TPF-C Technology Plan - Exoplanet Exploration Program - NASA

Chapter 3
(though not light-weight or off-axis) optics are compared in Figure 3-6 and fitted with a third
order function given by
A
PSD(k) =
⎛
1+ k ⎞
, where k = 3 ( k x) 2 + () k 2 5 2 2
y
, A ≈ 6× 10 Å cm , and k
0
= 0.025cycles/cm .
⎜ ⎟
⎝ k 0 ⎠
The TDM is to be manufactured with a PSD amplitude a factor of 2.5 below the fitted curve. For
5 2 2
the TDM, k
0
= 0.04cycles/cm and A ≈ 2.4× 10 Å cm are required with a goal of
A ≈ 6 ×10 4 Å 2 cm 2 . The performance requirements vary with spatial frequency as summarized in
Table 3-1. Manufacturing process development for the TDM will address materials effects,
structural integrity, thermal impacts, and measurement and test methods; coating process
development will address spatial reflective uniformity and experimental determination of coating
performance. Going through the process of fabricating and testing the TDM will provide insight
into achievable performance for the TPF-C PM and SM.
• Each of the three mirrors is optically finished
using different methods
• Black represents a third order drop
off with a knee at 40cm
Magellan
Kodak
HST
Figure 3-6. Power spectral density for three mirrors: Magellan (left) 6.5 m and made at the
University of Arizona Mirror Laboratory for ground-based astronomy, HST (middle), and a 1.5-
m development optic made at Kodak (right). PSD for the TDM is 2.5 times lower.
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