Fourth Quarter 1998

In October, further work on the design of the calibration box showed that the layout could be simplified by mounting all components to the top of the cryostat vacuum jacket, completely enclosed within telescope interface box. With the optical design complete all the calibration box optical components (integrating sphere, lenses and mirrors) were specified and ordered.

The plane reflective diffraction grations made by Carl Zeiss, Jena, Germany were received in October. All cryostat mirrors were sent to Denton Vacuum for coating with FSS-99 protected silver.

A second cold test was conducted in November with the objective of resolving the second stage temperature anomaly (see last quarter) and testing the newly installed slit-viewer filter wheel mechanism and its Hall Effect sensors. Using a calibrated temperature sensor the second stage reached the expected temperature of 11K and the filter wheel and Hall Effect sensors performed satisfactorily. The test also confirmed expectations that cooling of SpeX wheels and turrets through bearings is not adequate to reach temperatures below about 90K in 24 hours. Wheels will be painted black to enhance radiative cooling to meet this target.

On schedule, Phase IVa of the cryostat fabrication (the fore-optics mounts and image rotator assembly) arrived from EAS in November and assembly started immediately. Access to the Institute for Astronomy machine shop became available in time for routine small modifications and fixes to the Phase IVa parts required to complete successful assembly. Hughes Tools are several months behind schedule in delivering the Phase III parts (the spectrograph box components). Fabrication of the remaining cryostat parts (slit-viewer, dichroic turret and calibration box) in the IfA machine shop also started in November.