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NASA's deep-space reflectors measured with help of Leica Industrial Theodolites

Theodolites measure gravity deformation
All of NASA's Deep Space Network (DSN) 70-m reflectors were measured using
a Leica TDM-5000 theodolite. The main-reflector surface was measured at five elevation angles so that a gravity deformation model could be derived that described the main-reflector distortions over the entire range of elevation angles. The article describes the measurement equipment and accuracy and the results derived from the data.
One of NASA's current technology initiatives is to increase deep-space communications capacity by the implementation of 32-GHz (Ka-band) reception on all Deep Space Network (DSN) antennas. A major problem for Ka-band on the 70-m antennas is the loss in gain with elevation angle due to gravity-induced structural mechanical distortions of the main-reflector surface. One of the proposed solutions is to use a deformable at plate (DFP) in the optics path to compensate for the main-reflector distortions. However, the design of the DFP requires knowing the actual surface shape over all elevation angles. The initial experiment on the 70-m antenna used holographic measurements at three lower elevation angles to predict the surface over the entire elevation range. Holography does not provide a direct measurement of the surface above 47 deg and relies on extrapolation of the lower angle data to predict the surface at high elevation angles. Therefore, the accuracy of the high elevation surfaces is unknown. Consequently, Michael Brenner of Engineering Metrology Services (EMS) was contracted to measure the DSS-14, DSS-43, and DSS-63 main-reflector surfaces over the full range of elevation angles using a ranging theodolite. This article describes the measurement equipment and accuracy and the results derived from the data.