High-Resolution Bistatic Radar Imaging With The Deep-Space Network

Recent upgrades to the Deep Space Network's Goldstone Solar System Radar allow the transmitted waveform to be modulated at up to 40 MHz, providing resolution as fine as 3.75 m in line-of-sight distance for near-Earth asteroids (NEAs) and the Moon. Bistatic observations, transmitting with an antenna at Goldstone and receiving with either another Goldstone antenna or a larger antenna such as the Arecibo Observatory or the Green Bank Telescope, give the highest possible sensitivity combined with high resolution. High-resolution bistatic radar projects have revealed spin state changes and the presence of boulders on many NEAs. Examples include radar imaging campaigns on the NEAs 2005 YU55, Toutatis, 2012 DA14, and 2014 HQ124. In the near future, a new high-resolution transmitter on Goldstone's DSS-13 antenna will be able to transmit a signal modulated at 80 MHz, improving line-of-sight resolution by a factor of two to 1.875 m. This will allow many new projects: seeing previously-invisible surface details; measuring the size distributions of boulders and possibly craters on small NEAs; obtaining better estimates of the masses and densities of asteroids from radiation pressure perturbations to their trajectories; improved trajectory predictions for small spacecraft targets and potential Earth impactors; and possibly imaging the reconfiguration of asteroids' surfaces due to tides during extremely close Earth flybys. Somewhat further into the future, a 1.875-m-resolution transmitter may be installed on a 34-m antenna at the DSN's Canberra complex. This would allow radar imaging of objects in the far southern sky, which current radars cannot see. It would also facilitate rapid follow-up of newly discovered radar targets and before-and-after observations of NEAs making flybys close enough to cause tidal reconfiguration, which move very quickly across the sky at closest approach. As with the current 3.75-m-resolution system, these future high-resolution transmitters will provide the best scientific results when operated in bistatic mode with a large antenna as the receive station. Equipment to be installed at Arecibo and at Green Bank is able to record 80-MHz-coded radar echoes.