High Performance VO2-Based Thermochromic Smart Radiators for the Thermal Control in Micro- and Nano-Satellites
(Room Room 104-C)
29 Apr 19
11:00 AM
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11:20 AM
VO2 thermochromic coatings show good potential as smart radiator devices (SRD) for spacecraft, most notably for micro- and nano-satellites. Indeed, the inherent metal to insulator transition (MIT) of VO2 allows such a coating to act as a lightweight thermal regulator, eliminating the need for heavy and failure-prone mechanical louvers. However, spacecraft industry standards require an emissivity variation Δε of at least 60%, a value which, to our knowledge, has yet to be demonstrated. To reach and surpass this value, we first apply a modeling approach to optimize the optical properties and thicknesses of the individual constituent films of a typical SRD with the following architecture: mirror | dielectric resonant cavity | VO2 | top protective and antireflective film. This study then highlights various possible avenues to enhance the performance of the devices, one of these being the use of infrared transparent ultra low refractive index dielectric materials for the resonant cavity, e.g.: CaF2 (n @ 10 µm = 1.17). These theoretical results are then confirmed by a combination of sputter and e-beam evaporation deposition of various prototype devices with measured values of Δε in excess of 60% in the 3 to 25 μm wavelength range and thus bringing this technology one step closer to implementation. Specifically, we have presently reached a Δε value of 66%.