The Space-based Gravitational-wave Observatory (SGO) Family of Mission Concepts

LISA Symposium Paris, France 21-25 May 2012 1

The Space-based Gravitational-wave Observatory (SGO)

Family of Mission Concepts

Jeff LivasNASA Goddard Space Flight Center

for the SGO Core Team

LISA Symposium Paris, France 21-25 May 2012 2LISA Symposium Paris, France 21-25 May 2012

SGO Core Concept Team


Outline• Motivation for the study• SGO Family Description

– SGO-High– SGO-Mid– SGO-Low– SGO-Lowest

• Science Assessment• Cost Estimate• Summary


Motivation• Post March 2011 US activity question:

– Why, if there wasn’t enough money for a joint mission, was there money for two separate missions at ESA and NASA?

• Missions would be serial, not parallel

• US activity assumed:– No funding new Astrophysics mission before JWST (2018?)

o Except maybe a “Probe Class” Mission (~ $600 M)– Need to look for a “Probe Class” mission– Need to develop a flexible mission concept to match anticipated but

unknown future mission cost caps– Need to prepare for a possible ~$100M role in NGO

€

1+ 1 ≠ 2


Motivation• SGO concepts designed as progressively de-scoped cost points

from LISA baseline– Explore cost drivers

o Arm lengtho Orbitso Sciencecraft configurationo Number of (identical) spacecraft (Non-recurring vs recurring cost)o Number of links

– Investigate loss of science• Constraints are different for NGO so results are different

– SpaceX 9 launch vehicles assumed: lower cost– Restartable second stage?– Mass constraint less severe with Falcon Heavy


Previous Experience with De-Scoping

Conceptually - can’t really draw this curve, but 2 features:1) Threshold cost below which there is essentially no science2) lose science rapidly with modest cost savings


SGO Mission Concepts


SGO-High vs Mid (vs LISA baseline)• SGO Mid differs from LISA by:

• Detector arm length reduced from 5 Gm to 1 Gm• Science operations reduced from 5 to 2 years.• Nominal starting distance from Earth is reduced by

about a factor of 2.5 to a 9-degree trailing orbit.• Telescope diameter is reduced from 40 to 25 cm, and the

laser power out of the telescope is reduced from 1.2 to 0.7 W (end of life).

• In-field guiding is used instead of articulating the entire optical assembly

• SGO High differs from LISA by:• Preserves all LISA performance parameters• Single agency cost model (not joint mission)• Lower cost launch vehicle (shared launch on a

Falcon Heavy)• Demonstrated improvements in photoreceiver

performance• More economical trajectories to the operational

orbits

MidHigh


SGO-Low• Design Goal: Reduce LISA measurement concept to minimum four-

link design while retaining primary science targets.• Architecture: Four “identical” SC in 1Gm triangle, each with one

payload assembly• Two “corner” SC compare laser phase via 10km free-space link

very small telescopes for back link


SGO - Lowest

• 3 nearly identical “daughter” S/C– Single telescope handles 2 full-duplex beams?!– “corner” requires additional phasemeter and

processing• S/C 2 requires periodic corrections

– a milli-N thruster– Direct injection trajectory may not need a separate

prop module• 2 different arm lengths allow TDI frequency noise

suppression• Single string design for low cost


SGO Sciencecraft Configurations

High Mid Low, Lowest

• Small telescope means optical bench sets height• In-field guiding simplifies optical assembly• Launch stack fits easily into a Falcon 9 fairing

– 4th S/C for SGO-Low can be accommodated• drift away orbit requires little fuel, simplifying prop module


SGO-Mid Science


SGO-Low Science

Only one polarization


SGO-Lowest Science


SGO Science Comparison

• Covers decadal-endorsed science• Generally detects fewer sources of all types

• Main science risk is shortened mission duration– Event rates uncertain; science return lower if event rates are lower


Parameter Estimation (courtesy of Neil Cornish and the Science Performance Task Force)


Parameter Estimation Science Loss

Lowest

High

Mid

Low


Cost Estimates

• Cost model includes– Non-recurring Engineering costs– “learning curve” for multiple copies– 20% additional management reserves– Scaling with mission lifetime

• Scaling rates for NRE, learning curve from– Spacecraft/Vehicle-Level Cost Model– NASA/Air Force Cost Model

~ $0.5B


Summary• SGO Mission concepts cover a range of costs of $480M

– $1.2 to $1.66B– TeamX estimates ~ $0.5B higher

• SGO Science Performance goes from full LISA to very minimal over that cost range

• Most of the cost is NOT in the science instrument/payload• Full-on RFI study covered slightly larger range, but no Probe Class

mission identified

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The Space-based Gravitational-wave Observatory (SGO) Family of Mission Concepts