ORLANDO, Fla., Feb. 22 (UPI) -- NASA has delayed the test-firing of its SLS moon rocket that had been planned for Thursday to check out a faulty valve in the liquid propulsion system.
When it happens, the test will ignite four powerful engines on the 212-foot-tall core stage of the Space Launch System rocket for four to eight minutes at the John C. Stennis Space Center in southern Mississippi. NASA is preparing the rocket for an uncrewed test flight around the moon, possibly by October.
A previous attempt to complete a test-firing Jan. 16 ended prematurely when sensors shut the engines after a little more than one minute.
The test for the planned Artemis moon missions was the most powerful rocket test since the Apollo era at the facility. Even the truncated test-firing in January created huge clouds of steam from the cooling system, which uses 300,000 gallons of water per minute.
"This is not by any means a vanilla [simple] firing the core stage," John Shannon, vice president and SLS program manager at Boeing, which built the rocket, said during a press conference last week.
Shannon called the test "aggressive" because controllers will toggle the rocket's engines into various positions, putting stress on the components and systems.
"Our primary goal is to not only get the ... data, but also to protect the stage for the first flight," Shannon said. "So we're kind of threading the needle here between keeping the vehicle safe and gathering this data."
NASA leaders had warned that the test could be interrupted if test controllers felt the rocket would be damaged.
After the previous test, NASA said the agency had set parameters for the test too tightly, and while no significant problems developed with the rocket or its engines, more data was needed.
The test is intended to provide insight into how the rocket would perform during a launch toward the moon. The eight-minute firing time represents how long those engines would fire to propel the rocket to 100 miles above the Earth.
But the four-minute mark is "really where we collect all of our verification data, and so we're considering that as our minimum success time," said Julie Bassler, a NASA manager for the rocket program.
The rocket and its engines are covered with 1,400 sensors that will measure pressure, temperature and vibration, among other readings, NASA officials said.
After the test, NASA plans to refurbish the core stage and ship it to Kennedy Space Center in Florida.
The four engines emit 1.6 million pounds of thrust, which is slightly less than a SpaceX Falcon 9 rocket at 1.7 million pounds of thrust. The rocket uses RS-25 engines built by Aerojet Rocketdyne, which are the same type that were mounted to the space shuttle.
When the rocket is prepared for a lunar launch, it will have two large solid-rocket boosters to provide 8.8 million pounds of total thrust -- 15 percent more power than the Saturn V rocket that took astronauts to the moon during the Apollo era.
The first Artemis mission was supposed to be part of NASA's plan to return astronauts to the moon by 2024, but NASA only has received a fraction of the funding it has requested for that timeline.
The SLS program is over budget at more than $9 billion, according to an official report from NASA's Office of Inspector General.