NASA officials said Tuesday they are standing down from a cryogenic loading test on the agency’s Space Launch System moon rocket until after the launch of a commercial crew mission from a neighboring pad at the Kennedy Space Center.
A countdown test Monday was delayed by what NASA managers characterized as minor issues, including a liquid oxygen temperature concern and a manual valve that was left in the wrong configuration before teams evacuated the SLS launch pad.
The countdown dress rehearsal is a key test before NASA completes final preparations on the Space Launch System and Orion crew capsule. The giant rocket, standing 322 feet (98 meters) tall, is set to launch no earlier than June on the unpiloted Artemis 1 test flight around the moon, laying the groundwork for future lunar missions with astronauts on-board.
NASA’s launch team at Kennedy loaded about half of the SLS core stage’s 196,000-gallon liquid oxygen tank Monday on launch pad 39B, but stopped the practice countdown before pumping 537,000 gallons liquid hydrogen into the core stage. Both propellants are stored at cryogenic temperatures — liquid oxygen at minus 297 degrees Fahrenheit (minus 183 degrees Celsius) and liquid hydrogen and minus 423 degrees Fahrenheit (minus 253 degrees Celsius).
The test was delayed several hours due to an outage in the gaseous nitrogen supply at the Florida spaceport. The gas is used to purge parts of the SLS rocket to reduce the risk of fire during fueling.
The nitrogen supply, provided by Air Liquide from an offsite plant, was restored to the pipeline later Monday morning, allowing the launch team to begin preparations to load propellants into the Space Launch System.
But before tanking began, sensors at the pad detected the liquid oxygen was warmer than anticipated.
Charlie Blackwell-Thompson, NASA’s Artemis launch director, said computers stopped the loading process due to a concern about geysering, which can occur when there are warm bubbles of liquid oxygen in the feed lines.
“You can actually form a large oxygen gas bubble that can rapidly kind of expel,” she said. “It can kind of create this geyser effect, if you will. The way that we mitigate that is you actually have what we call helium inject. It uses helium, and you inject that into your feed line system and it helps to cool it down.”
The method of injecting helium into the liquid oxygen flow is called an “anti-geyser” system.
“You don’t want a big slug of warm LOX (liquid oxygen) going into your feed system,” Blackwell-Thompson said. “We monitor that very carefully because we want to mark sure that we’re not creating that warm effect, when you can create that big bubble … that can be expelled and then cause problems.”
The liquid oxygen temperature concern caused the launch team to rework their cryogenic loading procedures. That took several hours, before Blackwell-Thompson gave the “go” to resume operations Monday afternoon.
After starting to load liquid oxygen, engineers prepared to pump liquid hydrogen into the core stage, but an unresponsive vent valve on the rocket prevented teams from taking that step. Engineers traced that problem to a pneumatic pressure panel on the mobile launch tower next to the rocket.
Blackwell-Thompson called off the countdown dress rehearsal around 5 p.m. EDT (2100 GMT), 10 hours after the time when tanking was originally scheduled to begin. Technicians went back to the launch pad for inspections and determined a hand valve associated with the pressure panel was left in the wrong position when the pad team evacuated the complex earlier in the day.
NASA officials said the issues encountered during Monday’s test were relatively minor, and none were associated with any systems on the rocket or spacecraft. An earlier countdown test attempt Sunday was scrubbed because of malfunctioning supply fans needed to ventilate parts of the mobile launch platform and tower.
Tom Whitmeyer, head of NASA’s exploration development division, said Tuesday he is “feeling pretty positive” about the dress rehearsal, and none of issues are showstoppers.
“Most of the stuff we’re picking up is small or procedural in nature,” said Mike Sarafin, NASA’s Artemis 1 missions manager. “We need to adjust some of the limits slightly, or some of the sequencing or timing slightly … As far as the hardware, the rocket is fine. The spacecraft is fine.”
Ground teams at Kennedy are resupplying propellants at pad 39B to set up for another cryogenic tanking test in the coming days.
NASA officials said Tuesday the next SLS countdown dress rehearsal will occur after the launch of a commercial SpaceX Falcon 9 rocket from nearby pad 39A. That mission is scheduled to launch Friday at 11:17 a.m. EDT (1517 GMT) with an all-private crew of four astronauts heading into orbit on a 10-day flight to the International Space Station.
The commercial crew flight is managed by Axiom Space, which aims to fly a series of private astronaut and space tourist missions to the space station in the next few years. Axiom eventually plans to launch its own commercial module to the International Space Station, then construct a private research station of its own in low Earth orbit.
The Ax-1 mission set for launch this week is the first all-private crew mission to the International Space Station. Previous flights have all been managed by a government organization, either NASA or the Russian space agency Roscosmos.
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