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