±For
stationary pointing conditions under high wind loads the BUS rim wind shake is dominated by elevation motion for both
antennas.
±For
sidereal tracking during low wind conditions the tracking jitter of both antennas is largely due to elevation motion, with large
contributions in the 3-6 Hz range.
The largest jitter is observed at low elevation, while minimum tracking jitter is seen while crossing the meridian.
±For BUS
pointing stability during fast (0.5 deg/s) OTF scanning:
°VertexRSI
performance is strongly dependent upon the (Az,El) at which the scan is performed.
This is reflected in the standard deviation for this measurement.
°AEC
performance is affected by apex rotation feedback into the BUS motion. This apex motion died out after about 1 minute in most cases,
but also caused azimuth drive shutdown under certain conditions. The spread of 0.3 arcsec (1s) reflects this variable pointing stability.
±For the
AEC antenna the contribution due to apex motion to all pointing measurements has been investigated, but not included in
the results presented.
Accelerometer measurements could not properly distinguish between subreflector translation, which impacts pointing,
and subreflector on-axis rotation, which has no affect on pointing.