MEMS Deformable Mirror Technology Development for Space-Based Exoplanet Detection
Paul Bierden/Boston Micromachines
In the search for earth-like extrasolar planets that has become an important objective for NASA, a critical technology development requirement is to advance deformable mirror (DM) technology. High-actuator-count DMs are critical components for nearly all proposed coronagraph instrument concepts. The science case for exoplanet imaging is strong, and rapid recent advances in test beds with DMs made using microelectromechanical system (MEMS) technology have made them an enabling component.
The proposed research will advance the technology readiness of the MEMS DMs components that are currently at the forefront of the field, and the project will be led by the manufacturer of those components, Boston Micromachines Corporation (BMC). The project aims to demonstrate basic functionality and performance of this component in critical test environments while establishing model-based predictions of its performance relative to launch and space environments.
BMC MEMS DMs have been proposed in NASA space-based exoplanet mission concepts including Extrasolar Planetary Imaging Coronagraph (EPIC), Exoplanetary Circumstellar Environment and Disk Explorer (EXCEDE), Wide Field Coronagraph Space Telescope (WFCST) and Pupil-mapping Exoplanet Cononagraphic Observer (PECO), among others. BMC is one of two manufacturers that have fielded prototype MEMS DMs for this application in NASA test beds. Presently BMC is the only MEMS DM technology worldwide that has yielded fully functional DM components with more than 1000 degrees of freedom.
BMC high-actuator-count MEMS DM components have been integrated in exoplanet exploration test beds using multimirror array (MMA) architectures with 331 independent hexagonal mirror segments supported by three underlying electrostatic actuators per segment, and using continuous deformable mirror (CDM) architectures with compliant mirrors supported by 1020 underlying electrostatic actuators. Despite broad NASA interest in the technology and steady technical progress in DM development and use, BMC MEMS components have not been tested for their survivability upon exposure to mechanical shock and vibration at levels consistent with space launch.
The objective is to achieve two interrelated technology development milestones that demonstrate the capacity of the MEMS DMs to survive dynamic mechanical environmental stresses associated with launch and deployment in space. Without such technology development, a coronagraph mission using MEMS DMs would not be possible.
DM components will be evaluated at BMC and in three existing coronagraph ted beds: Jet Propulsion Laboratory (JPL) APEP test bed, for visible nulling with an MMA, Goddard Space Flight Center (GSFC) Vacuum Nulling Test bed (VNT), for vacuum visible nulling with an MMA, and Princeton University, High Contrast Imaging Laboratory (HCIL) for phase-induced amplitude apodization (PIAA) nulling with a pair of CDMs.
Components will be evaluated for their baseline performance as measured by null depth achieved in repeated closed loop experiments. Components will also be tested at BMC to quantify performance changes resulting from environmental exposure. Results will be correlated with electromechanical models of MEMS DMs. After baseline measurements, the components will be subjected to component-level prototype environmental testing at GSFC Environmental Test and Integration Facilities (ETIF). Environmental exposures will include random vibration, sine vibration, acoustic loading, and mechanical shock qualification.
Components subjected to ETIF dynamic mechanical tests will be characterized opto-electro-mechanically at BMC, and then returned to coronagraph test beds and evaluated for their post-test performance as measured by null depth achieved and null depth variance in repeated closed loop experiments. At the conclusion of the project, each test bed will retain the test DMs to support future development.
Strategic Astrophysics Technology