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Atlas 5 missile carrying astronauts was first loaded for launch on Monday night to increase The long-delayed Boeing Starliner crew ferry into orbit for its first manned test flight. But a problem with a valve in the rocket’s upper stage forced mission managers to order a cleanup just two hours before liftoff.

It was a disappointing disappointment for the commander Barry “Butch” Wilmore and co-pilot Sunita Williams, which were in the process of being prepared to launch when the washout was announced. The moment brings to mind one of Wilmore’s favorite sayings: “You’d rather be on the ground and wish you were in space than in space and wish you were on the ground.”

It wasn’t immediately clear when Boeing and rocket maker United Launch Alliance might try again, but engineers first need to figure out what caused the Centaur rocket’s upper stage oxygen relief valve to “chatter” during the late stages of refueling, and what may be necessary to repair it.

Years behind schedule and more than a billion dollars over budget, the Starliner is Boeing’s answer to SpaceX’s Crew Dragon, an already operational spacecraft that has carried 50 astronauts, astronauts and civilians into orbit on 13 flights, 12 of them to the space station .

NASA funded the development of the two spacecraft to ensure the agency would be able to launch crews to the outpost even if one company’s shuttle was grounded for some reason. Although Boeing took longer than expected to prepare its craft for crewed flights, it was all systems go for launch from Pad 41 at the Cape Canaveral Space Force Station at 10:34 p.m. EDT.

Engineers were in the process of completing fueling when the valve problem was discovered. After evaluating his work, the engineers could not be “calmed” by his behavior and the launch was canceled.

Clad in navy blue Boeing spacesuits, Wilmore and Williams, both veteran Navy test pilots and active astronauts with four previous space flights, began unbuckling their seat belts to exit the Starliner and await word on when they would get another chance to fly.

Atlas 5, making its 100th flight, is an extremely reliable rocket with a perfect launch record. The rocket is equipped with a sophisticated emergency fault detection system, and the Starliner, like SpaceX’s Crew Dragon, has a “full envelope” abort system capable of rapidly moving the capsule away from its booster in the event of a major failure at any point from the launch pad into orbit.

Whenever it lifts off, Atlas 5 will need just 15 minutes to put the Starliner into preliminary orbit. Once in space, the astronauts will then observe two quick thruster firings to fine-tune the craft’s orbit before taking turns testing the spacecraft’s computer-aided manual control system.

As with any other space station rendezvous, the Starliner will approach the lab from behind and below, rotating to a point just in front of the outpost and then moving to dock at the front port of the Harmony module

During final approach, Wilmore and Williams will again test the capsule’s manual controls, making sure future crews can change the spacecraft’s trajectory or orientation at will if needed.

The Starliner is also equipped with a fully manual backup system that allows the crew to directly control the ship’s thrusters using a joystick-like hand controller, bypassing the spacecraft’s flight computers. Wilmore and Williams will test this system after they leave the station around May 15 to begin the journey back to Earth.

Once docked, Wilmore and Williams will spend a little more than a week with the station’s seven long-time crew members: cosmonauts Oleg Kononenko, Nikolai Chub and Alexander Grebenkin, along with NASA’s Matthew Dominik, Michael Barratt, Jeanette Epps and Tracy Dyson.

If the Starliner’s test flight goes well, NASA managers expect to certify it for routine crew-rotation flights, launching one Crew Dragon and one Starliner each year to deliver long-term crew members to the station for six-month stints.

“Absolutely Critical Stage”

Jim Free, NASA’s associate administrator for space operations, called the Starliner Crew Flight Test, or CFT, “an absolutely critical milestone.”

“Let me remind everyone again, this is a new spacecraft,” he told reporters last week. “We certainly have some unknowns in this mission, we may encounter things we don’t expect. But our job now is to remain vigilant and continue to look for problems.”

While he said he was confident the Starliner was up to the task, Free said he didn’t want to “get too far ahead” because the crew has yet to complete a successful mission. But “when we do,” he added, “and when we certify the Starliner, the United States will have two unique human space vehicles that provide critical backup for access to the ISS.”

But it wasn’t easy.

After retiring the Space Shuttle in 2011, NASA awarded two commercial crew program contracts in 2014, one to SpaceX valued at $2.6 billion and the other to Boeing for $4.2 billion, to encourage development of independent spacecraft capable of transporting astronauts to and from the International Space Station.

The target date for CCP’s initial manned flights was 2017. A lack of funding in Congress and technical issues have delayed development, including an explosion during a ground test that destroyed the SpaceX Crew Dragon.

But the California rocket builder finally began manned flights in May 2020, successfully launching two NASA astronauts on a Crew Dragon test flight to the space station.

Since then, SpaceX has launched eight operational crewed rotation flights to the station, three research missions to the laboratory, funded by the Houston-based Axiom Cosmos and a purely commercial, a trip by two men and two women to low Earth orbit paid for by billionaire pilot and businessman Jared Isaacman. A total of 50 people have flown into orbit aboard Crew Dragons.

It was a different story for Boeing’s Starliner.

During an initial unmanned test flight in December 2019, a software error prevented the ship’s on-board computer from loading the correct launch time from its counterpart aboard Atlas 5.

As a result, the required orbital insertion burn did not occur in time, and due to unrelated communications problems, flight controllers were unable to regain control in time to proceed with the space station rendezvous.

The software issues were resolved after the Starliner landed, along with a number of other issues that came to light during post-flight review. Boeing chose to conduct a second test flight at its own expense, but the company encountered stuck propulsion system valves in the Starliner’s service module. Engineers were unable to resolve the problem and the capsule was removed from its Atlas 5 and returned to the processing facility for troubleshooting.

Engineers eventually traced the problem to moisture, likely from high humidity and heavy rain after deploying the pad, which chemically reacted with the thruster fuel to form corrosion. Corrosion prevents the valves from opening on command.

To clear the way for a launch the following May, valves in a new service module were replaced and the system was modified to prevent water from entering the launch pad. The second Starliner test flight in May 2022 was successful, boarding the space station as planned and returning to Earth with a precision landing.

But after the flight, engineers discovered new problems: problems with the parachute harness connectors and concerns about a protective tape wrapped around the cables that could ignite if shorted.

Work to correct those problems pushed the first crewed flight from 2023 to 2024. When all was said and done, Boeing spent more than $1 billion of its own money to pay for the additional test flight and corrective actions.