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This document outlines the successful adjustment and alignment of the FGS1r system for the Hubble Space Telescope (HST), addressing concerns about spherical aberration impacts on performance. It includes acknowledgments of key contributors, prerequisites, and the methodical approach taken for the adjustment, including the use of specific proposals for verification. Post-adjustment, significant improvements were noted, including an ~80% reduction in Y-axis misalignment and confirmation of operational capacity as a sub-dominant guider. The new alignment matrix has been delivered to STScI for database updates.
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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.
