CAPE CANAVERAL, Fla. — It may be several weeks before NASA can attempt to launch its massive Space Launch System moon rocket after it was unable to control what agency’s officials described as a large, unmanageable hydrogen leak that forced them to cancel a second flight on Saturday.

Agency officials said they believe it is likely they will have to roll the rocket back to its assembly building to make repairs after two unsuccessful attempts to launch it on a maiden test flight that would loft the uncrewed Orion spacecraft to the moon.

The decision follows another day of disappointment for the space agency, which had been hoping finally to launch the rocket after years of delays and setbacks and mark a significant milestone toward return astronauts to the surface of the moon.

Instead, the next launch attempt could come well into October, as NASA struggles to figure out a complicated, fickle beast of a rocket and its nettlesome propellant.

While NASA officials say the scrub is a normal part of spaceflight, especially with a new rocket, the inability of NASA to launch its flagship rocket is sure to renew criticism from some that it is a symbol of government mismanagement influenced by political whims and reliant on antiquated technology.

The rocket is billions of dollars over budget and years behind schedule, and by some estimates, each launch will cost between $2 billion and $4 billion. In creating the rocket, Congress dictated that it recycle engines and technology from the space shuttle program, which first flew in 1981 and was developed in the 1970s.

Unlike the rockets used by SpaceX to launch astronauts to the International Space Station, which return to Earth to be used again, the Space Launch System is not reusable.

Officials hoped getting the rocket to the pad for its first launch would make a statement that NASA had revived its deep-space ambitions. But instead of celebrating a triumphant flight that would put it on a path to the moon, NASA officials spent most of the morning Saturday scrambling trying to fix a leak of the volatile liquid hydrogen used as the rocket’s fuel.

Hydrogen, the lightest element, is kept in liquid form at minus 423 degrees Fahrenheit, and NASA has had a difficult time loading it into the rocket’s tanks without it leaking.

NASA encountered a similar problem during a launch attempt on Monday but was able to eventually overcome it. On Saturday, though, engineers started loading the hydrogen, then stopped at about 7:15 a.m. Then they started again but had to stop at about 9 a.m. after it started leaking again. They tried to warm the line, then use helium to pressurize it, but neither worked.

Nor did a second attempt at warming the line.

At 11:17 a.m., three hours before the launch window even opened, NASA called a scrub. The leak on was larger than the one they encountered Monday, said Mike Sarafin, the Artemis program manager. “The leak on Monday was a manageable leak,” he said. “This was not a manageable leak.” He said one of the hydrogen lines was inadvertently over pressurized, but it was unclear whether what caused the leak or exactly why the overpressurization had occurred.

Officials said they are considering whether they can repair the leak on the launch pad and then test it there by flowing the liquid hydrogen through it — a test they could not do if the rocket is taken back to the assembly building. If the repair cannot be done on the pad, they would have to roll it back to the assembly building and make the repairs there, but could not be certain the problem had been fixed till another launch try.

Either way, engineers will need to reset the rocket’s emergency flight termination system, which destroys the rocket in case it goes wildly off course during launch. That work can be done only in the assembly building.

Whether for technical reasons or bad weather, delays are nothing new to the space program. Officials noted Saturday that out of 135 space shuttle launches, 121 were scrubbed at least once. In 20 cases, the spacecraft was returned to the assembly building.

On Saturday, NASA Administrator Bill Nelson praised the SLS’s launch team, saying that the agency will be prudent and won’t rush the launch until it has all the systems working.

“We don’t go until then and especially now on a test flight,” Nelson said. NASA will “make sure it’s right before we put four humans on top of it.” Delays, he said, are “part of the space business.” He noted that scrubs are far less costly than a failure.

As a member of Congress, Nelson flew on the space shuttle in 1986, but had to endure repeated delays.

“We scrubbed four times,” he said. “We were delayed over the better part of a month. … This is part of our space program: be ready for the scrubs.”

When she was an astronaut preparing to fly on the space shuttle, Pam Melroy, who now serves as the deputy NASA administrator, used to tell her friends and family to plan a week’s vacation on the Florida Space Coast “and maybe you’ll see a launch.”

The Artemis I mission, as it is called, has no astronauts on board and is a test to ensure that the rocket and spacecraft are safe for humans to ride. If NASA is able to complete Artemis I, the next flight will put four astronauts on board for a flight around the moon, perhaps in 2024. A human landing on the lunar surface could come in 2025 or 2026.

But as Saturday’s setback shows, NASA still has many technical challenges to overcome. NASA is being particularly cautious with its SLS rocket. It has cost some $23 billion to develop, and the space agency hopes it will serve as the backbone of its Artemis program, designed to return astronauts to the moon.

Sarafin, the Artemis mission manager, told reporters this week that there are nearly 500 launch criteria that have to be met and that any number of things could force the space agency to scrub and try another day.

“There’s no guarantee that we’re going to get off,” he said. “But we’re going to show up, and we’re going to try, and we’re going to give it our best.”

Saturday’s scrub followed one from Monday, when engineers said they were unable to get one of the four engines mounted to the booster stage to the right temperature required for launch. After standing down and investigating the problem, they determined that a faulty sensor was to blame, and moved to try again Saturday.

Last year, NASA was able to successfully load the rocket with more than 730,000 gallons of liquid hydrogen and liquid oxygen and test fire the RS-25 engines for their full eight-minute duration. But it has been unable to repeat that success since then.

Earlier this year, in a series of fueling tests, it ran into all sorts of problems that prevented the space agency for running a full simulated countdown.

Despite those problems, NASA officials said they felt confident enough to proceed to a launch attempt. The attempts have essentially served as additional fueling tests.

Victor Glover, a NASA astronaut who could be among one of the crews chosen for an Artemis moon mission, said that the flight controllers should be praised for their decision to cancel the launch, especially given how much public attention it received.

“It’s hard to make a decision like this,” he said. ” We can be mad at the hydrogen leak, but the scrub is absolutely the right call, and it helps to build trust.”

NASA Administrator Bill Nelson said that if the Space Launch System rocket needs to be rolled back to its assembly building, a new attempt to launch the Artemis I moon mission may not happen until mid-October, at the earliest.

The space agency has an availability for the rocket to launch between Oct. 17 and Oct. 31.

In a post-flight interview aired on NASA’s website, Nelson said the agency will be prudent and not rush the launch but will ensure it has all the systems working.

“We don’t go until then and especially now on a test flight,” he said. NASA will “make sure it’s right before we put four humans on top of it.” Delays, he said, are “part of the space business.”

As a member of Congress, Nelson flew on the space shuttle in 1986 but endured repeated delays before actually going aloft.

“We scrubbed four times,” he said. “We were delayed over the better part of a month. … This is part of our space program: Be ready for the scrubs.”

Christian Davenport

NASA still has a couple more options to attempt to launch its Space Launch System rocket in the current launch period, which ends Tuesday. If it is able to fix the hydrogen leak, the space agency could, in theory, try again Monday. A 90-minute launch window would open at 5:12 p.m. Eastern. If the agency pushes it to Tuesday, it would only have a 24-minute window in which to launch. That window would open at 6:57 p.m Eastern.

NASA is limited in when it can launch because the Orion spacecraft needs to fly when it can remain in sunlight so that its solar arrays can power its batteries. If it does not launch by Sept. 6, the next availability could come as soon as Sept. 19 and last until Oct. 4. 

If the rocket has to be rolled back to its assembly building for extensive repairs, it may not be ready to launch until the launch window after that. That one opens Oct. 17 and lasts until Oct. 31.

NASA has said it will hold a media briefing at some point later today.

NASA on Saturday was once again unable to launch its massive Space Launch System rocket and Orion spacecraft, forced to endure yet another delay as the space agency works to figure out a complicated, fickle beast of a rocket and its troublesome propellant.

NASA officials spent most of the morning Saturday scrambling to fix a leak of the liquid hydrogen used as the rocket fuel. Hydrogen, the lightest element, is kept in liquid form at minus 423 degrees Fahrenheit, and NASA has had a difficult time loading it into the tanks without it leaking.

NASA encountered a similar problem during a launch attempt on Monday but were able to eventually overcome it. On Saturday, though, they started loading the hydrogen, then stopped at about 7:15 a.m. Then they started again but had to stop at about 9 a.m. after it started leaking again. They tried to warm the line, then use helium to pressurize it, but neither worked.

The NASA Space Launch System rocket team recommended a “no-go” for launch after engineers have been unable to fix a persistent hydrogen leak.

Charlie Blackwell Thompson, the flight director, is evaluating the recommendation but for now has only paused the fueling process. The launch countdown is holding, awaiting a final decision on whether to scrub the launch today.

If the rocket does not launch today, NASA has said it could possibly try again after 48 hours. But if it does not launch by Tuesday, the next launch window will not open until between Sept. 19 and Oct. 4.

Artemis I launch

NASA is once again struggling with a hydrogen leak as it works to fuel its massive Space Launch System rocket. Early this morning, the NASA launch director called a “go” for propellant loading, and NASA engineers were able to successfully start running liquid oxygen from storage tanks on the ground into the rocket’s fuel tanks.

They also started loading the liquid hydrogen, but at about 7:15 a.m. Eastern, engineers noticed there was a leak. They paused fueling the liquid hydrogen, which is kept at minus 423 degrees Fahrenheit, and attempted to warm the lines, a fix that they hoped would strengthen the seal. But when they started to reflow the hydrogen, they noticed another leak. This time, they used helium to pressurize the line, but this did not work either.

At the moment, only about 9 percent of the booster stage liquid hydrogen tank is full. The booster stage tank for liquid oxygen, the other component of the fuel, is nearly full. Meanwhile, the countdown clock continues. A two-hour launch window opens at 2:17 p.m. Eastern. “The team is doing what it can to preserve this launch window,” NASA commentator Derrol Nail said.

NASA encountered a similar problem during its attempt to launch the rocket on Monday but was able eventually to overcome it. That launch attempt was ultimately scrubbed after engineers were unable to get one of the four engines mounted to the booster stage to the right temperature required for launch. After standing down and investigating the problem, they determined that a faulty sensor was to blame and moved to try again Saturday.

Unlike recent SpaceX launches to the International Space Station, which had to go at a precise time to rendezvous with the ISS, Saturday’s launch window allows the rocket to be launched at anytime in a two-hour window that begins at 2:17 p.m.

If the rocket does not launch today, NASA has said it could possibly try again after 48 hours. But if it does not launch by Sept. 6, the next launch window will be between Sept. 19 and Oct. 4.

But NASA officials acknowledge there could be problems meeting that second launch window. That is because the rocket will need to be rolled back into its assembly building so that engineers can reset its flight termination system, the self-destruct feature that would destroy the vehicle if it veers wildly off course. The reset is required by the U.S. Space Force to make sure the system is certified to work properly.

NASA says it can schedule the Space Launch System for launch only about every two weeks because of “the complex orbital mechanics involved in launching on a precise trajectory toward the moon while the Earth is rotating on its axis and the moon is orbiting Earth each month in its lunar cycle.”

One of the main issues is sunlight. The Orion spacecraft cannot be in darkness for more than 90 minutes at a time. Its solar arrays need to stay illuminated so they can provide power to the spacecraft and ensure it maintains the correct temperature.

The launch date also must allow conditions for the “skip entry” technique of the Orion spacecraft as it returns to Earth. That reentry requires Orion to dip into the upper part of the atmosphere to slow it down, then skip back out into space before reentering for the final descent and splashdown in the Pacific Ocean. The technique allows technicians to “pinpoint” its splashdown location, NASA said, and helps lower the force of reentry, which can take a toll on the spacecraft and the astronauts.

The Artemis program is NASA’s flagship deep-space human exploration program, meant to return astronauts to the moon for the first time since the last of the Apollo missions in 1972. Created under the Trump administration and carried on by President Biden, it seeks to develop a permanent presence on and around the moon.

Saturday’s flight, known as Artemis I, is the first in a series of test missions. It would send the Orion crew capsule in orbit around the moon for about six weeks without any astronauts on board. The next flight, Artemis II, scheduled for some time in 2024, would send astronauts into lunar orbit but not to the surface of the moon. A lunar landing, Artemis III, could come in 2025 or 2026, if all goes according to plan.

Emmy Award, 2021. Peabody Award, 2010. On teams that were finalists for the Pulitzer Prize in 2005, 2010 and 2011.

The Space Barons: Elon Musk, Jeff Bezos and the Quest to Colonize the Cosmos (PublicAffairs, April 2018)

As You Were: To War and Back with the Black Hawk Battalion of the Virginia National Guard

Colby College, B.A., American Studies

Christian Davenport covers NASA and the space industry for The Washington Post's Financial desk. He joined The Post in 2000 and has served as an editor on the Metro desk and as a reporter covering military affairs. He is the author of "The Space Barons: Elon Musk, Jeff Bezos and the Quest to Colonize the Cosmos" (PublicAffairs, 2018).

Artemis I launch scrubbed again, new attempt may not come till October

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Artemis I mission faces weeks of delay after launch is scrubbed