GBT News Update
29 January 2001
We have tentatively agreed with Lockheed-Martin that full astronomical commissioning will begin on Monday, February 5. Pointing and focusing observations, involving tracking of the antenna in both axes, will begin that day. In the meantime, a full slate of outfitting and system testing is proceeding.
Commissioning activities last week included:
- Azimuth track tests. Four azimuth track base plate segments were welded together last week (three splice plates welded) in an effort to reduce the motion of the segments as the wheel trucks roll over them. The motion was measured last Friday (26 January). Data are still being analyzed at this writing, but a preliminary look indicates that the base plate motion was reduced from 0.055 in (1.4 mm) to 0.003 in (0.076 mm) on the welded segments. If these results hold up to further scrutiny, this represents a significant improvement.
- Elevation bullgear rigidity tests. A bullgear segment was reinforced last Thursday and stability against a static load was measured that evening. Results are not yet analyzed for those tests.
- Observations. Orion A was observed at L-Band last week in drift-scan mode. The 21 cm HI line was observed through the GBT Spectrometer.
- Baseline tests and spillover shields. The spillover shields were mounted late last week just below the subreflector, and are designed to reflect spillover radiation back onto the sky rather than into the signal path to the receiver where standing waves could be created. Baseline tests were made before the installation, and will now be done after the installation to look for differences.
- Prime Focus Receiver 1. PF1 was removed for repairs of the calibration system and an investigation of a possible cryogenic problem. The cal system was repaired, and no problem was found with the cryo system (the problem may have been a thermal short caused by frost). The receiver has been pumped down and will be recooled this week.
- S-Band Receiver. The S-Band Rx, currently mounted in the Receiver Room, has been pumped down and will be cooled this week, in preparation for first use.
- Elevation gear deck removed. This was a temporary deck installed by Lockheed-Martin for the bullgear realignment work.
- Telephones wires installed. Wires to the Receiver Room, Servo Room and Actuator Control Room were run. Phone connections are being made and service should be established this week.
Major activities for the current week are listed on the commissioning schedule (www.gb.nrao.edu/~pjewell/comm_sched.txt)
P. R. Jewell
M. M. McKinnon