Applying Electro-Optical Space Surveillance Technology to Asteroid Search and Detection: The LINEAR Program Results

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Abstract
Lincoln Laboratory has a long history of developing electro-optical space surveillance technology for resident space object search, detection, orbit determination, and catalog maintenance. Recent advances in large format, highly sensitive CCDs make possible the application of these technologies to the detection and cataloging of asteroids, including Near Earth Objects (NEOs). When equipped with the new Lincoln Laboratory focal plane, camera and signal processing technology, the modest sized (1-meter class) Air Force Ground-Based Electro-Optical Deep Space Surveillance (GEODSS) telescopes have considerable capability to conduct sensitive, large coverage searches for earth crossing and main belt asteroids. Field measurements have indicated that CCD-equipped GEODSS telescopes are capable of achieving a limiting magnitude of 22, over a 2-square degree field-of-view, with less than 100 seconds of integration. This is comparable to the sensitivity of considerably larger telescopes equipped with commercial cameras. In addition to the high sensitivity, the Lincoln CCD is configured for frame transfer operations which are well suited to high coverage rate asteroid search operations because each frame can be readout while the next frame is integrating. Technology development for asteroid search operations has been conducted at the Lincoln Laboratory Experimental Test Site in Socorro, NM over the past two years. Initial results, reported during the Space 96 meeting, indicated that the search system, now known as LINEAR (LIncoln Near Earth Asteroid Research), had considerable promise. Using the new large format 2560X1960 pixel, frame transfer CCD camera, forty-nine new asteroids were discovered over a period of several months, including one NEO. In addition, observations on seventy-nine knwn objects were collected and provided to the Minor Planet Center (MPC). Since those initial attempts, the search operations have been considerably improved and automated. Data acquisition has been streamlined, detection algorithms have been updated and the signal processing of the resulting data has been closely integrated with the data acquisition process. Field tests started again in January of 1997, with the objective of quantifying the capability of the search system to find new asteroids and provide quality metric measurements to the Minor Planet Center. Since the large 2560 x 1960 pixel CCD camera was unavailable during this time, an older 1024 x 1024 pixel CCD camera was used. The smaller format camera has slightly less sensitivity than the larger camera and fills only about 1/5th of the field-of-view of the GEODSS telescope (which is filled by the larger chip). Observations were conducted over the dark of the moon periods during the months of March, April and May. Each search area was covered three times over a period of three to seven days to generate discovery observations of each new object that could be limited from day to day. The Minor Planet Center requires that newly discovered objects be observed over at least two nights before granting the object a designation. In spite of the fact that a small format camera was employed during the search operations, the productivity was quite large during each of the observing runs. The search program was capable of repeatedly covering an area extending 15 deg. by 10 deg. over a period of a few days, to a limiting visual magnitude of approximately 21st. These series of observations validate that the Air Force GEODSS upgrade technology is quite effective when applied to the problem of discovering asteroids. Future development of this capability is planned to incorporate the large format, more sensitive camera and to automate the operations so that they may be run remotely or in a fully unattended operations mode. These enhancements will increase the already high search productivity of the LINEAR program by providing considerably higher sky coverage rates and allowing operations on more nights.

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