NASA just weeks away from trying again with SLS Moon rocket launch

Will it be third time lucky?

NASA will attempt, for the third time now, to blast off its Space Launch System (SLS) rocket to the Moon in late September.

Officials are targeting September 23 at the earliest, and September 27 as a potential backup should it have to scrub the launch yet again. Jim Free, NASA's associate administrator of Exploration Systems Development, confirmed at a briefing on Thursday the American space agency had asked the US Space Force division for approval to fly on those dates.

Designed to fly the first woman and another man to the Moon sometime this decade (ideally) under the Artemis program, the SLS is NASA's most powerful rocket to date.

Its launch, if and when it happens, will be the rocket's first major test, during which it will carry an unmanned crew capsule into space so that the pod can detach and circle the Moon before returning to Earth. When it is time to set foot on the lunar surface again, an SLS rocket will be used to send a capsule carrying astronauts to the Moon, using a SpaceX lander to bring them down to the regolith.

But with two failed SLS launches so far and costs totaling more than $20 billion for an expendable launch vehicle that was once planned to lift off in 2016, skeptics say NASA should stop building its own rockets and just subcontract it all out to private companies, such as SpaceX.

The SLS has remained grounded at the Kennedy Space Center in Florida since it was rolled out in August. The first attempt to launch on August 29 was called off due to a faulty sensor reading that led officials to believe one of its engines may be running too hot. The second attempt on September 3 was also cancelled after a hydrogen leak was detected.

Using liquid oxygen and hydrogen to put many tons of machinery into space is risky. Although they make for powerful and light fuels, the substances are difficult to contain.

The gases have to be pressurized and maintained at cryogenic temperatures to, among other things, prevent them from evaporating. Heat will cause the liquid to expand, and liquid hydrogen is prone to seeping out from tiny pores or seams. 

Hydrogen leaks have continued to plague the SLS, becoming apparent even in dry test rehearsals. Before the SLS flies, NASA will have replaced the seal on an interface called the quick disconnect that's used to pump liquid hydrogen fuel into the rocket via a feed line from the mobile launch tower [PDF]. That repair may prevent another leak.

Engineers will have to perform the fix directly on the launch pad, though the agency said it may have to roll the SLS back to the Vehicle Assembly Building to perform additional checks and to reset the system's batteries before it is launched.

Free, however, said NASA has sought a waiver from Space Force so it can launch in late September. "It's our job to comply with their requirements. So we will do that," he said. ®

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