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.

• 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

AMA
LOGO.049
Courtesy Linda A-Reed,
Goodrich

• 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.

• Prerequisites:

Determination of AMA move (Goodrich) based upon recently obtained FGS1r Scurves (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: finding the best pointing

• 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 NGC 5617

FGS1r-FGS Alignment NGC 5617

• 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.

• AMA move successful!
– ~80% of misalignment along Y-axis removed.
– X-axis alignment undisturbed (as desired).

As expected, ~5” shift of FGS1r in V2, small shift in V3.
– Courtesy Ed Kimmer (GSFC, SAC)

• 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.