Science News - September 15, 2018

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then, that side could get as hot as 1370° C. But
behind it, the bulk of the spacecraft will chill at
just 30° C on average (about 85° Fahrenheit).

“We hide in the shadows,” says solar physicist Eric Christian of NASA’s Goddard Space Flight Center in Greenbelt, Md. He’s the deputy principal investigator of the Integrated Science Investigation of the Sun experiment, which will measure solar particles across a wide range of energies. His team was able to use ordinary materials and skip the rigorous heat testing. “We’re the lucky ones.”

But Parker won’t always be near the sun. The spacecraft’s 24 orbits will bring it as far from the sun as Venus, where temperatures are a frigid –270° C. At that distance, the spacecraft needs onboard heaters to keep it at 20° C. So Parker needed to be tested for cold and extreme temperature changes, too.

“We’re not just worried about hot cycles,” Congdon
says. “We’re worried about hot then cold then hot
then cold.”
In January, the entire spacecraft was low-
ered into a thermal vacuum chamber at NASA
Goddard for two months of testing. The chamber,
a cylinder standing 12 meters tall and 8 meters
wide, was cooled to –190° C. A radiator glowing at
about 315° C represented the heat from the side
of the heat shield not facing the sun — but most of
that heat never reached the scientific instruments
because a titanium truss holds the heat shield at a
safe distance from the spacecraft’s main body. The
team cycled through hot and cold several times to
simulate what Parker will experience.

At all temperatures, the probe’s solar panels need to stay cool. “You think, obviously, you’re going to the sun, solar power makes the most sense,” Congdon says. “But solar panels don’t like to get hot.” So the panels are threaded with veins that carry water to cool them off. The water absorbs heat from the panels and carries it to radiators that release the heat into space.

The solar panels are also on a shoulder joint, so they can tuck behind the heat shield at Parker’s closest approaches to the sun. Only the last row of cells will see the sun then. “That single row of cells can produce the same amount of power as the full wing can when we’re by the Earth,” says solar physicist Nicola Fox of the Johns Hopkins University Applied Physics Laboratory, the probe’s project scientist.

Up and away

Making sure Parker would survive the launch into space (it did) took more preparation.

With its violent shaking, a spacecraft launch is
a tense time for scientists, even if they’ve tested
all of the parts in an acoustic vibration cham-
ber. Watching SWEAP’s vibration test “made me
swear,” Korreck says. “It’s very scary to watch this
thing you’ve spent 10 years on flop around as it
keeps shaking more and more.”
Her team faced an unusual challenge in making
Parker ready to rattle. The team could not use glue
to prevent the screws from shaking loose, because
epoxies would melt in sunlight. So the researchers
twisted thin niobium wire by hand to tie hundreds
of screws together in such a way that, if one comes
loose, the others hold it in.

Launch can be a high-pressure time for the spacecraft, too—literally. Engineers initially thought Parker’s launch aboard a powerful Delta IV Heavy rocket would subject the heat shield to a force 20 times that of Earth’s gravity. Later, however, the engineers realized the launch force wouldn’t be so severe. Still, to make sure the 72.5-kilogram shield wouldn’t bend or break, the team stacked 1,360 kilograms, or 150 reams, of paper on top of it.

Parker’s first scientific data should start trickling back to Earth in December. These missives will let scientists take a big step toward unlocking the secrets of the sun’s superheated atmosphere and its energetic winds.

“It’s like being a proud parent. I worry that something could happen, but I don’t worry that we didn’t prepare or test her well,” Fox says of the probe. “I just hope she writes home every day with beautiful data.” s

Explore more
s NASA’s Parker Solar Probe: bit.ly/NASAparker
s Nicola J. Fox et al. “The Solar Probe Plus
Mission: Humanity’s first visit to our star.”