Pointing and tracking software for the Gemini 8-m Telescopes

Patrick T. Wallace

doi:10.1117/12.268987

21 March 1997 Pointing and tracking software for the Gemini 8-m Telescopes

Patrick T. Wallace

Proceedings Volume 2871, Optical Telescopes of Today and Tomorrow; (1997) https://doi.org/10.1117/12.268987
Event: Optical Telescopes of Today and Tomorrow, 1996, Landskrona/Hven, Sweden

Abstract

The Gemini telescope control system (TCS) uses an integrated pointing/tracking scheme, based on the 'virtual telescope' (VT) concept, but extended to encompass autoguiding and control of the chopping secondary (M2). The TCS treats each autoguider probe as a separate VT, with a different target from the main telescope (namely a guidestar instead of a science source), different color, flexure and so on. The constraint that both the guider VT and the main-telescope VT share one mount (Az,El) enables the (x,y) of the guidestar image to be predicted. Comparisons between the predicted and measured (x,y) positions enable the guiding system to generate rapid adjustments to M2 tip/tilt, taking out windshake as well as other tracking errors. The TCS monitors M2 tip/tilt and adjusts the mount pointing as required, preventing unwanted buildup of M2 offset. Independent control of M2, to accomplish rapid scans while smoothly tracking the (Az,El) mount for example, is provided by having separate 'mount' and 'source' VTs. In this case, the constraint that there is only one mount (Az, El) enables the M2 tip/tilt to be determined which will place the target image in the required place. Chopping is done by implementing the different chop states as different VTs all running in parallel. The TCS is oblivious to the use being made of the different M2 tip/tilts that the different chop states call for, that being left to the various subsystems. The Gemini plan calls for five VTs (two permanent guide detectors and one on-instrument, plus the mount and target VTs), and all but the mount VT support three chop states. Operating at rate of 20 Hz, this means that the entire pointing calculation has to be performed 260 times per second, and some care has been taken to organize the computations efficiently.

Citation Download Citation

Patrick T. Wallace "Pointing and tracking software for the Gemini 8-m Telescopes", Proc. SPIE 2871, Optical Telescopes of Today and Tomorrow, (21 March 1997); https://doi.org/10.1117/12.268987

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available