Sunday night, the employees of spaceflight company Orbital ATK will hold their breath as they watch their Antares rocket take flight from NASA’s Wallops Flight Facility in Virginia. But their anxiety will stem from more than just pre-launch jitters. It’s been nearly two years since the Antares last launched — and the previous time the rocket flew, things didn’t exactly go according to plan.

That last launch, on October 28th, 2014, was supposed to be a routine flight: a cargo resupply mission to the International Space Station. The first two cargo runs had worked flawlessly, and there was no reason to think the third one would be different. But just seconds after launch, the rocket exploded in a spectacular fireball, destroying the vehicle and causing $15 million in damages to the Wallops launch pad.

"I’ve been through a couple failures in my 25-year career, and it’s always like a gut punch."

"I’ve been through a couple failures in my 25-year career, and it’s always like a gut punch. You feel deflated," Kurt Eberly, the deputy program manager for the Antares at Orbital, tells The Verge. "The team had been working so hard for years. We had just developed this new rocket, and the first flights were really spot on and worked really well. So it was extra disappointing."

Since then, the company has worked hard to overcome the failure and get back to launching its Antares rockets again — this time with new engines. Orbital is ready to show that the vehicle has fully recovered from the failure, especially since the company hopes to play a crucial role in the expanding space industry and the race to get to the Moon and Mars. A successful launch on Sunday could prove that the company is ready to be a major player in the years ahead. "This mission is about recovering from what happened before and looking to the future," says Eberly.

So, what happened in 2014?

Almost immediately after the accident, both NASA and Orbital ATK launched investigations to look into the failure. Orbital soon announced that it had pinpointed the likely origin of the explosion: one of the Antares’ main engines. At the time, the rocket was propelled by two AJ26 engines — Soviet rocket engines originally built in the 1960s and refurbished by American manufacturer Aerojet Rocketdyne. By the end of its investigation, Orbital determined that a defect in one of the engine’s turbopumps — a component that pumps fuel into the engine — was to blame, and the problem could be traced back to when the engine was manufactured decades ago, according to Space News.

The Antares failure on October 28th, 2014. (NASA)

But Aerojet had a different take on the failure. While the company agreed that the problem arose in the turbopump, it argued the component had been damaged by debris that came from elsewhere in the vehicle. (That would absolve Aerojet of blame.) Eventually, Aerojet paid out a $50 million settlement to Orbital to settle the matter. Meanwhile, NASA’s investigation agreed that the explosion originated in one of the engine’s turbopumps, too, but the agency could not determine if it was a manufacturing error or if debris was to blame.

The engines had to go

"Orbital did a very thorough job," says Sam Scimemi, the director of the International Space Station at NASA headquarters. "Obviously two different groups are going to come up with slightly different interpretations. But we accepted the cause identified by Orbital."

Regardless of the discrepancies, Orbital made a critical decision soon after the failure: the engines had to go. It was an easy call to make, since the company had already been in the process of looking for new engines for the Antares. So the company started the process of replacing the vehicle’s AJ26 engines with RD-181s — engines manufactured by Russian company NPO Energomash.

The road back to Antares

Replacing a rocket’s engines is no easy feat. There are a lot of complicated interfaces between the engine and the core of the rocket, and it takes a while to redesign the vehicle’s instrumentation. But in the meantime, Orbital ATK needed to launch cargo to the space station. The company holds a contract with NASA under the Commercial Cargo program, and it’s on the hook to periodically send cargo to the ISS through 2018.

Orbital's Cygnus cargo capsule. (NASA)

While the Antares was out of commission, Orbital still had its Cygnus — the cargo capsule it uses to transport supplies to the ISS. All it needed was another rocket to fly on, because Cygnus is designed to be compatible with different types of rockets. "It’s in our DNA to design our spacecraft to have the flexibility to go on multiple rockets," Frank DeMauro, vice president and general manager of the advanced programs division at Orbital ATK, tells The Verge. Orbital found a new ride in the Atlas V rocket, which is manufactured by the United Launch Alliance. The companies agreed that the Cygnus would launch on two Atlas Vs while the Antares was being retooled, and a year after the accident, the first of those missions launched without a hitch.

Meanwhile, NASA, Orbital, and the state of Virginia spent a year repairing the launch pad at Wallops to get it ready for flights again. And finally in May, the newly refurbished Antares underwent its first big test at the flight facility: a static fire. That’s when the rocket’s engines are turned on while the vehicle is constrained, to see if everything is working properly. The 30-second test was a success, according to Orbital. Since then, it’s been a matter of pinpointing a launch date, and after a number of delays and a meddling hurricane, the Antares is finally set to launch on October 16th at 8:03PM ET.

Launch and the future

Now, it’s time to see if the company’s hard work has paid off. But not everyone has been complimentary of Orbital’s return to flight plan. NASA’s Office of the Inspector General released a report last year criticizing the company’s tight schedule and expressing concern that the Antares wouldn’t undergo a flight test before its first mission. Orbital is confident that things will go well, though, but nerves will still be running high.

"In nine minutes you get to determine how you did for the last couple of years of work."

"It’ll be the usual heart attack and then when I start breathing again, we’ll pay attention to [data] we get back and the video," says Eberly. "I’m really anxious to see how it flies and performs. We think it’ll go very well." Once the rocket lifts off, it’s only nine minutes until the Cygnus spacecraft separates in space and ventures the rest of the way to the ISS. "In nine minutes you get to determine how you did for the last couple of years of work," says Eberly. "It’s just the nature of the business."

The updated Antares rolling out to the launch pad for this weekend's launch. (NASA)

Those nine minutes have the potential to reestablish Orbital as a launch provider and put it on course for a vibrant future ahead. Recently, the company announced that it had partnered with Stratolaunch Systems, to help launch satellites into space. The plan is for Orbital’s Pegasus XL rockets to launch from a massive plane that Stratolaunch is manufacturing. And beyond that, Orbital eventually wants to get into the space habitat business. The company has a plan of turning its Cygnus cargo capsule into a deep space habitat that could house astronauts near the Moon or even on the surface of Mars.

"We think we’re just getting started with Cygnus and that it has a bright future for many years to come," says DeMauro. "We’re always careful that we’re focused on the mission at hand, but we have to have goals and pull together those visions for the future. Orbital ATK is very well placed to take part in that future."