An annular “ring of fire” eclipse is always a bewitching event. This year, timed just right to herald in spooky season, the October 14th solar spectacular will cut a path of near darkness in the Western hemisphere through Oregon, Texas, Central America, Colombia, and northern Brazil.
Eclipses can be more than just emotionally stirring. Solar eclipses, when they happen, create waves of disturbances across electrically charged particles in the Earth’s ionosphere—a layer of the upper atmosphere that plays an important role in radio frequency communications. Here, the heated and charged ions and electrons swirl around in a soup of plasma that envelops the planet.
To understand the effect that eclipses have on this plasma, scientists from NASA are planning to shoot a series of 60-feet-tall rockets up to collect information at the source.
The ionosphere sits between 60-300 kilometers above the Earth’s surface, which is roughly 37-190 miles up. “The only way to study between 50 kilometers and 300 kilometers in situ is through rockets,” says Aroh Barjatya, director of the Space and Atmospheric Instrumentation Lab and principal investigator on the upcoming NASA sounding rocket mission, which is called Atmospheric Perturbations around the Eclipse Path. By in situ, he means quite literally in the thick of it.
[Related: How to watch Saturday’s ‘ring of fire’ eclipse from wherever you are]
“Satellites, which are flying at 400 kilometers, can look down, but they cannot measure in the middle of the ionosphere. It can only be doing remote sensing,” he adds. “And the ground-based measurements are also remote sensing.” Rockets are a relatively low-cost way to get right into the ionosphere.
Along with the rockets, the team will be sending up high-altitude balloons that will measure the weather every 20 minutes. These balloons will cover the first 100,000 feet, or about 19 miles, above the ground. Then come the stars of the show: three sounding rockets fitted with both commercial and military surplus solid propellent rocket motors. The trio are designed to give a view of the changes in the ionosphere over time, and they will be launched directly into the shadow of the eclipse from a site at the White Sands facility in New Mexico. One of the rockets will be sent up right before the eclipse, one during, and one after. Because they’re sounding rockets, they will go up to the target height, and come back down, which means that they’re equipped with a parachute recovery system.
“If you think of a big orbital vehicle sending a satellite up, they’re going to reach 14,000 miles/hour when they get into space. So they’re going to reach that orbital escape velocity and put their payload into orbit, and it’s going to stay up there for a long time,” Max King, deputy chief of the Sounding Rockets Program Office at NASA GSFC, Wallops Flight Facility, explains. “Ours are what we call suborbital. So they go up, but by the time we’ve gotten into space, we’ve slowed down to zero, and start falling back into the atmosphere. Over that curved trajectory, we get about 10 minutes in [the ionosphere] where we can take measurements and conduct science.”
[Related: We can predict solar eclipses to the second. Here’s how.]
Ten minutes may not seem very long. But a lot of data can be gathered during that time. As the rockets reach the ionosphere, electrostatic probes will pop out, measuring plasma temperature, density, as well the surrounding electric and magnetic fields. There’s a telemetry system that sends data back to the ground continuously.
The main objective of the mission is to study the plasma dynamics during the eclipse that can impact radio frequency communications. Any sort of unexpected turbulence can disrupt signals to a satellite, GPS, ham radio operators, or over-the-horizon radar that the military uses. “Ionosphere is the thing which bounces radio frequencies, and all of the space communications go through the ionosphere,” Barjatya says.
After the October mission, they’ll search the desert for the fallen parts of the rockets and refurbish the remnants of them for a second set of launches in April 2024 during the next eclipse, just so they can study its effects on the ionosphere a bit further out from the direct path. Getting more details about what happens to the ionosphere when the sun is suddenly blotted out will give researchers insight into what radio frequencies get affected, and how widespread the disturbance is. It will allow models to better prepare for these potential disruptions in the future.
NASA has launched quite a few rockets during eclipses. The last big campaign that NASA did was in 1970, where they launched 25 rockets in 15 minutes. “In 1970 the eclipse went right above the Wallops facility [in Virginia],” Barjatya says. But those rockets were mostly meteorological rockets. Today’s rockets each contain four small payloads filled with scientific instruments. “One rocket launch gives me five measurements at the same time,” he adds. “So one rocket of today is actually equal to five rockets of 1970.”
These rockets are not specialized for only glimpsing at the sky during eclipses. In fact, NASA uses them in about 20 missions a year, worldwide. “We go where the science is,” King says. Sounding rockets can be used to launch telescopes for spying on celestial bodies, supernovas, star clusters, or even flares and emissions from our own sun.
The main launch sites in North America are at the Wallops facility in Virginia, and the White Sands facility in New Mexico. Outside of the US, Norway is also a big launch site. There, scientists are using them to observe Northern lights and other auroral phenomena. Or, they could be used to take a gander at something called the cusp region, the closest portal in the sky to near-Earth space. “The cusp region is where the magnetic field lines all come into the same point,” King notes. “The only way you can really study that is to shoot a rocket through it.”
The agency will be live-streaming the launches, which you can watch here.