An important test performed on April 1st was to look for any interference where the instrument could be run into the telescope. Measurements had indicated that the yoke area would be a problem. Following the trip to Kitt Peak, Phoenix was cooled down for the first time. The performance exceeded our optimistic projections. The instrument reached a stable temperature of 50K in three days.
Phoenix is cooled only by dual compressed helium refrigerators.
We had expected that cooling could take as long as 5 days. At 70 K the thermal radiation contribution to the dark current becomes negligible. We are able to warm the instrument to room temperature in two days using resistive heaters. Without the use of heaters, the instrument is so well insulated that it would take weeks to warm. Phoenix on the 2.1-m telescope with NOAO engineer Neil Gaughan.