HEAT SHIELD

How NASA's Parker Solar Probe Will 'Kiss the Sun'

The six-and-a-half-year journey will take it 20 million miles closer to the sun than any

NASA/Johns Hopkins APL/Steve Gribben

Ever since NASA opened for business in 1958, spacecraft have explored our cosmic neighborhood, orbiting Mercury, flying by Venus, studying Saturn for over a decade, even speeding by Pluto just three years ago.

There is however, one place we’ve never explored: The sun.

That’s about to change. At least it was—NASA was scheduled to launch the Parker Solar Probe from Kennedy Space Center in Florida early Saturday morning but two minutes before launch it postponed the mission due to a technical glitch.

It was supposed to begin a six-and-a-half year journey to cozy up to our solar system’s star. And that's going to be huge when the Parker Solar Probe does take off: the spacecraft will be the first to visit the sun, coming within just four million miles of our solar system's star.

“We've been studying the sun for decades, and now we're finally going to go where the action is,” Alex Young, a NASA solar scientist, said in a statement on the mission.

No spacecraft has ever done this before. The closest previous solar mission got within 25 million miles of the sun; the Parker Solar Probe will break that record seven times over. Scientists have wanted to study the sun for over 60 years, but the technology needed to protect a spacecraft that approached the sun so closely never existed.

And while studying the Sun from Earth works in some ways, there are major mysteries about this giant fusion reactor that requires a mission all its own.

The Parker Solar Probe has three main mission objectives while on its stellar journey. First, it will study why the corona (the sun’s atmosphere) is hotter than the surface of the sun. Logic tells us that the further out you get from a heat source the cooler the temperature should be, but that is not what happens at the sun. The average temperature on the surface of the sun is around 10,000 degrees Fahrenheit while the corona can be up to three million degrees hotter.

Scientists have no idea why this disparity exists and Parker Solar Probe will hopefully help solve this riddle.

The probe will also attempt to understand the mechanism that forces solar wind to shoot outwards into space at a million miles per hour. Relatedly, it will try to understand why coronal mass ejections, or CMEs, spit high energy particles outwards at (almost) the speed of light.

“Mars probably lost its atmospheric water because of the solar wind over and over hundreds of millions of years.  We now know the solar wind blew away the Martian atmosphere,” Eric Christian, Deputy Principal Investigator for the Parker Solar Probe’s Integrated Science Investigation of the Sun, or ISIS instrument, said. So understanding why the solar wind behaves the way it does can help us piece together mysteries from the entire solar system, not just the stellar neighborhood.

The solar wind was first theorized by the spacecrafts namesake—Eugene Parker. Parker was a physicist who upended the field of heliophysics when he first proposed not just that the solar wind existed, but that the sun’s magnetic field was shaped like a spiral. "There are some theories about why the the solar magnetic field behaves this way,” Christian said—but we can’t know without going to where the action is.

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Understanding why and how these phenomena happen are important to understanding not only the cycles of the sun, but also their practical application for us earthlings. High energy particles and large magnetic burps from the sun can be harmful to our satellites. Being able to better predict solar weather can save our electronic resources, allowing us to have warning before a large solar storm is due to impact Earth’s magnetic field. And those particles accelerated out into space are harmful to astronauts as well.

But how does anyone design a spacecraft to study the sun so close? Four million miles from the sun’s surface might sound far, but the heat from that distance is enough to melt lead and aluminum. The Parker Solar Probe will not only study the sun for the first time, but also be the first spacecraft ever built capable of withstanding these scorching temperatures.

The truth is that despite the Parker Solar Probe’s announcement that it will “kiss the sun,” nothing can come close to touching the sun without getting totally destroyed.

Heat shielding strong enough to keep the spacecraft from vaporizing on its mission was only recently developed. Parker Solar Probe’s heat shield, also called the Thermal Protection System is made of from special carbon foam sandwiched between two carbon sheets. While it will be able to withstand temperatures of up to 2500 degrees Fahrenheit, it is only eight feet in diameter, 4.5 inches thick and 160 pounds. This white shield will reflect as much sunlight as possible, and will bear the brunt of the heat during the mission.

“The front side of the heat shield will get hot enough to melt aluminum,” Christian told The Daily Beast. In order to protect the fragile instruments on board, the spacecraft and its shield will stay facing the sun during the entirety of its mission.

Remarkably, despite the scorching lead-melting temperatures on the front of the spacecraft, “on the back side, by the time you get to the instruments the heat is down to room temperature.” They spent years developing the heat shield before they even began building the rest of the spacecraft because we knew without the heat shield we didn’t have a mission."

To prepare for these temperatures engineers at the Applied Physics Laboratory in Maryland created special ovens and lamps to get up to solar temperatures. They shook the spacecraft, warmed it up again to 2500 degrees Fahrenheit until they were sure it was ready for its journey to the sun.

The Parker Solar Probe and its carbon sandwich heat shield have already revolutionized the kind of thermal pressure a spacecraft can take, though it has miles to go before it reaches its destination.

After the spacecraft launches on Saturday, it will spend just over six years traveling towards the sun. When the spacecraft departs Earth it will take some of earth’s energy with it, speeding it up. But in order to arrive at the sun, the Parker Space Probe needs to slow down—a lot.

In order to do this it will fly by Venus, where it will give away some of its energy. It will act as a sort of a reverse gravity assist where we can use planets to speed up spacecraft. In this way, the Parker Solar Probe will use Venus’s gravity to slow itself down.

And although the spacecraft will be averaging speeds of 443,000 miles per hour, it will have to fly by Venus seven times over the next six years, sloughing off some of its speed each time in order to slow down enough so that it can fall into orbit around the sun. Each flyby will nudge it closer and closer to the sun, until it reaches its closest approach of four million miles from the surface. While it do-si-do’s around the sun and Venus, it will be collecting data about the solar wind, running engineering check ups in preparation for arrival and teaching us more about the environment of the inner solar system.

A mission to the sun has been waiting to launch for 60 years, but it’s finally going to have a chance to leave the launchpad and the team is thrilled.  “This is a mission that NASA has wanted to do since the very start of NASA,” says Christian. “Now we finally have the technology that we can actually do it. It’s very exciting.”