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Proposed REXIS Design Changes

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  1. Proposed REXIS Design Changes Harrison Bralower Sara Falcone Kyra Horne Becky Masterson 7/1/2013 Regolith X-ray Imaging Spectrometer - REXIS

  2. Reasons for Proposing Changes • Accommodation costs from LMSSC have doubled for the phase C contract, threatening REXIS reserves • Allows for a larger margin in stand off design • Removes TIL MLI • More robust to leakages through external MLI • No need for actuator heater if cover moves to top of mask • Makes the actuator heater an external heater • Allows use of a non-Frangibolt actuator • Serves as sunshade • Makes resetting the cover easier • Reduces detector contamination risk

  3. Alternate Radiation Cover

  4. Proposed Changes • Move the radiation cover to the top of the mask • Mounted on mask frame • Hinge on +X side so that cover acts as sunshade when open • Actuator wiring runs down truss • Fe-55 on cover shines through mask

  5. Advantages and Disadvantages • Advantages • Actuator heater (if necessary) is external • Actuator volume relaxed • Alternatives to Frangibolt can be considered • May serve as sunshade • Cover reset is simplified • Detector contamination risk greatly decreased • Moves heater farther away from detectors (good for calibration) • Mask protected from damage • Disadvantages • May be more massive • May pose higher contamination risk for spacecraft • Greater hazard to equipment and personnel • Fe-55 exposed externally when cover is open (80nCi source) • May disrupt mask alignment on cover rebound

  6. Actuator Trade Space

  7. Design Comparison 5.64cm 11.43cm 19.57cm 9.32cm 3.12cm 2.03cm

  8. Frangibolt Design 15.09cm 19.57cm 1.91cm

  9. Pinpuller Design 6061-T6 case 17.90cm Titanium flange 455 stainless steel pin (not shown) 5.72cm 3.94cm

  10. Field of View Clearance 19.57cm 18.20cm (excludes tab, which depends on actuator choice)

  11. Mask Cover Bar to hold torsion spring legs Lip (for Frangibolt design, would be shorter for a pinpuller) 18.20cm 3.05cm 11.43cm Doorstop feature can be designed to provide any opening angle and will have rubber to provide damping and prevent marring of mask frame

  12. Changes to Top Mask Frame Bushing housing 3 kickoff spring plungers 3 Shear uptake features Not shown: Alignment pins for mask

  13. Section View of Hinge 1.27cm diameter Vespel SP-3 bushing—bushing OD increased to support larger torsion springs Cover Doorstop hits top of mask frame to minimize disruption of mask alignment, which is controlled by bottom of mask frame

  14. Radiation Cover Analysis • Shaft size and bushing size based on current geometry • Hinge margin of safety is 2.8 (316 SS shaft) based on 4-point bending stress calculation • Bushing ID and OD sized based on vendor-provided Vespel design equations for temperature compensated clearance • Bushing OD increased for bushings placed under torsion springs for drag reduction since springs are now larger • OD will decrease and springs will become smaller once we transition to using CDR-level design factors • Torque margin calculated in same manner as described in clarification to RFA-2 response sent out last week, but with updated moment of inertia and mass for new door geometry • Design uses three torsion springs for cover opening sized to provide a torque margin of 0.087 using PDR-level design factors • TM = 0.45 using CDR-level design factors with this design

  15. Warm Truss

  16. Proposed Change • Stand off the DAM instead of the entire truss • Truss is warm • Thermal strap mounts to bottom of DAM • Flexprints attach to DE through top of Electronics Box • Radiator isolated from warm truss with torlon standoffs

  17. Advantages and Disadvantages • Advantages • No need for actuator heater if cover moves to top of mask • Simpler structural design • Reduced structural load on TIL • May remove trapped MLI • More robust to leakages throughexternal MLI • Holes in side shields closed off shielding CCDS further from radiation • Disadvantages • May be more massive • Less thermal margin for a given radiator size • Parasitics may pose greater thermal issue for detectors

  18. Modifications to Ebox/Truss Interface • E-Box and Truss • Some mass increase as truss panels extended to connect with e-box • Top of e-box shrinks, only necessary to support DAM • Flexprints move inside truss structure • TIL Standoffs • Connect directly from e-box to DAM • Move closer to center of assembly as top of e-box shrinks • Longer standoffs • DASS • Combines with top of e-box, no longer a separate part

  19. Mock-ups of Current and Alternate Designs Radiation cover is located on top of the mask frame 13.50cm 14.92cm 14.92cm 13.50cm 30.90cm Radiation cover is located on top of the DAM Thermal stand-offs are beneath the DAM DAM has a direct thermal strap (not shown) to radiator Truss structure and electronics box are separated by thermal isolation layer 27.78cm Thermal stand-offs are between the E-Box and DASS DASS and E-Box top plate are the same part Thermal strap (not shown) routes through truss panel and attaches to the DASS next to the DAM

  20. MEL Comparison • Mass of new REXIS design may exceed the allocated NTE of 5.50kg • Increase in total MEV largely due to the location change of the radiation cover and structural alterations of truss panels

  21. New “PDR-Level” FE Model Current Baseline Warm Truss

  22. Planned Analysis Cases to Run • Static stress analysis • 42g loading based on MAC applied to all three axes • Stress outputs for Torlon standoffs at TIL and radiator • Stress analysis using the “high-fidelity” standoff model • Modal analysis • Initial results • First natural frequency of entire instrument: ~170 Hz • TIL standoff margin of safety (FS = 2.0): 8.6 (x), 8.7 (y), 124 (z) • Timeline • Today: Finish model updates, incorporate GSFC feedback/suggestions • Tomorrow: Preliminary results presented at weekly team meeting • Wednesday: Final results