Full scale thermal simulator development for the solar probe plus thermal protection system

Solar Probe Plus (SPP) is a NASA mission that will go within ten Solar Radii of the sun. One of the crucial technologies in this system is the Thermal Protection System (TPS), which shields the spacecraft from the sun. The TPS is made up of carbon-foam sandwiched between two carbon-carbon panels, and is approximately eight feet in diameter and 4.5 inches thick. At its closest approach, the front surface of the TPS is expected to reach 1200°C, but the foam will dissipate the heat so the back surface will only be about 300°C. Solar Probe Plus is scheduled to launch in 2018, and the program is in the beginning stages of integration and testing. As part of the testing process, SPP's cooling system and the full spacecraft will undergo thermal tests. Radiation from the back of the TPS plays a large part in both of these systems thermal environment. To get the back surface of the TPS to 300°C, large amounts of energy needs to be put into the top of the TPS. However, there are not many thermal chambers that can accommodate the amount of energy required at the vacuum environment required to simulate space. It is also extremely risky to expose the flight hardware to that much energy. Instead, a Thermal Simulator will be used that mimics the thermal and geometric footprint of the bottom of the TPS. The Thermal Simulator is designed as an oven box, similar in size and shape to the flight TPS, which uses tubular heaters to heat a 32 mil thick aluminum bottom sheet. The heaters and bottom sheet are supported by a large stainless steel structure. The sides and top of the structure are blanketed using stainless steel sheets. To verify the concept, a miniature simulator was built and tested. Despite a successful trial simulator, there were difficulties extrapolating the design into a larger size. This paper will focus on the construction and testing of the full-sized simulator. After extensive structural and thermal analysis, the full simulator was fabricated and assembled. A thermal vacuum test was done at NASA Goddard Space Flight Center in chamber 238. At high vacuum, the bottom sheet was successfully brought to 250°C, 300°C, and 350°C with gradients of +/−30°C. Each temperature point was held for at least three hours after steady state was achieved. This simulator will be used in winter 2017 for the Integrated Thermal Vacuum Test, and again in the future for the full spacecraft test. By successfully executing the thermal system testing using GSE, we will prove that a full system can be validated using piecemeal testing.