THE COMBINATION

Radar monitoring of small particles of orbital debris at NASA’s Goldstone Tracking Station has resulted in the detection of 1124 objects in 38.4 hours of observations. Many of the objects orbit in clusters; the largest appears to be remnants of the West Ford Needles, launched 3 decades earlier. 1 . Introduction b d~(~~~ rbiting debris is recognized as a present and growing ~d for both humans and machines in space. Space collisions can have a closing velocity of 15 km s-l, and even small particles are a serious safety concern. Knowledge of the changing environment of debris is necessary for both space mission design and for the assessment of debris mitigation policies. Currently, the United States Space Command, Johnson (1993), maintains a catalog of orbital elements of space objects larger than about 10 cm. Monitoring of the flux of smaller ob-jects has been accomplished by routine ground-based optical, Potter (1995), and radar observations, Stansbery, et al (1993) . Very small particles of orbiting debris have also been detected by in situ spacecraft, Mandeville and Berthaud (1995), which have subsequently returned to Earth. Occasionally, a 3.5 cm radar at NASA’s Goldstone tracking station is available for orbital debris observations. This powerful radar which can detect a 3 mm conducting sphere orbiting at an altitude of 1000 km, helps to fill an observational gap in the on-going debris survey, Goldstein and Randolph (1992) and Goldstein and Goldstein (1994 and 1995).