(CBS NEWS)- NASA and Northrop Grumman geared up to launch a Pegasus XL rocket from the belly of a carrier jet Thursday. The launch will finally kick off a $252 million mission to study Earth’s electrically charged ionosphere, its interactions with the solar wind and how it affects communications and GPS navigation signals.

The L-1011 “Stargazer” carrier jet, cruising at an altitude of 40,000 feet due east of Daytona Beach, Florida, is expected to drop the rocket at 9:30 p.m. ET, running more than two years late. Five seconds after release, the 57-foot-long Pegasus XL’s first-stage motor is expected to ignite to begin an 11-minute climb to orbit. 

A launch attempt Wednesday was scrubbed before the carrier jet took off because of expected bad weather, but the outlook improved to 70 percent “go” Thursday.

The goal of the Ionospheric Connection Explorer, or ICON, mission is to better understand the physics of the extreme upper atmosphere, how it responds to major space weather events like solar storms and flares and how it affects radio communications and satellite navigation signals that pass through it.

“The sun has a profound impact on our atmosphere, in fact it ionizes it, so it takes the molecules that are there and actually gives them a charge,” said Nicky Fox, director of heliophysics research at NASA Headquarters. “We call that the ionosphere. It’s very important for us to study this region.”

“We use the ionosphere both to bounce radio signals off it … and we also send our GPS signals through it. And so this ionosphere is continually changing, and it’s very, very dynamic, and so that can have a big impact on our ability to do these type of communication.”

The ionosphere begins about 37 miles up and extends to an altitude of some 620 miles. The 634-pound ICON satellite was designed to operate in a 360-mile-high orbit, about 100 miles above the International Space Station. Equipped with four sensitive instruments to characterize the electrically charged particles in the ionosphere, ICON is expected to operate for at least two years.

NASA’s ICON ionosphere research satellite will begin its trip to space atop a Northrop Grumman Pegasus XL rocket dropped from the belly of the company’s “Stargazer” carrier jet. (Photo: NASA)

The spacecraft had an unusually rocky road to space. One of the booster stages was accidentally dropped during processing, prompting extensive inspections and analysis. Engineers then had to address concern about devices needed to separate the rocket’s nose cone fairing during the climb to space. Launch slipped from late 2017 to June 2018.

Then, during a flight to ferry the Pegasus to its original Pacific Ocean launch site, engineers noticed unusual readings in the booster’s rudder positioning electronics. The problem only showed up during flight, and it proved extremely difficult to resolve.

“This is an incredibly complex machine,” said Phil Joyce, Northrop Grumman vice president of space launch programs. “We saw some things on our previous launch attempt that none of us were comfortable with. We decided to stand down and go address those and make sure we understood exactly what was happening there.”

The detective work required “really extensive ground tests, modeling simulation and flight test activity to get to the bottom of what was an extremely challenging problem, one of the most challenging I’ve seen in my career in this business,” Joyce said. “But we got there.”

While no single root cause was identified, engineers modified the rudder positioning system electronics, replaced components in a positioning feedback system and carried out two L-1011 test flights to verify the system would work properly during launch. The work took nearly a year to complete.

“We wanted to get things right on this rocket,” said NASA launch director Omar Baez. “We have no second chances on these type of missions.”

An artist’s impression of the Ionospheric Connection Explorer – ICON – satellite in orbit. (Photo: NASA)