To say that NASA’s Parker Solar Probe spacecraft will be operating in a hostile environment is an understatement. The craft will fly closer to the sun than any other mission as it begins its first historic encounter with the sun’s corona in late 2018. Cooling systems have been engineered to protect the equipment onboard.
All instruments and systems on board Parker Solar Probe (with the exception of four antennas and a special particle detector) will be hidden from the sun behind a breakthrough thermal protection system (TPS). The eight-foot diameter shield will help the spacecraft defend itself against the intense heat.
Every system will be protected except for the two solar arrays that power the spacecraft. When the spacecraft is closest to the sun, the solar arrays will be receiving 25 times the solar energy they would while orbiting Earth, and the temperature on the TPS will reach more than 2,500 degrees Fahrenheit (1,370 C). The cooling system will keep the arrays at a nominal temperature of 320 degrees Fahrenheit (160 C) or below.
The very outermost edges of the solar arrays are bent upward, and when the spacecraft is closest to the sun, these small slivers of array will be extended beyond the protection of the TPS in order to produce enough power for the spacecraft’s systems.
A first-of-its-kind actively cooled solar array system was developed by APL, in partnership with United Technologies Aerospace Systems (UTAS) in Windsor Locks, CT (which manufactured the cooling system) and SolAero Technologies of Albuquerque, NM (which produces the solar arrays).
The cooling system includes a heated accumulator tank that will hold water during launch, two-speed pumps and four radiators made of titanium tubes and featuring aluminum fins just two hundredths of an inch thick. The system is powered by the solar arrays, and at nominal operating capacity provides 6,000 watts of cooling capacity — enough to cool an average-sized living room.
The coolant used is nothing more than regular pressurized water — approximately five liters, deionized to remove minerals that could contaminate or harm the system. During the mission, the coolant would need to operate between 50 degrees Fahrenheit (10 C) and 257 degrees Fahrenheit (125 C), and few liquids can handle those ranges like water. Pressurizing the water will raise its boiling point above 257 degrees Fahrenheit.
The cover glass on top of the photovoltaic cells is standard, but the way the heat is transferred from the cells into the substrate of the panel, the platen, is unique. A special ceramic carrier was created and soldered to the bottom of each cell, and then attached to the platen with a specially chosen thermally conductive adhesive to allow the best thermal conduction into the system while providing the needed electrical insulation.