TPF-C Technology Plan - Exoplanet Exploration Program - NASA

Structural, Thermal, and Spacecraft Technology
mechanism that supports the secondary mirror. The precision hexapod test-bed will be used to
investigate actuator and sensor designs and mechanism concepts and ultimately will prove the
feasibility of developing a 6-DOF mechanism that meets the TPF-C OTA wavefront quality
requirements.
The objective of this testbed is to demonstrate the capability of meeting the stringent positioning
requirements placed on the relative orientation between the secondary and primary mirrors and
to develop a facility which can be used to verify the engineering test unit and flight secondary
mirror mechanism performance.
Approach
The testbed will be developed in three stages. The first stage is the development of a facility
capable of measuring the orientation of an object in 6 DOF down to the sub-nanometer level. In
stage two, specific candidate actuators will be investigated and compared to derived engineering
requirements developed for the mechanism. Stage three involves the measurement and
verification of a prototype and engineering unit secondary mirror mechanism, which will also be
used to verify the flight mechanism.
This testbed will be a setup with which GSFC can accurately characterize sub-nanometer level
actuators, sensors, and hexapod systems. It will be used in conjunction with an actuator
qualification program including performance, environmental, and life testing. It will be used to
characterize the motion and stability of the hexapod system with both fine and course actuators
under loads (static and dynamic). The testbed would simultaneously measure 6 DOF over a
range of at least 5 mm. Commercially available interferometers, from Zygo for example, have
measuring capabilities down to 0.15 nm under ideal conditions. However, arranging them in a
quiet, turbulence and vibration free environment and including temperature stability and laser
wavelength compensation will require significant design effort.
The testbed consists of the following components as depicted in Figure 4-2:
• Vacuum enclosure with ion pump (no vibration) to maintain vacuum
• Vibration and acoustic isolation system
• Temperature stability system
• Measurement in 6 DOF.
• Data acquisition and processing hardware and software
• Stable optical bench
• Various candidate actuators and hexapod systems which can meet or show
promise of meeting the spaceflight requirements developed for the TPF-C
mechanisms
Progress to Date
This activity is currently in the requirements definition, conceptual design/formulation, and
planning stage of development. No other resources have been allocated for this particular
testbed activity up to this time, although other technology developments currently being
investigated will feed into this activity either directly or indirectly. For instance, characterization
of the micro-dynamics of mechanical attachments, material characterization, stable thermal
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