A comparison of statistical measurements of the orbital debris environment using radars

The U.S. Space Command maintains a deterministic catalog of orbiting satellites and debris, which dates back to the beginning of the Space Age. However, the sensors and techniques used to create and maintain the catalog limit the size of the tracked objects to sizes larger than about 10-30 cm diameter. In order to understand the orbital debris environment for sizes smaller than this, statistical sampling has been used. NASA has been using the Haystack radar to statistically monitor the orbital debris environment since 1990. The Haystack measurements have been NASA's primary source of data in the important 0.4-20 cm diameter size range. Although the Haystack data comprise the largest database of observations, other radars have also been used to statistically sample the debris environment. The Haystack Auxiliary (HAX) radar, co-located with Haystack, began collecting debris data in 1994. By sharing location, real-time data collection hardware and software, and post-mission data analysis, any differences in results should be attributable to wavelength effects. The Goldstone radar is slightly more sensitive than Haystack and actually began sampling the debris environment in 1989, although for only a few hours each year. In 1996, a radar measurement campaign coordinated by the inter-Agency Space Debris Coordination Committee (IADC) was conducted using Haystack, the FGAN/TIRA radar operated in a bi-static mode with the Effelsbeg radio telescope, and the TRADEX radars. During this campaign each radar collected approximately 24 hours of statistical debris data. Limited data are also available from the ALTAIR, MU, and Arecibo radars collected prior to 1990. This paper will compare the results of these different measurements and attempt to reconcile any observed differences.