Thermochromics with Very Low Transition Temperature

Triton Systems is developing an unpowered thermostatic film for application to spacecraft surfaces. We call our approach Phase Change Thermochromic Radiator (PCTR); it self-switches from low to high emittance above a designed temperature setpoint Tc, causing a surface in space to radiate heat only when it becomes too warm and conserving heat otherwise. Key to the operation of PCTR is a phase change material integrated into a multilayer thin film structure to produce a device which is reflective over the 3-35 micro;m IR band below a transition temperature Tc but strongly absorptive above Tc. PCTR has advantages over competing approaches to dynamic emissivity in that it requires no electrical drive power, is relatively simple to fabricate, and contains only stable and rugged materials. Phase I research showed a path to significantly reduce the operational transition temperature, with 5deg;C or below being the ultimate goal of the program. In Phase II, complete devices will be demonstrated with turndown ratio of at least 6:1 and potentially 10:1. Scalable fabrication methods will be developed. Key qualification tests will include thermal cycling, vibration, peel tests, surface charge and degradation over operational life.