140 Foot Telescope
Experiment
140 Foot Telescope
Experiment
The 140 Foot Telescope experiment was conceived several years ago as a test bed for the proposed use of the rangefinders for determining the pointing of the GBT. The idea is described in "Testing the Laser Metrology System on the 140 Foot Telescope" [GBT Archive Memo L0058] and a further description is given in "Status Report on GBT Laser Demonstration at the 140 Foot Telescope" [GBT Memo157].
Four laser rangefinders are placed on monuments adjacent to the 140 Foot Telescope situated so that they may track a retroreflector attached to the telescope back up structure. The rangefinders are connected via an ethernet connection to the controlling computer situated in the old 300 Foot Telescope control building a couple of miles away. To enable tracking the retroreflector the hour angle and declination of the telescope are transmitted over the ethernet connection also.
The experimental layout consists of four ground based rangefinders located at a radius of 80 meters from the spherical bearing of the 140 Foot Telesocpe tracking a retroreflector on the rear of the backup structure. Photographs of the experiment are shown in Figure 1 and Figure 2.
For this application a retroreflector with a wide acceptance angle is most desirable and the Optical Science Center at the University of Arizona has developed such a device for use on the GBT. A diagram of the device is given in Figure 3, a photograph in Figure 4 and a plot of measured range as a function of rotation angle is given in Figure 5. It may be seen that the acceptance angle is over 120 degrees.
This page was last modified on September 11, 1997.
