Briefing to STUC - STScI · Briefing to STUC David Leckrone HST Senior Project Scientist April 13, 2007. Topics ... 030507_PMB_ACS_Status.ppt 5 Goddard Space Flight Center Role of

042001_DL_Origins.ppt

Briefing to STUC

David LeckroneHST Senior Project Scientist

April 13, 2007

Topics

• Loss of ACS• Degradation of COS NUV Gratings• The Priority-setting Process• Important Questions Regarding SM4

MISSION GOAL: Five working, complementary instruments for the first time since 1993; Hubble at its APEX.

Batteries+Gyros+FGS = Sustained HST Lifetime

WFC3+ACS = Most powerful imaging ever

COS+STIS = Full set of tools for astrophysics

ACS SCIENCE: WHAT HAVE WE LOST?Survey efficiency at visible-red wavelengths, hampering wide field SN Ia surveys for dark energy studies and mapping of dark matter via galaxy weak lensing

Optimized coronography; partially restored by STIS

Grism spectroscopy of high-z SN; restored by

WFC3

t1

t2

3-D dark matter mapt1 - t2

Hubble Space Telescope Program

5030507_PMB_ACS_Status.ppt

Goddard Space Flight Center

Role of ACS in HST Post-SM4 Imaging CapabilityHST Discovery Efficiency

200 300 400 500 700 1000 2000Wavelength (nm)

100

1000

10000

Thr

ough

put x

Are

a (a

rcse

c2 )

ACS/HRC

WFPC2

WFC3/UVIS

ACS/WFC

NICMOS/NIC3

WFC3/IR

4xACS/WFC

2.5x

ACS/WFC superior to WFC3 survey efficiency at visible-red wavelengths


6070211_ACS_Status.ppt

Goddard Space Flight Center Yearly Time Allocation By Instrument (%)

Observing Cycle (July 1 – June 30)

FGS

WFPC2

NICMOS

STIS

ACS

2006200520042003

1.33.90.75.0

18.67.38.52.3

25.119.618.721.1

N/AN/A30.116.8

55.169.241.954.8

Logic Flow for Considering ACS Repair

• ACS advocates have begun lobbying for ACS repair, even if it means not repairing STIS

• Several scientists interested in STIS have urged that STIS repair be given priority

• The HST Senior Project Scientist is intent on translating this issue into a more constructive and appropriate form– White papers for post-SM4 science capabilities of STIS

and ACS, assuming COS and WFC3 have been installed

• Developed under STScI leadership– Useful for mission contingency planning– Useful in explaining mission content to the outside

world

Logic Flow for Considering ACS Repair (cont’d.)

• The issue of ACS repair requires answers to the following sequence of questions:– Can we identify the cause of the electrical short?– Was there any collateral damage to ACS?– Are there credible engineering concepts for repairing or

circumventing the problem that don’t place HST at further risk?

– If so, how much EVA time would they require?– Can we develop an EVA time line to accomplish ACS

repair without sacrificing other items on the manifest?– If not, what items could we remove from the manifest

that are of lesser priority than ACS repair and how would those relative priorities be established?

Possible Degradation of COS NUV Gratings

• COS G225M and G285M bare aluminum gratings showed unexpectedly low throughput in thermal-vac calibration measurements, relative to 2003

• Ambient monitoring of throughput every six months appears consistent with loss of ~1.2% per year in G225M and ~4.4% per year in G285M.– Worst case would be ~20-25% loss in throughput in G285M at

SM4 launch– Continuation of degradation after launch depends on root

cause• Search for root cause of degradation

– Oxidation of aluminum coating– Pin holes in coating that admit moisture below oxide layer– Uncontrolled polarization of calibration input sources– Upward migration of gold undercoat– Thin layer of surface contamination

Variances in measured COS sensitivities in vacuum 2006/2003

Variation Of COS NUV Bare Aluminum Grating Efficiency With Time

Possible Degradation of COS NUV Gratings (Cont’d.)

• Current status– Flight spare gratings show similar degradation with

time• Original test setup reproduced• Polarization well controlled

– Flight spare shows no evidence of gold migration– Latest ambient throughput measurement with

internal cal lamps shows degradation is continuing– Instrument level test for polarization sensitivity

consistent with grating degradation– Very preliminary results from lab measurements

point toward thin film surface contaminant on flight spare

Keyes – 18 January 2007Slide 13 of 19

Sensitivity Ratio: COS TV I vs STIS(no dark included)

COS M mode / STIS E230M throughput ratio (R~20,000 (0.12 Ǻ) binning)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

1600 1800 2000 2200 2400 2600 2800 3000 3200

Wavelength (Ǻ)

Rat

io

COS G185MR~16,000-20,000

COS G285MR~20,000-24,000

COS G225MR~20,000-24,000

STIS STIS aperture aperture throughput throughput includedincludedNo COS No COS degradationdegradationincluded included No darksNo darksincludedincluded


Impacts: Ratios of exposure to achieve same S/N with degraded sensitivity

0.09 (0.24)0.09 (0.24)1.45 (1.64)1.45 (1.64)1.e1.e--1515

1.68 (1.76) [>40 orbits]1.68 (1.76) [>40 orbits]1.62 (1.74) [>40 orbits]1.62 (1.74) [>40 orbits]

1.50 (1.69)1.50 (1.69)

1.35 (1.41)1.35 (1.41)1.33 (1.34)1.33 (1.34)

COS Exposure ratio COS Exposure ratio to reach S/N = 10to reach S/N = 1025%25%--degraded Sdegraded Sλλvsvs nono--loss COS Sloss COS Sλλ

with COS ground dark with COS ground dark (with worst(with worst--case oncase on--orbit dark)orbit dark)

0.04 (0.21) [>40 orbits]0.04 (0.21) [>40 orbits]1.e1.e--16160.05 (0.22) [>40 orbits]0.05 (0.22) [>40 orbits]2.e2.e--1616

0.07 (0.23)0.07 (0.23)5.e5.e--1616

0.29 (0.36)0.29 (0.36)1.e1.e--14140.43 (0.44)0.43 (0.44)1.e1.e--1313

COS/STIS Exposure ratio COS/STIS Exposure ratio to reach S/N = 10to reach S/N = 10

25%25%--degraded COS Sdegraded COS Sλλvsvs STIS SSTIS Sλλ

with COS ground dark with COS ground dark (with worst(with worst--case oncase on--orbit dark)orbit dark)

Object Object FluxFlux


Impacts: COS Orbits Required to Execute Large STIS programs using E230M (worst-case COS dark)

withwith

22

88

88

88

33

33

88

88

COSCOSsettingssettings

33/setting33/setting6666








COS orbits noCOS orbits no--loss Sloss SλλTotal orbits neededTotal orbits needed

130 / 6130 / 61. e1. e--1414

42 / 342 / 34. e4. e--15 [S/N~15]15 [S/N~15]

48 / 148 / 13.e3.e--14 [S/N=50]14 [S/N=50]

45 / 245 / 25.e5.e--15 [S/N~25]15 [S/N~25]

30 / 130 / 12. e2. e--15 [S/N~10]15 [S/N~10]

38 / 238 / 24. e4. e--15 [S/N~15]15 [S/N~15]

40 / 140 / 11.1 e1.1 e--15 [S/N<10] *15 [S/N<10] *

57 / 157 / 11.e1.e--14 [S/N~40]14 [S/N~40]

STIS orbits / No. TargetsSTIS orbits / No. TargetsFFλλ [S/N][S/N]

1015110151(J. (J. HowkHowk))

86738673(B. (B. JannuziJannuzi))

93599359(R. (R. CayrelCayrel))

91869186(J. Webb)(J. Webb)

91739173(J. (J. BechtoldBechtold))

90409040(D. (D. ReimersReimers))

84718471(E. Jenkins)(E. Jenkins)

81118111(C. (C. SnedenSneden))

ProgramProgramIDID









COS orbits degraded SCOS orbits degraded SλλTotal orbits neededTotal orbits needed

*=at STIS detection limit


16


Flowchart.ppt

Priorities Determination ProcessInitial Ordering

• Spacecraft Health & Safety• New Science Instruments

• Science Maintenance

Update Evaluations• Changes to Health & Safety

• Performance Trending• Science Impacts

• Available Shuttle Resources• Life Extension Efforts

Baseline Draft Priorities• Level 2 Requirements

• PIP

Input to EVA Timeline

Construction

EVA Efficiency Evaluation• Choreography

• EVA Resources

Current Status

Reassess Priorities

User Community Vetting• Science Community• Center Management

•SSP•HQ

Revise Priorities

?

Finalize Priorities

No

YesNo

Final EVA TimelineReduced Mission

Flight RulesMission Success

Criteria

Concurrence from SMD

AA?

Yes

SM4 Issues and Questions

Relative priority of WFC3 and COS in contingency planning– STUC conclusions

The best arguments against further SM4 launch slips– Spacecraft issues– Science issues– Programmatic issues

Decision regarding replacement of COS NUV grating(s)– Availability of high quality replacements– Risks versus benefit of “surgery” on instrument– Possible mitigation versus replacement

Continuation of ACS/SBC Side 1 operations up to SM4– Risks to ACS reparability if Side 1 fails again before SM4

Relative priority of STIS and ACS repair in contingency planning– ACS repair option strongly driven by EVA timeline efficiency

Vetting of SM4 manifest priorities in general

18


071804_SM4_CDR.ppt

HUBBLE SPACE TELESCOPE PROGRAMSM4 Mission CDR/TRR

BACKUP

Relative Priorities of COS and WFC3

• Priorities will need to be set as part of overall prioritization process• Once EVA’s begin it is highly probable that both instruments will make

into HST– Prioritization is a formality that guides both pre-mission contingency

planning and real-time responses to in-orbit emergencies (very low probability)

– It is a painful, divisive process that hopefully will have no use in the end, but it must be done

• Priorities may change with time and unfolding events– Loss of redundancy on ACS influences priority of WFC3 because of

threat to overall imaging capability of Hubble– Loss of STIS influences priority of COS; there currently is no UV

spectroscopic capability in space other than FUSE– Possibility of restoring STIS can’t a priori influence priority of COS since

contingency decisions would likely have to be made prior to attempt at STIS repair and STIS repair is uncertain.

• Priorities should be driven by science – the most compelling science should have highest priority

• This is a scientific “Sophie’s Choice”• STUC’s inputs on this question are solicited as part of the bigger process

– Would like recommendation and supporting rationale by next Spring

Documents

Briefing to STUC - STScI · Briefing to STUC David Leckrone HST Senior Project Scientist April 13, 2007. Topics ... 030507_PMB_ACS_Status.ppt 5 Goddard Space Flight Center Role of