TPF-C Technology Plan - Exoplanet Exploration Program - NASA

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Chapter 7 7.5.3 Precision Structural Stability Characterization Scope The goals of the Precision Structural Stability Characterization activity will be achieved through staggered delivery of test facilities and testing of materials and components representing progressively higher levels of assembly and higher levels of flight hardware fidelity. In pre- Phase A, we will focus on collecting material data and validating models for the basic physics of microdynamic stability. Data will be obtained for a regime consistent with the end requirement of 10 -9 contrast, and scaling laws will be validated where appropriate. Material properties will be maintained within a controlled TPF-C Material Database for approved use on all Project modeling activities. Information on material variability and modeling errors will be assessed to develop a modeling uncertainty propagation approach for TPF-C. This implies that all test facilities will be required to perform an error calibration prior to performing tests to incorporate experimental accuracy within the formulation of the modeling uncertainty factors. In Phases A through B, the focus will progressively shift towards using the validated physics models of pre- Phase A to building and validating models representing higher levels of assembly. Ultimately, the technology developed herein will be delivered to the Flight Design team for use in the flight analyses, and to the Secondary Mirror Tower Partial Structure Testbed for validation of the testbed models. The schedule for precision structural stability characterization is given in Table 7-13. Table 7-13. Precision Structural Stability Characterization Schedule Planned Completion Date Planned Activities Performance Targets TRL Pre-Phase A September FY05 Measure CTE and dimensional stability of relevant optics class materials Calibrate MTC, deliver to JPL and measure microslip for relevant hinge/latch materials Design and build PSS and FSC testbeds Establish Project controlled Material Database document Measure CTE and stability to 10 ppb Calibrated performance of MTC better than nm-level measurements N/A Pre-Phase A September FY06 Calibrate measurement accuracy of PSS and FSC Collect composite material dimensional stability data Characterize friction parameter sensitivity to system dynamic performance Validate material dimensional stability and dynamic hinge/latch stability models to an accuracy consistent with 10-9 contrast requirement. N/A Phase A Collect dimensional stability and dynamic stability for representative composite structure sub-assembly Deliver material dimensional stability and dynamic hinge/latch stability requirements consistent with 10- 9 contrast requirement N/A Phase B Incorporate model and material property results into flight design analyses Test actual flight sub-component hardware and validate models Validate that flight design meets 10-9 contrast requirement N/A 122
Plan for Technology Development 7.5.4 Vibration Isolation Testbed Scope During pre-Phase A stage, significant effort will be invested in developing high-fidelity models of the candidate isolation designs. The analytical models will be correlated with existing test data to ensure that the actual behaviors of the isolators are properly captured. These isolation models will also be incorporated in the integrated model, combining structure, optics, and control models, to support end-to-end disturbance-to-performance analyses. The objective during pre- Phase A is to demonstrate the vibration suppression capabilities of the isolators via analysis and show that the stability requirements described in the error budget can be met. Since the vibration isolation architecture has significant implications to different subsystems within the TPF-C system, system engineering trades that account for these interdependencies must be completed before down-selecting the isolation architecture. The system-level trades will take into account cost, risk, and how performance margins may affect other subsystems requirements. By the end of pre-Phase A, the relative merits of different isolation point designs will be assessed, and an isolation design will be selected based on its vibration-suppression performance and the results of the system engineering trades. At this point, it is also necessary to develop detailed test plans to improve the maturity level of the isolation component technology and determine testbed requirements. The Phase A isolation sub-system test is envisioned to use the flight payload isolator design attached to mass simulators that mimic the mass and inertia of the payload and the spacecraft (i.e., a 1:1 scaled test). The mass simulators will need to be gravity offloaded so that their fundamental suspension frequencies are significantly below the isolator mode (on the order of 0.01-Hz suspension frequencies). The spacecraft mass simulator will be excited using 6 force shakers arranged to give 6 DOF forcing (e.g., in a Stewart platform). Two types of tests will be performed. The first type measures the 6 × 6 transfer function matrix from disturbance inputs to payload response. The next type will measure the isolator performance when the motion at each side of the isolator is actively driven to mimic the behavior of analytical models of the spacecraft and the payload. The spacecraft mass simulator response will be actively driven to mimic the behavior of the analytical flexible spacecraft model, driven by the reaction wheel disturbances. The response at the payload interface will be actively driven to mimic the analytical model of the payload. The performance metrics will be the optical stability of the payload analytical model. The metrics for isolation acceptance will include the isolator resonant frequencies (below a specified frequency), damping (greater than a given percent damping), and attenuation above the isolator resonance (greater than a specified, frequency-dependent requirement). The test will need to be conducted in a thermal-vacuum chamber since the damper performance is a function of temperature, and joint pumping and acoustics can introduce additional damping. The input forcing levels should be consistent with expected disturbance force magnitudes to ensure that nonlinear effects show up properly in the test results. Test data must be comprehensive enough to tune the isolator models, and to characterize variability and uncertainty in the isolator behavior. The correlated isolator models (with uncertainty model) will be used to generate an improved system performance prediction, with uncertainty bounds produced by isolator variability. During Phase B, the isolation sub-system testbed will be integrated with the pointing testbed to demonstrate the pointing and stability performance of TPF-C. This testbed should be a subscale 123
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JPL Publication 05-8 Technology Pla
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TECHNOLOGY PLAN TERRESTRIAL PLANET
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Recent Highlights Technical progres
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Figure i-4. Deformable mirror deliv
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Chapter 4 enclosures, and stable la
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Chapter 4 facilities from which dat
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Chapter 4 Figure 4-5. Microslip Tri
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Page 152 and 153: Appendices Appendix F: Acronym List
Page 154: Appendices RWA SAO SBIR SIM SM SMFA
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TPF-C Technology Plan - Exoplanet Exploration Program - NASA

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