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Soil Moisture Active and Passive (SMAP) White-Painted Expanded Polystyrene (EPS) Radome Survivability TestNASA's SMAP Mission launched in January 2015 into a 685 km near-polar, sun-synchronous orbit. The SMAP instrument architecture incorporates an L-band radar and radiometer which share a common feedhorn and mesh reflector. The instrument rotates about the nadir axis at approximately 15 rpm, thereby providing a conically scanning wide swath antenna beam that is capable of achieving global coverage within three days. The radiometer and its associated electronics have tight thermal stability requirements in order to meet the required surface emittance measurement precision from space. Maintaining the thermal stabilities is quite challenging because the radiometer is located on a spinning platform that can either be in full sunlight or eclipse, and thus exposed to a highly transient environment. Stability requirements were met by integrating a light-weight Expanded Polystyrene (EPS) radome into the design to prevent solar illumination of the feed horn interior. The radome was painted white since the thermo-optical properties of bare sunlit EPS degrade rapidly over the three-year mission. Milling of the EPS and solvent within the white paint created cavities on the EPS surface which may introduce localized hot spots possibly violating the EPS glass transition temperature of 96degC and leading to structural integrity concerns. A three-day thermal test was conducted in a vacuum chamber to verify survivability of the radome during a simulated non-spin fault condition at end of mission. A portable solar simulator illuminated the test article and the beam irradiance was kept nearly constant during the entire 50 hour test, except during the first hour which simulated the expected 79degC on-orbit surface temperature of the radome. The test article survived based on the established pass criteria for three separate metrics: dimensional, optical property, and color. If any hot spots exist locally, they did not cause any observable permanent deformation when compared to pre- and post-test images. The test results increase confidence that there is a high probability that the radome will survive the worst-case scenario of a no-spin fault condition at the end of mission.
Document ID
20170008189
Acquisition Source
Jet Propulsion Laboratory
Document Type
Preprint (Draft being sent to journal)
External Source(s)
Authors
Mikhaylov, Rebecca
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Kwack, Eug
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Stegman, Matthew
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Dawson, Douglas
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Hoffman, Pamela
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Date Acquired
September 1, 2017
Publication Date
July 12, 2015
Subject Category
Solar Physics
Earth Resources And Remote Sensing
Launch Vehicles And Launch Operations
Report/Patent Number
ICES-2015-276
Meeting Information
Meeting: International Conference on Environmental Systems
Location: Bellevue, WA
Country: United States
Start Date: December 12, 2015
End Date: December 16, 2015
Sponsors: International Conference On Environmental Systems, Inc.
Distribution Limits
Public
Copyright
Other

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