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Software Simulations Of The Detection Of Rapidly Moving Asteroids By A Charge-Coupled Device

Because of the considerable interest in a space probe mission to a near-Earth asteroid, we are developing the techniques necessary for a ground-based telescopic survey to increase the known number of such objects. The faintness (apparent magnitude = 18 to 21) and angular speed (up to 1 arcsec per second) make the techniques of detection different from the photographic and vidicon methods currently being used to observe distant asteroids and artificial satellites. The geometric stability and regularity of the pixels in a CCD will allow better measurements of relative positions of stars and asteroids than are possible with film or vidicons, but to take full advantage of CCD's we have considered the effects of the earth's atmosphere, the image scale (arcsec/pixel), the spectral bandpass, the exposure time, the detective quantum efficiency of the CCD, the direction of asteroid motion with respect to the CCD channel boundaries, and the time between the two scans from which the asteroid motion is to be inferred. Two interesting tradeoffs are (i) the high signal-to-noise ratio of a broad spectral bandpass versus the sharper images due to the small atmospheric dispersion associated with a narrow bandpass and (ii) the greater sensitivity to motion resulting from a long time interval between the two scans versus the greater changes of atmospheric dispersion, seeing, and anomalous refraction over long time intervals.