|Space Telescope Science Institute|
|FGS Instrument Handbook Cycle 23|
Long term monitoring of the FGS1r S-curves revealed a slow but continuous degradation of the Y-axis S-curve until about 2005. However, changes after 2005 were insignificant, indicating that FGS1r had finally reach long term stability. In late 2008, when HST’s science instrument compliment was reduced to ACS/SBC, WFPC2, and FGS, the reduced science pressure on access to HST assets motivated the decision to allocate the resources needed to re-optimize the FGS1r S-curves via an AMA adjustment. BF Goodrich optical engineers successfully executed the AMA adjustment (see Figures 2.7 through 2.9 for reference). It is expected that the current FGS1r interferometric performance, with its restored ability to detect and resolve close binary star systems, will be in place for the remainder of the HST mission.