TPF-C Technology Plan - Exoplanet Exploration Program - NASA

Structural, Thermal, and Spacecraft Technology
be implemented. The facility will be required to provide extreme thermal stability and control, as
well as accurate means to decouple the response of the test article itself from external error
sources such as those typically attributed to instrument misalignment, load path parasitics, and
nonlinear interactions with mounting the hardware.
Material data and validated models gained from this activity will be collected within the Project
controlled Material and Model Databases and used by the modeling team for prediction of flight
performance.
Frictional Stability Characterization Facility
The Frictional Stability Characterization (FSC) facility will be developed at the University of
Colorado by Prof. Lee Peterson and Dr. Jason Hinkle to evaluate, on a generic frictional
interface, the various parameters contributing to microdynamic stability. The facility will be a
simplified representation of the PM to SM telescope assembly with an inter-changeable frictional
interface whose parameters, such as preload, stiffness, and surface roughness, can be varied to
study the impact of the microdynamic stability at the simulated optics positions. These
parameters are those included in existing models for frictional nonlinearities, and the
measurements will be used to validate the sensitivity of these parameters to the microdynamic
requirements on TPF-C, (e.g., less than 300 pm PM to SM position stability). In particular,
performance analysis models that bound the microdynamic performance will be developed and
validated, and nonlinear analysis tools to model localized nonlinear behavior of hinges and
latches will also be validated. A secondary goal of this test facility is to define the parameters
and mechanical performance requirements of hinges and latches that will be levied on the actual
TPF-C flight mechanisms.
Progress to Date
Progress has only been made on the Precision Dilatometer Facility (PDF), since its development
has been funded by JWST, and some material information has already been collected. Of
particular interest is the calibration that is currently being performed on a sample of single
crystal silicon, shown in Figure 4-7. The CTE data collected on the sample matches almost
exactly, to within 5 ppb/°C, the data measured on another extreme precision facility in Australia
by K. G. Lyon over 30 years ago.
Preliminary data has been obtained on a representative Zerodur sample. Very intriguing
nonlinear effects have been characterized, the behavior of which has been confirmed by the
vendor, Schott, in Germany. Figure 4-4 shows hysteresis in the material, as well as thermal
relaxation at constant temperature. Being able to maintain temperature anywhere between 305 K
and 30 K to within 10 mK is a unique capability of the PDF. Similar tests were performed on a
ULE sample, which did not display hysteric behavior, also shown in Figure 4-4. Additional tests
on Zerodur and ULE will be performed using annealing and surface treatments on the samples
consistent with mirror fabrication standards to obtain data more relevant to TPF-C analysis
needs. Several ULE samples will be extracted from the TDM (Technology Demonstration
Mirror) material to directly correlate the TDM test results with its analytical predictions.
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