Appendix B: Design Parameters

B.1. Optical design

Design and analysis by Robert Woodruff, Lockheed Martin
Figure 5-1: Wide field telescope design for imaging astrometry and coronagraphy. [gif]
The telescope is a TMA designed to provide a high quality PSF over a 0.2 deg - radius FOV. A focal plane, 800mm behind M1 surface, provides a good location for a flat fold mirror (not shown) and extraction of the narrow central field for the coronagraph. A pupil plane, located also ~800mm behind M1 in this unfolded view, provides a second location for a fold mirror with little impact on the astrometric performance (no beam walk). The imaging focal plane is at F/40.
The on-axis PSF at the intermediate focus is 6 arcsec wide, and the coronagraph optics are designed to compensate for this wavefront offset.
Figure 5-2: Beam footprint on M3. [gif]
Mirror M3 is the optical element where the beam footprint varies the most with sky angle.

B.2. Mask design

The primary mirror mask serves two functions: it provides a sufficiently bright reference to measure the position of the central star on the focal plane array and it allows calibration of field distortions introduced by optics and also focal plane mechanical properties.