TPF-C Technology Plan - Exoplanet Exploration Program - NASA

Structural, Thermal, and Spacecraft Technology
Material property measurements will not be limited to CTE alone. The Project will establish a
list of all material properties required for assessing performance stability using the integrated
thermal, structural and optical models. Included in this material property list are all elements in
the dynamic and thermal load paths, including joints, cables, etc. Data will be needed for these
properties as a function of temperature, wavelength, frequency, and load cycle as appropriate.
Published literature data will be reviewed, and if it is established that the quality of the published
data does not meet TPF-C accuracy requirements, then additional materials testing will be
performed. Accuracy requirements on material property data will be defined later as more
analysis is performed to understand the sensitivity of material data error on predicted
performance. Allocations for material data error will eventually be folded into the Modeling
Uncertainty Factor allocation. Ultimately, all material property data assembled under this
endeavor will be gathered within a Project-controlled database for use on all TPF-C modeling
activities.
Microslip Tribometer Characterization Facility
The (Cryogenic) Microslip Tribometer Characterization (MTC) facility will measure the
coefficient of friction in the microslip regime well below the onset of gross Coulombic slip. This
information is required as a physical parameter within established microslip hysteresis model
forms which combine both stress-induced and roughness-induced microslip. Data will be
collected for representative materials of frictional interfaces, such as hinges and latches, with
varying surface roughness specifications and over the temperature range of 305 K and 20 K to
investigate thermal sensitivities. The MTC, shown in Figure 4-5, is designed, built, and
calibrated in air by Dr. Jason Hinkle at the University of Colorado. The apparatus will be
delivered to JPL to be placed within a thermally controlled cryogenic vacuum chamber.
Representative data sets are shown in Figure 4-6. Data collected on this facility will be enclosed
in the TPF-C Project Material Database.
Precision Sub-Structure Test Facility
The Precision Sub-Structure (PSS) test facility will be developed at JPL to characterize the
thermo-mechanical stability of composite materials, composite structure sub-assemblies, and
eventually actual flight hardware including hinges and latches. The facility will derive
experience gained on the Precision Dilatometer test facility to incorporate a sub-nm
interferometric metrology system within a thermally controlled vacuum chamber to enable
distortion and strain measurements for these mechanical sub-assemblies. The current testbed goal
is to achieve better than 1-nm measurement accuracy over a 1 minute time interval, which is
consistent with current requirements on the SM tower stability. Better measurement
performances have already been achieved on the Precision Dilatometer test facility and the SIM
Thermo-Optical Mechanical testbeds, so the measurement capability itself is not seen as a risk.
The immediate goal will be to collect property data for non-optical materials. The focus will be
on measuring and understanding the thermal strain, CTE, material variability, microdynamics,
and dimensional stability of proposed composite materials on TPF-C. Of special interest are the
materials forming the PM support structure, the SM tower, and the coronagraph optical bench.
Over time the facility will be used to investigate the dimensional stability and thermal sensitivity
of critical sub-assemblies such as bonded composite parts, bearings, hinges and latches, and
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