As surviving inhospitable trips go, NASA’s Parker Solar Probe having to withstand more than a million degrees Fahrenheit as it approaches the Sun seems on paper like an insurmountable challenge. Turns out, though, a mere 4.5-inch thick solar shield is all the spacecraft needs, as NASA has explained.
The Parker Solar Probe is expected to blast off this summer, the start of a seven year mission to the star at the center of our solar system. It’s designed to orbit through the Sun’s corona, the fiercely hot region of the solar atmosphere that contains materials at temperatures greater than a million degrees Fahrenheit. When there, NASA expects the probe to make 24 orbits as it takes measurements.
Given scientists have struggled to make us a Hot Pocket that can survive a simple kitchen microwave if you don’t get the timings right, a spacecraft surviving that sort of environment seems unlikely. In fact, though, the Parker Solar Probe benefits from both some high-tech materials and a fistful of physics that make the whole thing a little more straightforward.
On the physics side, it comes down to heat versus temperature. High temperature materials may be measured in the millions of degrees around the Sun, but as they’re high moving and relatively scarce in number, they’re actually relatively low heat and transfer little energy. “The corona through which Parker Solar Probe flies, for example, has an extremely high temperature but very low density,” NASA explains. “That means that while Parker Solar Probe will be traveling through a space with temperatures of several million degrees, the surface of the heat shield that faces the Sun will only get heated to about 2,500 degrees Fahrenheit (about 1,400 degrees Celsius).”
That’s where the Thermal Protection System, or TPS, comes in. An 8 foot diameter shield mounted at the front of the probe, it was designed by specialists at the Johns Hopkins Applied Physics Laboratory. Two carbon plates form a sandwich either side of a carbon composite foam, and are finished off with a lick of white ceramic paint.
It may only be 4.5-inches thick, but the combination of materials and coating mean the TPS can handle up to 3,000 degrees Fahrenheit in heat. The spacecraft in its shadow will be held at around 85 F, in contrast, poking only a couple of instruments over the edge.
One of those, the Solar Probe Cup, measures ion and electron fluxes and flow angles involved in solar wind. NASA made that from sheets of Titanium-Zirconium-Molybdenum, which has a roughly 4,260 F melting point, combined with tungsten chips, which don’t melt until 6,192 F. Niobium wiring is suspended in specially grown sapphire crystal tubes.
Since its debut test can’t really be on approach to the Sun, NASA built a simulator back on Earth. A particle accelerator was used to emulate the radiation the Solar Probe Cup is meant to measure, while IMAX projectors ramped up to higher levels simulated the sort of fierce heat it’ll need to withstand. Then, it went into the Odeillo Solar Furnace which acted as a magnifier for the Sun’s power as felt all the way from 92.96 million miles away from the star.
Throw in specially-cooled solar arrays – which will peek just slightly around the edge of the TPS to minimize exposure – and autonomous flight adjustments that use solar sensors to correct the probe’s position, and the spacecraft is pretty much complete. NASA designed it so that the whole system will effectively self-navigate: the sensors will lock onto the position of the Sun, and then make sure the TPS is always in alignment.