of its time. Goldstone is the only one of NASA’s three 70-meter telescopes (the others are in Spain and Australia) equipped with a high-power transmitter. The long-term future of Goldstone is uncertain; the DSN is considering decommissioning all of its 70-meter telescopes after 2015 and switching to an array of 34-meter-diameter telescopes. Whether a radar capability comparable to the present Goldstone capabilities would continue is unclear.
Because it is fully steerable, Goldstone can track objects significantly farther north and south than can Arecibo, and for up to several times longer per day. Limits on Goldstone’s coverage are also imposed by the requirement that targets be 20° above the horizon. Opportunities known well in advance are scheduled months or even years ahead. However, the Goldstone radar competes for telescope time with numerous NASA spacecraft missions that have higher priority and that often limit the time available for radar observations. The antenna is also available for short-notice target-of-opportunity observations if the flight projects have sufficient scheduling flexibility to accommodate changes, and if radiation clearance can be obtained in time from the numerous military and other government organizations whose airspace surrounds Goldstone. NEO radar observations have been scheduled in as few as 2 days after a request, but recent urgent requests have been at least 2 weeks in advance. In general, Arecibo has significantly greater flexibility for responding to short-notice target-of-opportunity observing requests than Goldstone has.