Estimation of the on-orbit distortion of the Mars Orbiter Laser Altimeter (MOLA II) primary mirror

摘要

Abstract: This paper describes the analyses performed to estimate the on-orbit distortion of the Mars Orbiter Laser Altimeter (MOLA II) primary mirror. MOLA II is one of five scientific instruments that will be flown on the Mars Global Surveyor. The MOLA II instrument will map the surface profile of Mars for a full Marian year to a resolution of 2 meters vertical and 160 meters horizontal. The MOLA II telescope is an f/6 Cassegrain telescope with a 0.85 milliradian (mrad) field of view. The telescope is made entirely of Brush Wellman S200F vacuum hot pressed beryllium. The primary mirror diameter is 508 mm with a base radius of curvature of 711.2 mm. This mirror is plated first with electroless nickel and then with electrolytic gold. The purpose of these analyses was (1) to estimate the on-orbit distortion of the large primary mirror due to thermal loading, interface stresses, and gravity release and (2) to calculate the expected damage to the mirror surface due to micrometeroid impacts. A detailed NASA structural analysis program finite element model was used as a tool for evaluating the mirror performance. The results of the analyses indicate that a stability error of 2.4 microns peak-to-valley and 0.6 microns root mean square is expected for the on-orbit distortion of the primary mirror surface. The estimated surface damage due to micrometeoroids is 0.03 cm$+2$/, which is 0.002 percent of the total surface area. Both of these results are within mission acceptance parameters. !4