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SWEA Deflector Thermal Concerns

SWEA Deflector Thermal Concerns. Paul Turin SSL 1/29/10. SWEA Deflectors. The SWEA deflectors are thermally isolated and open to space through the aperture grids.

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SWEA Deflector Thermal Concerns

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  1. SWEA Deflector Thermal Concerns Paul Turin SSL 1/29/10

  2. SWEA Deflectors The SWEA deflectors are thermally isolated and open to space through the aperture grids. As a result, they are subject to heating from solar radiation, thruster plumes, as well as atmospheric friction during deep dips. Current deflector design is gold plated Ultem. Deflectors

  3. SWEA SC Mounting Unlike solar radiation, 100% of plume and atmospheric friction heat fluxes are absorbed ( a conservative assumption specified by LMC). At original 10 boom angle, flux from 6 maneuvering thrusters was 4.4 suns. SWEA boom tilted to 45 reduces thruster heat flux to ~1 sun. Flux from aero heating is ~0.7 suns, so thruster heating is the limiting case. 45

  4. Simple Deflector Thermal Model Projected area • Modeled deflector as a single node at periapsis • Absorbing area = projected area perpendicular to axis of symmetry • Radiating area = ½ of deflector outer surface area • Ultem is poor conductor, so ½ of deflector not exposed to flux does not helpful as a radiator • This would change with Al deflectors (significant conduction to addt’l radiating area on deflector far side) • Modeled a variety of finishes in an attempt to lower temps • Calculated equilibrium temp in sun and in shadow, including albedo, IR glow, and Thruster heat flux • Simplifications ignore: conduction and radiation to instrument, blockage of view by other deflector, angle of illumination, radiation to/from spacecraft, absorbing area > 180 due to thruster spread • Good enough to ballpark temps Radiating area

  5. Deflector Finish Options and Predicts (Periapsis) Deflector Finish: Predicts:

  6. Conclusions • Gold plated Ultem will fail • Gold plated anything will get very hot • Al better due to conduction to far side • Paints reduce temps, but probably not a good choice -- possible degradation due to atomic Oxygen • Black Chrome has potential • Guaranteed optical properties from plating vendor • Very durable • Any finish that doesn’t get excessively hot will get very cold in shadow • CTE issues? Ultem will shrink relative to Al ~.5mm • Grids and exposed gold housing have same issues

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