November 28, 2022

NASA’s Artemis 1 moon rocket ready for ride back to launch pad

NASA’s Space Launch System moon rocket inside High Bay 3 of the Vehicle Assembly Building. Credit: NASA

After replacing and recharging batteries in the Vehicle Assembly Building, NASA ground teams plan to roll the more than 30-story-tall Space Launch System rocket back to its launch pad early Friday at Kennedy Space Center for another try Nov. 14 to send the Artemis 1 test flight around the moon.

A hydrogen fuel leak kept the mission from launching in early September, then NASA rolled the SLS moon rocket back inside the VAB on Sept. 27 to take shelter from Hurricane Ian. The spaceport did not suffer any significant damage as Hurricane Ian weakened to a tropical storm before its center passed directly over Kennedy Space Center.

During October, technicians replaced batteries on different elements of the rocket, including its range safety flight termination system. One of NASA’s diesel-powered crawler transporters rolled into High Bay 3 on Wednesday and positioned itself under the SLS mobile launch platform.

NASA managers met Thursday and evaluated the weather forecast for rollout early Friday, and discussed computer models that suggest a weak tropical weather system could impact Florida’s Space Coast next week. The meeting concluded with a go-ahead to begin rollout of the 322-foot-tall (98-meter) moon rocket from the VAB around 12:01 a.m. EDT (0401 GMT) Friday.

After emerging from the VAB, the rocket, its mobile launch platform and tower, and the crawler will head for Launch Complex 39B on a journey expected to take between eight and 12 hours. The crawler, upgraded after earlier use on the Apollo moon program and the space shuttle program, will reach a top speed of 0.8 mph on the 4.2-mile (6.8-kilometer) trip from the iconic rocket hangar at Kennedy to pad 39B

The full stack weighs about 21.4 million pounds for rollout. After arriving at pad 39B later Friday morning, the crawler’s hydraulic jacking and leveling system will lower the mobile launch platform onto pedestals, positioning the rocket over the flame trench at the seaside launch complex.

The huge SLS moon rocket is the largest ever built by NASA, and is the centerpiece of the agency’s Artemis moon program, which aims to return astronauts to the lunar surface later this decade. NASA is preparing the first SLS moon rocket for the Artemis 1 test flight, a demo mission to send an unpiloted Orion crew capsule around the moon and back to Earth on a shakedown cruise before it flies with people.

Cliff Lanham, NASA’s Artemis 1 flow director at Kennedy, said technicians spent the last few weeks repairing minor damage to foam insulation and servicing batteries on the SLS moon rocket. Teams also recharged batteries on the Orion spacecraft, the pressurized capsule sitting on top of the moon rocket, and on five of the 10 small rideshare CubeSat payloads riding the Space Launch System into deep space.

Technicians replaced batteries on the solid rocket boosters, which provide more than 75% of the Space Launch System’s 8.8 million pounds of thrust at liftoff.

“The execution by the team has been excellent,” Lanham told reporters Thursday. “Our initial focus was on gaining access to the vehicle so we could get to work on the second stage, which was our critical path. Work included battery changeouts, transducer replacement, and other testing.

“As this work was proceeding, we were changing out core flight termination system components, including the batteries and as well as we changed out the booster batteries. This past weekend, we have performed our flight termination system testing,” Lanham said.

Much of the battery replacement work occurred on the forward section of each solid rocket booster, and in the section of the SLS core stage between the liquid hydrogen and liquid oxygen tanks.

The flight termination system would be triggered by a range safety officer on the ground if the rocket veers off course after liftoff. Pyrotechnic charges would fire to blow up the rocket.

The U.S. Space Force’s Eastern Range is responsible for public safety during all rocket launches from Kennedy Space Center or Cape Canaveral Space Force Station. The flight termination system needs an independent battery system and command receiver to still function in the event of a catastrophic rocket failure.

The range has certified the batteries on the Artemis 1 moon rocket’s flight termination system for 25 days after testing in the VAB, although NASA officials believe the batteries can last much longer. NASA won a waiver from the range to extend the flight termination system battery certification for nearly two months, which would have allowed teams to mount another Artemis 1 launch attempt in October, had Hurricane Ian not forced the rollback of the rocket to the hangar.

NASA can only perform the flight termination system testing and replace the destruct system batteries when the rocket is in the VAB, so officials decided to swap the batteries and re-test the system before rolling the Space Launch System back to pad 39B.

Other tasks completed inside the VAB included recharging and replacement of radiation instruments on the Orion capsule, and an accelerometer on a crew seat inside the spacecraft. The sensors will gather data on the radiation environment and forces astronauts will be exposed to on future crew missions to the moon using the SLS moon rocket and the Orion spacecraft.

Once the rocket is back at the launch pad, ground teams will replace biological research specimens on a science payload inside the Orion crew module. Then teams will close the Orion hatch for flight.

“We have been able to gain about a one day of margin for the pad operations to account for … weather,” Lanham said. “That gives them some margin to really help our probability of hitting that Nov. 14 first launch attempt. Also at the pad, we’ll be refreshing some samples for our space biology payload. Right now, we are very confident in our team and our systems, and we’re looking forward to getting back out to pad and getting launched on the 14th.”

This illustration shows the components of the Space Launch System’s Block 1 configuration, which is the version scheduled to fly on the rocket’s first mission, designated Exploration Mission-1. Credit: NASA

Unlike the previous launch attempts for the Artemis 1 moon mission, the launch times available to NASA this month are mostly at night. The launch window Monday, Nov. 14, opens at 12:07 a.m. EST (0507 GMT) and extends for 69 minutes. NASA has scheduled backup launch opportunities Nov. 16 and 19.

The Federal Aviation Administration would require NASA to stand down from launch attempts most of the week of Thanksgiving, as the federal regulator prioritizes airspace near Kennedy Space Center for civilian air traffic during the busy holiday travel period. NASA could potentially try again to launch the Artemis 1 mission on Nov. 25, the day after Thanksgiving.

On its first test flight, NASA’s huge Space Launch System rocket will send an unpiloted Orion crew capsule on a four-day voyage toward the moon. The Orion spacecraft will enter a distant retrograde orbit around the moon, executing two close flybys about 60 miles (100 kilometers) above the lunar surface on the outbound journey and then again on the return trip to Earth.

Different launch dates come with different mission profiles. Some launch dates set up the Artemis 1 mission for a shorter duration of about three-and-a-half weeks, while other launch dates have mission profiles with durations extending up to six weeks.

If the Artemis 1 test flight takes off Nov. 14, the Orion spacecraft would fly a shorter-duration 25-and-a-half day mission profile, resulting in a splashdown of the crew capsule in the Pacific Ocean on Dec. 9.

The November launch period opens Nov. 12 and runs through Nov. 27. NASA has about two weeks of launch availability in each Artemis launch period, followed by around two weeks when the mission would be not be feasible. The primary driver of the launch periods is the position of the moon in its 28-day orbit around Earth, but there are other factors, including NASA’s requirement for the trajectory to culminate in a splashdown of the Orion spacecraft in the Pacific Ocean in daytime.

As NASA prepares for another series of Artemis 1 launch attempts, engineers continue evaluating the condition of different parts of the rocket, which has been fully stacked on its mobile launch platform for more than a year.

Stacking of the five-segment solid rocket boosters on the launch platform began in late 2020. Conservative engineering limits originally only certified the boosters for 12 months after stacking of each booster’s aft center segment on top of the motor’s lowermost piece, a milestone that occurred in January 2021.

That limit has been extended to 23 months, Lanham said, thanks to additional engineering reviews and data gathered on the condition of propellant inside each booster segment before stacking. The current certification for booster propellant expires on Dec. 9 for one booster, and Dec. 14 for the other, Lanham said Thursday.

Jim Free, the NASA manager who oversees the SLS moon rocket and Orion spacecraft programs, said engineers could further analyze the status of the booster propellant to extend the certification beyond December.

NASA officials said they are optimistic that a persistent hydrogen leak encountered during fueling of the SLS core stage will not recur on the next launch attempt. Teams detected a leak in a quick disconnect fitting between the core stage and the mobile launch platform during several countdown dress rehearsals earlier this year, and most recently on a Sept. 3 launch attempt.

Managers stood down from the Sept. 3 launch attempt after the most recent leak. Workers swapped out seals in the leaky connection and modified the sequence they use to flow super-cold liquid hydrogen into the SLS core stage. Although a smaller leak was detected on a tanking test Sept. 21, hydrogen concentrations in the area around the umbilical connection remained below safety limits.

In a briefing to a NASA Advisory Council committee Monday, Free’s deputy said the agency has not nailed down the cause of the hydrogen leak.

“I have confidence,” said Amit Kshatriya, NASA’s assistant deputy administrator for exploration systems development. “I think we did the right level of engineering analysis. We have not gotten to what I would say is a full proximate cause on the leak. We have some data from taking the seal apart and evaluation on the bench.

“We did have the team do a full-up failure analysis, so they have been progressing through that entire fault tree,” Kshatriya said. “That fault tree has not been entirely dispositioned. There are still open branches on leaves of that tree that we still need to go through, and we’re going to continue to do that work. We’re trying to balance some of the workload with the rest of what we’re trying to do with regard to mission preparation.”

Kshatriya said NASA has “operational mitigations and engineering mitigations” aimed at reducing the chance of a leak on the next launch attempt. Those mitigations were demonstrated on the Sept. 21 tanking test.

“We almost have to kind of chill in the seal as we go, which is what we learned, and we’re primarily using the cryopshere pressure to start that initial flow instead of hitting it pretty hard with a fast slug of LH2 (liquid hydrogen) at the beginning,” he said. “We’ve done the processing and the swap outs ,and we’ve also got operational mitigations for some of the commanding and protocols to make sure we get it right during that part of the sequence.”

The changes mean it will take somewhat longer to load hydrogen into the core stage, but Kshatriya said the modified sequence gives NASA the best chance to successfully fuel the rocket. Liquid hydrogen is chilled to minus 423 degrees Fahrenheit, and the cryogenic conditions can change the shape of seals and create a leak path not detectable at ambient temperatures.

“Dealing with the LH2 system, and given its complexity, absolutely it is something we’re worried about, and we’re trying to do our best to get our arms around it,” Kshatriya said Monday.

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