HESSI Imaging Capability Pre Environmental Review Brian R. Dennis GSFC Tuesday, February 29, 2000

HESSI Imaging Capability

Pre Environmental Review

Brian R. Dennis

GSFC

Tuesday, February 29, 2000

Brian R. Dennis 2/29/2000


HESSI Imaging

• Confidence that Imaging will work within specifications– Grids and Telescope

• Initial Alignment

– Grid characterization measurements – optical, X-ray, and mechanical

– Shims under grid mounts to align field of view to telescope axis

– CMM measurements of grids & trays at ETH in Zurich

– Alignment of trays on telescope tube using CMM at PSI

• Confirmation of Alignment

– TMS measurements of grids 1 – 8 and both trays at PSI

– Gridlet test for grids 1 – 6 at PSI

– Direct optical confirmation for grids 6 - 9

– Tilt test for grids 1 – 6 at PSI

– TMS measurements at SSL

• Imaging Simulation Test at SSL



HESSI Imaging Confidence that Imaging will work within specifications

Solar Aspect System (SAS) - Functional• SAS solar exposures at PSI with 3 CCD’s

– <0.5 arcsecond (1) spatial resolution verified• Functional electrical tests on spacecraft at SSL

– Baseline read-out speed = 128 Hz– Dark level negligable (<1 ch – 0.5 mV)– Not affected by any noise source on spacecraft

• SAS generated ACS signal for S/C (redundancy for FSS) tested at PSI

SAS Alignment• Optical axis measurements of SAS lenses at Fisba (Switzerland) to 2 – 3 m

• CMM measurements of SAS CCD pixels and lens fiducials at ETH in Zurich



HESSI Imaging

Roll Angle System (RAS) – Functional

CCD RAS provided by PSI

• Exposed to stars at the Jungfraujoch in Switzerland

– Sensitivity confirmed with m~0 stars

– PSF 0.52 pixels (1 sigma)

– Required 1 arcminute roll angle accuracy achieved

• Functional electrical tests on spacecraft at SSL

– RMS noise @17C = 0.3mV (0.7 ch.) – baseline m2 star gives 12 chs.

– Increase trigger efficiency by summing (2-4) spatial pixels

– Transmitting selected matrix in time and space around star signal

Redundant PMT RAS provided by SSL

RAS Alignment Confidence• Optical axis determined at PSI relative to tooling balls

– Stable to <1 arcminute through vibration

• Portable CMM alignment measurements of CCD RAS on spacecraft at SSL

• Optical alignment measurement of PMT RAS on spacecraft at SSL



HESSI Imaging

• Confidence that telescope will survive environmental tests

• Vibration and thermal cycling of all grids and mounts at GSFC

• Telescope vibration and thermal cycling at Contraves in Switzerland

• CCD RAS vibration at PSI and thermal cycling at PSI and SSL

• PMT RAS tests at SSL

• Plans for checking imaging capability after environmental tests

• TMS measurements of grids 1 – 8 and grid trays

• SAS functional electrical tests with photodiode stimulators

• CCD RAS CMM alignment measurement & functional electrical tests with lasers for star simulation & photodiodes for Earth albedo simulation



X-Ray Grid Characterization Results

Typical On-Axis Fractional TransmissionsCd109 Data

Grid Front Rear Nominal 1 0.56 0.55 0.60 2 0.54 0.55 0.60 3 0.47 0.47 0.60 4 0.55 0.56 0.60 5 0.57 0.57 0.60 6 0.60 0.60 0.60 7 0.52 0.54 0.52 8 0.51 0.51 0.51 9 0.52 0.51 0.54



P A U L S C H E R R E R I N S T I T U T

Laboratory for Astrophysics

Principle of Twist Monitoring System TMS

Rear Grids: 4 Laser DiodesFront Grids: 2 Annuli 3mm Dia

Interference Pattern on CCD Camera



TMS SUMMARYGrids 1 - 4

-80

-60

-40

-20

0

20

40

60

80

0 1 2 3 4

GRID

TW

IST

[a

rcse

c]

TMS Measurement Limits

Grids 4 - 8

-400

-300

-200

-100

0

100

200

300

400

4 5 6 7 8

GRID

TW

IST

[

arc

se

c]



History of TMS Results

-20

-10

0

10

20

30

40

2-Aug-99 1-Sep-99 1-Oct-99 31-Oct-99 30-Nov-99 30-Dec-99 29-Jan-00 28-Feb-00

TW

IST

(a

rcs

ec

)

Grid1 Grid2 Grid3 Grid4 Tray

Gridlet Test

Sept. 8

CM M 2

Vibration and

Thermal Cycling

CM M 1



Gridlet Test Setup

1550 mm 1550 mm

Scintillation Detector Front Grid

Grid Gridlet

Cd109 Source

Mask

Rear Grid Grid

Slits run parallel to plane of figure. paper.

Source & Gridlet

Move into Paper



GRIDLET TEST

• Objective is to verify relative twist of the front and rear grids.

• Any subsequent changes in twist can be monitored by the TMS.

• Method:

– Cd109 source is located behind a ‘gridlet’ located in front of imager

– Two side-by-side detectors measure X-ray transmission through subcollimator.

– Motion of the source perpendicular to slits modulates the observed count rates.

– Grid twist is indicated by difference in modulation phase as seen by twin detectors.

– Modulation is due to 2nd harmonic response of front grid.

• Results are completely independent of GSFC grid characterization data.

• Modulation phase is independent of any test setup misalignments.

• Test-setup misalignments affect only the amplitude of the modulation.



GRIDLET TEST RESULTS



GRIDLET TEST

RESULTS



GRIDLET TEST RESULTS

Grid No.

Phase Difference (degrees)

Relative Twist (arcminutes)

Mod. Eff.

Goal Measured Goal Measured CMM Goal

1 49 5.0 0.33 0.03 -0.09 94.9%

2 43 2.6 0.5 0.03 -0.17 96.2%

3 30 20.3 0.6 0.41 0.09 98.2%

4 28 7.4 1.0 0.26 -0.30 98.3%

5 26 24.8 1.6 1.50 1.30 98.6%

6 24 4.7 2.5 0.49 -0.09 98.8%



GRID TILT TEST

– Objective is to measure the angle between the direction of maximum grid throughput and the imager axis.

– Tilt test results verify:• Correct calculation and installation of shims;

• Flatness of trays;

• Absence of tilt due to grid-frame distortion.

– Test setup is same as for gridlet test, except:• Gridlet tray is removed.

• Source displacement steps are ~cm, instead of ~microns

• Slit over detector to limit range of angles

– Correct tilt is confirmed if maximum count rate is achieved when source is positioned on subcollimator axis.



RESULTS OF SEPTEMBER 1999 TILT TESTS AT PSI

<Residual Tilt> arcminutes

Grid No.

XGCF Tilt Test Req’mnt

FOV arcmins

1 -0.4 1 12 60 2 -0.5 -2 12 60 3 -0.6 +2 12 60 4 -0.8 -2 12 60 5 -5.5 -8.3 12 60 6 -0.6 -4.3 12 60 7 2.1 n/a 12 264 8 1.8 n/a 12 450 9 -2.1 n/a 12 168



Tilt Test Results



HESSI Imaging Simulation Test Test Image

List of Randomized Photon Arrival Times

Hardware injection of timed sequence of pulses into detector test inputs

T/M file generated by imager, S/C, & GSE

Analysis of T/M file using HESSI software

analysis package

Output Image

Software conversion to telemetry format



Imaging Simulation Test ResultsSingle gaussian source, 2 arcseconds wide, 10,000 photons/s/collimator for 4 s

Test Image Output Image

Documents

HESSI Imaging Capability Pre Environmental Review Brian R. Dennis GSFC Tuesday, February 29, 2000