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NASA has a historic launch coming this July, and the destination is hotter than any summer day.

The agency will send the Parker Solar Probe on a trip that is closer to the sun than any spacecraft in history. But first, crews at NASA Goddard Space Flight Center will send the probe to Kennedy Space Center this Sunday, where it will eventually launch July 31.

The solar probe will get within 3.7 million miles of the sun, which is nearly eight times closer than any previous spacecraft. Its mission is to study the sun’s corona, a hazy aura of plasma that surrounds it and other stars like a halo.

People normally cannot see the corona except during a total solar eclipse, such as the event last August.

Solar mystery waiting to be solved

NASA is working with Johns Hopkins University’s Applied Physics Laboratory, which designed and built the spacecraft, and which will manage the mission for NASA. Nicky Fox, a project scientist with APL, said a lot is unknown about the corona but the solar probe’s mission is to find out more.

“Why are we going to the corona?” Fox told reporters Wednesday at the NASA Goddard campus. “It’s where all the magic happens.”

Despite being further away from the surface of the sun, the corona is actually about 300 times hotter. Fox said this phenomenon, as well as solar wind, have perplexed scientists. Solar wind occurs when billions of tons of solar material are hurled away from the sun at millions of miles per hour.

Fox says this wind can break away from the sun’s gravity and wash over all the planets in the solar system.

“That’s important for us here on Earth because it carries the sun’s magnetic field with it,” she said.
It can interact with our Earth’s magnetic field, and it can cause space weather. And so it’s extremely important for us to go into this region, because it is really the missing gap — the last piece of the puzzle — for us to fully model the sun and its effect on Earth.”

A spacecraft unlike any other

This mission has been in the works for so long that it actually predates NASA. In 1958, at the dawn of the Space Age, the National Academy of Science added a solar probe mission to its list of top priorities. But NASA spent decades researching how to keep a solar-powered space probe that close to the sun.

Betsy Congdon, the heat shield lead engineer for the Parker probe, said the solar cells on the spacecraft are sensitive to heat.

“We’re going to the sun, obviously you’re going to use solar power,” she said. “But the problem is, solar cells don’t like to be hot — they’re a lot less efficient.”

Congdon said two things had to happen: figuring out how to develop solar cells that work at the sun, and developing a cooling system to keep the solar cells cool. The latter is done by running water through the solar panels and tucking them into the spacecraft when the probe gets closer to the sun.

Where the solar probe is headed, the sun can get as hot as 3 million degrees Fahrenheit. But Fox said the spacecraft’s heat shield will only need to account for a fraction of that.

“There’s a difference in temperature and heat. You think ‘3 million degrees, oh my goodness.’ There aren’t an awful lot of particles there, it’s not particularly dense, so if you think about putting your hand into an oven that’s set at 400 degrees, you won’t burn yourself unless you touch a surface,” Fox said.”

The amount of particles that will touch the probe’s heat shield will come out to only about 2,500 degrees Fahrenheit. Meanwhile, the instruments that sit in the main body of the spacecraft will be at a comfortable 82 degrees Fahrenheit.

Testing the probe

But the probe faces a number of challenges before it gets anywhere near the sun. At NASA Goddard, crews have kept the probe in a large hangar nicknamed the “Chamber of Horrors,” where the team tries to simulate the harsh conditions of a rocket launch and extreme temperate changes the machine will encounter in space.

“After launch, you have vibration and acoustics happening at the same time,” said Bill Chambers, a project engineer at NASA Goddard. “The bottom of the rocket is actually shaking as much as a foot side-to-side, and that’s a very violent thing. And when it’s also hit with a reverberation of the sound coming off the ground.”

Chambers said the small circuit boards and the computer systems on board are highly susceptible to damage to that type of environment. To ensure the probe can withstand the force of vibrations during the rocket launch, the crew tested it in a room with speakers large enough to generate more than 150 decibels — a level which is lethal to humans.

“You just kind of put it in there, close the doors, say a prayer and then hit it with a whole bunch of sound,” Chambers said. “Three minutes later, it’s done.”

The test is performed in a series of increments, and then the crew runs a thermal vacuum test inside a room-sized vat. Air is removed to create a cold vacuum, followed by the addition of 35 kilowatts of heat,.

“That type of test verifies that your material is strong enough for space flight,” Chambers said. “That test is pretty much a solar simulator.”

Three months after launch, the Parker probe will reach its first close approach to the sun. Over the course of seven years, it will take 24 orbits around the sun and fly by Venus seven times.

At its closest approach, the probe will travel at 450,000 miles per hour, or fast enough to travel from Washington, D.C., to Philadelphia in a second. Once the probe gets that close to the sun, Fox said it is on its own.

“It takes light 8 minutes to get from the sun to the Earth, so if [the] solar probe has any issue, we can’t joystick that aircraft,” Fox said. “She has to be able to look after herself, and so she is fully autonomous. If anything happens, she has to correct it.”

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