The LDEF Interplanetary Dust Experiment

Abstract

The Long Duration Exposure Facility was launched for the first time on April 6, 1984 by the NASA space shuttle Challenger. An array of solid-state detectors record the arrival time and approximate direction of an impacting particle. Two levels of detector sensitivity provide an indication of particle energy and mass. The active area is nearly 1 m2. We therefore expect count rates of about 30 per day over an exposure time of about a year. The orbit of the particle cannot be obtained, except statistically. We know the orientation of the detector, the position of LDEF in earth orbit, and the position of the earth in relation to other celestial bodies. From this information we can extract essential orbit information.An earlier flight on the Explorer 46 satellite gave first evidence of the existence of submicron-sized particles, mostly associated with fresh meteor streams. We hope to obtain more precise data and estimate lifetimes in interplanetary space.To study the fate and origin of IP (interplanetary) dust, we measure various kinds of time variations. Among the most interesting is the secular variation, i.e., the flux in various meteor streams, as a function of the passage of a comet.One of the challenging problems will be to distinguish IP dust from man-made space debris. The separation will depend on knowing something of the orbits of debris. Probably more important will be the chemical analysis of the particles. The two types of information are in a sense complementary.