The Wide Field Camera 3 (WFC3), to be installed in the Hubble Space Telescope (HST) in the fourth servicing mission in early October 2008, underwent its third and final thermal vacuum campaign in its flight configuration at the Goddard Space Flight Center from late February through March 2008. A brief description of the instrument and details of the thermal vacuum tests and stimuli for an earlier campaign were described in Cassiopeia Summer 2007 (No. 133). In this latest round of tests, ~31 days were fully dedicated to science calibration activities. These were bracketed by detector alignment and system functional tests in ambient environment. Approximately 265 data acquisition scripts were executed and 10605 exposures were acquired, so far bringing the total number of exposures to ~60000 over the entire ground calibration of the instrument.
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Fig. 1: The vacuum chamber (and banner) in the final testing of WFC3 at GSFC. |
In late May, the successful Guest Observer programs were announced for Cycle 17 (Jan-Dec 2009) and WFC3 was by far the most popular instrument on HST, garnering approximately 45% of the total number of approved orbits (a majority going to its infrared observing channel, a 1kx1k HgCdTe array (120″x140″) cooled thermoelectrically). The WFC3 team at STScI is now documenting the technical aspects of the instrument based on the recent ground testing, supporting the principal investigators of the approved programs, and updating the WFC3 documentation.
The programs for the Servicing Mission Orbital Verification (SMOV) are also being finalized. There are approximately 45 programs that will exercise all aspects of WFC3 in the three months following the release of HST from the space shuttle bay and before the start of the science observations. The activities cover basic items such as focusing the optical and IR channels, exercising the internal mechanisms such as the filter wheels and channel select paddle, testing the internal calibration system, refining the plate scales and the PSF shape, characterizing the detector behavior during passage through the South Atlantic Anomaly, measuring the total throughput for the primary filters, etc.... During this period, the WFC3 activities will be intertwined with those of the other HST instruments and in December, the SMOV programs will be interspersed with Early Release Science Observations. On-orbit calibration programs are also being formulated for the entire duration of Cycle 17 to update and monitor the behavior of the instrument.
Some team members are also participating in full-blown simulations of the servicing mission. These simulations are designed to be as realistic as possible : they track the timelime of the astronauts' Extra-Vehicular Activities and all decisions concerning the health and safety of the instrument immediately after installation in the telescope are made in real-time through the entire chain of command. Evaluation of system functional test data is made at both GSFC and at STScI. Some simulations are also conducted in tandem with the astronauts working in the neutral buoyancy pool at the Johnson Space Center. WFC3 will rejuvenate HST with powerful new capabilities that will lead to new discoveries for years to come.
More information on WFC3 can be found at the Web sites of STScI/WFC3 and GSFC/WFC3.