Chances good for NASA Artemis SLS Moon launch on Saturday

Fingers crossed this prodigious test will have a good weather experience

Updated NASA will try to launch its Space Launch System (SLS) rocket to the Moon on Saturday after its first attempt on August 29 was scrubbed due to what turned out to be a faulty sensor on one of its core engines.

The flight is the first-ever proper trial of the super heavy-lift rocket. It was designed for the US space agency's Artemis program, which intends (with the help of SpaceX) to put the first American woman and another man to the Moon ideally some time this decade.

Saturday's mission will be to test that the huge SLS rocket – NASA's most powerful to date at a cost of billions of dollars – can successfully blast off with an unmanned crew capsule on top. The capsule is expected to circle the Moon and return to Earth. In future, there'll be astronauts in the pod.

Monday's attempt at a lift-off was paused 40 minutes from ignition after one of the rocket's four core-stage RS-25 engines seemingly failed to cool to the correct temperature, using some of the cryogenic fuel as a coolant, and the launch was ultimately scrubbed.

John Honeycutt, NASA SLS program manager, later blamed a faulty sensor for giving a false reading. "We know we had a bad sensor," he said during a news briefing.

"We've had time to go back and look at the data and compare many sources of data, and do some independent analysis that confirmed it's a bad sensor and we're getting good quality propellant through the engine."

If NASA encounters the same issue in the next launch, it will just ignore it. John Blevins, NASA's SLS chief engineer, explained the sensor was used to measure how well the engine was being chilled by the liquid hydrogen propellant and was not a critical piece of information that affects the rocket's operation. "We do not need the sensor for flight," he said.

Although NASA said the higher-than-normal temperature reading was what ultimately led to the postponement of the SLS's flight to Saturday, Mike Sarafin, Artemis mission manager, admitted the agency had encountered other issues, such as a hydrogen leak in a ground umbilical and a faulty vent valve before the official countdown began. Thus, scrubbing the launch wasn't such a bad idea.

"We were off the script in terms of the normal tanking operation," he said. "One of the worst things you can do when you find yourself in a hazardous condition is just go even further off-script." Sarafin said the team had other ways to check for the thermal condition of the engines that do not rely on its sensors.

If things go smoothly this weekend, the SLS will blast off into space on September 3 around 1417 EDT (1817 UTC). The whole mission – launch, Moon orbit, and return – is expected to last 37 days and will be the first test to see if the SLS and Orion are up to the job of sending humans off to our natural satellite.

The weather at the launchpad at NASA's Kennedy Space Flight Center in Florida looks promising with clear skies, and an 80 percent chance of launch, according to our vulture there on the ground. 

If the trip is called off again, however, NASA can make a third attempt on September 5. The Register will be bringing you updates as they happen. ®

Updated to add

Record scratch. Freeze frame.