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Session 34 - Real Instruments.
Display session, Tuesday, June 09
Atlas Ballroom,
The Heinrich Hertz Telescope of the Submillimeter Telescope Observatory was built and is operated as a collaborative project of the Max-Planck-Institut für Radioastronomie and the University of Arizona's Steward Observatory. It is a 10 m diameter telescope sited at an elevation of 3200 m on Mt Graham, Arizona. For holography measurements, the subreflector is removed and a receiver on loan from NRAO is installed at the prime focus. The prime focus signal is phase referenced with a lens/horn combination pointed directly at the transmitter. The two IF signals are sampled with a digital signal processor which then calculates the relative phases and amplitudes numerically.
The surface was previously adjusted in Feb 1995 using the 38 GHz beacon of the Lincoln Labs Experimental Satellite #8 (LES-8). At that time the surface was set to an accuracy of about 25 microns rms in the outer ring of panels and to about 20 in the two inner rings. In mid 1995, the beacon on the twenty year old LES-8 satellite failed. A similar satellite, LES-9, has a beacon which transmits at 37 GHz. LES-9's beacon still works, although its 20 year old power plant can no longer operate it simultaneously with its wide band transponder, which is needed for its primary mission as a communications satellite. Although this satellite is in greater demand than was LES-8, the US Air Force (which controls the usage of this satellite) generously assigned us over 20 6-hour blocks of time. The latest adjustments result in a surface with rms errors in the range 16-18 microns over the entire surface. We believe that this is the most accurate setting of a large radio telescope's surface ever done via holography.
