NASA to live-stream SLS rocket fuel leak repair test

NASA will televise a test on Wednesday to confirm whether a repair made to its Space Launch System (SLS) rocket has fixed the hydrogen leak that forced officials to scrub a previous launch attempt.

The super heavy launch vehicle has yet to leave the launchpad at the Kennedy Space Center in Florida since it was first rolled out last month. The plan is to fly the SLS off to the Moon so that its empty Orion capsule can circle the natural satellite before returning to Earth. The US space agency wants to ultimately use SLS to send humans – the first woman and another man – to the Moon, as part of the Artemis program, this decade with those astronauts riding in the Orion podule.

NASA has tried to send the rocket off to space twice now, but engineers have run into issues every time they try to load the multi-billion-dollar rocket with propellant. Hence all the attention now on it.

Liquid hydrogen makes for an effective light fuel, when combusted with oxygen, but it is a tricky substance to deal with. It has to be pressurized and stored at cryogenic temperatures, and is prone to leaking. NASA has since removed and replaced seals to plug a leak at a quick disconnect point, where the fuel gets pumped to the base of the rocket. It's that leak that forced it to cancel its latest launch attempt on September 3. 

Before NASA makes a third attempt for liftoff, it will perform a final check to see if hydrogen fuel is still leaking from the vehicle on September 21 during a live-streamed event starting at 0715 EDT (1115 UTC). 

"The demonstration test will allow teams to confirm the repair to a hydrogen leak seen during an early September Artemis I launch attempt, evaluate updated propellant loading procedures, and conduct additional evaluations," the space agency said in a statement. "The demonstration will conclude when the objectives for the test have been met."

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The test result will be crucial in deciding whether NASA can make a third attempt to launch the SLS on September 27. If the repair has not fixed the issue, officials will delay liftoff until the next launch window on October 2. 

Mike Sarafin, the Artemis mission manager, said there was a slight chance lightning on Wednesday could force them to postpone the test. If the weather permits, engineers will refuel the rocket gently to minimize the risk of a pressure and thermal spike, he explained in a briefing on Monday. NASA boffins will be measuring the content of hydrogen in certain enclosed areas of the rocket to detect any leakages.

"Ideally, we want to keep it to less than four percent," Jeremy Parsons, deputy manager, Exploration Ground Systems Program at NASA's Kennedy Space Center, said at the briefing of the maximum amount of gas NASA was prepared to leak. "The reason the four percent is set is the flammability of hydrogen in the air. It's really a relatively conservative limit, that being said, that's where we have set it because you want to keep that all controlled."

When the previous attempt was scrubbed, officials had detected eight per cent – double the accepted limit – of hydrogen seeping into components within the launch vehicle. 

The SLS has never been flown into space before. A successful launch will allow NASA to test its rocket and Orion capsule for the first time. The capsule will be put in orbit around the Moon for a little over a month before returning to our home world. Orion is expected to carry astronauts to the Moon by 2025 at the earliest. ®