United Launch Alliance has successfully launched more than 150 rockets into space in its 18-year history, but none have carried humans.

That is about to change.

The Centennial-based aerospace company has its first human launch scheduled on Monday for 8:34 p.m. MST. ULA’s Atlas V rocket will carry Boeing’s Starliner spacecraft with NASA astronauts Barry “Butch” Wilmore and Sunita “Suni” Williams onboard.

It’s an important milestone as SpaceX is currently the only U.S. private company to have sent humans outside of Earth’s orbit. 

The joint ULA-Boeing mission will be a test flight for potential future trips to the International Space Station as part of NASA’s commercial crew program and will launch from the Cape Canaveral Space Force Station on Florida’s East Coast.

And once the ISS is put out of commission by 2031, NASA administrator and former U.S. Sen. Bill Nelson told reporters Friday, then the spacecraft could be used to transport astronauts to future space stations operated by private companies.

“This is very much a part of our exploration of space in what I call the golden age of space exploration,” Nelson said.

The weather forecast for Monday is highly favorable with a 95% chance of good launch weather, said NASA launch weather officer Brian Cizek on Friday.

NASA has backup launch days in case of delays set for May 7, 10 and 11.

Who are the astronauts on board?

Williams, a 59-year-old former U.S. Navy captain and an astronaut since 1998, will pilot the test mission.

She has been in space for a total of 322 days during the course of two missions and broke several world records for women for number of spacewalks and time spent on spacewalks.

She accumulated more than 50 hours through seven spacewalks, a record later broken by Peggy Whitson with 10 spacewalks. The last time she was in space was in 2012, launching from Kazakhstan with a Roscosmos cosmonaut and Japanese astronaut for a research trip at the ISS.

The commander of the Boeing test flight is Wilmore, who’s been an astronaut since 2000 and already been on two trips to the space station.

Wilmore, 62, was a pilot for a 2009 flight on the Space Shuttle Atlantis for his first trip. He later went back to space in 2014 and spent nearly half a year at the space station.

He has spent a total of 178 days in space and 25.5 hours on four spacewalks.

Commercial companies take lead for space station trips

The astronauts have been key in helping ULA and Boeing design the Atlas V Starliner for human flight, said Gary Wentz, ULA vice president of government and commercial programs.

“Butch and Suni have spent a lot of time in our facilities interacting with every employee within the ULA team,” Wentz said, “and they’ve become part of our family.”

The Atlas V rocket is 172 feet tall with the Boeing Starliner aboard.

It’ll be the 100th Atlas launch from the same family of rockets used in John Glenn’s historic 1962 flight that made him the first American to orbit Earth.

The Atlas rocket got its start in 1957 and was designed by aerospace giant Lockheed Martin. United Launch Alliance — headquartered in Centennial and a joint venture between Lockheed Martin and Boeing — now operates this model of rockets.

ULA amended the Atlas V Starliner for the company’s first human flight with an emergency detection system to monitor all the vehicles systems and automatically trigger an abort mission, Wentz said.

It also has a “Dual Engine Centaur,” a fuel reserve of liquid hydrogen and oxygen, which gives the rocket double the thrust – allowing more control of the flight’s trajectory and making it easier to abort the mission at any time in flight and safely bring the astronauts back to earth in an emergency.

It was a feature used on all Atlas rockets between 1962 and 2000 and was brought back for the Starliner, according to ULA.

“When you look at our team, we’ve been highly focused on the safety of the vehicle, the safety of the payload as well as Butch and Suni, keeping in our minds, them, their families and the needs of the nation,” Wentz said.

The ULA and Boeing mission is the second crewed-flight NASA has contracted with private companies to take its astronauts to the space station.

The first was SpaceX’s Dragon spacecraft launched by the Falcon 9 rocket. NASA has already certified SpaceX and has begun official missions.

NASA will review Monday’s test mission to determine if Boeing’s Starliner, which can hold up to seven passengers, can get its certification to fly crews regularly.

“This will give us that additional capability because we always look for a backup,” said Nelson, the head of NASA.

NASA is increasingly relying on private companies to lead flights to low-earth orbit and the space station so it can focus on deep space projects such as the Artemis missions aiming to bring humans to the moon and potentially Mars.

What the mission entails

Once launched, the Atlas V rocket will detach its boosters 4.5 minutes into the flight. The centaur and Starliner will stay attached and the centaur will start its main engine nearly five minutes in. It will burn for about seven minutes before separating from Boeing’s Starliner at about 15 minutes in.

The Atlas V will then reenter Earth’s atmosphere and is expected to land in the Indian Ocean.

The Starliner will then take a daylong journey to the ISS, where the astronauts will test the spacecraft’s docking and undocking abilities to the station and its return to Earth. They plan to stay at the space station for about a week.

If the mission goes well, Wentz said ULA may also work on getting its other rockets ready for human space travel. The Vulcan, ULA’s next generation of rockets, already has similar hardware and avionics to the Atlas V.

“We’re looking forward to the opportunity to fly Vulcan as well with humans onboard,” Wentz said.