Upgrading the Telescope for the 21st Century

Abstract

UKIRT had been designed as an inexpensive telescope, but in some respects these cost saving decisions turned out to be advantageous in the long run. For example, its thin and hence flexible, primary mirror was, thanks to the commitment of that £9325 of extra spending in 1977, of a quality comparable to an optical telescope. Furthermore, to save money, the original planners had opted for the smallest possible dome. Even though the dome design was later increased in size to allow flexibility when mounting alternate telescope top-ends, it was still a very tight fit. The dome was never intended to be actively ventilated, but would eventually turn out to be comparatively easy to modify. Finally, the telescope’s deliberately lightweight structure had lower thermal inertia than any similar-sized telescope and this, if properly exploited, could aid temperature stabilisation which was a known factor for improving image quality. However, even after a decade of operations UKIRT had many problems. The pointing was not very good, and once on target, its tracking was unreliable. The small dome offered little protection from the wind and, until the advent of the new windblind went someway to improving the situation, the telescope would shake if pointed into even a modest breeze, severely degrading the image quality being produced by the excellent mirror. Alignment of the optical elements was poor and a turned down edge in the secondary mirror, which allowed the main beam to “see” the heat emission from warm structure surrounding the secondary, led to poor performance in the thermal infrared. Finally, warm air plumes rising from the ever increasing number of electronics racks underneath the mirror further degraded the local image quality.