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D. Koch (NASA Ames), F. Witteborn (Orbital Sci), E. Dunham (Lowell Observ), J. Jenkins (SETI Institute), W. Borucki, W. Webster (NASA Ames)
A testbed facility has been constructed to perform end-to-end laboratory tests of the photometric method for finding terrestrial-size planets. The main objective of the facility is to determine the effects of various induced noise sources on the capability of a CCD photometer to maintain an instrument relative precision of better than 1x10-5.
The photometry facility includes: a simulated star field with a source to approximate a solar spectrum, fast optics to simulate the telescope, a thinned back-illuminated CCD similar to those to be used on the spacecraft operating at 1 MHz read rate, shutterless operation, and computers to perform the onboard CCD control and data handling. The test structure is thermally and mechanically isolated. Each source of noise is introduced in a controlled fashion and evaluated as to its contribution to the total noise budget. Pointing noise or changing thermal gradients in the spacecraft can cause star-image motion at the milli-pixel level. These motions are imposed by piezo-electric devices that move the photometer relative to the star field.
Signals as small as those associated with terrestrial-size transits of solar-like stars are produced in the facility. This is accomplished by electrical self-heating and expansion of fine wires placed across many of the star apertures. The effective small decrease in stellar brightness is used to demonstrate that terrestrial-size planets can be detected under realistic instrument noise conditions and at the shot-noise-limited level. Algorithms identical to both the onboard and ground processing systems are used to extract and process the data. These processes use differential photometry to construct light curves and search for transits. Examples are presented of the effects of imposing several noise sources and the resulting detectability of planets.
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The author(s) of this abstract have provided an email address for comments about the abstract: dkoch@mail.arc.nasa.gov