Yarkovsky Thermal Drag on LAGEOS

Abstract

Thermal drag accounts for about 70% of the observed average drag on LAGEOS. This estimate is based on a new thermal model which includes the radiative heat transfer between the retroreflector, its mounting rings, and the aluminum cavity in which it sits. The new estimate is a significant increase over the 47% of the old model, which did not include these interactions. Neutral particle drag accounts for about 13% of the average drag, and charged particle drag, at least 5%. Thus approximately 88% of the observed average drag can be reasonably explained. The rest can probably be attributed to more charged particle drag than the lower limit given above. A better thermal model would probably alter the above figures only slightly. The thermal drag calculation assumes that the LAGEOS spin axis has remained fixed in space and is where the telemetry data say it was after apogee kick motor separation. Ground measurements of the spin axis direction would be desirable.