Editor’s Notes: Updated June 23 with additional information and quotes from a NASA spokesperson.
Regardless of another countdown rehearsal, NASA plans to return the first Space Launch System rocket to the assembly hangar at Kennedy Space Center next week to repair hydrogen leaks and prepares for launch on the Artemis 1 lunar mission.
With the countdown dress rehearsal complete, ground crews at Kennedy prepare to transport the 322-foot (98 m) Space Launch System Moon rocket to the Vehicle Assembly Building. The return to the VAB will end the wet-clothes rehearsal, or WDR, as NASA gets close to launching its long-delayed Artemis 1 test flight around the moon, sources said late Wednesday.
NASA spokeswoman Kathryn Hambleton confirmed Thursday that the SLS team is announcing the WDR campaign is complete, and said managers are “working with plans to address some of the remaining (test) targets before returning to VAB.”
The Artemis 1 launch will begin an unguided demonstration mission of the powerful SLS lunar rocket and Orion spacecraft ahead of future Artemis flights that will carry astronauts to the Moon. The Space Launch System has been in development for more than a decade, and has cost more than $20 billion to date, making it one of NASA’s most expensive programs at the time.
NASA’s launch team encountered several technical issues that prevented the SLS rocket’s cryogenic fuel tanks from being fully loaded in three countdowns in April. But a fourth exercise on Monday kept the countdown deep, and the launch team fueled the rocket with its 755,000-gallon supply of ultra-cold liquid hydrogen and liquid oxygen for the first time.
But engineers discovered a hydrogen leak in a 4-inch quick-disconnect device on Monday, forcing the launch team to adjust procedures in the final stages of a training countdown.
The NASA launch team originally wanted to go through the final 10-minute countdown sequence twice, reaching the T-minus 9.3 seconds in the final run, before the primary stage’s main engine ignition time during a real launch attempt. The engineers spent several hours evaluating the hydrogen leak, and the managers finally decided to continue the countdown with just one run during the final 10-minute sequence.
Engineers reconfigured the ground-based countdown regulator to mask a hydrogen leak, which would normally interrupt the countdown clock. With the workaround in place to tell the ground launch sequencer’s computer to ignore the leak, the clock on the T-minus lasted 29 seconds, one second after the countdown control was delivered from the ground console to the automated sequencer on board the SLS moon rocket.
NASA officials said Tuesday that computers on board the rocket were ordered to hold at T-minus 29 seconds, when sensors showed the primary stage engines were not ready to ignite. A leaking hydrogen conductor was discovered Monday associated with a system to thermally condition or cool down RS-25 primary-stage engines.
Despite the leak and a 9-second countdown before the T-minus was reached, NASA officials said the rehearsal achieved most of its goals.
“I would say we’re in the 90th percentile in terms of where we need to be overall,” said Mike Sarafin, NASA’s Artemis 1 mission manager, on a conference call with reporters on Tuesday.
But Sarafin said there were still some “open items” that were not done during Monday’s countdown rehearsal. One of those items was the start-up of the hydraulic power units on the SLS solid rocket boosters, which was supposed to occur in the last 30 seconds of the countdown to thrust the booster nozzles by checking the steering gimbal with the thrust vector control mechanisms, according to John Blevins, chief engineer. SLS program at the Marshall Space Flight Center.
Blevins said Tuesday that engineers will assess the risks of moving forward toward launch without making it through the last 20 seconds of the countdown rehearsal. The worst case scenario to go on without another rehearsal is a problem that leads to a miscarriage in the last seconds of the countdown to launch day.
“We’re going to have a successful launch or a scrub because we have protection in the system for those targets we didn’t hit, if they didn’t function properly on launch day,” Blevins said. “So they’re not really about making the craft safer to fly. They’re really about to hit the launch target for our window which is perfect for our mission to the moon.”
Tom Whitmer, director of NASA’s Exploration Systems, said Tuesday he was “extremely encouraged” by the outcome of the countdown rehearsal.
“We think we had a really successful rehearsal,” Whitmer said.
“There is a relative risk of continuing to practice hardware on the stage (for another rehearsal),” Whitmer said on Tuesday. “This is not necessarily a non-risk situation.”
A robust Space Launch System, powered by remnants of Space Shuttle engines and boosters, is central to NASA’s lunar mission planning. The rocket will send its crews toward the moon on an Orion capsule, which will be attached to a landing stage that is delivered into lunar orbit in a separate launch. The lander will then transport the astronauts to the lunar surface and return them to the Orion spacecraft to return to Earth.
The program’s first lunar landing will come after Artemis 2, a mission that will send four astronauts on a path beyond the far side of the Moon and back to Earth. Artemis 1 mission is a precursor to Artemis 2.
Once the Artemis 1 rocket is back inside the vehicle assembly building, the Artemis ground team will explore the leaking hydrogen conductor discovered Monday. Technicians will also complete preparations for the flight termination system, which will be activated to destroy the missile if it deviates from its course after takeoff.
Final checks and shutdowns are also taking place inside the VAB, and the ground team will recharge the batteries on some of the secondary CubeSat payloads installed below the Orion spacecraft.
NASA has not set a target launch date for the Artemis 1 mission, but agency officials said last week that the earliest flight that might be ready for launch is late August. NASA has Artemis 1 launch dates available in intervals lasting about two weeks, when the moon is in the correct position in its orbit, and the path ensures that the Orion spacecraft’s power-generating solar panels do not shade for more than 90 minutes at a time.
Other limitations include requirements to meet specific re-entry criteria and daylight scattering for the Orion capsule at the end of the mission.
The next viable Artemis 1 launch period begins in August. 23 and closes on September 9th. On September 6, more launch opportunities will be available starting from September 11th. 19.
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