THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
1995 AND 1996

6. UKIRT Upgrades

The Upgrades Programme has taken several major strides since the last Report. Important improvements in day-to-day performance have been achieved, approximately doubling the effectiveness of the telescope.

The programme of improvements to the telescope itself were set out in detail in the last Report. They include:

• Modifications of, and upgrades to, the primary mirror support system, with the addition of active control of the figure
• A new top-end comprising a single ring with stiff, vibration-damped, projecting vanes with reduced wind resistance, which carry the hexapod precision positioning system and the momentum-compensated piezo-electric high-bandwidth tip/tilt actuation system for the secondary mirror
• A new, more rigid, high-precision crosshead at the bottom of the Instrument Support Unit, carrying an interface unit to which are attached the acquisition and guide systems
• The CCD fast guider unit
• Improved ventilation of the dome via more powerful extraction fans and sixteen louvred apertures around the periphery of the dome
• Forced cooling of the primary mirror
• Insulation of the dome floor
• The electronic and computer controls for most of these

By the end of 1996 several of these systems were implemented and operational, although not completely optimised. Details of the system and telescope performances are given in the following subsections. The new top-end was installed in August 1996. Its hexapod allows accuratemaintenance of optical alignment while the tip/tilt system, controlled by the fast guider, stabilises against vibration, windshake and tracking errors and removes any image motion component of the seeing. The primary mirror figure control is installed but its lookup table is still being assembled, based on an ongoing programme of all-sky wavefront sensing.

The programme for the management of the dome thermal environment is less advanced because of staff shortage, and at the time of writing only the enhanced extraction fan capacity is in routine use. The Dome Ventilation System is installed but completion of its control system is not complete. ⁴ Work has begun on the Primary Mirror Cooling System, but this will not be completed until 1998. Installation of the dome floor insulation also is expected in 1998.

Notwithstanding the incomplete thermal management programme and primary mirror figure control system, users of the telescope now enjoy half-arcsecond images on a regular basis. Further improvements in this are expected once the primary mirror lookup table is completed and used, ⁵ the primary mirror cooling system is in operation, and the dome floor insulation is installed.