Millstone Hill Radio Star Calibration Observations.
Abstract
A comprehensive analyses of all radio-star calibration measurements made since May 1975 with the Millstone Hill Tracking Antenna is described. No evidence is found to indicate that mechanical offsets in the antenna structure have changed during this period. Previous suspicions that such changes might be continually occurring are shown to have arisen from acute mathematical correlation ambiguities encountered in fitting models to the monthly results. In addition, it is found that the high stability of the LED-type encoders installed in November 1977 has virtually eliminated this last source long-term variation in pointing offset. Only known mechanical modifications, causing discrete changes in pointing error model, have caused the pointing-error model to change since this date. Calibration of the octagonal rail/cam-follower system used by the Tracking Antennas as an off-axis azimuth encoder system is also investigated. Evidence is presented that the primary pointing errors that arise from inaccuracies in this system are due to an offset between the azimuth axis and the geometric center of the rail octagon, an ellipticity of the tower perimeter upon which the rails are mounted, and a slight bowing of the rails, the center offset being an estimated 0.3 mm, the rail geometry being 0.05 mm out of round, and the rails being bowed a maximum of 0.02 mm from straightness. These deficiencies cause pointing errors on the order of 10 mdeg. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 09, 1979
- Accession Number
- ADA079037
Entities
People
- William L. Oliver
Organizations
- Massachusetts Institute of Technology