NASA isn’t planning another Artemis 1 countdown dress rehearsal – Spaceflight Now

NASA’s Artemis 1 moon rocket at Launch Complex 39B earlier this month. Credit: NASA/Ben Smegelsky

After forgoing another countdown, NASA plans to return the first Space Launch System rocket to the assembly hangar at Kennedy Space Center next week for a hydrogen leak repair and continuing preparations for launch on the Artemis 1 lunar mission. .

With the countdown dress rehearsals complete, Kennedy ground crews prepare to roll the 322-foot-tall (98-meter) Space Launch System moon rocket toward the Vehicle Assembly Building. The return to the VAB is expected to end the Wet Dress Rehearsal, or WDR, campaign as NASA got closer to launching the long-delayed Artemis 1 test flight around the moon, sources said late Wednesday.

The launch of Artemis 1 will be the start of an unmanned demonstration mission of the powerful SLS moon rocket and Orion spacecraft before future Artemis flights take 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 moon rocket’s cryogenic propellant tanks from fully loading during three practice countdowns in April. But a fourth dress rehearsal Monday went deeper into the countdown, with the launch team filling the rocket for the first time with its stock of 755,000 gallons of super-cold liquid hydrogen and liquid oxygen.

But engineers on Monday discovered a hydrogen leak in a 4-inch quick-disconnect fitting, forcing the launch team to adjust procedures in the final stages of the practice countdown.

NASA’s launch team originally wanted to go through the final 10-minute countdown twice, reaching T-minus 9.3 seconds on the final run, just before the core stage’s main engines would ignite during an actual launch attempt. Engineers spent several hours evaluating the hydrogen leak, and managers finally decided to continue the countdown with just one run through the final 10-minute run.

Engineers reconfigured the countdown sequencer on the ground to mask the hydrogen leak, which would normally cause the countdown clock to break. With the workaround of telling the ground launch sequencer computer to ignore the leak, the clock remained T-minus for 29 seconds, one second after the countdown control was transferred from the ground controller to an automated sequencer aboard the SLS moon rocket.

The rocket’s onboard computers commanded the hold at T-minus 29 seconds, when sensors showed the core-stage engines were not yet ready for ignition, NASA officials said Tuesday. The leaking hydrogen connector discovered Monday is associated with a system to thermally condition or cool the RS-25 core-stage main engines.

Despite the leak and the interruption of the countdown before reaching T-minus 9 seconds, NASA officials said the dress rehearsal accomplished most of its goals.

“I’d say we’re in the 90th percentile of where we need to be globally,” Mike Sarafin, NASA’s Artemis 1 mission manager, said in a conference call with reporters Tuesday.

But Sarafin said that during Monday’s countdown rehearsal, there were still some “open points” left unfinished. One was starting the hydraulic powerplants on the SLS solid rocket boosters, which John said should have happened in the last 30 seconds of the countdown to drive the booster nozzles through a gimbal control with their thrust vector control mechanisms. Blevins, chief engineer of the SLS program at the Marshall Space Flight Center.

Blevins said on Tuesday that engineers would evaluate the risk of progressing to launch without making it through the last 20 seconds of the countdown rehearsal. The worst-case scenario of continuing without a rehearsal is an issue that causes a break in the final seconds of the launch day countdown.

“We will either have a successful launch or a scrub because we have protection in the system for those targets that we missed if they didn’t perform well on launch day,” Blevins said. “So it’s not really about making the vehicle safer to fly. It’s really about whether we can reach the launch target in front of our window that is optimal for our lunar mission.

Tom Whitmeyer, NASA’s exploration systems manager, said Tuesday he was “very encouraged” with the outcome of the countdown rehearsal.

“We think we’ve had a really successful rehearsal,” Whitmeyer said.

“There is a relative risk of continuing to practice the hardware on the pad (before another rehearsal),” Whitmeyer said Tuesday. “That’s not necessarily a non-risk situation.”

The powerful Space Launch System, powered by leftover space shuttle engines and boosters, is central to NASA’s lunar mission planning. The rocket will send crews to the moon on the Orion capsule, which will be docked with a dock that will be put into orbit in a separate launch. The lander will then take astronauts to the lunar surface and back to the Orion spacecraft for return to Earth.

The program’s first moon landing comes after the Artemis 2 flight, a mission that will send four astronauts on a trajectory past the far side of the moon and back to Earth. The Artemis 1 mission is a precursor to Artemis 2.

Once the Artemis 1 rocket is back in the Vehicle Assembly Building, the Artemis ground team will fix the leaking hydrogen connector detected Monday. Technicians will also prepare for the flight termination system, which would be activated to destroy the missile if it strays from its course after launch.

Final inspections and close-outs are also taking place in the VAB, and the ground team will recharge the batteries of some of the CubeSat secondary payloads mounted beneath the Orion spacecraft.

NASA has not set a target date for the launch of the Artemis 1 mission, but agency officials said last week that the flight could be ready for launch by late August at the earliest. NASA has Artemis 1 launch dates available in periods of about two weeks, when the moon is in the correct position in its orbit, and the trajectory ensures that the Orion spacecraft’s power-generating solar panels don’t stay in place for more than 90 minutes at a time. standing in the shadows.

Other limitations include requirements to meet specific reentry parameters and a daylight splash from the Orion capsule at the end of the mission.

The next viable Artemis 1 launch window will start on August 23 and close on September 6, after which more launch options will be available from September 19.

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Follow Stephen Clark on Twitter: @StephenClark1

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