NASA launch controllers called off plans to load super-cold liquid hydrogen and liquid oxygen into the first fully-assembled Space Launch System moon rocket Sunday for a countdown dress rehearsal, giving time for ground teams to troubleshoot problems with fans used to ventilate the giant rocket’s mobile launch structure at the Kennedy Space Center.
The practice countdown, known as a wet dress rehearsal, started Friday and was supposed to culminate in the pumping cryogenic propellants into the 322-foot-tall (98-meter) Space Launch System rocket Sunday on launch pad 39B.
But the SLS launch team scrubbed the simulated countdown shortly before noon EDT (1600 GMT), prior to the start of propellant loading. The countdown was paused much of Sunday morning while the launch team evaluated problems with fans needed to pressurize, or ventilate, the mobile launch tower.
The fans blow air into the mobile launcher to ensure hazardous gases don’t build up during tanking, reducing the risk of a fire or other emergency, according to Charlie Blackwell-Thompson, NASA’s Artemis launch director.
One of the fans ran into trouble early Sunday, so officials paused the countdown to allow a team to go back to the launch pad to troubleshoot the problem. The launch team switched to a backup fan and prepared to continue the countdown, but then the second fan encountered a different issue, Blackwell-Thompson told reporters Sunday afternoon.
“The purpose of that pressurization is to prevent hazardous gas intrusion during load, so it provides a positive pressure,” she said. “So in the event that you were to have a leak or have some sort of hazardous commodity out of at pad, that you didn’t have, those gases intrude into those areas and potentially cause a fire hazard.
“So we decided that we wanted to really understand (the fan problems), given it was the first-time loading of the vehicle, and we made the decision to stand down to get in a configuration to go troubleshoot that, and then to be ready to make another run at it tomorrow,” Blackwell-Thompson said.
The mobile launcher stands 370 feet (113 meters) tall, with retractable umbilical arms to route gases and propellants to the rocket, and a crew access arm to allow astronauts to board the Orion spacecraft for future Artemis moon missions.
The ventilation fans are located in a building along the perimeter of pad 39B, a few hundred feet away from the rocket and mobile launcher. Air from the fans is routed through ducting in the launch pad’s environmental control system.
Blackwell-Thompson said engineers do not believe the cause of the malfunctioning fans is related to four lightning strikes observed inside the perimeter of pad 39B during a thunderstorm late Saturday afternoon. However, ground teams were still troubleshooting the fans when she spoke with reporters Sunday, and NASA officials weren’t sure of the reason the fans ran into problems.
NASA is assessing whether a lightning strike this afternoon at pad 39B impacted any systems on the SLS rocket, Orion spacecraft, or ground facilities before loading cryogenic propellant into the vehicle tomorrow for a countdown dress rehearsal. https://t.co/lpGi5xTj6Y pic.twitter.com/XKnWnF8RMH
— Spaceflight Now (@SpaceflightNow) April 2, 2022
Engineers determine the lightning strikes did not impact the Space Launch System or ground facilities. Three of the strikes hit the launch pad’s lightning towers, and another struck the catenary wiring system used to route electricity away from the rocket while it is exposed at the pad.
NASA is testing the Space Launch System for its first test flight, known as Artemis 1. The countdown rehearsal at Kennedy is a full-up practice run for launch day. Once the countdown proceeds into the final steps before liftoff, the clock will stop at T-minus 9.3 seconds, just prior to main engine ignition.
If ground teams at Kennedy are able to resolve the fan problems overnight, NASA’s mission management team will meet at 6 a.m. EDT (1000 GMT) Monday to give a “go” or “no go” for the start of propellant loading.
That propellant loading should begin shortly after 7 a.m. EDT (1100 GMT) for the giant Boeing-built core stage, covered in orange foam insulation to prevent ice build-up on the rocket’s outer skin.
Liquid oxygen, chilled to minus 297 degrees Fahrenheit (minus 183 degrees Celsius) will begin loading first into the core stage. Then liquid hydrogen, stored at minus 423 degrees Fahrenheit (minus 253 degrees Celsius), will start pumping into the rocket’s main stage at pad 39B.
It will take about three hours to load liquid oxygen into the core stage, and an hour-and-a-half for liquid hydrogen. In flight, the propellants will feed the rocket’s four RS-25 main engines, leftovers from the space shuttle program, for a burn lasting more than eight minutes.
Then the launch team will move on to loading hydrogen and oxygen into the rocket’s cryogenic upper stage, powered by a single Aerojet Rocketdyne RL10 engine. Here’s a breakdown of the propellants that will be loaded into the rocket Sunday:
• Core Stage liquid oxygen: 196,000 gallons
• Core Stage liquid hydrogen: 537,000 gallons
• Upper stage liquid oxygen: 5,000 gallons
• Upper stage liquid hydrogen: 17,000 gallons
Another 30-minute build-in hold is planned when the countdown reaches the T-minus 10 minute mark Sunday afternoon. After a final “go/no go” pre-launch readiness poll, NASA launch director Charlie Blackwell-Thompson will give approval for the countdown clock to resume.
If all goes according to plan, the countdown will target a simulated launch time of 2:40 p.m. EDT (1840 GMT) Monday. In the final 10 minutes of the countdown, the core stage and upper stage propellant tanks will be brought to flight pressure, the boosters will be armed, and the rocket will be switched to internal power.
The countdown will cut off at T-minus 33 minutes and recycle to the T-minus 10 minute hold. NASA’s launch team plans a second run through the terminal countdown later Sunday afternoon, culminating in a hold at T-minus 9.34 seconds, just prior to ignition of the main engines.
Then the core stage and upper stage will be drained of cryogenic propellants, and NASA engineers will evaluate the rocket’s performance during the dress rehearsal, before eventually rolling the rocket back to the Vehicle Assembly Building for final pre-launch testing and closeouts.
NASA plans to announce a target launch date for the Artemis 1 mission after the wet dress rehearsal is complete. The launch dates currently under consideration are in June.
The Artemis 1 mission will send an Orion crew capsule into orbit around the moon, where mission control will run the spacecraft through a series of demonstrations before astronauts fly on the next SLS/Orion flight, named Artemis 2, on a looping trajectory around the moon.
Future missions after Artemis 2 will attempt to land astronauts on the moon with a commercial lunar lander, and build out a mini-space station near the moon called the Gateway.
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