Abstract
Direct calorimetric measurements of a solid state passive switchable radiator for spacecraft thermal control have been performed in a simulated space environment. Dynamic emissivity control is provided by the thermochromic phase change in a multilayer VO2 thin film based resonant absorber. The measured radiated power difference between 300 K and 373 K was 480 W/m2 corresponding to a 7× difference in radiative cooling power. We present theoretical and experimental radiator values for both normal and hemispherical as well the optical properties of VO2 as determined via infrared spectroscopic ellipsometry.
Highlights
Thermal control is essential for the proper operation and longevity of space borne assets
A more direct approach would modulate the emissivity of the radiator itself such that when the spacecraft temperature is lower than ideal, the emissivity is decreased to reduce radiative heat loss and when the spacecraft temperature is higher than ideal, the emissivity is increased to radiate the unnecessary heat, maintaining a stable spacecraft temperature
The VO2-based thermal radiator, which consists of a BaF2 dielectric spacer sandwiched between a VO2 layer and an Au reflecting layer, achieves passive and switchable thermal emissivity control based on the VO2 phase transition
Summary
Thermal control is essential for the proper operation and longevity of space borne assets. A more direct approach would modulate the emissivity of the radiator itself such that when the spacecraft temperature is lower than ideal, the emissivity is decreased to reduce radiative heat loss and when the spacecraft temperature is higher than ideal, the emissivity is increased to radiate the unnecessary heat, maintaining a stable spacecraft temperature To address this matter, electrochromic[7] and thermochromic[8,9] variable emittance coatings have been proposed to provide efficient thermal control for spacecraft. Hendaoui et al reported a sandwich-like multilayer structure that consists of an 850 nm-thick SiO2 film sandwiched between a front VO2 thin film (30 nm) and a back infrared reflecting Au layer (350 nm) deposited on a quartz substrate This multilayer structure provides a near normal emissivity change of Δε = 0.49 between 300 K and 373 K19,26. The VO2 front layer will slowly oxidize into highly-valent V2O5 when exposed to atomic oxygen flux conditions, which greatly deteriorates its thermochromic properties[9]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
