Scientists have been trying to figure out how to explore the sun since the 1950s — such a daring mission was on a short list that helped spur the inception of NASA.
After nearly 60 years — not to mention millennia of solar worship, folklore and fascination — a spacecraft being built in Laurel will get closer to the sun's surface next year than any man-made object before it.
Engineers at Johns Hopkins Applied Physics Laboratory are putting finishing touches on the $1.5 billion Parker Solar Probe, which will pass through the blazing shroud known as the sun's corona two dozen times over seven years.
Key to the mission is an engineering feat that created a 4.5-inch thick carbon shield that will face temperatures of up to 6,000 degrees on one side while keeping scientific instruments at about room temperature on the other.
The hope is that observations by the probe's sensors and camera will help explain why the sun's outermost layer is so much hotter than its surface — and what causes it to periodically and unpredictably spew torrents of energized particles known as coronal mass ejections.
The phenomena are poorly understood. Though they can overwhelm satellite communications and power grids on Earth, current technology is not capable of precisely forecasting them until less than an hour before they arrive.
"Our whole concept of the sun could change," said Betsy Congdon, lead engineer for the Parker probe's sun shield. "A few months in, we'll start taking science we haven't gotten before."
The mission has taken a generation of technological advances, including a decade of work specifically devoted to the shield. NASA hired the Hopkins lab in 2008 to design and build the probe.
It required not only withstanding the corona's heat but also gathering enough data to make the journey worthwhile. Earlier plans allowed only hours-long fly-bys that required nuclear propulsion, said Nicky Fox, the mission's project scientist.
"It really was, how do you do this and not melt?" Fox said.
The answer is a cone-shaped spacecraft that packs instruments measuring magnetic fields and the speeds, densities and temperatures of energetic electrons and protons within the shelter of the 8-foot-wide shield. Some of the sensors extend from four antennae off the shield's corners, so they will be enveloped in the inferno of the corona.
The shield, containing carbon materials similar to graphite epoxy used in golf clubs, had to be designed for both heat tolerance and durability. It is expected to get as hot as 2,500 degrees on its sunny side and 600 degrees on the other, with a system of radiators between it and the heart of the spacecraft. But it also will get as cold as 200 degrees below zero — swinging through both extremes with each of 24 orbits around the sun.
Solar panels attached as arms of the spacecraft extend beyond the shield's shadow, but retract inwards to expose only a line of their outermost cells when the spacecraft makes its closest approaches to the sun. At that point, the sun's energy will be so intense that a sliver of solar cells will produce as much energy as all the panels will from the distance of Venus.
Sensors around the core of the spacecraft ensure that it can autonomously shift its orientation so the shield constantly faces the solar surface.
Unlike other spacecraft the Hopkins lab has managed — such as the New Horizons Pluto mission or the Van Allen Probes exploring Earth's magnetic field — the Parker probe won't be in communication with the scientists for days or weeks at a time, so it is being designed to be more autonomous than other space missions.
"This one is probably the most complicated mission we've ever done," said Jim Kinnison, mission systems engineer.
It's also, he added, "by far the coolest."
The Parker probe will be a key addition to NASA's study of the heliosphere — a term for all reaches of the solar system touched by the solar wind, the steady stream of charged particles emanating from the sun's surface. Observing solar activity from close up is as much about learning the inner workings of the sun as it is about how the solar wind shapes Earth and the rest of the solar system.
Previously known as Solar Probe Plus, the mission was renamed last month in honor of University of Chicago astrophysicist Eugene Parker. In 1958, the now-90-year-old wrote a scientific paper asserting that energized matter and magnetism were escaping the sun and rippling across the solar system.
NASA officials say it's the first time a space mission has been named for a living person.
Scientists are intrigued to get a better view of the bursts of energy from the corona that have been known to stymy satellite communications, fry electricity infrastructure and create dramatic displays of "Northern lights" on Earth. If the Parker probe ever finds itself in the midst of one, it "would be like hitting the lottery," Fox said.
"We don't want to go just to find a quiet sun," she said. "It's important to see varying conditions."
So-called "solar storms" on par with one that hit the planet in 1859 and another that just missed Earth in 2012 could be paralyzing, so scientists hope that by better understanding the sun's corona, they will be able to better predict and detect coronal mass ejections.
"If we can get better data, we can better prepare for those types of storms here on Earth," said Steven Clarke, director of the heliophysics division of NASA's science mission directorate. "That's critical."
The Parker probe is preparing to enter its final stages of testing at the Hopkins lab, and later this fall at the NASA Goddard Space Flight Center. In Laurel, engineers will expose the spacecraft to the loud noises it will be exposed to when it's launched next summer from the Kennedy Space Center in Cape Canaveral, Fla., aboard NASA's largest rocket.
At Goddard in Greenbelt, the probe will be exposed to extreme temperatures inside a massive vacuum chamber — with an oven temporarily simulating the heat expected to come off the sun shield. That crucial piece of the spacecraft is being built by contractor Carbon-Carbon Advanced Technologies in Texas and will be integrated with the rest of the probe in Florida.
Once it launches during a three-week window that starts July 31, 2018, the Parker probe won't have that long of a journey to its target. It will take about two months to reach Venus — scientists will use that planet's gravity to steer and slow the spacecraft toward the sun — and then two more months to make its first pass by the sun.
On that initial fly-by, the Parker probe will come about 14 million miles from the sun — twice as close as Helios, a pair of probes launched in 1974 that currently hold the record for closest approach. It will sweep through the corona at 430,000 mph — for 11 days.
"The sun is big," Fox joked. "It takes a while to get around it."
On its final approach seven years later, the probe will cut that distance to less than 3.7 million miles — more than seven times closer than mankind has been from the glowing ball of gas that makes life possible.