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The Multiband Imaging Photometer for Spitzer (MIPS) provides long wavelength capability for the mission, in imaging bands at 24, 70, and 160µm and measurements of spectral energy distributions between 52 and 100µm at a spectral resolution of about 7%. By using true detector arrays in each band, it provides both critical sampling of the Spitzer point spread function and relatively large imaging fields of view, allowing for substantial advances in sensitivity, angular resolution, and efficiency of areal coverage compared with previous space far-infrared capabilities. The Si:As BIB 24µm array has excellent photometric properties, and measurements with rms relative errors of 1% or better can be obtained. The two longer wavelength arrays use Ge:Ga detectors with poor photometric stability. However, the use of 1.) a scan mirror to modulate the signals rapidly on these arrays, 2.) a system of on-board stimulators used for a relative calibration approximately every two minutes, and 3.) specialized reduction software result in good photometry with these arrays also, with rms relative errors of less than 10%.
We describe the test approaches and results for the Multiband Imaging Photometer for SIRTF (MIPS). To verify the performance within a "faster, better, cheaper" budget required innovations in the test plan, such as heavy reliance on measurements with optical photons to determine instrument alignment, and use of an integrating sphere rather than a telescope to feed the completed instrument at its operating temperature. The tests of the completed instrument were conducted in a cryostat of unique design that allowed us to achieve the ultra-low background levels the instrument will encounter in space. We controlled the instrument through simulators of the mission operations control system and the SIRTF spacecraft electronics, and used cabling virtually identical to that which will be used in SIRTF. This realistic environment led to confidence in the ultimate operability of the instrument. The test philosophy allowed complete verification of the instrument performance and showed it to be similar to pre-integration predictions and to meet the instrument requirements.
NASA's planned Kepler mission uses a space-born Schmidt telescope to search for Earth-size and smaller planets around distant stars using differential photometry. This paper reports the successful design, analysis and implementation of suspending a large actively cooled (-90C) focal plane array with associated electronics inside the warm (0C) Kepler photometer. Since a Schmidt Telescope requires the focal plane to be in the middle of the telescope, it must be suspended while obscuring only a small portion of the incoming light. The Kepler focal plane is comprised of 21 individual science CCD modules and 4 guidance sensor modules covering an area that is roughly 1200 square centimeters in a telescope with a 0.95m aperture. The Kepler system requires the detector data to be digitized near the focal plane, so a detector electronics box is also suspended behind the CCD array. A total of 65 kilograms is supported by the spider structure inside the telescope and must remain stable through environments and during on-orbit operations. Key to the performance of the system is a stiff, light-weight composite structure that supports the focal plane and electronics above the primary mirror. This spider structure is used to align the focal plane with respect to the primary mirror in the system, and is intentionally over-constrained after alignment. Techniques used to align the focal plane to the optical system are discussed and predicted alignment performance and stability are reported. BACKGROUNDThe planned Kepler mission will find out how common Earth-like planets are, and whether or not the structure of our solar system is unique. This is achieved by surveying a large sample of stars to: 1) Determine the percentage of terrestrial and larger planets there are in or near the habitable zone of a wide variety of stars; 2) Determine the distribution of sizes and shapes of the orbits of these planets; 3) Estimate how many planets there are in multiple-star systems; 4) Determine the variety of orbit sizes and planet reflectivities, sizes, masses and densities of shortperiod giant planets; 5) Identify additional members of each discovered planetary system using other techniques; and 6) Determine the properties of those stars that harbor planetary systems.Kepler will search for Earth-size and smaller planets in the habitable zone around distant stars using the transit method. A transit is detected when the light from a star dims slightly due to a planet passing in front of the star. When a planet crosses in front of its star as viewed by an observer, the event is called a transit. Transits produce a small change in a star's brightness of about 1/10,000 or 100 parts per million (ppm) for terrestrial planets and lasting for 2 to 16 hours. This change must be absolutely periodic if it is caused by a planet. In addition, all transits produced by the same planet must be of the same change in brightness and last the same amount of time, thus providing a highly repeatable signal and robust detection method.Once detected, the planet's orbit...
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