FLUX OF MILLIMETRIC SPACE DEBRIS

In 21.4 hr of zenith radar observations on 4 days at 8510 MHz, we foun d 831 particles with altitudes between 177 and 1662 km. From the durat ion of the echoes and the angular size (0.030 degrees) of the antenna beam 157 particles were identified as passing through the side lobes a nd not through the main beam. Our analysis is based on the 674 particl es that did not broaden the beam. On the assumptions that these partic les went through the main beam, their radar cross sections vary betwee n 0.02 and 260 mm(2), and their radial velocities vary between +/-700 m/s. if they are conducting spheres, their diameters lie between 2 and 18 mm. If not, they must be larger. The flux of these particles, that is the number per km(2) day, was determined in 100 km intervals. The maximum flux, 3.3 particles per km(2) day, occurs at 950 km altitude. The small and large particles are not well mixed. The largest particle s occur beyond 1000 km and middle-sized particles are missing below 30 0 km. if the earth's atmosphere caused the smallest particles to lose energy from initial orbits identical to those of the large particles, the orbits would have lower eccentricity at low altitudes. We find a l arger eccentricity for the inner particles, and conclude that two or m ore populations are present. (C) 1995 American Astronomical Society.