TPF-C Technology Plan - Exoplanet Exploration Program - NASA

Chapter 2
Table 2-1. Requirement on Stability of Thermal Deformation of Optical Surfaces (Angstroms)
Zernike Primary Secondary Small Flats OAPs DM
4 8.0 2.0 1.0 1.0 1.0
5 8.0 2.0 1.0 1.0 1.0
6 8.0 2.0 1.0 1.0 1.0
7 4.0 1.0 0.5 0.5 0.5
8 8.0 2.0 1.0 1.0 1.0
9 6.0 1.5 0.75 0.75 0.75
10 8.0 2.0 1.0 1.0 1.0
11 0.1 0.025 0.0125 0.0125 0.0125
12 0.1 0.025 0.0125 0.0125 0.0125
13 0.1 0.025 0.0125 0.0125 0.0125
14 0.1 0.025 0.0125 0.0125 0.0125
15 0.1 0.025 0.0125 0.0125 0.0125
eliminate thermally induced motions of the secondary tower, but it is not designed to control
vibration-induced motions. Thus for thermally induced motion, the primary-secondary
positioning is controlled, independent of temperature. For vibration-induced motion, the
vibrations must induce motions smaller than those given in Table 2-2.
Table 2-2 shows the allowed motion of secondary mirror relative to primary mirror. The “dL”
line gives the motion consistent with a laser metrology truss with 27-nm rms measurement
precision, while the “Frequency dF/F” line indicates motion consistent with 1 × 10 -9 relative
frequency changes. “Fast changes” are not measured by the metrology system—these must be
limited by proper design of vibration isolation and damping systems.
All other optics in the system up to the Lyot stop are required to be stable in position to 100 nm
and 10 nrad 3σ rms. As with the secondary mirror, this is required to limit beam walk. The
positional stability requirement also limits beam walk contributions.
Table 2-2. Motions of Secondary Resulting From Random Metrology Errors and Vibrations
Mirror
x-tilt
(nR)
y-tilt
(nR)
z-tilt
(nR)
x-trans
(nm)
y-trans
(nm)
Secondary (dL) 45 30 130 65 137 27
Secondary (Frequency dF/F) 0 0.2 0 2 4 12
Secondary (Fast Changes) 2 1 5 2 5 1
z-trans
(nm)
26