Parametric Study of Novel Passive Thermal Control Technology for Spacecraft

Abstract

Thermochromic variable emissivity materials (VEMs) are a relatively new passive thermal control technology used for spacecraft radiators. VEMs passively change their emissivity based on their temperature, with VEMs having low emissivity at low temperatures and high emissivity at high temperatures. This property of VEMs allows for spacecraft to have reduced heater power and less extreme temperature swings without adding active thermal control systems. There is a potential for VEM technology to become more widely used in spacecraft radiators. Because thermochromic VEMs are still a relatively new technology, there has not yet been a study with a parametric sweep of some possible VEM profiles and common spacecraft parameters to determine the best-case uses of particular VEM profiles. This thesis models a single-node spacecraft in an equatorial low Earth orbit, varying the spacecraft’s shape, surface area, and thermal mass using Thermal Desktop. The temperature history of the spacecraft in orbit, particularly its orbit minimum temperature, orbit maximum temperature, orbit average temperature, and orbit temperature range, is recorded, and twelve VEM profiles are compared against default black and white paint materials to see how the twelve VEM profiles change orbit minimum temperature, maximum temperature, average temperature, and temperature range. The desired outcome is for the VEMs to reduce the temperature range the most compared to black or white paint while keeping temperatures within typical temperature requirements for spacecraft components. It is found that, compared to white paint, VEMs always increase the orbit minimum temperature, maximum temperature, average temperature, and temperature range across all nodal thermal masses and surface areas studied. For spacecraft with lower surface areas, having only white paint decreases the temperature too much for typical spacecraft components, so even though white paint always decreases temperature range compared to VEMs, it is recommended to have VEMs instead of white paint for lower surface area spacecraft due to VEMs being better than white paint at keeping components within typical temperature requirements. When VEMs are compared to black paint, it is found that black paint has lower minimum temperatures and greater maximum temperatures than all VEMs at greater surface areas. For lesser surface areas, the node covered in black typically has minimum and maximum temperatures in the middle of the VEMs’ minimum and maximum temperatures. For all surface areas and thermal masses, the average temperature of the black node is typically in the middle of the average temperatures of the nodes with VEMs; in relation to the VEMs’ average temperatures, the black average temperature decreases as node height increases. For all node heights and thermal masses, VEMs always decrease the temperature range compared to black. VEMs are shown to be better than black paint in having spacecraft components stay within typical temperature requirements, and which VEM to choose depends on what the specific spacecraft component is and its specific temperature requirements. The biggest difference in individual VEM profiles compared to each other is the orbit average temperature; the lower the VEM’s transition temperature, the lower the average temperature. Only at the greatest nodal surface areas and smallest nodal heights is there a significant difference in temperature range between individual VEM profiles; typically, the lower the transition temperature of the VEM, the less its temperature range. Future work includes expanding on the parameters studied and studying spacecraft in different orbits, different spacecraft shapes, and different VEM profiles.