Telescope Characteristics

The characteristics of the telescope mount and control system are, in general, yet to be established definitively. The values given here are the requirements and goals taken from the Science Requirements Document 3.0.

Pointing accuracy

Absolute pointing (driven by the desire to acquire a guide star within the ~5 arcsec instantaneous field of view of the peripheral wavefront sensor):

• Requirement (for zenith distance less than 60°) is 2 arcsec rms.
• Goal is 1 arcsec rms.

Recent measurements have produced values of less than 1 arcsec rms (see the results from a recent pointing test).

Tracking and guiding precision

Open loop tracking is required to be consistent with pointing and sufficiently stable for guide star acquisition.

Slow correction (e.g. of flexure using OIWFS):

• Requirement is 100 milli-arcsec rms in 10 min., 250 milli-arcsec in 1hr.
• Goal is 20 milli-arcsec in 10 min., 50 milli-arcsec in 1hr.

Fast correction (e.g. with image motion compensation using PWFS or OIWFS):

• Requirement is 10 mas rms in 1hr.

Offsetting accuracy

Open loop:

• Requirement is 100 milli-arcsec precision over 10 arcmin offset.
• Goal is 50 milli-arcsec precision over a 10 arcmin offset.

Closed loop (e.g. loop closed around peripheral wavefront sensor):

• 10 milli-arcsec precision over a 10 arcsec offset.

Slewing overhead

Slewing times:

• 1 sec for offsets of up to 5 arcsec.
• 5 sec for offsets of up to 60 arcsec.
• 30 sec for 10 degree slews.
• Maximum of 300 sec between any two positions on the sky.

Last update August 31, 2000; Phil Puxley