TPF-C Technology Plan - Exoplanet Exploration Program - NASA

Chapter 4
Figure 4-12. Fine guiding sensor offset versus jitter required for an 8 m TPF-C. Using the 8 th -
order masks, the pointing requirement is relaxed by roughly a factor of 8 from what is shown in
this figure.
Approach
Both the first and second requirements are very challenging, and the verification is also
difficult—0.3 mas (or 1.44 nanoradians) is a length of 1.5 μm seen from 1 km. This pointing
requirement results in the corresponding testbed requirements:
(a) Demonstrate capability to perform S/C rigid body stability to 4 mas 1σ /axis
(b) Demonstrate control to met the jitter and offset pointing capability
Both a physical testbed, shown in Figure 4-13, which is needed to demonstrate the capability of
the components, and a high fidelity simulation that models the expected environment are
necessary to develop and demonstrate the needed flight capability. The simulation testbed would
also then be responsible for the generation of models for inclusion into any more extensive S/C
system model. The critical testbed components include disturbance models and disturbance
inducing mechanisms.
The TPF-C pointing and control hardware testbed must allow demonstrations of sub-mas
pointing capabilities while undergoing spacecraft-equivalent vibration and other disturbances
and using “reference stars” and ACS sensors for measurements. While the TPF-C has a space
environment, the PCT will be operated in a ground facility where external disturbances such as
acoustics, air disturbances (at least when not in vacuum), and ground transmitted vibrations are
very difficult to eliminate. A list of key testbed components, disturbance sources, and comments
follow.
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