Parker Solar Probe: How NASA Plans to "Touch the Sun" and Not Melt

The Parker Solar Probe is not only one of NASA’s most ambitious missions, but it seems to defy logic. The spacecraft slated to launch this summer will enter the sun’s corona and travel through material with temperatures greater than a million degrees Fahrenheit. So, why won’t it melt?

Parker Solar Probe will embark August 4 on what NASA calls “a mission 60 years in the making,” coming within four million miles of the surface to collect unprecedented data about the sun’s corona, or outer atmosphere. If successful, it will become the first spacecraft to enter the sun’s corona and enjoy a balmy inside temperature of just 85 degrees while its outer shell is surrounding in the sun’s blaze. The probe will essentially be the embodiment of “this is fine” dog.

NASA revealed the science behind why this space dog will not melt in such an extreme environment on Thursday. To understand why the Parker Solar Probe won’t melt, the space agency explained key concepts of heat versus temperature, its custom heat shield, and the spacecraft’s unique innovation.

Parker Solar Probe’s Temperature vs. Heat

The difference between heat and temperature will help in making the Parker Solar Probe’s mission seem a little more (but not much more) feasible. Temperature is a measurement of how fast particles are moving, while heat refers to how much of that energy is transferred. Thus, in a place that is mostly empty like space, high temperatures don’t always mean high heat. Particles could be moving fast and creating high temperature, but since there are so few of them, they won’t transfer that much heat towards the spacecraft.

While Parker Solar Probe will be traveling through a space with temperatures of several million degrees, it won’t feel most of that heat, and the surface of the heat shield will only reach 2,500 degrees Fahrenheit.

Parker Solar Probe’s Heat Shield

That’s still pretty hot, though. Experiencing 2,500 degrees Fahrenheit is nothing to scoff at, and ensuring an unmelted Parker Solar Probe may have caused some delays in scheduling the launch. To withstand the heat, NASA installed a shield known as the Thermal Protection System, or TPS.

Designed by the Johns Hopkins Applied Physics Laboratory, TPS is made of a lightweight carbon foam core that is flanked by two carbon-carbon composite panels. The sun-facing panel is sprayed with a white coating that will reflect as much of the sun’s energy away from the spacecraft as possible. It’s just 4.5 inches thick, and yet it’s expected to keep almost all instrumentation safe.

Parker Solar Probe’s Measuring Cup

Not every instrument will be protected by TPS, however. The Faraday cup is a sensor that will poke out over the heat shield to measure the solar wind, and in order to get an accurate read, it could not be sheltered by TPS.

So, why doesn’t Faraday melt?

“Due to the intensity of the solar atmosphere, unique technologies had to be engineered to make sure that not only can the instrument survive, but also the electronics aboard can send back accurate readings,” NASA’s Susannah Darling explained. The cup is made from sheets of Titanium-Zirconium-Molybdenum, an alloy of molybdenum, giving it a melting point of about 4,260 degrees Fahrenheit. The chips that produce an electric field for the Faraday cup are made from tungsten, the metal with the highest known melting point. With a threshold of 6,192 degrees Fahrenheit before melting, Faraday has the wiggle room to collect the solar wind data it needs.

After launching on August 4, Parker Solar Probe will use Venus’ gravitational pull to shrink its orbit around the sun. These flybys will take roughly seven years, eventually bringing the probe as close as 3.7 million miles from the center of the solar system. Its final loop within the sun’s corona is expected in late 2024. But thanks to this slew of innovative technologies, it should keep cool the whole time.