The Artemis Moon rocket will make a second launch attempt

SLS rocket

The US space agency will attempt once again in the next few hours to launch the most powerful rocket ever.

Nasa was stymied by a mix of technical and weather problems when it tried to lift the Artemis I Moon mission away from Earth on Monday.

But the mood remains positive at Florida’s Kennedy Space Center.

“We have to show up, we have to be ready and we have to see what the day brings,” Mike Sarafin, director of Nasa’s Artemis mission, told reporters.

Saturday’s attempt to send the Space Launch System (SLS) rocket is scheduled to launch in a two-hour window starting at 14:17 local time (19:17 BST, 18:17 GMT).

The 100-meter-tall vehicle’s goal will be to launch a human-rated capsule in the direction of the Moon, something that hasn’t happened since Project Apollo ended in 1972.

Artemis I is a technology demonstration, so there will be no crew in this case, but if all goes according to plan on the mission, then Artemis II, which is expected to fly in 2024, will definitely carry people.

NASA astronaut Jessica Meier said everyone should exercise some patience as the SLS moves toward its maiden flight, and not to be surprised if there is a further delay.

“Yes, of course it’s disappointing for everyone, but it’s not unexpected,” he told BBC News.

“It’s part of how we do things at Nasa. The SLS will eventually have people on it, my friends, my colleagues. So we have to make sure this test flight goes well.”

Graphic SLS

Graphic SLS

Monday’s bid to fly SLS was ultimately cleared because controllers could not be sure the four large engines under the rocket’s core stage were properly prepared for flight.

Shuttle-era power units are cooled during the countdown to -240C to prevent shock from the sudden injection of cryogenic propellants at the time of launch. But a sensor was showing that the #3 engine might be 15-30 degrees cooler than it should be.

Bill Muddle of Aerojet manufacturer Rocketdyne is convinced the sensor was faulty, and if he plays again on Saturday it will probably just be ignored.

“Having looked at the data and all the other indicators, the No. 3 engine could have been a bit colder than the others on Monday,” he said.

“Now we understand what we need to look at to get comfortable to start.”

If the SLS gets away with it this time, it’s sure to be an impressive sight.

“It’s going to be ‘buses on steroids,'” said Doug Hurley, who piloted the shuttle’s last mission in 2011.

The former astronaut now works for Northrop Grumman which builds the big white solid boosters on the sides of the SLS.

“What I always thought was the coolest thing about shuttle launches was that you saw it take off and it was well away from the tower before you heard anything, and then it was even a little bit over before you felt it,” he explained.

“In terms of weight, the SLS is very close to what the shuttle was. Apollo’s Saturn V rocket was drastically different. I never saw it in person, but it beat the cushion. For the shuttle, it looked like it was clean in an instant, almost as soon as the boosters came on. The SLS should be the same,” he told BBC News.

Moon path

Moon path

The first phase of the SLS ascent will last just over eight minutes.

This would put the rocket’s upper stage, with the Orion capsule still attached, into a highly elliptical orbit that would see the two crash back to Earth without any further effort.

Thus, the upper stage should lift and circle the orbit before then boosting Orion in the direction of the Moon.

Confirmation that the capsule is alone, in orbit and speeding through space at 30,000 km/h (19,000 mph) should come two hours and five minutes after launch.

The planned duration of the shipment is just under 38 days. This would result in Orion returning to Earth for a dive in the ocean off San Diego, California on October 11.

Thirty-eight days is far longer than the 21 days that capsule maker Lockheed Martin says is the maximum time astronauts should spend in the spacecraft.

But Annette Hasbrook, senior adviser on the Orion program at Nasa, said engineers wanted to stretch the spacecraft on this mission to understand its limits.

Artwork: Orion sent to the Moon

Artwork: The rocket’s upper stage will put the Orion capsule on a course toward the Moon

“Try to test the edges of your boxes, not your nominal profile,” he explained.

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