TPF-C Technology Plan - Exoplanet Exploration Program - NASA

Chapter 4
(5) The Fine Steering Mirror (FSM) and Fine Guidance Sensor (FGS) are key to the pointing.
The FSM will demonstrate small angle jitter reduction and high accuracy pointing control, in
tandem with the FGS focal plane detector measurements and centroiding algorithm. The focal
plane is included for demonstration of centroiding accuracy, bandwidth (frame rate), and
measurement noise characteristics. The end-to-end performance of the FGS/FSM will need to
demonstrate the centroiding algorithm. The focal plane can demonstrate separately centroiding
accuracy, bandwidth (frame rate), and measurement noise characteristics. The end-to-end
performance of the FGS/FSM will need to demonstrate ~1/300 λ/D centroiding performance as
defined by contrast requirements.
(6) Because of the reliance on image shape, a simulation of FGS optical path will be used to
produce a simulation of the “spot.” This includes the key reference surfaces (such as the
reflection off the coronagraph spot), or diffraction pick-off locations used to pick off the science
reference star signal. This will be used as part of the test with the FGS. This test may require
copies of particular surfaces, including any substrates used as reflecting surfaces.
(7) Isolation of testbed from acoustics and external vibration. This will require both a vacuum
and isolation of key testbed components for full demonstration, which may be too expensive for
this size testbed; a reduced approach would test the FSM and FGS separately in an isolated
vacuum chamber and use measured performance to evaluate overall performance.
The entire spacecraft would be required for full testing. Since this is not feasible, individual
components will be tested in a reduced testbed. The ACS of the S/C and coronagraph is as shown
in Figure 4-14. The testbed, shown in figures 4-13 and 4-15, introduces realistic disturbances and
incorporates key components and measurement (for performance validation) devices.
Progress to Date
This testbed is currently in the requirements definition and planning stage. No other resources
have been allocated for this particular testbed activity up to this time. Detailed design work for
the testbed is scheduled to begin near the end of Phase A.
Figure 4-14. Simplified ACS diagram.
74