The current irregularities in the track produce raw pointing errors on the
sky with peak-peak values of order 10
. To counteract this, an
inclinometer system (MTPPN002) is used to make a look-up table of YAW, PITCH
and ROLL as a function of antenna azimuth, and this is used to make a
real-time correction to the telescope pointing. This appears currently
to correctly account for about 70-80% of the track pointing error,
allowing us to reach the current rms pointing accuracy of around
1.6
. Although not currently done on a routine basis, a similar
correction could be made for phase errors in interferometry data.
As far as the astronomical specification is concerned, there is little difference between an ideal track which does not require any inclinometric correction, or an arbitrarily poor track were a perfect inclinometry system available. The astronomical specifications are therefore made without regard to how these will be achieved. In practice, we expect that the current inclinometry system will continue to be used, and potentially improved, and the engineering specification can correspondingly be relaxed to take this into account.