by Lina Tran
NASA’s Goddard Space Flight Center
GREENBELT, Md. — It will be a dark winter’s night when Solar Orbiter launches from Florida on its journey to the source of all light on Earth, the Sun.
The mission, a collaboration between ESA (the European Space Agency) and NASA, is scheduled to begin Feb. 9, 2020, during a two-hour launch window that opens at 11:03 p.m. EST. The two-ton spacecraft launches from Cape Canaveral on a United Launch Alliance Atlas V rocket.
Seeking a view of the Sun’s north and south poles, Solar Orbiter will journey out of the ecliptic plane — the belt of space, roughly aligned with the Sun’s equator, through which the planets orbit. Slinging past Earth and repeatedly around Venus, the spacecraft will draw near the Sun and climb higher above the ecliptic until it has a bird’s eye view of the poles.
There, Solar Orbiter will try to answer basic questions about the Sun, whose every burp and breeze holds sway over the solar system. What drives the solar wind, the gust of charged particles constantly blowing from the Sun? Or, what churning deep inside the Sun generates its magnetic field? How does the Sun’s magnetic field shape the heliosphere, the vast bubble of space dominated by our star?
“These questions are not new,” said Yannis Zouganelis, ESA deputy project scientist at the European Space Astronomy Centre in Madrid. “We still don’t understand fundamental things about our star.”
In solving these mysteries, scientists seek to better understand how the Sun shapes space weather, the conditions in space that can impact astronauts, satellites, and everyday technology like radio and GPS.
Over the next seven years, Solar Orbiter will travel as close as 26 million miles to the Sun — closing about two-thirds the distance from Earth to the star. It will climb 24 degrees above the ecliptic for a vista of the poles and the far side of the Sun.
“We don’t know what we’re going to see,” said Teresa Nieves-Chinchilla, NASA deputy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Our view of the Sun is going to change a lot in the next few years.”
Enabling its scorching voyage is a heat shield sporting a black coating of calcium phosphate, a charcoal-like powder similar to pigments used in cave paintings tens of thousands of years ago. All but one of the spacecraft’s telescopes peer through holes in the heat shield. At closest approach, the front of the shield will near 1,000 degrees Fahrenheit, while the instruments tucked behind it will remain at a comfortable range — for them — between minus 4 F and 122 F above zero.
Because Earth orbits through the ecliptic plane, we don’t get a good view of the poles from afar. It’s a bit like trying to glimpse Mount Everest’s summit from the base of the mountain. Crucially, the poles are still missing from space weather models that scientists use to forecast solar activity.
Like Earth’s own North and South poles, the Sun’s poles are extreme regions quite different from the rest of the Sun. They’re covered in coronal holes, cooler stretches where the fast solar wind comes gushing from. There, scientists hope to find the footprints of knotted magnetic fields underlying solar activity. Many think the poles hold the first clues to the intensity of the next solar cycle, which comes roughly every 11 years, as the Sun swings from seasons of high to low activity.
With a powerful array of 10 instruments, Solar Orbiter is like a lab in orbit, designed to study the Sun and its outbursts in great detail.
“What makes Solar Orbiter unique is this combination of really high-resolution imagers and in situ instruments, getting perspectives we haven’t seen yet,” said Daniel Müller, ESA project scientist at the European Space Research and Technology Centre in the Netherlands.
Ideally, Müller said, Solar Orbiter will image where solar wind bubbles on the surface and study the properties of that gust of wind as it flows from the Sun and passes the spacecraft. For the first time, scientists will be able to map what comes out of the Sun to precisely where it came from.
The instruments are also designed to work in concert, enhancing their observing power, said ESA payload manager Anne Pacros. When something fleeting like an X-ray solar flare blazes on the surface, the spacecraft’s X-ray instrument will see, and alert the others to pay attention.
“They enter burst mode, where they take more data, faster, responding to solar activity in real time,” Pacros said. “This promises much more science with what we have on board.”
Solar Orbiter’s destination is largely uncharted, a little-explored region of the heliosphere. Its unique vantage point is key to a complete understanding of the Sun’s activity and cycles. By offering regular views of the far side of the Sun, and the first images of the solar poles, Solar Orbiter joins a team of NASA heliophysics missions seeking to understand how the Sun affects the space around Earth and all the planets.
“We have all these amazing missions located in exactly the right place we want to study,” said Nicola Fox, director of the Heliophysics Division at NASA Headquarters in Washington. “They’re in places that allow us to do big system science, more science than you could do with just one mission alone.”
In particular, Solar Orbiter will work closely with NASA’s Parker Solar Probe. The two are natural teammates. Together, they’ll provide a never-before-seen global view of our star.
The duo makes new multi-point measurements possible; these are useful for tracking how flows from the Sun develop and change. As Parker Solar Probe samples hot solar gases up close, Solar Orbiter can tell us more about the very space Parker flies through. Or, they might simultaneously image the same structure in the corona, the solar atmosphere, sharing views from the poles and equator. At various points, the two missions will make coordinated observations.
“Parker Solar Probe and Solar Orbiter, in orbit together, is a big milestone,” Nieves-Chinchilla said. “This is something heliophysicists have been waiting on for decades. In the next decade, together, the two will be sure to change the field.”
After launch, the operations team will conduct three months of commissioning to ensure the instruments are operating properly. Once this check-out period is complete, the in situ instruments will turn on; the remote-sensing instruments will remain in cruising mode until Solar Orbiter’s first solar approach in November 2021.
Solar Orbiter is an international cooperative mission between ESA and NASA. ESA’s European Space Research and Technology Centre (ESTEC) in the Netherlands manages the development effort. The European Space Operations Center (ESOC) in Germany will operate Solar Orbiter after launch. Solar Orbiter was built by Airbus Defence and Space, and contains 10 instruments: nine provided by ESA member states and ESA. NASA provided one instrument, SoloHI and an additional sensor, the Heavy Ion Sensor, which is part of the Solar Wind Analyzer (SWA) instrument suite.
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