Filters

3 Filters required: Sloan u, GALEX NUV filter, fail safe hole;

filter changer to be provided by USTUTT (filter details to be

provided by EKUT; Filters procured by EKUT)

Final -

R-UV-

SCI-03

Visible channel complement

The payload shall allow complementary simultaneous imaging

capabilities in a visible channel. These shall offer the choice of

the following filter bands: Sloan g, r, i, z?, block, open

TBC PDR

Sky Coverage

R-UV-

SCI-04

The mission shall allow coverage of regions within the galactic

plane. (specific regions TBD)

TBD in observation plan

TBD PDR

R-FL-

SCI-05

The mission shall allow coverage of regions within the galactic

plane. (specific regions TBD)

TBD in observation plan

TBD PDR

Field of View and Resolution

R-UV-

SCI-06

UV payload field of view

The primary UV payload shall have a field of view of at least 30

x 30 arcmin

Final -

R-UV-

SCI-07

UV payload pixel size

The primary UV payload shall have a pixel size on the sky of not

more than 1.1 arcsec

Final -

G-UV-

SCI-08

Visible channel complement (Goal)

The visible camera shall provide complementary images with a

field of view of at least 8 x 8 arcmin

TBC PDR

G-UV-

SCI-09

Visible channel complement (Goal)

The visible camera shall provide complementary images with a

pixel size on the sky of not more than 1.1 arcsec

TBC PDR


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5.3 STUDIO FUNCTIONAL REQUIREMENTS

Pointing System Status

RF-UV-

TEL-01

Telescope elevation

The primary telescope shall be able to observe at elevation angles

between TBD deg (flexibility, determined by technical limitation)

and TBD deg (determined by reasonable length of flight train)

TBD TDR

GF-UV-

TEL-

02a

Image Stabilisation (Goal) – Mode 1

The PSF center on the UV detector shall be positionally stable to

less than 0.5 arcsec over the integration time of TBD s

(Await Modtran calculations; will be the longer one of the

flare/hot compact science integration time requirements)

TBD TDR

GF-UV-

TEL-

02b

Image Stabilisation (Goal) – Mode 2

The PSF center on the UV detector shall be positionally stable to

less than 40 arcsec.

Final -

GF-UV-

TEL-03

Pointing Accuracy

The pointing of the telescope line of sight shall be accurate to +/-

40 arcsec in both elevation and azimuth (uncritical)

Final -

RF-UV-

TEL-04

Pointing Knowledge

The sky position of the image center shall be reconstructable

without information from the UV instrument to within +/- 0.5

arcsec in both elevation and azimuth at a time resolution of 2 kHz

Final -

RF-UV-

TEL-05

Tracking velocity

The pointing system shall allow sidereal tracking.

Final -

RF-FL-

TEL-06

Integration time

The observation system shall allow for a maximum observation

time of 60 s for flare observations

TBC TDR

RF-FL-

TEL-07

Time resolution

The observation system shall allow for a minimum time

resolution of 60 s for flare observations matching time resolution

with visible instrument

TBC TDR

Telescope

RF-UV-

TEL-08

Instrument contamination

The telescope and optical bench shall be sealable to allow

protection of the optical elements against dust and other

contaminants during ground handling, launch, ascent and descent.

Final -

RF-UV-

TEL-09

Outgassing

Outgassing of the carbon composite telescope tube or other parts

within the optical system during launch or flight shall be avoided.

Final -


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RF-UV-

TEL-10

Mirror coatings

Standard aluminium mirror coatings are sufficient for the UV

instrument. Overcoating with SiO2 is allowed.

(TBC)

TBC TDR

5.4 STUDIO OPERATIONAL REQUIREMENTS

Balloon Flight Status Def.

RO-UV-

FLI-01

Transmission altitude

The observational pressure altitude of the balloon shall be at least

TBD km / shall allow at least access to transmission windows in

between 180 to 220 nm & 280 to 330 nm

TBD after Modtran simulations and THISBE measurement

crosscheck

TBD PDR

RO-UV-

FLI-02

Pressure measurement

Precise pressure measurement shall be taken during the flight to

allow precise reconstruction of the pressure altitude at the time of

observations.

Final -

RO-UV-

FLI-03

Telescope elevation

Observations for the hot compact stars science case shall take

place at elevation angles between TBD deg and TBD deg.

TBD after sky brightness Modtran simulations

TBD PDR

RO-FL-

FLI-04

Telescope elevation

Observations for the flares science case shall take place at

elevation angles between TBD deg and TBD deg to ensure

observability of the Mg II line.

TBD after sky brightness Modtran simulations

TBD PDR

Communication

RO-UV-

COM-

01

Scientific data downlink

The system shall be capable of downlinking at least one full frame

per instrument at each new field acquisition.

Everything else TBD in operation plan

Final

/TBD

- /PDR

RO-UV-

COM-

02

Payload operations and manual control

The baseline operational concept of the flight system shall rely

upon pre-scripted, pre-programmed observations that are executed

automatically with minimal external interference.

The system shall, however, allow full manual command at all

times.

Final -


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5.5 STUDIO INTERFACE REQUIREMENTS

Communication interface Status Def.

RI-UV-

COM-

01a

Data Rate – Mode 1

The communication interface shall allow science data to be sent

from the FEE to the payload OBC of up to 3.4 Mbit/s (t_int = 10s;

2k x 2k, 8 bit) (compression TBC)

Final -

RI-UV-

COM-

01b

Data Rate – Mode 2

The communication interface shall allow science data to be sent

from the FEE to the payload OBC of up to 12.6 Mbit/s (X & Y

coordinates, 12 bit each; time stamp, 20 bit; up to 300,000

events/s)

Final -

RI-UV-

COM-

02

Time support signal

The UV payload OBC shall receive an external support time

signal (preferably global GPS time) at least every 1 min.

Final -

RI-UV-

COM-

03

Data storage

The payload data storage shall be able to record the scientific data

produced during up to 30 h.

Final -

Power supply

RI-UV-

POW-

01

Voltage

The UV instrument (single power supply line) shall be supplied

by a DC voltage between 24 and 36 V.

Final

RI-UV-

POW-

02

Voltage stability

The voltage supply to the UV instrument shall be stable to within

24 & 36 V during operation.

Final

RI-UV-

POW-

03

Average power

The power supply shall be able to provide, via one single

interface, an average power of 25 W to the detector head, front-

end-electronics, and the high-voltage power supply (1 W DH, 21

W FEE, 3 W HVPS).

Numbers are CBE for the worst case, driven by the RAM. To be

measured with the integrated hardware.

CBE

Next

est.:

end

2018

RI-UV-

POW-

04

Peak current

The power supply shall be able to provide peak current of up to

TBD A to the detector head & front-end-electronics and of up to

TBD A to the high-voltage power supply.

(CBE: 2 A)

CBE Est.

end

2018


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5.6 STUDIO ENVIRONMENTAL REQUIREMENTS

MCP Detector Head Status Def.

RE-UV-

DH-01

Temperature Range

The temperature of the detector head shall not exceed the

following limits:

Operating: min.: TBD; max.: 60 °C

Inactive: min.: -40 °C; max.: 60 °C

TBC End of

May

2018

RE-UV-

DH-02

Temperature Stability

Temperature stability and temporal gradient of the detector head

are not critical.

Final -

RE-UV-

DH-03

Radiation shielding

No radiation shielding of the detector head shall be necessary.

Final -

Front-End-Electronics

RE-UV-

FEE-01

Temperature Range

The temperature of the front-end-electronics shall not exceed the

following limits:

Operating: min.: -44 °C; max.: 75 °C

Inactive: min.: -44 °C; max.: 75 °C (not separately tested)

(the critical element is the beetle chip; everything else is MIL

grade, with an operating range of -60 °C to 125 °C)

Final -

RE-UV-

FEE-02


Temperature stability and temporal gradient of the front-end-

electronics are not critical.

Final -

RE-UV-

FEE-03

Radiation shielding

No radiation shielding of the front-end-electronics shall be

necessary.

Final -

High-Voltage Power Supply

RE-UV-

HV-01

Temperature Range

The temperature of the high-voltage power supply shall not

exceed the following limits:

Operating: -20 to +60 °C (Tested)

Inactive: not supplied

Final -

RE-UV-

HV-02


Temperature stability and temporal gradient of the high-voltage

power supply are not critical.

Final

RE-UV-

HV-03

Radiation shielding

No radiation shielding of the high-voltage power supply shall be

necessary.

Final


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RE-UV-

HV-04

Condensation/water protection

The high voltage power supply shall, under all operation

conditions and circumstances, be protected against the intrusion

of water and against internal condensation.

Final -

5.7 STUDIO PHYSICAL REQUIREMENTS

Status Def.

RP-UV-

01

Mass

The payload structure shall foresee the accommodation of the

detector head & FEE with a mass of 3.75 kg (2.5 kg CBE+20%

conting.+25% sys. Margin, including cables) on the optical bench.

The gondola shall foresee the accommodation of the HV with a

mass of 1.375 kg (1 kg CBE + 10% conting. + 25% sys. Margin)

RP-UV-

02

Physical size (HV)

The gondola shall foresee the accommodation of the HV as

specified by the technical drawing in document STU-EKU-

DWG-1243-00.0000-vx.xx.

Final -

RP-UV-

03

Physical size (FEE)

The telescope assembly shall foresee the accommodation of the

FEE as specified by the technical drawing in document STU-

EKU-DWG-1242-00.0000-vx.xx.

(Current version is CBE, but no large changes are expected)

CBE PDR

RP-UV-

04

Detector assembly

The telescope assembly shall foresee the accommodation of the

detector assembly as specified by the technical drawing in

document STU-EKU-DWG-1241-00.0000-vx.xx.

(Current version is CBE, major changes, particularly of the

interfaces, are still expected)

CBE PDR

6 ADD-ON SCIENCE NEEDS AND REQUIREMENTS

In addition to the telescope instruments, the ESBO flight platforms will provide space and

support for add-on platform instruments. Those instruments could be nadir-viewing, side-

viewing, or not requiring a view at all. They can potentially cover a wide range of interesting

applications, from Earth observation and atmospheric research to research and tests under

analogue conditions for space or combined stress.

Providing these flight opportunities will allow a significant benefit to additional scientific

and technical communities at a small additional effort for ESBO flights.


Page 18 of 20

6.1 ADD-ON MISSION STATEMENT

The ESBO flight platforms will provide flight opportunities for add-on platform instruments,

not utilizing the main telescope, to cover a wide range of scientific and technical

applications.

6.2 ADD-ON INSTRUMENTS REQUIREMENTS

The following requirements were identified during the ORISON project to allow an effective

use of add-on platform instruments [RD1]. As the add-on instruments are not regarded as

design drivers, their requirements are expressed as goals.

Functional Requirements

GF-

ADD-

01

Pointing stability

The ESBO platforms shall provide pointing stability of +/- 100 arcsec or better

in azimuth for add-on instruments

GF-

ADD-

02

Single instrument mass

The ESBO platforms shall allow the installation of add-on instruments with a

mass of at least 4 kg for an individual instrument

GF-

ADD-

03

Total instruments mass

The ESBO platforms shall allow the installation of add-on instruments up to a

total mass of at least 20 kg.

GF-

ADD-

04

Telemetry

The ESBO platforms shall provide a limited downlink capability to add-on

instruments during flight.

GF-

ADD-

05

Power supply

The ESBO platforms shall provide limited power supply to add-on instruments.

Operational Requirements

GO-

ADD-

01

Exchange of instruments

The ESBO system shall allow the exchange of add-on platform instruments in

between flights.

7 PRELIMINARY TECHNOLOGY DEMONSTRATION

PROTOTYPE NEEDS

In addition to the scientific mission aspect, the ESBO prototype will also need to serve a

technology demonstration function, particularly for the following technologies:

o A highly precise and reliable astronomical image stabilization system for flying

platforms on different scales;

o Soft landing systems for scientific balloon payloads;

o Modular and scalable scientific balloon gondolas and subsystems.


Page 19 of 20

In the following, the background for each technology is shortly described, along with the

associated needs with regard to the prototype.

7.1 PRECISE IMAGE STABILISATION SYSTEM

In order to access the full potential of a balloon-borne stratospheric observatory it is

necessary to consider pointing control systems that enable stable performance close to the

diffraction limit. This is definitely a challenge on a moving platform that causes disturbances

in terms of structural deformation and vibrations. In addition, aerodynamic forces and the

rigid-body movement of the gondola itself have to be considered and possibly compensated

to achieve precise pointing. Other airborne platforms, e.g. SOFIA, aim for high image

quality to achieve its scientific goals, translating in a pointing requirement of 0.4 arcsec rms

image stability. The overall excitation level on a balloon-borne telescope at cruise altitude

(>20 km) is considerably lower than on a plane like SOFIA, however wind gusts and

pendulum motion of the gondola could pose possible challenges [RD4],[RD5]. Different

balloon missions have already shown that precise pointing is possible. The SUNRISE

mission mostly managed pointing stability of less than 0.04 arcsec rms [RD4] over a rather

long time window. However, the sun is a very specific bright source for tracking and

pointing, which is usually not the case other than in solar astronomy. Other astronomical

balloons aim at a pointing level of several arcseconds or arcminutes, e.g. BLAST [RD6] or

SPIDER [RD5], a balloon-borne polarimeter.

Ultimately, ESBO shall work with a large, 5-meter-class telescope in the far-infrared, e.g. at

the wavelength of the interstellar cooling line of singly ionized carbon (CII), λ = 158 µm.

Critical sampling of the diffraction limited point spread function λ/D = 6.5 arcsec requires

pixels of 3.3 x 3.3 arcsec2. As a rule of thumb, the pointing stability should be about 1/10 of

the pixel size, i.e. ~ 0.3 arcsec. The STUDIO pre-cursor mission in the UV requires a

pointing stability of 1 arcsec, which will be a good preparation for the final FIR mission and

for potential intermediately sized missions.

Similar to other airborne astronomy platforms, such precise attitude control will only be

achievable with a multi-stage design. STUDIO therefore foresees a two-stage

Needs

Demonstrate highly precise image stabilization for astronomical observations based on a

scalable and extendable two-step pointing system using a closed-loop inner stage with a

tip/tilt mirror and a tracking sensor.

7.2 SOFT LANDING TECHNOLOGY

All flight systems of ESBO will be designed to allow safe payload recovery and re-flight

with minimum turnaround efforts. This is a key element of the ESBO DS D2.1 Requirements

Baseline - UV concept that is crucial in making the operation as an accessible observatory

economically feasible. Safe recovery with minimal damage to the gondola and payload will

be achieved by the use of steerable parafoils instead of the typical round parachutes. The

adaptability of this technology has been demonstrated for lower-flying balloon payloads

from 30 km altitude by the U.S.-based company World View, with highly accurate flights

to the landing zone and structural landing loads on the payload considerably lower than the

structural loads during parachute opening. Similar developments are also under way in

Europe.


Page 20 of 20

Needs

Steered parafoil solutions can be procured as stand-alone systems, including the deployable

parafoil and an aerial guidance unit [RD2]. These systems can be installed on or above the

payload. The approach within ESBO DS is to procure such a system, to integrate it with the

prototype flight system and to demonstrate it with one of the first flights following the ESBO

DS project period. The prototype platform therefore needs to foresee:

o Ways to integrate the steered parafoil system into the flight train;

o Ways to potentially integrate parts of the steered parafoil system into the gondola;

o Potential structural implications for the gondola;

o Means to add “landing hear” and protection specific to landings with a steered

parafoil system.

7.3 MODULAR AND SCALABLE GONDOLA AND SUBSYSTEMS

Balloon gondolas are currently built specifically for single missions or mission sequences.

While some subsystems are available separately, they are not necessarily easily compatible.

This includes flight control and piloting systems, power systems, communication systems,

and the balloons themselves.

Needs

Demonstrate ways to provide standardized systems and interfaces, particularly including

systems vital for astronomical observatories (but also beneficial for other applications) such

as attitude stabilization.

D2.1 - REQUIREMENTS BASELINE – NIR & FIR

Version 1.0

31.05.2018

Status: Released

ESBO DS Requirements Baseline – NIR & FIR Version: 1.0

Page 1 of 21

Deliverable





ESBO DS


Duration: Mar 1, 2018 - Feb 28, 2021

WP WP 2 Del. No D2.1 Part 2 Title Requirements Baseline – NIR & FIR Lead Beneficiary “MPG”

Nature “Report”





Version 1.0

Date 31.05.2018

Status Released

Authors P. Maier, [email protected], USTUTT

B. Stelzer, [email protected], EKUT

D. Angerhausen, [email protected]

A. Krabbe, [email protected], USTUTT

L. Venuti, [email protected]

J., Alcala, [email protected]

1 External collaborator, Center for Space and Habitability, Universität Bern 2 External collaborator, Institut für Astronomie und Astrophysik, Universität Tübingen 3 External collaborator, INAF - Osservatorio Astronomico di Capodimon


Page 2 of 21

TABLE OF CONTENTS



1 INTRODUCTION .................................................................................................................... 9

2 SCOPE ...................................................................................................................................... 9



2.3 Coverage of the Needs/Requirements Logic ........................................................... 10

3 NEAR INFRARED SCIENCE NEEDS AND REQUIREMENTS .................................... 11

3.1 Exoplanet Atmospheres Transit Observations ........................................................ 12

3.2 Accretion in Young Stellar Objects ........................................................................ 13

3.3 Small Bodies ........................................................................................................... 15

4 FIR SCIENCE NEEDS .......................................................................................................... 17

4.1 Overview of the Current Situation .......................................................................... 17

4.2 FIR Science Areas and their Needs ......................................................................... 18

4.2.1 Surveys ............................................................................................................... 18

4.2.2 Discrete Sources................................................................................................. 18

4.2.3 Solar System ...................................................................................................... 21


Page 3 of 21



AO Adaptive optics


Telescope


EChO Exoplanet Characterisation Observatory


FIR Far-Infrared


HST Hubble Space Telescope

IRAS Infrared Astronomical Satellite

ISM Interstellar Medium

ISO Infrared Space Observatory

JAXA Japanese Aerospace Exploration Agency-

JWST James Webb Space Telescope

KAO Kuiper Airborne Observatory

MIR Mid Infrared

NASA National Aeronautics and Space Administration

NIR Near Infrared

PACS Photodetector Array Camera & Spectrometer

PMS Pre-Main Sequence

SOFIA Stratospheric Observatory for Infrared

Astronomy

STO Stratospheric Terahertz Observatory

TBC To be confirmed

TESS Transiting Exoplanet Survey Satellite

UV Ultraviolet

YSO Young Stellar Object

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[RD58] Hartogh, P., Lellouch, E., Moreno, R., Bockelée-Morvan, D., Biver, N.,

Cassidy, T., et al., Direct detection of the Enceladus water torus with

Herschel. Astronomy and Astrophysics, 532: L2, 2011.


Page 9 of 21

1 INTRODUCTION

The Requirements Baseline contains the top-level user needs and requirements as defined for the

infrastructure to be developed, upon which all subsequent development within ESBO DS will be

based. It thereby summarizes and documents the work performed under WP2, “Detailed Science

Case Analysis”.

2 SCOPE


The purpose of the Requirements Baseline is to document the needs and requirements of scientific

users with regard to the ESBO infrastructure, i.e. the first / second level of the requirements

hierarchy as also further described in chapter 3 of part 1 of this document. Detailed technical

requirements on the system level and below are foreseen to be documented in further Technical

Requirements Specification documents.



o User needs and requirements for UV (ultraviolet) science, i.e. already relevant for the

prototype development within ESBO DS;

o User needs and requirements for near infrared (NIR) science, including exoplanet science,

i.e. relevant for the mid-term platform of ESBO;

o User needs and requirements for far infrared (FIR) science, i.e. relevant for the long-term

platform of ESBO;




requirements of these four categories are known at this time (e.g. for UV science, system level

technical requirements have been identified already), the requirements baseline is implemented as

a series of three documents:



requirements already identified and relevant for the prototype development within ESBO

DS;


Contains descriptions of the driving science and scientific needs as well as requirements to

the degree known at this point for the two mid- and long-term platforms currently

envisioned for ESBO;


Contains user needs of the scientific community regarding the infrastructure’s operational

concept beyond the scientific needs of each science case and applicable to all three

scientific areas / envisioned flight platforms.

Particularly parts 2 and 3 of the Requirements Baseline are, to large extents, based on findings of

the ORISON H2020 project.


This document – the Requirements Baseline - NIR & FIR – covers the currently foreseen driving

science in the near and far infrared, the derived scientific needs, and partly the associated scientific


Page 10 of 21

requirements for the mid- and long-term platforms envisioned for ESBO. For both platforms, no

concrete instruments are known yet, so that this part of the Requirements Baseline rather serves to

collect and document potential driving science, based on which instruments (and platforms) will

be studied. It may thus well turn out that different instruments will be necessary / make sense to

study the different science cases.

For the NIR platform, a timeframe until a potential flight at the order of 5 years is currently

considered realistic. Within this timeframe, the development of technology is somewhat

foreseeable, so that it is sensible to already define more concrete requirements for the instruments.

For the FIR platform, a more likely timeframe is expected in the range of around 15 years. In this

case, it is more sensible to more generally assess the scientific needs & science areas of interest

within the FIR community. This will, particularly in WP 3 Infrastructure Analysis and WP 5

Conceptual Design, then be used as a basis for the exploration of different instrument options.

2.3 COVERAGE OF THE NEEDS/REQUIREMENTS LOGIC

As figure 1 illustrates, the content of this document focuses on the scientific needs from the user

perspective. Where possible, it also goes into the associated user requirements. Particularly for the

FIR part, these will be derived and documented in the subsequent work packages mentioned in

section 2.2, also following D3.1 (Concept presentation to scientific audience). Technical

requirements for the near infrared part of the infrastructure will also be derived and documented

within these following work packages. For the far infrared infrastructure, a set of general technical

requirements will be derived and different concept options explored within the abovementioned

work packages.

For a general description of the high-level flowdown of needs and requirements within ESBO

DS and a description of the different elements, please refer to Part 1 of the Requirements Baseline

[RD1].


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Figure 1: Elements of the needs and requirements hierarchy covered in this part 2 of the Requirements

Baseline

3 NEAR INFRARED SCIENCE NEEDS AND REQUIREMENTS

For the mid-term platform, we list three scientific areas that have been identified to be of particular

interest. While they all benefit from the mostly unobscured access to the NIR region in the high

stratosphere, it should be pointed out that the instrumental focus of the areas described in sections

3.1 and 3.2 is quite different to that of the scientific area described in section 3.3 (small bodies).

While most of the “small bodies” science cases require a very high spectral resolution (at the order

of R ~ 20,000 to 40,000), for the Exoplanets Atmospheres case (section 3.1) and the Young Stellar

Objects (YSOs) Accretion case (section 3.2), a spectral resolution below R = 1000 suffices. The

Exoplanets Atmospheres case furthermore has quite unique requirements to the instrument,

telescope, and platform with regard to photometric stability. While from the current point of view,

the Exoplanets Atmospheres case and the YSO Accretion case seem to be approachable by one

instrument, this will require confirmation during further in-depth study. This analysis will also

consider whether some of the spectrally less demanding “Small Bodies” cases might be coverable

by the same instrument.

It should furthermore be noted that while the focus of the ESBO mid-term platform so far has been

on science in the NIR, the analysis of the science cases below showed that for all of the science

areas considered, simultaneous observations in the UV would add considerable value to the

scientific yield. As adding UV capabilities to the same telescope might pose considerable

challenges (additional detector technology required, wide-band reflectance of mirrors from UV to

NIR required, UV requirements on optical surface quality might drive the mirror design), this

option will need to be considered carefully.

User Needs

User Requirements



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Page 12 of 21

3.1 EXOPLANET ATMOSPHERES TRANSIT OBSERVATIONS

Science Description:

Little more than 20 years after the discovery of the first exoplanet, more than 3500 planets in more

than 2600 planetary systems are known today. The study of exoplanets has become the most

rapidly growing field in modern astronomy; holding the promise of finding an Earth-like planet in

a potentially habitable zone, and potentially, signatures of life. Evidence for a terrestrial planet at

our closest neighboring star, Proxima Centauri [RD2] or the detection of a multiplanet system

around the near-by late type star TRAPPIST-1 [RD3] have caught attention by the public world-

wide.

The field has moved from detecting and analyzing individual systems to an era of “comparative

exoplanetology”. A particular priority in exoplanet science will be spectroscopy of exo-

atmospheres of edge-on planetary systems in transit, eclipse, or throughout their orbits as a

continuous time series to create phase curves. A variety of questions exists that are potentially of

interest for a balloon borne mission:

Clouds and Hazes in Exoplanet atmospheres: multicolor transit depth observations,

preferably reaching from the UV to the NIR, act as low resolution transmission spectroscopy

of exoplanet atmospheres (see references in Narita et al., [RD4]); providing e.g. clues on

presence of haze or clouds. Wide spectral band observations of atmospheres were conducted

for a few 10s of exoplanets, implying the existence of aerosols. Balloon based observations

can be designed to characterize clouds over a range of planet sizes and effective temperatures.

Understanding Exoplanet Formation and Evolution Pathways: The proposed balloon

platform would provide measurements of elemental abundances of exoplanets that will place

chemical constraints on their formation and migration mechanisms.

Vetting Candidates for JWST observations: in the context of the aforementioned science

cases, the proposed observations can be used to vet candidates for the James Webb Space

Telescope (JWST). E.g. “cloud-free” planets or planets with particular impact on formation

theories can be identified in order to use JWST time most efficiently.

Spectroscopic Phase Curves: a balloon platform will complement JWST by providing long

time baselines to map the spectral variation of planets over their full orbits.

Understanding stellar contributions: It should be noted that simultaneous multiband

photometry of a transit are one way to mitigate systematic effects, as stellar activity (e.g.

flares, sun spots) can affect luminosity and hence transit depth. (details in White Paper by

Apai, et al, 2018 [RD5] or SOFIA science case in [RD6]).

Challenges:

Spectroscopy at long wavelengths (up to ~16 µm) would be desirable, but presents major

challenges (availability of detectors, characteristics of detectors, warm telescope) and has been

discarded for the envelope of a balloon mission, given that the wavelength range of 1-5 µm already

contains most key molecular signatures of interest. Particularly above 2 µm, where some of the

interesting molecules have vibration-rotation bands, strong signatures can be found already.

A balloon borne mission for low resolution exoplanet spectroscopy in the 1-5 µm band based on a

~0.5 m telescope has been discussed by Pascale et al. [RD9],[RD10]. Being limited to relatively

small telescope diameters, such a mission would focus on characterizing hot Jupiters and warm

Neptunes, but would potentially allow to study a significant sample of this population. Again, this

science case is unique to a balloon-borne platform as it provides unobscured access to wavelengths


Page 13 of 21

that are affected by telluric bands for ground based observations. Observations would potentially

be even possible during daytime [RD9].

Science Needs:

Two different instrumentation approaches can be used to cater the abovementioned science cases.

Approach 1: high precision multichannel imager for absolute transit photometry (compare also

the NIMBUS instrument proposal for the Stratospheric Observatory for Infrared Astronomy

(SOFIA) [RD11]).

Spectral region: visible, NIR, preferably supported by UV.

Spectral resolution: standard filters, e.g. Sloan g,r,z, or JHK, R~10 to 20.

Type of observation: absolute photometry.

Required sensitivity: for atmospheric characteristics: 0.01% (per spectral element).

Better suited for phase curve observations and vetting of JWST candidates.

Approach 2: slit-less (TBC) spectrometer (compare also the proposed instrumentation for the

Exoplanet Characterisation Observatory (EChO) [RD12]).

Spectral region: NIR (1-5µm), preferably supported by UV and optical (especially for

clouds and hazes).

Spectral resolution: ca. 30-50 for chemical census; ca. 200-300 for first insights into

atmospheric processes (with spectral oversampling and binning as an option).

Type of observation: transit spectroscopy.

Slit size: sufficiently large to minimize slit losses & photometric variations due to slit

losses caused by pointing instability. Preferably slit-less.

Better suited for the study of clouds and hazes, required for the detailed measurement of

elemental abundances.

Perhaps more importantly, both approached share the following needs that are very specific for

exoplanet transit observations:

Long-term photometric stability: over 3-6 h for 1-3 h transits.

Photometric precision: at ppm-level.

Addendum:

In addition to the abovementioned transit science cases, balloons might offer an opportunity for a

coronographic exoplanet imaging mission that leverages the low seeing in the upper atmosphere

(see the similarly equipped PICTURE-C mission to directly image debris disks around nearby stars

from a balloon [RD13],[RD14]).

3.2 ACCRETION IN YOUNG STELLAR OBJECTS


Mass accretion is among the prime physical processes governing the evolution of accretion disks

around young low-mass stars (< 2 Msun). The mass accretion rate is an important parameter in disk

evolution models [RD15] and disk clearing mechanisms [RD16], and references therein), and is a

key quantity for the studies of pre-Main Sequence (PMS) stellar evolution and planet formation.


Page 14 of 21

Matter accretes from the disk onto the star channeled by the magnetic field [RD17]. This leads to

the formation of accretion columns along the field lines and hot spots at the point of impact on the

stellar surface. The additional luminosity produced by accretion in YSOs is a consequence of the

conversion of kinetic energy of the accreted matter into radiation. The mass accretion rate can,

therefore, directly be obtained from the observed accretion luminosity, Lacc. This accretion

luminosity can be measured as an excess above the photospheric luminosity of the star visible at

UV wavelengths. In addition, emission lines are produced in the heated gas of the accretion

streams. Considerable effort has been put in calibrating the empirical relation between the UV

luminosity excess and the optical and near-IR emission line fluxes of YSOs (e.g. [RD18]).

As low-mass stars are faint in the UV, line emission is generally a more easily accessible diagnostic

of accretion. The different excitation conditions of various sets of lines, e.g. lines from different

elements, different ionization stages and different line series, probe distinct regions in the accretion

flow. As a result of the large abundance of hydrogen, the optical line spectra of accreting YSOs

are dominated by Balmer lines. Individual lines of the Paschen and Brackett series have been

detected in near-IR spectra of YSOs. However, the strongest line of the Paschen series (Pa α @

1.875 μm) and the higher-n lines of the Brackett series (e.g. Br δ @ 1.944 μm, Br ε @ 1.817 μm)

have remained unobserved in YSOs because they are located in wavelength regions with strong

atmospheric telluric lines. Moreover, the strongest transitions of the Brackett series (Br α @ 4.015

μm) and the whole Pfund series have wavelengths longward of the K-band where few

spectroscopic observations are available. These important diagnostics have, therefore, been elusive

in previous studies. Spectroscopic observations from locations above (most of) the Earth’s

atmosphere and at wavelengths > 2μm are, therefore, required to assess the accretion physics

associated with the higher-n series of hydrogen.

A spectroscopic balloon mission will enable establishing empirical relations between the fluxes of

the above-mentioned, so far unexplored, emission lines and the accretion luminosity Lacc obtained

from previously measured UV excess of the same stars. Calibrating such relations for bright YSOs

is an essential step for subsequent studies of embedded protostars for which the UV and optical

spectra are not accessible and the near-IR lines represent the only ways to probe and to quantify

mass accretion.

Science Needs:

Spectral resolution: R >= 800, absolute minimum: R = 500 to 600;

Accurate pointing and limited field of view preferable to avoid source confusion;

Sensitivity / targets: number of bright targets in northern sky is limited, observations from

the Southern hemisphere might provide access to more targets at a given sensitivity.

As per the current knowledge, the science needs of the YSO Accretion case may also be coverable

by an instrument designed for medium spectral resolution transit spectroscopy of exoplanet

atmospheres (“Exoplanet Atmospheres” Approach 2). The required spectral resolution to study

YSO Accretion is higher, but spectral binning could be applied for exoplanet observations to reach

the required signal to noise ratio with an instrument that offers higher spectral resolution than

absolutely required. Secondly, the limited field of view requirement might be reachable by adding

an exchangeable narrow slit to the instrument, depending on the instrument design.

Careful considerations during further iteration steps taking into account the needs of both science

cases will need to show whether a reasonable instrument design can cover both.


Page 15 of 21

3.3 SMALL BODIES


Small solar system bodies are remnants and direct witnesses of our solar system’s formation

process, whose material is thought to have only been slightly altered since the formation of the

planets. Their study thus can reveal a wealth of information about many aspects of the solar system

formation process, among others about the distribution mechanisms of water, the local distribution

of processes during the formation, their

timescales, and even about the formation

routes to complex organic molecules.

Small bodies have received considerable

attention over the last years, particularly

through in-situ missions to comets and

asteroids, such as NASA’s Deep Impact

mission, JAXA’s Hayabusa mission, or

most recently ESA’s Rosetta mission, but

also through highly-sensitive space-based

observations and high-dispersion ground

based observations. However, many

important questions remain to be answered.

Comet volatiles. The abundance and

precise composition of volatiles on comets

provides a good record of their past and

their potential origin. A good

understanding of the current account of

volatiles in different groups of comets,

particularly in Oort cloud comets and

Kuiper Belt objects would provide an

important test of current models of solar

system formation [RD21], in particular the

“Nice Model” which predicts a

considerable mixing between the abovementioned dynamic populations [RD19],[RD20].

Particular volatiles whose abundances and mixing ratios are of interest (and which have already

been detected through gas state emissions on comets) are CO2 [RD23], CO [RD23], OH [RD22],

HCN [RD24], H2O [RD23], and organics such as CH4 [RD22], C2H6 [RD24], and CH3OH [RD24].

Among these, the organics are additionally interesting in respect to the question where and how

complex organic molecules first started to form. Another measurand of particular interest is the

abundance of deuterated water (HDO) on comets, since it allows (in combination with the easier

measurable abundance of H2O) the comparison of D/H ratios in cometary and terrestrial water and

thus might provide a clue towards the origin of Earth’s water [RD25]. The difficulty to measure

these species during the perihelion passage of a comet differs considerably. All of them show

emission lines in the NIR and very short MIR between 2.7 µm and 5.6 µm, however at considerably

different line widths and line strengths. Many of them are very present in the Earth’s atmosphere

and thus can only be measured if either the telluric contribution is precisely known and subtracted

or if telluric and cometary lines are separated due to Doppler shift (and can be discriminated by

very high spectral resolution measurements) [RD24]. These telluric lines are weaker, but still

present at altitudes reachable by airplane. Balloon-borne observations at altitudes around 40 km

would allow the measurement of some of these volatile species and other undetected ones around

Species Wavelength [µm] Line strength

[W/m2]

H2O 2.7 [RD23] 1.6E-16 [RD23]

CO2 4.25 [RD23] 1.3E-16 [RD23]

CO 4.65 [RD23] 7.6E-17 [RD23]

CH4 3.3 [RD22] 1E-17 [RD22]

OH 3.28 [RD22] 3E-18 [RD22]

HCN 3.02 [RD24] 1.5E-19 [RD24]

C2H6 3.35 [RD24] 1.5E-18 [RD24]

CH3OH 5.52 [RD24] 1E-18 [RD24]

HDO 3.7 [RD25] < 1.5E-19 [RD25]

Table 1: Emission wavelengths and measured emission

line strengths of confirmed gaseous species in comet

comas. Some line strengths were calculated from flux

densities, some converted to an assumed 5 mag comet.


Page 16 of 21

cometary perihelion passage without the restrictions and the considerable effort (e.g. use of

adaptive optics (AO) systems) applicable to ground-based or airborne observations and cheaper

than with space-based instruments.

Small bodies compositions. Another diagnostic tool to probe the formation of the solar system and

the applicability of the current formation models is the mineral/solid state composition of asteroids.

Findings about their composition help to trace their origin, their thermal origins, but can also

provide views into the interior of once-larger parent bodies [RD26]. In a first step, asteroids are

routinely grouped into spectral classes. Closer investigation of smaller and weaker features in the

spectrum of reflected sunlight however

also allow the detection of certain species

or classes thereof. Such detectable

species are water ice [RD28], frozen

methanol or photolytic products of

methanol [RD29], hydrated minerals

through the detection of OH [RD27], but

also mineral classes through e.g. the

detection of different iron ions (Fe2+,

Fe3+) [RD30],[RD32] (for band

positions, see table 2). Traces of water

and iron-rich minerals (which can also be

used as a potential indicator of dissolved

platinum group metals [RD31]) in main

belt or near-Earth asteroids are

additionally interesting to pre-filter

potential targets for asteroid mining.

Observations of these absorption features from the ground are partly possible, but severely

complicated by strong telluric absorption bands and night-sky emission lines. UV features (details

of the absorption edge below 400 nm [RD33], absorption features around 300 nm [RD34] and

200 nm [RD29]) are not accessible from the ground at all.

Science objectives:

Case 1: Study the potential local distribution of evaporation and condensation of solids from hot

gas by determining volatile abundances on different small solar system bodies.

Case 2: Test the solar system formation models by determining potential differences in volatile

abundances of Oort cloud and Kuiper belt comets.

Case 3: Determine the chemical paths to complex organic molecules by studying the distribution

of precursor molecules in Kuiper belt objects, Oort cloud objects, and asteroids.

Case 4: Determine the source of terrestrial water and other volatiles.

Case 5: Constrain the effect of space weathering on small body surfaces by studying the

reflectance slope at the boundary between NUV and visible.

Case 6: Study the surface composition of asteroids (particularly near-Earth asteroids) and comets.

Science needs:

Case 1: Measure molecular emission lines of volatiles (H2O, CO2, CO, CH4, OH, HCN, C2H6,

CH3OH, see table 1) in cometary comas around perihelion passage with a sensitivity of at least

4 Most prominent and unambiguous indicator [RD35].

Species Wavelength [µm] Band depth [%]

OH 2.8 [RD27] < 4 [RD27]

H2O 3.14 [RD28]

2.04 [RD29]

10 [RD28]

12 [RD29]

CH4 2.27 [RD29] 9 [RD29]

Fe ions 0.2 [RD30]

~1 [RD30]

~0.5 [RD30]

0.43 [RD32]

n.a.

n.a.

n.a.

3-4 [RD32]

Table 2: Measured absorption features of selected species

on asteroids.


Page 17 of 21

1E-18 W/m2. Spectral region: 2.7-5.6 µm. Type of observation: spectroscopy. Required spectral

resolution: R~20,000. Required angular resolution: > 3 arcseconds.




resolution: R~20,000. Required angular resolution: > 3 arcseconds.




resolution: R~20,000. Required angular resolution: > 3 arcseconds.

Case 4: Measure molecular emission lines of volatiles, including HDO (H2O, CO2, CO, CH4, OH,

HCN, C2H6, CH3OH, see table 1) in cometary comas around perihelion passage with a sensitivity

of at least 1E-19 W/m2. Spectral region: 2.7-5.6 µm. Type of observation: spectroscopy. Required

spectral resolution: R~40,000. Required angular resolution: > 3 arcseconds.

Case 5: Measure the UV-vis reflectance slope of asteroids in different parts of the solar system.

Spectral region: 0.2-0.4 µm. Type of observation: medium-resolution spectroscopy. Required

spectral resolution: > 1 nm, i.e. R~200 to 400. Required angular resolution: > 1 arcsecond.

Case 6: Measurand: absorption features in the reflectance spectrum. Spectral region: NUV to IR

(0.2 - 3.1 µm). Type of observation: spectroscopy. Required spectral resolution: down to 2 nm

preferable to detect features of metallic species as well, i.e. R~100 to 1500. Required sensitivity:

< 1%.

4 FIR SCIENCE NEEDS

4.1 OVERVIEW OF THE CURRENT SITUATION

The Far Infrared (FIR) spectral range is very important for astronomy. About half of the radiation

from evolving galaxies in the early Universe reaches us in the FIR and submillimeter wavelength

ranges [RD36], also cosmic dust has its maximum emission in this wavelength range. As the FIR

range is not accessible from the ground, the FIR astronomy community only slowly started to

develop (and is still developing) thanks to a series of space-based and airborne observatories. Most

of them, however, have been spacecraft with a limited lifetime or instruments with limited spectral

range or resolution. As such, after the end of the Herschel mission, the community is currently left

with one active FIR observatory, SOFIA, and sporadically flying balloon missions (such as

BLAST [RD39], STO [RD38], or PILOT [RD37]).

Astronomers, especially astrochemists are still waiting for new FIR telescopes. It is thus the time

to plan the next mission that will cover the gap in the FIR sky.

Next steps of FIR science will, as expressed e.g. by the European Far-Infrared Space Roadmap

[RD40], further investigate the origins of water on planets in our and distant solar systems, study

mechanisms and details of star and planet formation by investigating chemical evolution and

cooling processes throughout the universe, and further investigate the Interstellar Medium (ISM),

its interaction with stellar environments, and its energy cycle, by observations of dust and gas.

Taking these scientific steps forward will require telescopes with better angular resolution, more

observational capacity (in terms of spectral coverage and observation time), and higher sensitivity.

Balloon-borne telescopes are particularly well suited to address the first two needs, while offering

the possibility to regularly use the most up-to-date instrumentation.


Page 18 of 21

The following sections list a number of outstanding scientific areas in need of further observational

infrastructure for which balloon-borne observatories would offer particular advantages. As they

are collected from an infrastructure provider’s point of view, they are grouped by types of

observation required: surveys / mapping; (pointed) observations of extrasolar discrete sources;

(pointed) observations within our solar system.

4.2 FIR SCIENCE AREAS AND THEIR NEEDS

4.2.1 Surveys

100 µm continuum map of our galaxy after IRAS

While the 0.3 m-Infrared Astronomical Satellite (IRAS) surveyed the whole sky at 12 µm, 25 µm,

60 µm, and 100 µm, follow up missions like the Infrared Space Observatory (ISO), Spitzer, and

Herschel were observatories executing mostly dedicated and pointed observations. The same is

true for the Kuiper Airborne Observatory (KAO) and for SOFIA. The only complete continuum

sky survey at 100 µm existing today is therefore by IRAS at an angular resolution of 1.5

arcminutes. The Photodetector Array Camera & Spectrometer (PACS) FIR instrument on board

Herschel has at least mapped the central part of our galaxy and other galaxies. A dedicated far-

infrared camera for mapping out dedicated regions in our own galaxy as well as in other galaxies

at an angular resolution of 5 arcsec is an indispensable tool in the post-Herschel and post-SOFIA

era in order to be at least somewhat compatible with the arcsec and subarcsec angular resolution

of ALMA (sub-mm) and the upcoming JWST (mid-IR).

Spectral line maps of our galaxy

Even more important are dedicated spectral line surveys. Far-infrared fine structure spectral lines,

in particular the 157.7 µm (CII) line and the 63.18 µm (OI) lines are very important galactic

emission lines, which by themselves may radiate up to several percent of the entire galaxy’s energy

output. As such they serve as very important cooling lines not only for our galaxy but for many

galaxies, in particular the active ones. While these lines are important features of the energetics of

our own galaxy, very little is still known about their spatial distribution across our galaxy. Maps

of a representative number of large molecular clouds within the Galaxy do not exist. These lines,

due to their far-infrared wavelengths, do suffer only very little from foreground extinction making

them ideal tools for a galactic inventory of such cooling processes. Mapping out these and other

important far-infrared spectral lines (such as the 128 µm HD line) across a major fraction of our

own galaxy as well as of other galaxies with a high signal to noise ratio will boost our

understanding of the chemical evolution of our galaxy and of galactic evolution in general.

A balloon observatory can achieve about 1000 hours of observing time during a 6-weeks mission

with one instrument attached. Such a set-up is very much suited for executing large surveys.

4.2.2 Discrete Sources

Spectroscopy of light hydrides

Light hydrides (molecules with a single heavy element atom and one or more hydrogen atoms,

such as OH, NH, CH, or SH) were discovered thanks to their electronic transitions in the visible

range. However, due to the nature of molecular lines, they can be best seen in the infrared spectral

range. Light hydrides belong to the first molecules to form in atomic gas and are thus at the starting


Page 19 of 21

point of astrochemistry and the building blocks of larger molecules [RD44]. Their study allows

fundamental insight into the first building steps towards interstellar molecules. As their chemical

formation process only involves a few steps, the interpretation of their abundances is comparably

straightforward and they can provide key information about their environments, including on

dynamical processes (shocks, turbulence, large scale winds), cosmic ray ionization rate, and

presence of molecular hydrogen [RD44].

The observation of light hydrides thus promises to provide a valuable tool to understand planet

and star formation, and, through the measurement of isotopic ratios, also to understand the origin

of volatiles in our own solar system. ALMA and NOEMA are already enabling highly sensitive

and spatially highly resolved observations of light hydrides in distant galaxies, for which the

ground state transition lines are sufficiently redshifted to fall into the sub-mm / mm spectral

regions. For observations in the ISM in our own galaxy, or neighboring galaxies, however, the

lines have to be observed at (or close to) their original wavelengths in the FIR.

Affected species particularly include H2, CH2, CH+, OH, H2O, H3O+, HF, SH, HCl+ and their

isotopologues [RD44], which all have a multitude of emission and absorption lines in the FIR.

Picking out single most attractive lines for observation is difficult, as different lines often trace

different physical and chemical conditions. For known H2 lines, see e.g. [RD41], for CH2 lines

[RD42], for CH+ lines [RD43], for OH lines [RD45], for H3O+ lines [RD46], for HF lines [RD47],

for SH lines [RD48] ([RD49] for the detection with SOFIA/GREAT), for HCl+ lines [RD50]

([RD51] for the detection with Herschel/HIFI).

Science Needs:

High spectral resolution and high sensitivity observations at the wavelengths of light hydrides

ground states in many targets across the Galaxy.

Ice features in the FIR

For years, dust annoyed astronomers by covering their favourite stars. With the development of

infrared observatories, however, cold dust and ices became a hot topic. Among other things, their

study now allows important insights into the process of star and planet formation and the migration

of water through evolving planetary systems.

Both in dark clouds and protoplanetary disks, atoms and molecules freeze out onto the cold surface

of dust grains, forming icy mantles. In dark clouds, this process is accompanied by hydrogenation,

forming small molecules such as CO, CO2, H2O, H2CO, CH3OH, CH4, HCOOH, OCN- and other

hydrogenated species [RD52]. Within protoplanetary disks, particularly more complex molecules

formed during the protostellar phase freeze out onto grain mantles, where ice from the pre-stellar

phase may still be present, in cold regions of the disk.

So far, mainly features in the near- and mid-infrared have been used to detect and characterize

these molecular ices. As their FIR emission features are attributed to intermolecular vibration

modes, however, observing them makes it furthermore possible to determine the structure and

transitions between phases of the observed medium (e.g. amorphous vs. crystalline). In particular,

the FIR band positions and widths are, in addition to the abundance of the emitting species,

sensitive to the grain geometry and size distribution, the environment temperature and density

structure. Combined with modelling of protoplanetary disk emissions, the analysis of the FIR

features thus allows to infer the abundance and location of ices within the disk, making it, with

sufficient data, possible to constrain the location of the snow line [RD53].


Page 20 of 21

So far, only water ice features have been detected in the FIR in a few disks, while the band strengths

of other ices are thought to be not strong enough to have been detected. Giuliano et al. [RD54]

provide band locations and band strengths of several ices from laboratory measurements as

summarized in table 3, providing an indication of which observations offer the most information

(and which might be feasible in terms of sensitivity). In terms of feature width, McClure et al.

[RD53] find, e.g., the equivalent band width of the 63 µm water feature to be in between 1 and 4

µm for different disks.

Table 3: Molecular ice emission features in the FIR, from [RD54]

Species

(ice)

Wavelength of

feature [µm]

Ice structure

H2O 44.1 Crystalline

45.7 Amorphous

62.55 Crystalline

CO26 85.5 Amorphous

144.9 Amorphous

CH3OH 28.8 Crystalline

33.0 Amorphous

56.5 Crystalline

CH4O7 33

CO / CH4 No features in FIR

Science Needs:

Medium spectral resolution and high sensitivity observations at the wavelengths of ice features in

many targets across the Galaxy.

Other science fields

Several other topics that partly overlap with the ones discussed before but are important enough to

separately point them out would equally benefit from high-stratospheric observations in the far

infrared. They will not be discussed in detail in this document, but will still find consideration in

the following design study:

- Study of the 70 µm CO2 feature in protoplanetary disks at medium spectral resolution;

- Spectroscopy of water in the FIR in different regions;

- Observation of hyperfine transitions in dark clouds at high spectral resolution;

5 Presence / absence of feature may be an indication of cubic or hexagonal ice 6 Bands only narrow in the transition from amorphous to crystalline 7 Band shows frequency shift at state conversion


Page 21 of 21

4.2.3 Solar System


Observations in the submillimetre domain provide a unique window for the study of atomic and

molecular gas. The very high achievable spectral resolution allows not only to study molecular

abundances, but also to determine the shapes of absorption lines. In a solar system context, this

allows e.g. conclusions about vertical distributions of molecules in atmospheres of planets and

satellites or in comae.

Submillimetre and FIR observations are severely limited from the ground. Particularly in between

30 µm and 300 µm, atmospheric absorption makes observations from the ground practically

impossible. Conditions at SOFIA altitudes are better, but telluric absorption lines are still

considerably pressure broadened in the remaining atmosphere. At 30 to 40 km altitude, the line

width of telluric absorption lines is narrow enough to allow discrimination between the telluric

lines and Doppler shifted absorption features on solar system objects.

Recent flights of the Stratospheric Terahertz Observatory (STO) [RD38] and the Balloon-borne

Large Aperture Submillimetre Telescope (BLAST) [RD39],[RD55] have strikingly demonstrated

the feasibility of carrying out submillimetre / FIR observations on interstellar and galactic targets

from balloons. In the solar system, space based observations have been carried out with e.g.

Herschel, which, among others, lead to the detection of water vapour around the dwarf planet

(1) Ceres [RD56], the first detection of the D/H ratio in a Jupiter family comet [RD57], and the

first detection of the Enceladus water torus [RD58]. With the required cryogen supplies on

Herschel, Spitzer, and Akari having depleted, however, no space-based capabilities in this region

are currently available, while many questions regarding gas atmospheres on the planets, their

moons, and small bodies remain to be answered.

Science Objectives:

Measure the abundance and vertical distribution of gases (O2, H2O, HCl,…) and their

isotopologues in the atmospheres of solar system comets, planets, and their moons. Measure the

abundance, local distribution, and temporal variation (rotational, seasonal, orbital) of gases around

small bodies.

Science Needs:

Measurable: absorption bands at high spectral resolution with a sensitivity of at least 1 Jy. Spectral

region: submillimetre / FIR. Type of observation: spectroscopy. Observation of small bodies and

planetary moons at different points on their orbit and the orbit of their host planet.

Science Requirements:

Wavelength coverage Absorption bands at 750, 1100, 1250, 1650 GHz

Required sensitivity At least 1 Jy

Required spectral resolution TBD

Required spatial resolution Better than 1 arcmin

D2.1 - REQUIREMENTS BASELINE – COMMON

OPERATIONAL NEEDS

Version 1.0

31.05.2018

Status: Released

ESBO DS Requirements Baseline – Common Operational Needs Version: 1.0

Page 1 of 15

Deliverable





ESBO DS


Duration: Mar 1, 2018 - Feb 28, 2021

WP WP 2 Del. No D2.1 Title Requirements Baseline – Common

Operational Needs Lead Beneficiary “MPG”

Nature “Report”





Version 1.0

Date 31.05.2018

Status Released

Authors T. Müller, [email protected], MPG

P. Maier, [email protected], USTUTT

Approved by P. Maier, [email protected], USTUTT


Page 2 of 15

TABLE OF CONTENTS



1 INTRODUCTION .................................................................................................................... 4

2 SCOPE ...................................................................................................................................... 4



2.3 Coverage of the Needs/Requirements Logic ............................................................. 5

3 APPLICABILITY OF OPERATIONAL REQUIREMENTS ............................................. 6

3.1 Scope of “Infrastructure” .......................................................................................... 6

3.2 Possible Perspective / Development Sequence ......................................................... 7

4 GENERAL OPERATIONS & INFRASTRUCTURE CONCEPT ..................................... 8

4.1 Constraints Imposed by Balloon Operations ............................................................. 8

4.2 Consequences for Observations ................................................................................ 9

4.2.1 Constraints ........................................................................................................... 9

4.2.2 Advantages ........................................................................................................... 9

5 COMMON OPERATIONAL NEEDS & REQUIREMENTS ........................................... 10

5.1 User Needs for Efficient Scientific Exploitation ..................................................... 10

5.1.1 General User Needs for operation...................................................................... 10

5.1.2 Needs for the operation of PI instruments (also in shared-time) ....................... 11

5.1.3 Needs for the operation of facility instruments .................................................. 11

5.1.4 Services and support for instrument developers ................................................ 12

5.1.5 Need for reliable operation and derived needs from the operator’s perspective 12

5.2 Operational User Requirements .............................................................................. 12


Page 3 of 15



AO Adaptive optics


Telescope



ESBO European Stratospheric Balloon Observatory

ESBO DS European Stratospheric Balloon Observatory

Design Study

FIR Far-Infrared


GPS Global Positioning System

HK Housekeeping

PI Principal Investigator

TAC Time Allocation Committee

TBD To be determined

TC Telecommand

TM Telemetry

REFERENCE DOCUMENTS


Requirements Baseline – UV. 31 May 2018.


Requirements Baseline – NIR and FIR. 31 May 2018.


Page 4 of 15

1 INTRODUCTION

The Requirements Baseline contains the top-level user needs and requirements as defined

for the infrastructure to be developed, upon which all subsequent development within ESBO

DS will be based. It thereby summarizes and documents the work performed under WP2,

“Detailed Science Case Analysis”.

The foremost focus of ESBO DS lays on developing an infrastructure that provides easy

access to stratospheric observations to the broad scientific community. In practice, it shall

provide operations and accessibility comparable to current ground-based astronomical

facilities. The operational concept and the system layout thus need to focus on this primary

infrastructure goal, providing a system that is sufficiently flexible to accommodate the needs

of different researchers and research communities, and at the same time affordable enough

to allow regular operation.

This part of the Requirements Baseline summarizes these user needs in terms of

infrastructure operation and services.

2 SCOPE


The purpose of the Requirements Baseline is to document the needs and requirements of

scientific users with regard to the ESBO infrastructure, i.e. the first / second level of the

requirements hierarchy as also further described in chapter 3 of part 1 of this document.

Detailed technical requirements on the system level and below are foreseen to be

documented in further Technical Requirements Specification documents.



o User needs and requirements for UV science, i.e. already relevant for the prototype

development within ESBO DS;

o User needs and requirements for near infrared (NIR) science, including exoplanet

science, i.e. relevant for the mid-term platform of ESBO;

o User needs and requirements for far infrared (FIR) science, i.e. relevant for the long-

term platform of ESBO;




requirements of these four categories are known at this time (e.g. for UV science, system

level technical requirements have been identified already), the requirements baseline is

implemented as a series of three documents:



requirements already identified and relevant for the prototype development within

ESBO DS;


Contains descriptions of the driving science and scientific needs as well as

requirements to the degree known at this point for the two mid- and long-term platforms

currently envisioned for ESBO;


Page 5 of 15


Contains user needs of the scientific community regarding the infrastructure’s

operational concept beyond the scientific needs of each science case and applicable to

all three scientific areas / envisioned flight platforms.

Particularly parts 2 and 3 of the Requirements Baseline are to large extents based on findings

of the ORISON H2020 project.


This document, the Requirements Baseline - Common Operational Needs – covers the user

needs of the scientific community regarding the infrastructure’s operational concept beyond

the direct requirements of each science case. Topics addressed in this document include,

inter alia, exchangeability of instruments, frequency of flights/observation opportunities

from the perspective of continuity, real-time access to observation data and instrument

command, methods of observation time allocation, provision of observer tools, provision of

data processing tools, and provision of further support.

The needs and requirements as documented in this document will be passed on to WP3

(Infrastructure Analysis), WP5 (Conceptual Design), and WP6 (Observatory Operations and

Governance Concept) to be taken into account for the mid- and long-term development of

the infrastructure.

The needs and requirements compatible with the constraints of the prototype development

will also be passed down to the prototype requirements (mostly WPs 8, 10, and 11).

While it will need to be decided during the further course of the prototype definition and

development, which of the operational requirements from this document can already be

taken into account for the prototype, the association of the requirements to the likely

operational development phases as described in section 3.2 provides a first indication.

2.3 COVERAGE OF THE NEEDS/REQUIREMENTS LOGIC

As figure 1 illustrates, the content of this document focuses on needs and requirements from

the user perspective, namely the User Needs and the User Requirements. Detailed technical

requirements for the infrastructure will be derived and documented in the subsequent work

packages mentioned in section 2.2 as the way of fulfilling the operational user requirements

(and to some extent also the exact user requirements applicable in each development phase

of the project) will heavily depend upon the operations and governance concept eventually

applied.

For a general description of the high-level flowdown of needs and requirements within

ESBO DS and a description of the different elements, please refer to Part 1 of the

Requirements Baseline [RD1].


Page 6 of 15

Figure 1: Elements of the needs and requirements hierarchy covered in this part 3 of the Requirements

Baseline

3 APPLICABILITY OF OPERATIONAL REQUIREMENTS

3.1 SCOPE OF “INFRASTRUCTURE”

The term “infrastructure” in the context of ESBO and ESBO DS does not only refer to the

flight infrastructure / flight systems carrying telescopes and instruments. It rather refers to

the entire observatory infrastructure including everything required to operate ESBO as a

stratospheric balloon observatory and to provide the foreseen services. As figure 2

User Needs

User Requirements



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Figure 2: Illustration of ESBO infrastructure elements


Page 7 of 15

illustrates, this includes the flight systems (dark blue), the ground systems (light blue),

proposal and other observer tools as well as data pipelines and processing tools (red) and the

governance structure / organisation (orange).

The operational needs and requirements covered within this document refer to this full

infrastructure.

3.2 POSSIBLE PERSPECTIVE / DEVELOPMENT SEQUENCE

As already described in more detail in part 1 of this requirements baseline, the ESBO concept

foresees different kinds of users with different degrees of involvement in the infrastructure,

namely scientific users / groups that provide an own instrument (“PI instrument”) and users

/ groups that use observation time on instruments provided by the observatory operators

(“Facility instruments”), or on PI instruments via open time access.

Which type of instruments (and users) will be used (or dominate) at a certain implementation

phase of ESBO will be highly dependent upon the eventual governance structure, the

financing, and the backers of each specific phase.

It appears likely, however, that the implementation of ESBO firstly will be dominated by PI-

instruments, before facility instruments are deployed on a larger scale. In order to also duly

take into account the prototype phase, which will have particular constraints on operations,

the following potential development phases are used to indicate which operational needs and

requirements will be relevant for which operational setup (these phases should not be

misunderstood as a hard plan for the sequential development of ESBO, but rather as a way

to associate the needs and requirements with different operational setups).

The envisioned general strategy, reflected in the phases, is to, during the early development

of ESBO, have the data calibration, processing, and related tools be taken care of by the

instrument teams. Centralized processing tools, calibration procedures, observation modes,

etc. may be defined and developed during the further process of including instruments into

the ESBO facility itself.

1. Prototype Phase (within ESBO DS)

- The Prototype Phase refers to the development and the first flights of the

prototype platform with one UV instrument (EKUT), which is being designed

and manufactured within ESBO DS and one supportive visible light instrument

(USTUTT)

- All responsibility for the instrument, for calibration plans, for commissioning

plans, science verification plans, etc. in this phase resides with the scientific PI

(i.e. EKUT for the UV instrument, USTUTT for the visible light instrument)

- All responsibility for data processing, calibration, archiving, etc. also resides with

the respective PI

- Responsibility for housekeeping & technical data (pointing, stability,

environment conditions, altitude, telemetry, other atmospheric data, timestamps

(reliability & accuracy), etc.) as well as general performance verification

measurements reside with the observatory operator (entire consortium)

2. PI-driven Phase

- The subsequent development and operation of ESBO after the prototype flight(s)

will likely be dominated by scientific groups with an interest to fly their own

instruments. While this does not necessarily exclude the option of providing


Page 8 of 15

observation time to other groups, operations in this phase would be driven by the

interests of the PI.

- Responsibility for data processing, calibration plans, instrument operations, etc.

in this scenario would be mostly the responsibility of the PI, with comparably

little involvement of the observatory operator.

3. Open Observatory Phase

- This phase describes the scenario in which ESBO operates own facility

instruments with open access to observation time, or PI instruments with a large

portion of observation time open to the community.

- In this case, likely a large part of the responsibility for data processing,

calibration, archiving, data delivery, but also for proposal selection and time

allocation will need to be taken care of by the observatory operator.

The requirements table in section 5.2 includes an indication for each requirement during

which phase it will likely be relevant.

4 GENERAL OPERATIONS & INFRASTRUCTURE CONCEPT

4.1 CONSTRAINTS IMPOSED BY BALLOON OPERATIONS

Launch locations and flight trajectories

Ground handling and launch of large balloons with payload masses of several hundred kg

and respective balloon sizes of several 100.000 m3 pose significant challenges to ground

infrastructure and launch conditions. On the technical side, this includes the necessity to

have large launching areas, provide sufficient amounts of helium, and ground handling

equipment for the balloon, flight service equipment, and the payload. On the side of

environmental conditions the constraints mostly include suitable wind conditions in order to

avoid damage to the balloon during ground/launch operations or during ascend due to sheer

winds.

Several launch providers are working towards making it possible to choose flexible launch

locations and part of the effort within ESBO DS is to study different options to ease the

operation of large balloon launches and to ensure regular and predictable flights. For flights

in the short- and mid-term, it needs to be assumed, however, that launch locations would be

used that offer existing ground facilities, comparably easy access, and cost-efficient

operation. In addition to the suitability of launch locations, stratospheric wind patterns and

overflight regulations constrain possible flight trajectories.

Depending on the desired flight duration, established launch locations with respective

trajectory options include e.g. Esrange in northern Sweden (offering 10-40 hour flights

above the base during “turnaround conditions”, or up to ca. 14 day flights on transatlantic

trajectories), or the McMurdo base in Antarctica (offering the opportunity of circumpolar

flights of typically 30 to 40 days duration). Experience at both locations (and all others)

shows that weather conditions may force the shift of launch dates by days or weeks.

Flight altitude and atmospheric conditions

While balloon flights aim at reaching specific altitude intervals during flight, the altitude

cannot be expected to be constant during a flight. The reasons for this can be

- That altitude changes are required for navigational purposes to reach different wind

layers (e.g. very relevant for flights during “turn-around” conditions over Esrange);


Page 9 of 15

- That altitude changes occur due to the heating and cooling of the lifting and

surrounding gas over day/night cycles. This oscillation can be minimized by

dropping ballast and venting lifting gas, however, a more stable altitude consequently

requires more ballast, which reduces the available payload mass, reachable altitude,

or possible flight duration.

These changes in altitude also cause changes in the surrounding atmospheric conditions in

terms of air density and of column density of telluric species.

4.2 CONSEQUENCES FOR OBSERVATIONS

4.2.1 Constraints

The abovementioned constraints of balloon flights consequentially lead to a difficulty to

precisely predict and pre-plan observation conditions. This concerns details in the visibility

of targets, which depends on the time of flight, and also the detailed quality of observation

conditions that depends on the flight altitude / the composition of the remaining atmosphere

along the line of sight.

These consequences need to be taken into account carefully when designing the operations

concept, as a well-planned operations concept can compensate parts of the difficulties caused

by the flight constraints.

4.2.2 Advantages

On the other hand, the unique operations conditions of balloons bring about a number of

advantages for the scientific operation:

- Regular access to instruments in between flights

Depending on the flight duration, instruments can be accessed after several days or

weeks of flight time and, at that occasion, can be refurbished, serviced, or updated.

- Return of data storage hardware

In contrast to space missions, the data storage hardware can be retrieved after each

flight, making it unnecessary to downlink all scientific data during flight. On the one

hand, the light and cheap availability of data storage makes it possible to generally

collect more data (the capabilities of space missions, including instrument size and

duty cycle, are frequently limited by their data downlink capacity). On the other

hand, it makes it unnecessary to put as much effort into on-board data compression

and on-board data processing as typically done for space missions. This means that

raw data can be saved and accessed without losing any potentially valuable

information, while at the same time the complexity of on-board data processing units

can decrease significantly.

- Design for reliability of hardware

Two aspects distinguish the requirements for hardware design of space missions to

those of balloon missions: the environmental conditions at balloon flight altitudes,

particularly in terms of radiation, are less challenging, and hardware does not have

to be designed for an uninterrupted service life of 5 to 15 years, as typical for space

missions.


Page 10 of 15

5 COMMON OPERATIONAL NEEDS & REQUIREMENTS

5.1 USER NEEDS FOR EFFICIENT SCIENTIFIC EXPLOITATION

As mentioned above, ESBO will cater different types of users. The definition of each “user”

type is given in 3.1 in the first part of D2.1 (Requirements Baseline – UV), distinguishing

between the general community desiring a certain observational capability, a group or

scientist with an own instrument, and a scientist who wants to use an existing astronomical

facility.

Each user group will have different dominance during each of the likely development phases

(“Prototype Phase”, “PI-driven phase”, “open observatory phase”) so that it makes sense to

examine the needs separately.

Instrumentation concept

As mentioned above, ESBO will, at least during the early development, rely on instruments

provided by scientific groups (“PI instruments”). This provides the advantage that one can

rely upon the expertise of research groups specialized in instrument development and that

the instruments at the same time will certainly cater the scientific needs of the developing

and or associated research groups. In addition, PI instruments create (as compared to “facility

instruments” owned and operated by the observatory institution) relatively little overhead on

the side of the observatory institution, as calibration, data processing, instrument servicing,

etc. would mostly be taken care of by the PI institution.

Facility instruments, on the other hand, allow an observatory institution to very freely

manage observation time and to provide a maximum of openly available observation time

to parts of the community that do not develop their own instruments. It is not decided at this

point whether ESBO shall aim at operating true facility instruments at some point or rather

aim at PI instruments with a shared time approach for the “open observatory” phase, within

which access to observation time, calibration tools, pipelines, etc. is also provided to external

observers.

5.1.1 General User Needs for operation

One important prerequisite for all scientific users of balloon telescopes is a basic summary

of the conditions during the observation phase. It is essential to know the environmental

temperatures, atmospheric conditions, water vapor, altitudes, flight geometries, sky

brightness, and also the expected timescales for changes in these parameters. This

information will need to allow an observer to judge which observations are possible and at

what quality. This includes the need to have tools to calculate the visibility of a given object,

to do exposure time calculations, and to have observing sequences and observation templates

available.

The second block of general needs is directly related to the operations: pre-scheduled

observations can be executed in an autonomous fashion (as baseline), but the possibilities

for data downlink and interventions have to be stated clearly. Many instruments will also

require intermediate data or control frames of the cameras or instruments to judge the

instrument performance and health of the instrument (e.g. the first frame of every

observation). It might also be required to change the observing plan or sequence, depending

on the outcome of the control frames or the auxiliary HK values.


Page 11 of 15

5.1.2 Needs for the operation of PI instruments (also in shared-time)

All the above needs for the general operations also apply for the operation of PI instruments.

In addition to information about the observation phase (nominal altitude phase), providers

of PI instruments also need to be informed in detail about conditions on ground, during

takeoff, ascending phase, descending phase, landing phase, and during the time until the

gondola is recovered. The description should include relevant aspects of the expected ground

weather, temperatures, winds, humidity, etc. during preparation and launching phase, as well

as for landing and recovery phases. For takeoff and landing it is important to know the

maximum accelerations and the potential risks for the gondola and the payload. For the

operation phase it is necessary to also know the environmental conditions in more detail than

for general observers.

In addition, the PI instrument operations requires detailed information about the telescope

operation and performance, about the telescope and subsystem HK and frequency, details

on the time referencing (central clock vs. instrument clock), GPS information, power

interfaces, the data storage procedure, including data format, exchange protocols, data rates,

amount of data, the necessary steps for accepting commands from ground, procedures for

downlinking information and so on. PI instruments are very useful for the early development

phases to test and consolidate operational aspects. When the instrument operations,

calibration and data handling is established, one should consider options to include part of

the astronomical community to broaden the scientific outcome. Part of the PI instrument

observing time can then be made available in an open time call, but always in close

collaboration with the PI instrument team. Here, it is important to document the instrument,

the observing modes, the performance characteristics, sensitivities, calibration, data

reduction schemes, data formats, and to have a selection of conducted observations available

in a database. At this stage, also data reduction software (including documentation) and

worked-out examples are important.

5.1.3 Needs for the operation of facility instruments

The needs for the operation of facility instruments include all the general needs and also the

above-mentioned aspects for PI instruments. It addition, the policy for observing time has to

be defined: regular (open) observing time, large programmes, instrument/observatory teams

guaranteed time, director’s discretionary time, observing time for targets of opportunity,

technical/calibration time. The procedures for nominal calls for observing time have to be

established: frequency of calls, total amount of observing time, ranking of proposals,

procedures for implementing observations, sorting by priorities and sky availability,

efficiency of the observatory, availability of instruments, restrictions from observing

conditions, etc. This “nominal” operation phase also requires proper storage of data (science

data, calibration data, supplementary data), availability of pipelines, interactive analysis and

calibration tools, means to do quality assessment for each observation, and proper

documentation of all steps involved.

The scheduling of observations is also different from the way it is done for ground-based

observatories: balloon flights have some uncertainties in the flight times, directions, and

durations. Therefore, there is a need to keep some flexibility in handling observations

(visibilities might become more important than priorities for a given programme). In order

to avoid time-consuming adjustment of observation requests due to changes in observation


Page 12 of 15

conditions, observations should be defined in observation blocks which can be picked up by

an automatic scheduler.

5.1.4 Services and support for instrument developers

In order to facilitate the deployment of PI instruments, ESBO will need to provide support

to the developing scientific groups. This concerns technical topics related to the connection

of instruments to the gondola and telescope, including support systems, but also support for

the development of hardware to operate under stratospheric conditions.

ESBO will need to offer support systems for instruments, including the observatory control

computer, telemetry and telecommand (TM/TC), and data downlink through the service

system, but also thermal control to a certain degree. Besides providing these systems

themselves in a way in which they can support different instruments, the observatory

organisation will also need to provide support to the teams developing instruments on

interfacing with the gondola, telescope, and support systems. This may include the need to

provide adjustments to the support systems based on the particular needs of instruments.

Given the aspired long flight times and comparably low, but non-negligible launch and flight

costs, ESBO will need to operate with a high reliability. This holds true for the flight

platforms, but also for the instruments. As most groups that may provide instruments will

likely not have experience with building hardware for the high stratosphere, ESBO will need

to provide support on designing for reliability under flight conditions in the high

stratosphere. Providing good design guidelines will not only be important in order to ensure

reliability, but also to avoid significant increases in development effort due to over-

engineering, e.g. for space conditions. One way to provide these guidelines and to ensure

reliability may be to offer flight worthiness certification from the side of ESBO.

5.1.5 Need for reliable operation and derived needs from the operator’s perspective

In order to provide meaningful scientific output, it is imperative to assure reliable technical

functioning of the instruments, which implies that the gondola itself needs to function

reliably and provide the necessary conditions to the instruments.

This requires, besides correspondingly careful design, permanent access to critical

housekeeping (HK) parameters of the gondola, the telescope, the instrument(s) and the

control units. There should be also means to verify the pointing performance of the telescope,

the functioning of auxiliary systems or instruments (e.g., water vapor monitoring,

temperature sensors, radiation sensors, clocks, etc.), and to have the necessary access to GPS

information. It is also important to document the needs for activation, initialization,

calibration, switch-off, standby, and safe modes of the telescope, the instruments and the

relevant subsystems.

5.2 OPERATIONAL USER REQUIREMENTS

The following table lists the preliminary operational user requirements derived from the user

needs in terms of observation described above. This list is represents the first iteration to

serve as a basis of more detailed analysis particularly in WP 6, where they will be reviewed

and adjusted if necessary depending on the operations concepts studied. In particular, the

current list of requirements is not to be considered as complete. The requirements are


Page 13 of 15

grouped into categories for better orientation, but follow one single numbering scheme (R-

OPS-SCI-XX, where XX is a running number). In addition, an indicator in the last column

shows for which of the likely development phases each requirement will likely be relevant.

The following nomenclature applies:

- 1 – Prototype phase

- 2 – PI instruments driven phase

- 3 – Open observatory phase

Flight Systems – Instruments Phase

R-

OPS-

SCI-

01

Exchange of instruments

The ESBO flight systems shall allow the exchange of instruments and/or

telescopes in between flights.

2 & 3

R-

OPS-

SCI-

02

Update of instruments

The design of the ESBO flight systems shall facilitate the

update/manipulation of instruments and/or telescopes in between flights

2 & 3

R-

OPS-

SCI-

03

Exchange of platform instruments

The ESBO flight system shall allow the exchange of add-on platform

instruments in between flights

all

R-

OPS-

SCI-

04

Community-developed instruments

The ESBO flight systems shall allow the installation of community

developed instruments (PI instruments) of both telescope and platform

instruments

all

Flight Systems – Operation

R-

OPS-

SCI-

05

Automated operation

The baseline operation of ESBO flight systems shall be automatic operation

of the scientific payload following scheduled observations / procedures.

All

R-

OPS-

SCI-

06

Manual interference

ESBO flight systems shall allow the manual control of the telescope and

instruments. Frequency/responsivity and degree of interference TBD.

All

R-

OPS-

SCI-

07

Access to data during observations

During baseline operation it is required to have access to the necessary HK

of the gondola, the telescope, the science instrument(s) and auxiliary

systems. In addition, it shall be possible to downlink snapshots of the

science data in regular intervals, e.g. the initial frame of each observing

block or a calibration image.

All

R-

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Regularity of flights 2 & 3


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ESBO flights shall be organized at a regular and preferably long-term

(years) predictable basis to facilitate planning, development, and

deployment of instruments.

Observation Time Policy

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Time allocation policy

ESBO observation time allocation policy shall foresee different types of

observations requests/proposals and associated types of observation time,

among them at least:

a) During nominal PI instrument operation phase: part of the

observing time will be opened up to the general community, but

always in close contact with the PI team, the remaining time is

guaranteed for the PI team, in close collaboration with the

observatory lead, and fulfilling also the needs for technical and

calibration time.

b) During nominal facility instrument operations: there shall be

regular calls for observing time, including options for nominal

open-time observations and large programmes. There shall also be

options for director’s discretionary time and programmes with

targets of opportunity.

(2 &)

3

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Community access to observation time

ESBO flights shall generally provide at least TBD % of the observation time

as proposal-based open time to the community.

3

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Time allocation

Open time shall be allocated in a transparent manner by a time-allocation

committee (TAC)

3

Data Policy

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Data access (via data catalogue or science publications)

Reduced & calibrated data underlying scientific publications shall be

available from the PI upon request after a reasonable proprietary period.

Details TBD.

2 & 3

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Data access (all data)

The ESBO data policy shall, as a baseline, foresee public availability after

a maximum of 1 year after data delivery, at least for measurements taken in

validated observing modes (in a form suitable for scientific analysis).

2? &

3

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Data protection

The ESBO data policy shall foresee a proprietary period with exclusive

access by observation PIs after the data delivery, at least for measurements

taken in validated observing modes (in a form suitable for scientific

analysis). The baseline duration of this period shall be 1 year.

2 & 3

Provision of Tools and Services to Observers


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Data pipelines

ESBO shall provide validated data pipelines for facility instruments / ensure

access to validated data pipelines for shared-time on PI instruments.

3

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Calibration services

ESBO shall provide calibration procedures and tools for facility instruments

/ ensure access to calibration procedures and tools for shared-time on PI

instruments.

3

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Data processing tools

ESBO shall provide validated data processing tools for facility instruments

/ ensure access to validated data processing tools for shared-time on PI

instruments, including TBD.

3

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Data archiving and provision

ESBO shall ensure structured data provision to the scientific community,

including an accessible, searchable data archive. This shall apply at least for

facility instruments and shared-time on PI instruments. (TBC)

3

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Other observer tools & services

ESBO shall provide access to visibility calculation tools, tools to prepare

observations, exposure time calculators, tools to calculate the influence of

varying parameters, like the water vapour content, on the instrument

sensitivity, etc.

2 & 3

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Documentation

ESBO shall provide detailed documentation on the platform, environmental

conditions, observation conditions, and the accessible instruments.

2 & 3

Provision of Services to Instrument PIs/Developers

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Instrument support systems

The ESBO flight and ground systems shall provide support systems for PI

instruments, including functions of observatory computer, commanding and

power switching of instruments and components, TM, TC, and data up- and

downlink capabilities, and 1st-level thermal control of the instrument.

2

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Interfaces to instrument support systems

ESBO shall provide clear options to interface with the instrument support

systems, suitable to support a range of instruments. In addition, ESBO shall

offer the option to adjust support systems to the needs of instruments within

a reasonable range.

2

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Design guidelines / flight worthiness certification for instruments

ESBO shall provide support to instrument teams to design their instruments

and hardware efficiently to operate with high reliability under flight

conditions.

2

Documents

D2.1 - REQUIREMENTS BASELINE - UV - Uni Stuttgart...2018/05/31 · Del. No D2.1 Part 1 Title Requirements Baseline - UV Lead Beneficiary “MPG” Nature “Report” Short Description