The Parker Probe: what happens next
NASA has launched the fastest vehicle in history – and it’s in for a wild ride. Richard A Lovett reports.
NASA’s latest space mission, the Parker Solar Probe, roared off Cape Canaveral at 3:31 US eastern daylight time on Sunday August 12, atop a 71-metre rocket that in a matter of a little more than 40 minutes sent it hurtling toward the sun at tens of thousands of kilometers per hour.
The launch had originally been scheduled for the day before, but a last-minute glitch caused it to be delayed. When it did happen, however, it went smoothly. “It was very boring, which is awesome for this kind of launch, says Omar Baez, the mission’s launch director. “It went off like clockwork.”
The launch was to some degree overshadowed by American Vice President Mike Pence’s announcement three days earlier that the Trump Administration would be pressing ahead with the President’s desire to create a new branch of the military, called the Space Corps.
But that wasn’t enough to steal attention from the Parker’s bold mission, sometimes described as an effort to “touch the sun”.
At its closest approach, the $1.5 billion probe will be flying through the sun’s corona — the ghostly halo seen by much of North America during last year’s total solar eclipse. To put that in perspective, says NASA spokesperson Karen Fox, that’s less than 5% of the distance from the Earth to the sun.
“Parker Solar Probe will be giving us our first-ever close-up view of the star we live with,” she says.
It will also be going extremely fast, building up to speeds of 700,000 kilometres per hour as it falls towards its destination. That will make it the fastest-moving object ever created by humanity.
In fact, the next step is a flyby of Venus, where, rather than getting a gravity boost, as is used for spacecraft heading for Jupiter or other outer planets, it will instead use the planet’s gravity to slow down.
“That allows us to shrink our orbit,” says Nicky Fox of Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland, US, the mission’s project scientist.
On subsequent orbits, it will make additional Venus flybys, gradually reducing its orbit until it is making a close passage of the sun about once every three months.
Eventually, it will be passing within 6.2 million kilometres of the star, through a zone where the corona is known to be about two million degrees Celsius. Not that the spacecraft itself will become that hot. But that close to the sun it is exposed to sunlight more than 600 times more intense than that which bathes the Earth or the moon.
To survive that, says project manager Andrew Driesman, also of Johns Hopkins, “we need to bring an umbrella, just as you might wish you had on a hot, sunny day.” But this is no ordinary umbrella. It’s a carbon composite sandwich 11 centimetres thick, with a carbon foam core. “It took 18 months to build,” Driesman adds.
If you tried to build such a heat shield in the 1960s, when the mission was first dreamed of, he explains, it would have required an excessively heavy amount of metal. “Carbon is the magic element,” he says. Even though it’s nearly 2.5 metres in diameter, it only weighs 73 kilograms.
The spacecraft’s solar power array also needs cooling, but in this case it’s “active cooling” that pumps water through it like the radiator in a car. And the instrument sensors that peek out around the edges of the heat shield are made of exotic materials such as niobium, says project scientist Fox.
One of the difficulties in design, Fox adds, is that temperatures near the sun are extremely hot, while further out, near the orbit of Venus, they are quite cold. That means the sensors need to be able to survive not just heat, but dramatic extremes, over and over again. “There was an enormous amount of testing,” she says.
The spacecraft is named for Eugene Parker, who in 1958 first posited the existence of the solar wind, which consists of streams of high-energy particles flung away from the sun’s outer atmosphere. At the time, it was a controversial idea, but today we take it for granted.
“There is no other name that belongs on this mission,” says Thomas Zurbuchen, head of NASA’s Science Mission Directorate.
Parker, now 91, attended the launch. “All I can say is ‘wow, here we go,’” he said afterwards. “It’s a whole new phase [of solar research] and it’s going to be fascinating throughout.”
The primary mission envisions 24 passages through the corona, beginning this November, and extending until 2025. But hopefully that’s just the start. The limiting factor, Driesman says, will be fuel to keep the spacecraft oriented so that the heat shield protects its critical components.
“Eventually we’ll run out of propellant,” he says. But, he says, that might not happen for 10 or 20 years.
In the process, scientists hope to learn not just basic science, but important details about the solar wind and how to better understand and predict dangerous solar storms.
Although the mission has been planned for years, it gained momentum from the 2017 total eclipse, which occurred only 10 months before the launch. Zurbuchen notes that prior to 2017, he himself had never seen an eclipse.
“I didn’t realise how emotional I was going to get,” he says. Within seconds of the initial wow, he explains, he was thinking, “This is where Parker’s going to go.”
Unfortunately, Fox says, the spacecraft isn’t designed to provide dramatic close-up photos of the sun, like NASA’s Juno mission is doing for Jupiter. Instead, the only photos will be of the corona — “not of the sun but of what the spacecraft is about to plow through,” she says.
The reason is that while Juno’s launch weight was 3625 kilograms, the need to launch the Parker at much higher speed reduced its maximum weight to only a bit more than 600 kilograms. “The mass is limited,” Zurbuchen says. “We want to use every single pound for fuel.”
“We need to be light,” adds Fox. “We don’t carry anything extra.”