SLS Green Run test team perseveres through hurricanes, technical challenges

After a valve repair, the Space Launch System core stage is moving forward to wet dress rehearsal and hot fire

November 24, 2020 in Space

Engineers and technicians have successfully repaired a faulty prevalve in the Space Launch System core stage propulsion system while the stage remained in the B-2 test stand at NASA’s Stennis Space Center. The core stage is being tested on the ground to identify issues before flight.

NASA photo

Testing of the Boeing-built core stage for NASA’s first Space Launch System rocket has been slowed by impacts from five hurricanes and a tropical storm during Gulf Coast storm season, and more recently by a problem with a prevalve on one of the stage’s liquid hydrogen propellant feed lines.

But the test team at NASA’s Stennis Space Center in Mississippi has persevered through all challenges as the core stage continues its Green Run test series, with just two major tests to go. 

During a pause in on-site work for Hurricane Zeta earlier this month, engineers reviewed data from the core stage’s first six tests. They focused on inconsistent performance from one of four prevalves that supply liquid hydrogen to the RS-25 engines. Boeing and the valve supplier designed an innovative tool to remove and replace the valve’s faulty clutch while the core stage remained in the B-2 test stand, without removing the entire valve. Subsequent testing of the repaired valve confirmed that the system is operating as intended. 

“We’ve got an innovative team, applying decades of knowledge and creative thinking to all problems, and coming up with options that can preserve our schedule,” said Mark Nappi, Green Run test director for Boeing. “Hurricane season has consumed our margin, so we’re focused on maintaining our schedule to ship to Kennedy Space Center in January, though the next two test dates have moved.” 

The next Green Run test, wet dress rehearsal, is targeted for the week of Dec. 7. The team will load, control and drain more than 700,000 gallons (roughly 2.6 million liters) of cryogenic propellants and simulate a countdown up to the moment of firing the engines.  

If all goes well with Test 7, the team will move on to Test 8, a full countdown and hot-fire for up to eight minutes. All four RS-25 engines will fire at a full, combined 1.6 million pounds (over 700,000 kilograms) of thrust, just as they will on the launch pad. Thrust increases as the rocket ascends and the atmosphere thins, ultimately reaching the “vacuum” level of more than 2 million pounds (roughly 900,000 kilograms) of thrust.

After that, Boeing engineers and technicians will refurbish the stage and prepare it to be delivered to Kennedy. There, it will be joined with waiting components — including the Orion human-rated spacecraft and the Boeing–United Launch Alliance Interim Cryogenic Upper Stage — ahead of launch on NASA’s uncrewed Artemis I launch in late 2021.