CAPE CANAVERAL—A procedure to thermally condition the Space Launch System (SLS) main engines for flight failed during the closing hours of the launch countdown on Aug. 29, prompting a scrub.
NASA had hoped to test the so-called hydrogen kick-start procedure during its June 20 wet dress rehearsal for the launch of the SLS and Orion capsule for the Artemis I flight test. But that practice countdown ended before the test due to a hydrogen leak in a quick-disconnect fitting that attaches the tail service mast on the mobile launcher to the rocket’s core stage.
The SLS and Orion were returned to the Vehicle Assembly Building at Kennedy Space Center in Florida for repairs and final launch preparations.
The hydrogen kick-start procedure puts pressure on the core stage tanks so that they bleed off some cryogenic propellant to the engine, chilling them to the proper temperature for ignition.
On Aug. 29, in a test of the procedure ahead of when it would be needed for the actual engine firing, the bleed—or reverse flow—worked as intended with only three of the four core-stage RS-25 engines, prompting a round of troubleshooting.
The bleed pressure within the SLS hydrogen tank was increased and recycled and a flow valve closed in efforts to address the concern with the affected engine, but without success. Finally, the circulation of the liquid hydrogen used to thermally condition all four of the engines was channeled into the problem engine, No. 3, also unsuccessfully.
The countdown went into an unplanned hold at the T-minus-40-min. mark to give the launch team time to assess options, but at 8:35 a.m. EDT Launch Director Charlie Blackwell-Thompson called a scrub.
“You don’t want to light the candle until it’s ready to go,” Administrator Bill Nelson said in an interview on NASA TV. “This is just part of the space business, particularly a test flight.”
NASA had planned to launch the SLS, carrying an uncrewed Orion spacecraft, during a 2 hr. window that opened at 8:33 a.m. EDT. The next launch opportunity is at 12:48 p.m. EDT on Sept. 2, if the engine conditioning issue can be resolved in time.
The Artemis I Mission Management team plans to meet at 3 p.m. EDT on Aug 30 to review data and assess repair and launch options. “Friday is definitely in play,” Mission Manager Mike Sarafin told reporters. “We just need a little bit of time to look at the data.”
Early on Aug. 29, the rocket’s core stage was filled with cryogenic liquid oxygen and liquid hydrogen, following resolution of a potential hydrogen leak in the tail service mast umbilical, located at the base of the core stage.
The launch control team also assessed an apparent crack along a SLS core stage flange, a connection joint linking the liquid hydrogen and oxygen tanks where a line of frost had formed. Engineers concluded the crack was in the exterior insulating foam and the ice they could see had formed when the air around the crack was exposed to the cold temperatures on the exposed exterior of the tank
Artemis I mission managers cleared the Kennedy Space Center launch team to begin propellant loading shortly before midnight, starting first with the preparations to begin the loading of liquid oxygen and then liquid hydrogen propellants. Fueling, however, was delayed nearly an hour due to storms off the coast of the Florida launch site.
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