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12 October 2004 The state of the focus and image quality of the Spitzer Space Telescope as measured in orbit
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We describe the process by which the NASA Spitzer Space Telescope (SST) Cryogenic Telescope Assembly (CTA) was brought into focus after arrival of the spacecraft in orbit. The ground rules of the mission did not allow us to make a conventional focus sweep. A strategy was developed to determine the focus position through a program of passive imaging during the observatory cool-down time period. A number of analytical diagnostic tools were developed to facilitate evaluation of the state of the CTA focus. Initially, these tools were used to establish the in-orbit focus position. These tools were then used to evaluate the effects of an initial small exploratory move that verified the health and calibration of the secondary mirror focus mechanism. A second large move of the secondary mirror was then commanded to bring the telescope into focus. We present images that show the CTA Point Spread Function (PSF) at different channel wavelengths and demonstrate that the telescope achieved diffraction limited performance at a wavelength of 5.5 μm, somewhat better than the level-one requirement.
© (2004) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Robert Douglas Gehrz, Edward A. Romana, William F. Hoffmann, John P. Schwenker, John Eric Mentzell, Joseph L. Hora, Peter R. Eisenhardt, Bernhard Rainer Brandl, Lee Armus, Karl R. Stapelfeldt, Dean C. Hines, Amanda K. Mainzer, Erick T. Young, and David G. Elliott "The state of the focus and image quality of the Spitzer Space Telescope as measured in orbit", Proc. SPIE 5487, Optical, Infrared, and Millimeter Space Telescopes, (12 October 2004);

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