NASA is slated to launch a long-awaited satellite from Florida on Thursday night that’s designed to help scientists better predict how space weather events will behave high above Earth. But to get to space, the rocket launching this satellite won’t take off from the ground like most others do. Instead, it’ll launch from underneath a giant airplane, climbing to space from midair.

The mission is named ICON — for Ionospheric Connection Explorer — and it was originally supposed to launch in the summer of 2017. However, technical issues with the rocket, called Pegasus, forced the launch to be put on hold for the last two years. Now, Northrop Grumman, which operates the Pegasus system, says the rocket is ready to fly after making a few modifications to the vehicle and performing a variety of qualification tests.

If ICON finally gets off the ground this week, scientists are particularly eager about what the satellite might tell us about Earth’s mysterious ionosphere — a huge layer of our planet’s atmosphere that begins 30 miles up and spans all the way to 600 miles high. This part of our planet’s atmosphere overlaps with the boundary of space and is responsible for what is known as space weather. It’s here where charged particles streaming from the Sun interact with particles in our atmosphere, charging them up and creating strange phenomena such as the aurora and geomagnetic storms.

The challenge, though, is that scientists have a hard time forecasting how the ionosphere is going to behave. “What we know about the ionosphere is that it really changes from one day to the next quite a bit,” Thomas Immel, the principal investigator for ICON at the University of California Berkeley, tells The Verge. “And the other thing we know is that those changes are hard to predict.”

That’s a problem since space weather events can have a very real impact on electronics and systems here on Earth. Various satellites fly through the ionosphere, as well as astronauts on the International Space Station. GPS signals also travel through this region. Disturbances in the ionosphere can muck up these signals and equipment and even disrupt our power grid on the surface below.

One way to help predict space weather is to image the Sun and understand its activity, which NASA is doing with various missions like the Parker Solar Probe. But right now, it’s still difficult to know how the atmosphere will respond to solar events. And that makes it hard to plan for storms and other weird space weather behavior. “You would be sort of surprised at how poorly you could sort of plan your days if you didn’t know the weather tomorrow,” says Immel, “which is something of our situation with the ionosphere.”

To better understand this enigmatic area of space, the ICON mission team is sending the satellite right into the thick of things. The vehicle is going to an altitude of about 360 miles, just above the peak of this atmospheric layer, which is about 120 to 200 miles high, according to Immel. ICON will also circulate Earth at a low latitude over the planet; that’s where the ionosphere is densest. “We’re focusing on that region because that’s where all the action is,” says Immel.

ICON is equipped with various instruments designed to get a more complete understanding of what the ionosphere is up to. The satellite will measure the temperature and winds of the particles and plasma within this region, and the vehicle will also measure the atmosphere’s density as well as all of the chemicals that are present. It will even measure how the atmosphere glows, which indicates how the ionosphere is moving in space. All of these measurements could be used to make better models about how the ionosphere will act at any given time. “We are looking to be able to inform modelers and theorists about what needs to be measured to make better predictions for the ionosphere tomorrow,” says Immel.

While in space, ICON will work in tandem with another mission called GOLD, which launched in January 2018. GOLD is actually a NASA instrument attached to a commercial satellite that lives 22,000 miles above the Earth’s surface. From this vantage point, GOLD has been collecting data on the ionosphere from above. Together, the two missions will provide very different information about the atmosphere from different locations.

“We’re looking at space weather like what happens with hurricanes,” Immel said during a pre-launch press conference. “Where the GOES [weather forecasting] satellites provide large-scale imaging, and we actually fly airplanes into the hurricanes to sample them and gain more information. And that’s what ICON and GOLD are going to be able to combine to do for space weather.”

ICON was supposed to be working in sync with GOLD much earlier, as it was originally set for launch in 2017 and then in 2018 from the Kwajalein Atoll. The first, the launch was delayed due to concerns that parts of the Pegasus rocket might not separate properly during the mission, while the second flight was postponed after some unexpected noise was detected in the rocket’s controls. The launch was then moved to Cape Canaveral, Florida, and scheduled for October 2018, but the noise problems popped up again.

Since then, Northrop Grumman found several causes for the noise problem and switched up some of the electronics and hardware to correct the issue. “I want to apologize for delaying you guys for the last 11 months,” Omar Baez, the senior launch director for NASA’s Launch Services Program at Kennedy Space Center, said during the pre-launch press conference. “But we wanted to get things right on this rocket.”

During the wait, the ICON team periodically checked on ICON to make sure it was still functioning as expected. The engineers took the vehicle out of storage, turned on all of the instruments, and made sure all of its basic functions were working as expected. “We feel super good about the prospects for a great mission,” Immel said.

The ICON launch is currently scheduled for October 10th at 9:30PM ET out of Florida. The Pegasus rocket will “take off” under its carrier aircraft, a Lockheed L-1011 TriStar called Stargazer, and move out over the Atlantic Ocean. Once the plane reaches the right altitude and drop zone, it’ll release Pegasus, which will then ignite its main engine and zoom into orbit. This method is known as air launch, and it’s a very rare way of getting into space. Only a handful of other companies plan to attempt this kind of technique — notably Virgin Galactic’s spinoff company called Virgin Orbit.

NASA’s coverage for the ICON launch will get underway at 9:15PM ET. Weather is looking relatively good for the mission, as there’s a 70 percent chance that conditions will be favorable. NASA already had to delay the mission from Wednesday due to bad weather. If tonight’s mission doesn’t occur as planned, Northrop Grumman has a backup launch date on Friday, October 11th. For now, the team is proceeding normally, so check back later to see if this extra-delayed mission finally makes it to space.

Update October 9th, 2:55PM ET: NASA delayed the ICON launch due to bad weather at the rocket’s drop zone. The agency will try again on Thursday, October 10th at 9:30PM ET. The weather forecast is much better, with a 70 percent chance of favorable conditions.