NASA-LMT: Orbital Object Detection via CCD Sidereal Drift-scanning Mode


The detection of an orbiting object via the sidereal mode of CCD operation. The CCD has been set such that its read

direction and read rate exactly match the sidereal drift. A rotating asymmetrical beam chopper is used so that the

angular rate and direction may be determined for any object passing through the FOV. The fixed rotation rate yields

either the object field crossing time or segments of known duration, and the blade asymmetry yields a deterministic

pattern to the streak segments and gaps (long and short) to yield direction of motion. In this example, the object is

Satellite Number 20472 which is an operational Russian Molniya communications satellite (#1-78) in a highly elliptical

orbit with a RCS diameter of 4.45 m. The object was at an altitude of 13,054 km with an angular velocity of 0.0388

degrees/sec, a position angle of motion of 102 degrees, and a solar phase angle of only 36 degrees. Since the CCD

was sidereal drift-scanning, the object signal photons were spread over the detector as it passed through the FOV,

rather than concentrated on several pixels as with DM mode. The object exposure was 7.29 seconds based on its

angular rate and trail length, whereas the field exposure was 97 seconds. The excess background exposure and

image spread contribute to a significant reduction in SN ratio and thus a loss in sensitivity relative to DM mode

detections.  Based upon the estimated flux above background (127,000 ADU), coupled with the assumption of a

0.1 albedo and a specular phase function, the object OCS based diameter is 2.00 m.  This white light image was

acquired with the LSP 2K CCD with 1x1 binning.