South Pole Telescope Design
8 December 2003

 

South Pole Telescope Design

bulletSPST342
bulletSPST320
bulletSPST313
bulletSPST 307
bulletSPST304
bulletSPST298
bulletSPST271
bulletSPST208
bulletSPST183
bulletSPST148
bulletSPST152
bulletSPST129
bulletSPST129 summary
bulletSPST129B
bulletSPST67

SPST129 works especially well because

  1. It is an essentially simple design: Gregorian focus, followed by a two-element focal reducer.  The only complications are that there is a field mirror at the Gregorian focus for control of field curvature and a "fold" mirror inside the focal reducer in order to place the focal plane at a convenient position.
  2. The mirrors in the focal reducer bend the beam the "right way" to minimize aberrations.

The result is a design which meets all science requirements:

  1. Excellent correction of aberrations over a 1║ diameter field of view.  Usable at 200Ám wavelength.
  2. About 6% distortion at edge of field.
  3. No cross-polarization at symmetry plane of detector.
  4. Includes Lyot stop and place for filters

Disadvantages:

  1. Secondary is large: 2330 mm X 1970 mm
  2. Dewar window is large: 260 mm diameter
  3. Dewar is large: about 2 m diameter x 3 m long, about 2 tons.
  4. Filters are large: about 400 mm diameter

Scaling back design:

  1. Dewar window size is roughly proportional to field of view.
  2. A large secondary can feed both large and small fields of view; a small secondary can only feed small fields of view.
  3. Dewar weight is approximately proportional to volume.
  4. Shaped secondary is specific to design; for example, in SPST129B, it is not possible to correct the distortions introduced by the SPST129 secondary mirror with just a single additional optic.