DASI: A Degree Angular Scale Interferometer for Imaging Anisotropy in the Cosmic Microwave Background
N. W. Halverson, J. E. Carlstrom, M. Dragovan, W. L. Holzapfel, and J. Kovac

6. Mount

The mount for DASI must meet stringent pointing and tracking criteria, and be able to weather the extreme environmental conditions at the South Pole. In order to be able to accurately subtract point sources and mosaic multiple fields, the pointing error must be less than a few degrees of the narrowest fringe spacing on the sky. This corresponds to a very stringent pointing requirement of 5 arc-seconds in azimuth and elevation. Additionally, the aperture plane is able to rotate about its central axis, both to improve the synthesized beam through rotational synthesis, and to provide for consistency checks and offset subtraction by exploiting the 3-fold rotational symmetry of the aperture array pattern. The mount must be operable in the extreme cold conditions at the South Pole, where the temperature averages -30 C in the Austral summer, and -60 C in the Austral winter.

The mount is being designed in collaboration with TIW Systems, Inc.[9]. As shown in Figure 6, it consists of a counterbalanced gear and pinion elevation drive, a geared radial bearing for the aperture rotation axis, and a 4 wheel azimuth drive, with matching symmetry on the azimuth ring supports for homologous deformation of the ring. The azimuth and elevation axes have 2 drive motors each with differential torque to eliminate backlash. The telescope is well insulated, with a flexible insulated sleeve between the elevation and azimuth structures to maintain a comfortable working environment. In addition, the back-end electronics are temperature regulated with water cooled VME crates.

Figure 7: DASI mounted on the 11 m high tower. The tower is connected to the Martin A. Pomerantz Observatory (MAPO) building (not shown). Access is enabled by a room under the telescope connected directly to the laboratory building.


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Last modified Apr 23, 1998