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FGS1r AMA Adjustment. STScI/TIPS 02/19/09 Ed Nelan Special Acknowledgements: HSTMO, NASA/GFSC, Merle Reinhart , Denise Taylor, Matt Lallo, Ed Kimmer (GSFC), Linda A-Reed (Goodrich), Mike Wenz, Art Bradley, & the Guide Star Acquisition Working Group. FGS1r AMA Adjustment: Motivation.
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FGS1r AMA Adjustment STScI/TIPS 02/19/09 Ed Nelan Special Acknowledgements: HSTMO, NASA/GFSC, Merle Reinhart, Denise Taylor, Matt Lallo, Ed Kimmer (GSFC), Linda A-Reed (Goodrich), Mike Wenz, Art Bradley, & the Guide Star Acquisition Working Group.
FGS1r AMA Adjustment: Motivation • HST has a spherically aberrated primary mirror. FGS optics does not compensate for the spherical aberration. • Small misalignment of FGS optics degrades interferometric response, and hence performance as a science instrument.
AMA Courtesy Linda A-Reed, Goodrich
FGS1r AMA Adjustment • Concerns & risks: • AMA was last moved October 12, 1998. • Does it still work? • Can AMA failure lead to degradation or loss of FGS1r as a guider? • GSFC convened a review of the proposed AMA move. Participants • STScI • GSFC • MOSES • Goodrich • Approval to proceed granted after FMEA study indicated low risk.
FGS1r AMA Adjustment • Prerequisites: • Determination of AMA move (Goodrich) based upon recently obtained FGS1r S-curves (from science programs 11212, 11943, 11944) • FGS1r OFAD re-calibration (proposal 11870), Dec 12 - 20, 2009 • Preparation of phase2 (11964) proposal to verify OFAD across AMA move, and to provide data to update FGS1r-FGS alignment. • Astrometric field in NGC 5617 • UCAC3 coordinates • Yale proper motions (“special plate” ZZZT) • Alignment shift of ~5” anticipated • Identification of post-AMA move target star to verify FGS1r S-curves are optimal (proposal 11963). • AMA move successfully executed Jan 22, 2009.
FGS1r-FGS Alignment NGC 5617 guide star pairs
FGS1r-FGS Alignment Preparations • Phase2 proposal used “Spacecraft Pointing”, which specifies the RA,Dec of the V1 axis (rather than a POS TARG on a star in FGS1r). • easiest way to generate test visits in APT for finding good guide star pairs. • once a good pointing was found, the S/C pointing was removed and replaced with the equivalent POS TARG in FGS to retain same pointing
FGS1r-FGS Alignment Preparations • Phase2 proposal used “Spacecraft Pointing”, which specifies the RA,Dec of the V1 axis (rather than a POS TARG on a star in FGS1r). • easiest way to generate test visits in APT for finding good guide star pairs. • once a good pointing was found, the S/C pointing was removed and replaced with the equivalent POS TARG in FGS to retain same pointing • but, this made two of the guide star pairs invalid!!!! • use of S/C pointing was put back in to regain the guide star pairs • At SMS generation, S/C exposure lines resulted in “illegal SMS”. • Merle Reinhart “fixed” this by manipulating post-SPIKE files. • All worked out fine.
Post AMA-adjustment verification star, HD 233877 • Standard FGS calibration star known to be single (point source) • Well isolated, tolerant of FGS1r-FGS alignment errors.
Results: S-curves • AMA move successful! • ~80% of misalignment along Y-axis removed. • X-axis alignment undisturbed (as desired).
Results: FGS1r-FGS Alignment As expected, ~5” shift of FGS1r in V2, small shift in V3. • Courtesy Ed Kimmer (GSFC, SAC)
Results: FGS1r-FGS Alignment • New FGS1r-FGS alignment matrix has been delivered to STScI (from Ed Kimmer). • Database updates planned for week of March 1. • Since Jan 22, FGS1r has not been used as the “dominant guider”. • The 5” misalignment would miss-point the telescope by that amount. • FGS1r continues to be used successfully as a sub-dom (or roll control) guider.
