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NASA Will Roll Back Its SLS Rocket for Repairs

NASA engineers hope to have their massive moon-bound Space Launch System ready for liftoff in a couple of months, but so far they’ve encountered some bumps in the road. On March 17, NASA rolled the world's most powerful rocket out onto the launchpad at Kennedy Space Center in Florida to ready it for the Artemis program’s inaugural lunar mission later this year. Since then, technicians have completed a raft of checks on the huge rocket’s systems, but after three tries they haven’t been able to make it through the final test, a practice countdown called the “wet dress rehearsal test.”

The key problems have been a faulty helium check valve and a liquid hydrogen leak, which led to several pushbacks of the test countdown. Finally, NASA officials decided over the weekend to disconnect the rocket and, starting next Tuesday, carefully roll the SLS and Orion crew capsule back to the Vehicle Assembly Building, a facility with the equipment needed for them to perform rocket surgery. They hope to have a quick turnaround, returning to the pad soon afterward to complete the countdown test, but the first Artemis mission around the moon—originally planned for early June—might be delayed.

“The mega moon rocket is still doing very well. The one check valve is literally the only real issue we’ve seen so far. We’re very proud of the rocket,” said Tom Whitmeyer, a deputy associate administrator at NASA headquarters in Washington, at a press conference this afternoon. “But we have a little bit more work in front of us.”

The precautions aren’t surprising; NASA doesn’t want to take a chance on its most expensive rocket or debut Artemis launch failing. “It comes down to what we consider to be the acceptable level of risk,” said Mike Sarafin, the Artemis mission manager, at an earlier press conference on April 15.The test itself began on April 1, after the rocket had been ferried from the assembly building to Launch Complex 39B via an enormous crawler. Jeff Spaulding, the senior NASA test director, and his team began their process by hooking up the rocket’s electrical power and pressurization systems and filling the pair of white boosters on the side with propellants. Then they started loading the big orange fuel tank with more than 700,000 gallons of liquid hydrogen and liquid oxygen, supercooled to a frigid -423 and -297 degrees Fahrenheit, respectively. (That’s the “wet” in “wet dress rehearsal test.”) Their goal was to simulate the entire countdown process to just under T-10 seconds—the closest thing to a real launch without firing up the core stage’s RS-25 engines.

Throughout the test, Spaulding and his colleagues monitored instruments, pressures, temperatures, and valves to check that all the systems were working within acceptable parameters. (“If it turns out they’re a little outside of the limits, that’s what we want to know now—if there’s something we need to fix or adjust,” he had said in the days leading up to the rehearsal.)

The test revealed the need for several adjustments. The process was delayed the first time on April 2 by lightning bolts, which hit the towers around the rocket. Then the following day, NASA officials encountered problems with launch tower fans and their backups, according to Charlie Blackwell-Thompson, the Artemis launch director. These fans provide pressure in the mobile launcher, the tall structure next to the rocket, to keep out hazardous gasses. That led to a delay while the fan malfunction was resolved.

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They hit another snag during their second attempt on April 4, while loading the core stage. They pumped half the liquid oxygen but had to stop before loading up the liquid hydrogen. They weren’t able to open a vent valve in the mobile launcher, which is needed to relieve pressure while the tank is fueled up, and they identified the faulty helium check valve on the SLS’s upper stage.

After pausing on April 8 for the Axiom 1 launch, which lifted off from a nearby pad, last week NASA engineers had a third go at it. This time they modified the test, limiting the fueling of the upper stage because of the helium valve. But partway through loading, the umbilical cable attached to the core stage (not the rocket itself), intended to supply liquid hydrogen propellants, sprung a leak. They also had an outage of gaseous nitrogen, used to purge oxygen from the rocket before tanking and to provide a nonflammable environment. Ultimately, the engineers had to scrub the countdown test again and drain the propellants.

Encountering obstacles isn’t abnormal when readying a new, complex rocket that’s never been blasted to space before; that’s why every space agency and private company conducts tests to spot potential problems well before launch day. It took five tanking attempts before the iconic space shuttle was finally ready for its first launch on an orbital flight, noted Blackwell-Thompson at a press conference last week—and NASA ultimately operated its shuttle fleet for more than 30 years.

The SLS’s main predecessor isn’t really the space shuttle—which looped the planet and docked with the International Space Station in low Earth orbit—but the huge Saturn V rocket, which until 1973 launched the Apollo program missions, including the historic moon landing by Neil Armstrong and Buzz Aldrin. The SLS’s primary job will be to ferry people and equipment for the Artemis mission, which should include at least five lunar launches over the next five years.

The first SLS voyage will give an uncrewed Orion spacecraft enough thrust to take a spin around the moon, and it will also deploy an array of satellites for a variety of smaller missions and technology demonstrations. That flight will set the stage for future missions with astronauts on board, including a moon landing. “I’m super excited. It’s kind of a dream come true, to finally have a chance to work on a program that will be taking people back to the moon,” Spaulding had said in the days leading up to the tests. The Artemis mission is also envisioned as a first step toward the human exploration of Mars.

Blackwell-Thompson and her team currently plan on rolling the SLS back to the pad for a fourth countdown test as soon as possible. But they’re also considering other options, including conducting more work on the rocket in the Vehicle Assembly Building first, or even rolling out the rocket later this year to perform the countdown test right before the launch itself.

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In any case, the reveal of the date for the real show, when the SLS rocket lifts toward the moon, will have to wait. NASA officials will announce the Artemis 1 launch date once they complete all the necessary repairs and tests. But hitting their first launch window in early June now seems “challenging,” Whitmeyer says; they may have to wait until the next one opens up between June 29 and July 12. After that, another window opens in late July.

Despite these glitches and delays, NASA officials remain optimistic. “NASA does some of its best work when it’s solving problems. I couldn’t be any more proud of our team,” Blackwell-Thompson said last week, as Sarafin added: “There’s this recognition of how hard it is to get through the first time.”

Updated 4-18-2022 7:00 pm ET: This story was updated to clarify the timeline of the SLS's rollback and repairs.


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