Azimuth-track level compensation to reduce blind-pointing errors of the deep space network antennas

The 34-meter antennas of the NASA Deep Space Network are "wheel and track" antennas. The latter term refers to a set of wheels at the base of the stru cture, which roll on a circular steel track supported by a concrete foundat ion ring. The track is assumed flat, however, its level varies due to manuf acturing imperfections, structural loads, non-uniformity of the soil, and t emperature variations. It is specified that the deviations of the azimuth-t rack level shall not exceed +/- 0.5 mm. During tracking, this amplitude of deviations causes deformations of the antenna structure, resulting in point ing errors of +/- 2 mdeg, which exceed the required accuracy for 32-GHz (Ka -band) tracking. However, structural deformations caused by the azimuth tra ck unevenness are repeatable; therefore, a look-up table can be created to improve the blind-pointing accuracy. This paper presents the process for cr eation of the look-up table, describes the instrumentation necessary for de termining the pointing errors, and describes the processing of inclinometer data. It derives algorithms for the pointing-error estimation, and for the azimuth-axis tilt using the inclinometer data. It compares the error corre ctions based on the created look-up table and actual measurements of pointi ng errors using the conical scanning (conscan) technique. This comparison s hows a satisfactory convergence that justifies the implementation of the ap proach in forthcoming NASA missions.