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Space Telescope Imaging Spectrograph

ACTIVITY TITLE: STIS Corrector and Focus Alignment Contingency



DESCRIPTION: This is a contingency activity that will only be needed if STIS-11 finds a significant problem with the STIS focus or optical alignment. Visits will be prepared to repeat the coarse alignment sweeps that were done during SMOV2 (program 7075), and the fine alignment sweeps that were prepared for SMOV3a/b (programs 8512/8966), and to repeat the checks done by STIS-11. Only those visits that are judged necessary will be executed. Coarse sweeps will be done by taking images of a bright star using the F28X50OII filter; phase retrieval techniques will then be used to analyze the focus and alignment. Fine sweeps will use the G230LB grating together with the 0.1x0.09 aperture, and the optimal focus and alignment will be defined as the settings that maximize the throughput for this combination. After the optimal corrector positions have been determined and set, the observations done by STIS-11 will be repeated to confirm the success of these procedures.

IMPLEMENTATION METHOD: Stored commanding & real-time commanding. Stepping of mechanism during sweeps and data acquisition can be done with stored commanding, but uplinks of updated mechanism position values will be done using planned real-time commanding.

DEPENDENCIES: The activity will not be done unless the analysis of data from STIS-11 shows a significant problem that can be fixed by adjustments of the STIS corrector mechanism. The beginning of this activity may also require waiting until the HST focus can be independently determined via measurements with other HST instruments.

DURATION: 16 Orbits (external). Coarse alignment: 3 orbits over 3 days. Fine alignment: 8 orbits (tip/tilt) followed 24 hours later by 4 orbits (tip/tilt). Final confirmation of throughput and image quality: 1 orbit.

DATA REQUIREMENTS: Coarse alignment 1.5 Gbit; fine alignment 1 Gbit.

ANALYSES & EXPECTED RESULTS: Coarse-alignment data will be analyzed using phase retrieval techniques to estimate desired tip, tilt, and focus values. Fine alignment data will be analyzed to determine the position that will maximize the throughput of the 0.1X0.09 aperture. If this activity is needed, most or all STIS external observations that executed before the final corrector settings had been determined and uplinked, may need to be repeated. Requires support of TEL branch personnel to analyze some data.

COMMENTS: The tip and tilt of the corrector should be set to within 1 step of their optimal values and focus should be set within about 250 steps of the position required to achieve maximal transmission through the 0.1x0.09 aperture.

AUTHOR/telephone/email: Charles Proffitt/410-338-4938/

DATE: September 21, 2007