TPF-C Technology Plan - Exoplanet Exploration Program - NASA

Structural, Thermal, and Spacecraft Technology
noise from the laboratory environment to much better than 1 mg. Using the Lockheed Martin
DFP is a possibility since it is capable of at least 40 dB of vibration attenuation, and as an active
system can be used to simulate the input of RWA disturbances through the telescope system.
Other disturbances can be incorporated to drive the microdynamic instabilities such as base
shakers, heaters, and shear loading devices near the hinge/latch interfaces.
The test article itself will be appropriately mass loaded so as to provide the same inertia to the
truncated tower as would the full-length flight tower. The primary goal is to exercise the
mechanisms in the right frequency regimes and inertial loading configurations.
The position stability of the assembly will be monitored through a suite of precision instruments
such as a displacement interferometer, micro-g accelerometers, nano-strain gauges, eddy current
sensors, temperature sensors, and load cells. This instrumentation suite will enable the highfrequency
measurements of relative tower motions, harmonic distortions, hysteresis, modal
frequencies and damping, and acoustic emissions—all phenomena that can adversely impact the
SM stability requirement.
Materials and testbed sub-components are expected to be tested individually prior to testbed
assembly. The testbed data will then be used to validate the assembled testbed model, focusing
primarily on the interface models and nonlinearities. Material and sub-component testing can be
performed as part of the Precision Structural Stability Characterization activity at JPL and/or at
the contractor facility. In any case, although the contractor will be responsible for delivering
validated models of the testbeds, NASA will conduct an independent modeling activity for
verification.
Progress to Date
This activity is currently in the requirements definition and planning stage. No other resources
have been allocated for this particular testbed activity up to this time. Other technology
developments currently being investigated will feed into this activity, in particular the Precision
Structural Stability Characterization testbed suite.
4.2.3 Pointing Control Testbed (PCT)
Objective
TPF-C faces challenging pointing requirements. The major pointing requirements are (1)
maintain stability of the telescope pointing to 4 mas 1σ /axis, and (2) direct the star light to the
coronagraph mask to an accuracy that maintains an “acceptable” contrast ratio that results in a
trade between jitter and offset requirements, as shown in Figure 4-12, which refers to the
previous pointing requirement. Currently, if there is a pointing offset (bias) of 0.3 mas, the
pointing jitter can be up to 0.3 mas 1σ, RMS. This fine pointing mode was recently relaxed by a
factor of nearly 8 from what is shown in Figure 4-12. The objective of the pointing control
testbed is to demonstrate the required sub-mas pointing.
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