Dynamic Control of Radiative Surface Properties with Origami-Inspired Design

For a spacecraft to be mission ready, it must be able to regulate its own temperature. Necessary system electronics, sensitive scientific instruments and especially astronauts onboard the spacecraft must operate within a specific temperature window or the mission will fail. However, the tendency of a spacecraft's temperature is to increase. The sun and the earth radiate heat that is absorbed into the spacecraft while on-board electronics and personnel generate heat inside the spacecraft. On earth, this excess heat would normally be removed by air around the spacecraft. However, the spacecraft is in the vacuum of space. As such, the heat must ultimately be emitted away from the spacecraft as radiation. Components designed to emit this excess heat are called radiators and are a vital part of the thermal management system of any spacecraft. However, because the heat load on a system varies with orbit, radiators are designed for a worst-case heating scenario. As such, any heating configuration outside of the designed heating scenario causes the radiator to behave in an undesirable way, emitting more heat than desired or absorbing too much heat from the surroundings. Likewise, these radiators are heavy, often comprising 30 - 40% of total spacecraft weight. A simple yet effective solution, as discussed in the Thermal Management Systems Roadmap, is to develop a lightweight radiator which is able to manipulate its heat rejection rate in real time. This proposal discusses a light weight, variable heat rejection technology that may be utilized in many applications, including that of a deep space radiator. A thin, mirror-finish aluminum foil is folded into a simple, origami-inspired V-groove pattern. This pattern allows for the foil to be compressed, such that the V-grooves are very steep and tightly compacted, or stretched until it resembles a flat sheet. As the foil is compressed, the amount of heat radiated into space or the amount of heat absorbed is greatly increased. When pulled flat, the foil will emit and absorb very little radiation. This variable heat rejection capability is useful for both radiator and heat shield applications. As a radiator, the foil will give the user control of how much heat is entering or leaving the system. This technology will eliminate unnecessary radiator weight while delivering optimum heat rejection performance for the entire mission duration. Likewise, these foils may be used as heat shields, placed over components sensitive to temperature fluctuations (such as cryogenic fluid tanks). When illuminated by the sun, the shield can assume a flat state, reflecting 98% of the sun's energy away from the sensitive component. Upon entering the Earth's shadow, the shield will assume a compressed state, emitting excess heat originating from the spacecraft into deep space instead of reflecting this heat onto the cryogenic fluid tank. Preliminary work characterizing the behavior of V-grooves when exposed to radiation has been completed. However, the bulk of the work remains. The total heat rejected from a foil sample, accounting for emitting surface area, must be characterized. Likewise, the relationship between the foil and the surface it is protecting must be determined. Next, an actuation system and fixation components must be developed. Finally, the complete thermal system must be modeled and experimentally proven capable of maintaining the temperature of a protected surface under varying heat loads. Ultimately, the purpose of this work is to model a complete thermal system involving the use of a variable heat rejection shield, develop this technology to a space-ready state and experimentally validate its ability to maintain the temperature of a protected surface when exposed to varying heat loads. More »