Scrubbed Artemis 1 launch raises concerns over unfinished rehearsals

SLS on the launch pad at Kennedy Space Center in Florida.

SLS on the launch pad at Kennedy Space Center in Florida.
Photo: NASA

On Monday, NASA failed in its first attempt to launch the unmanned Artemis 1 mission, with engineers difficulty solving a problem with the engine cooling. It’s not a surprising result at all, given that NASA was unable to complete a single wet dress rehearsal, four of which were attempted earlier in the year. The space agency appears to be doing it, with the failed launch attempt effectively serving as the fifth wet dress rehearsal, in what’s a disturbing sign.

NASA’s Space Launch System (SLS) was supposed to fly Monday morning, but instead we wonder how the program went as a whole. NASA will provide more updates on the rocket later in the evening, including whether a launch on Friday or Monday is possible, or whether the 322-foot-tall (98-meter) rocket makes its now-known 4-mile (6.4-kilometer) pull back to the Vehicle Assembly Building for repairs.

The unflown SLS mega-missile is critical to NASA’s Artemis Program, which is pursuing a permanent and lasting return to the moon. For the Artemis 1 mission, an unmanned Orion rocket will be sent to the moon and back on a multi-week mission. A successful integrated test of SLS and Orion would provide the basis for a manned Artemis 2 mission in about two years, and a manned mission to land on the lunar surface later this decade.

A Friday launch seems unlikely, and not just because of the gloomy weather forecast. NASAs launch attempt on monday did not come close to success, with the countdown not going past T-40 minutes. A “bleeding engine” problem prevented one of the rocket’s four RS-25 engines failed to reach the required ultra-cold temperature for launch, resulting in the scrub.

Thousands of spectators had gathered at the launch site, as well as hundreds of reporters. Vice President Kamala Harris also attended the Kennedy Space Center in Florida. Everyone left disappointed, but it doesn’t take a rocket scientist to admit that a launch on Monday would always be unlikely. Since ground teams failed to complete a single full-fledged wet dress rehearsal, it seemed like a stretch to believe that NASA would somehow get everything right on the first attempt to launch the Artemis 1 mission.

Indeed, the problems started almost immediately early Monday morning, with the threat of lightning delaying tank operations by nearly an hour. Operating under an accelerated timeline, ground teams continued the six-hour refueling process. A problem arose when the team switched from slow to fast refueling, with a leaking 8-inch intake valve causing increased hydrogen readings. The leak was resolved by returning to slow filling and going through the process again, which allowed full refilling of the hydrogen tank in the core phase.

However, when using the propellant to cool the four RS-25 engines, the team found that one of the engines — engine number three — refused to cool to the required ultra-low temperatures. Engineers worked their way through previously established troubleshooting guidelines in an effort to get more liquid hydrogen into the engine. They tried to increase the pressure in the tank, but this led to the discovery of another problem: an apparently leaking vent valve between the liquid hydrogen and liquid oxygen tanks.

Mike Sarafin, NASA’s Artemis mission manager, told reporters yesterday that engineers “wanted to increase the pressure in the tank to determine the hydrogen venting,” but the “vent valve was not cooperating.” That was the final straw, and the team “decided it was appropriate to announce the scrub because we just wouldn’t make it to the two o’clock window,” Sarafin said, adding that it was “one of those situations where we just knew we needed more time.” He insisted that the problem is not with the engine itself, but rather with the “vent system that thermally conditions the engine”.

The engine bleeding issue is one of an unknown number of items that were not tested during the wet rehearsals. After closing the last wet dress held in June, NASA officials said 90% of all test targets were met, while no details were released on the remaining 10%. The last wet dress is not completed by an unresolved hydrogen leak linked to a faulty quick coupling. For that rehearsal, NASA officials had hoped to run the countdown to T-10 seconds, but it never got past T-29 seconds, leaving much doubt about the final launch phase.

After the partial completion of the third wet dress in April, SLS has been returned to the Vehicle Assembly Building for repair, to return to Launch Pad 39B in early June. During the four rehearsals, engineers recorded a slew of seemingly minor issues, a list of failed fans on the mobile launcher, a misconfigured manual vent valve, too low temperatures and frost while loading propellant, a small hydrogen leak on the tail service mast umbilical cord, problems with the supplier of gaseous nitrogen and a faulty helium check valve that had to be replaced.

That said, it was during the fourth wet dress that SLS was finally fully charged with propellants, with more than 755,000 gallons of liquid oxygen and liquid hydrogen added to the rocket’s two stages. Despite failing to meet 10% of the test targets, Tom Whitmeyer, NASA’s exploration systems manager, said “We think we had a really successful rehearsal,” and there were risks to running a fifth trial run.

Jim Free, NASA associate administrator for the development of reconnaissance systems, spoke to reporters yesterday and echoed this earlier sentiment, saying that another wet dress rehearsal was not necessary. “We would have taken another cycle of roll-out and back,” he said, and that would have introduced further risks, including wear and tear. “We won’t know until we know, but we won’t know until we try,” Free added. “We felt we were in the best position to try it.”

Keith Cowing, editor of and a former rocket scientist at NASA, said the space agency considered the first launch attempt of Artemis 1 to be essentially the fifth wet dress rehearsal. Cowing, who spoke to me on the phone, said NASA should have done all the required pre-testing to avoid these new problems.

“These things happen,” Cowing said. “But this is heritage hardware, with several pieces of rockets that have flown before.” By heritage hardware, Cowing refers to the fact that the current SLS configuration “uses existing hardware from the Space Shuttle inventory as much as possible to save costs and speed up the schedule”, according to to NASA. These elements include the core stage boosters and motors, along with the integrated spacecraft and payload element. “NASA shouldn’t expect everything to work as expected because there will be integration issues,” Cowing told me. To which he added: “Testing is good, and it has to be done methodically, so when you finally try to launch, you know what you tested – instead of using launch attempts as de facto wet dresses.”

Cowing is concerned about the state of the program and the already archaic nature of SLS. Unlike SpaceX rockets, which can be modified and repaired on the launch pad, SLS must return to the Vehicle Assembly Building for hardware modifications (this may be the case with the aforementioned leaky vent valve, but we’ll have to wait for the official word from NASA). And at an estimated cost of $4.1 billion per launch, Cowing predicts SLS launches will be rare events, quote NASA’s Inspector General Paul Martin, who described the price tag as “unsustainable” earlier this year.

NASA officials are probably feeling the pressure, hence the desire to finally get SLS off the ground. It makes for some uncomfortable theatre, though, with Monday’s scrub being a prime example. The odds of a launch were exceptionally low (or so I guessed), but NASA had no qualms about publicizing the event and inviting a large number of dignitaries and celebrity guests.

The megarocket doesn’t look ready for launch yet, but NASA is doing its best to convince us that it is. Unfortunately, the “pretend” launch attempt from earlier this week probably won’t be the last.

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