(abstract) Asteroid Radar Astronomy at Goldstone in the 1990s

Since 1990, much effort has been devoted to optimizing Goldstone's capability to study near-Earth objects (NEOs). Three different configurations are now available. The nominal system on the 70-m antenna (DSS 14) uses separate feed horns for transmitting and receiving, and the 15-plus seconds required for transmit-to-receive switching renders the system useless for targets much closer than about 0.025 AU (about 10 lunar distances, about 25 seconds of echo time delay) and unwieldy even for targets twice that far. However, an additional, recently installed single horn system shrinks switching time to about 5 seconds, letting DSS 14 observe NEOs as close as about 5 lunar distances. Closer targets will require two-station observations, with DSS 14 transmitting continuously while DSS 13, a 34-m antenna 22 km away, receives. That configuration, first used for Toutatis, will also be required for delay-Doppler imaging that places thousands of pixels on any NEO whose rotation period P(h) and echo roundtrip time delay RTT (s) satisfy P > RTT. Between January 1990 and June 1994, the Goldstone radar has detected 11 asteroids. During the next 2 years, seven asteroids are scheduled for Goldstane observations. After completion of the Arecibo upgrade, Goldstone will play an important complementary role to that much more sensitive instrument.