The solar array cooling system for the Parker Solar Probe spacecraft is shown undergoing thermal testing at NASA Goddard Space Flight Center in Greenbelt, Maryland, in late February. Image credit: NASA/JHUAPL
The spacecraft that will come closer to the sun than ever before is using a cooling system that is powered by solar energy.
NASA’s Parker Solar Probe, which is expected to fly in the sun’s corona in 2018, will keep cool using solar arrays at peak performance, despite extremely hostile conditions.
The spacecraft is designed so every instrument and system on board, besides four antennas and a special particle detector, will be hidden from the sun behind a new thermal protection system (TPS)—an eight-foot diameter shield that defends itself against the intense heat and energy of the sun.
Every system will be protected besides two solar arrays that power the spacecraft. The solar arrays will receive 25 times the solar energy when they are at the closest to the sun than they would be while orbiting Earth and the temperature of the TPS will reach more than 2,500 degrees Fahrenheit, with the cooling system keeping the arrays at 320 degrees Fahrenheit or below.
“Our solar arrays are going to operate in an extreme environment that other missions have never operated in before,” Mary Kae Lockwood, the spacecraft system engineer for the Parker Solar Probe, said in a statement.
The outermost edges of the solar arrays are bent upward, allowing the small slivers of array to be extended beyond the protection of the TPS when it is closest to the sun to produce enough power to operate the spacecraft’s systems.
The cooling system includes a heated accumulator tank that holds water during launch, two-speed pumps and four radiators made of titanium tubes and sporting aluminum fins that are two hundredths of an inch thick.
In the cooling system, the coolant used is regular pressurized water—approximately five liters, deionized to remove minerals that could contaminate or harm the system.
Further analysis shows that during the mission the coolant needs to operate between 50 degree Fahrenheit and 257 degrees Fahrenheit.
“Part of the NASA technology demonstration funding was used by [the Johns Hopkins Applied Physics Lab] and our partners at [the United Technologies Aerospace Systems] to survey a variety of coolants,” Lockwood said. “But for the temperature range we required, and for the mass constraints, water was the solution.”
NASA will use a special ceramic carrier that is soldered at the bottom of each photovoltaic cell that is then attached to the platen with a specially chosen thermally conductive adhesive to allow for optimal thermal conduction into the system while providing the needed electrical insulation.
After it launched the solar arrays and cooling system radiators will drop to temperatures ranging from -85 degrees Fahrenheit to -220 degrees Fahrenheit before it is warmed by the sun.
Less than an hour later, the spacecraft is expected to separate from the launch vehicle and begin the post-separation sequence by rotating itself to point at the sun. The solar arrays will release from their launch locks and rotate to point to the sun, while a latch valve will open to release the warm water into two of the four radiators and the solar arrays. The pump will also turn on and the spacecraft will rotate back to a nominal pointing orientation, warming up the two coldest and inactivated radiators and power from the cooled solar arrays will begin recharging the battery.
For more information on the launch of the Parker Solar Probe, visit R&D Magazine’s earlier article on the mission.
