TPF-C Technology Plan - Exoplanet Exploration Program - NASA

Chapter 4
Third, precise thermal control of all critical conductive and radiative paths between the
spacecraft and the PSS, between the PSS and the AMS, and between the AMS and the SM tower
is maintained.
Thermal control of an optical system in a space telescope of the TPF-C size with the required
precision has never been attempted, and thermal modeling accuracy is insufficient to eliminate
the risk inherent in the thermal design. In addition, it is very unlikely that at the full-scale
OTA/Payload protoflight level adequate thermal stabilities can be maintained to allow
verification by test/analysis of the thermal system. To retire this risk an approximately 1/4 th scale
testbed is designed (the smaller size permits the external vibration and thermal disturbances to be
much better controlled) incorporating the main elements of the thermal design. The intent is to
directly demonstrate that the absolute magnitude and stability of the thermal gradients on the PM
meet specification in the presence of flight-like thermal loads. However, if local disturbances and
test instrumentation result in too much sensor noise to allow flight level performance to be
directly measured, the thermal model could be correlated with responses produced by
overdriven levels of simulated solar illumination and the flight response levels analytically
predicted using this correlated model. Another way of addressing concerns regarding system
response below measurement noise floor would be to modulate the thermal disturbance such that
the system response could be extracted from the noise and allow model performance to be
correlated at flight-level precisions even in the presence of a relatively noisy background.
However, the likely relaxation in the required temperature stability due to the use of the 8 th order
mask makes the need for this test complication much less probable. A diagram of the proposed
testbed is shown in Figure 4-16.
Figure 4-16. Conceptual diagram of testbed to validate the TPF-C Sunshield and Isothermal
Cavity thermal design. The object is to determine if, under flight-like thermal loads, the mirror
temperatures can be maintained stable to within the required sub-milli-Kelvin limits.
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