NATIONAL RADIO ASTRONOMY OBSERVATORY
DATE: August 27, 1996
TO: Roger Norrod
FROM: Ron Maddalena
SUBJECT: Time line for holographic measurements on the 140-ft with GBT systems
For the most part, the July/August tests of the GBT M&C system on the 140-ft were very encouraging. With a few more tests of the GBT M&C system I think we can attempt with some confidence holographic measurements on the 140-ft in preparation for similar measurements on the GBT.
This report updates the time line of my June 1996 memo on preparing for
holography. The tests that I labelled (1) and (2) in that memo were successfully
completed in July/August. A full memo describing the results of that test is in
preparation. Below I give my views on how to proceed with the tests (3) and (4)
in my original memo.
1. Pointing accuracy and repeatability
Pointing accuracy and repeatability was successfully measured in July/August
and the results compare very well with the best results obtainable with the
existing 140-ft Modcomp system. In brief, the pointing accuracy and
repeatability were measured to be around 3" in both hour angle and
declination. A broad, smooth 50" shape in the pointing residuals from the
GBT M&C tests was identical to what was measured with the existing Modcomp
system. Thus, the residuals were not due to the GBT M&C system. In fact, the
GBT M&C system was the principal means were by a problem with the 140-ft was
detected. I see no reason to repeat these tests.
2. Large-scale pointing accuracy
The large-scale pointing accuracy was also successfully measured in
July/August with results that compare favorably with what has been determined
before with the existing Modcomp system. The number of data points I could use
from the July/August tests was fewer than I usually have on hand when I made
similar measurements with the Modcomp system so, if we have some spare time
during later GBT tests, we might want to repeat these measurements. But I am
confident that the pointing of the GBT M&C system is good enough for an
attempt at holography.
3. On-the-fly mapping
I believe we still need to test on-the-fly mapping with the GBT M&C system. The following updates my July memo:
The experiment is designed to test whether the GBT M&C system can generate an on-the-fly map with sufficient accuracy for holographic measurements. This can be accomplished by mapping a typical celestial point-source and mapping a hard-edged source like the moon.
a. Hardware requirements:
b. Software requirements:
d. Time line:
To test whether the GBT systems can successfully complete a holographic map of a telescope and to compare the resulting maps with those generated previously of the 140-ft with the Modcomp and UniPops system.
a. Hardware required:
b. Software required:
d. Time line: