The IUCAA Telescope Surpasses its Performance Milestones
November 2005

Recent tuning of the IUCAA telescope has demonstrated the exceptional performance of TTL's 2m class telescopes. Current testing has clearly demonstrated consistent RMS pointing performance over the whole sky on consecutive nights of 1.32", whilst tracking telescope focus and de-rotating the image plane at the Cassegrain focus.

The RMS pointing residual to the fit over about 90 stars has been as good as 1.14" on an individual night. Again, what is impressive about the performance achieved on IUCAA is that the same pointing model used on consecutive nights without additional calibration has achieved better than 1.4" RMS performance. The data from the sampled nights has been sent to Patrick Wallace of TPoint Software, who has verified TTL's results stating that they are "very encouraging".

Patrick's analysis of the IUCAA pointing data for 3 nights

On sky tracking performance has met our expectation with ease:
· Average open-loop tracking over 60 seconds = 0.21" (cf. specification of 0.25")
· Average open-loop tracking over 10 minutes = 0.40" (cf. specification of 0.4")
· Average closed-loop tracking over 30 minutes = 0.18" (cf. specification of 0.25")

Again, during individual observations the open-loop tracking over 10 minutes on individual runs has been as good as 0.349". Closed-loop tracking performance of 0.146" has been observed on individual tracking tests lasting over 2 hours. All tracking data have been measured using star centroid positions on the camera instrument, to give the telescope performance measured as true on-sky performance.

The measured image quality of the telescope is sub-arc second, without measurable coma (optical alignment), astigmatism, spherical aberration or higher order aberrations. Residual aberrations are below the effective image quality. An optical wavefront sensor will be used soon to quantify any residual errors under the seeing experienced on the site.

These results have been achieved during seeing conditions at the site of 1". The anticipated effects of seeing have NOT been removed from these test results. TTL expect further performance improvements in the near future.

This true on-sky performance obtained is an excellent starting point for the design of the new TTL 2.5m telescopes for the Las Cumbres Observatory Global Network of telescopes (LCOGT.NET), which will push the performance beyond the existing TTL telescope design