NASA’s first full-up, on-the-ground test for the main engines on its heavy-lift Space Launch System rocket ended prematurely today due to an automated shutdown.
“Today was an important day,” NASA Administrator Jim Bridenstine said after the test. “I know not everybody is feeling as happy as we otherwise could, because we wanted to get eight minutes of a hot fire, and we got over a minute.”
Despite the early shutdown, NASA said the “Green Run” engine test produced valuable data in preparation for the first honest-to-goodness SLS launch, currently set for late this year.
That launch would kick off an uncrewed round-the-moon trip for NASA’s Orion spacecraft. The mission, known as Artemis 1, is a key step in the plan to send astronauts around the moon on NASA’s Artemis 2 mission in the 2023 time frame, and then put them on the lunar surface by as early as 2024 during the Artemis 3 mission.
Today’s test at Stennis Space Center in Mississippi focused on the SLS rocket’s core stage and its four Aerojet Rocketdyne RS-25 engines. The engines are refurbished leftovers from the space shuttle program, and had been used on shuttle missions going as far back as 1998.
Each of the engines delivers more than 400,000 pounds of thrust, adding up to 1.6 million pounds of thrust when all four engines are firing. When the Artemis 1 mission lifts off, the SLS’ solid rocket boosters will bring total thrust to more than 8 million pounds. In comparison, the Saturn V moon rocket’s first stage delivered 7.6 million pounds of thrust back in the 1960s and 1970s.
NASA’s SLS team put months of work into the preparations for today’s test. More than 700,000 pounds of super-chilled hydrogen and oxygen were loaded into the core stage’s tanks for the engine firing. When the countdown reached zero, all four engines roared into life on cue, sending giant clouds of steam billowing into the air.
About 45 seconds into the firing, one of the ground controllers reported an MCF, or major component failure, on one of the engines.
“We’ve still got four good engines, right?” the test director asked.
“Copy that,” the controller replied.
But about 20 seconds later, the engines could be seen fizzling out, due to a computer-commanded shutdown.
During a post-test news conference, John Honeycutt, the manager for the SLS program at NASA’s Marshall Space Flight Center in Alabama, said it was still too early to report what tripped off the shutdown.
“There were a lot of dynamics going on at that point in time,” he said. “We did see a flash come from around the interface between the thermal protection blanket and Engine 4.”
During the days ahead, NASA and its commercial partners — including Aerojet Rocketdyne and Boeing — will review the data collected during the abbreviated test to determine the next steps. Depending on the team’s conclusions, those steps may involve minor tweaks to the engines, or there may have to be a major overhaul to the rocket — and to the schedule for the Artemis moon missions.
“It very well could be that it’s something that’s easily fixable, and we could feel confident going down to the Cape and staying on schedule,” Bridenstine said. “It’s also true that we could find a challenge that’s going to take more time.”
He said “it’s still too early to tell” whether the Artemis 1 launch will have to be delayed beyond 2021.
The SLS program has already weathered years of delay and nearly $3 billion in cost overruns. NASA currently estimates the development cost for the rocket and its ground support systems at $11.5 billion.
Questions have been raised about the timeline for an Artemis 3 moon landing in 2024, due to the transition in the White House as well as congressional appropriations that are less than what NASA asked for. Today’s setback is likely to add to the questions.
Update for 9:45 p.m. PT Jan. 19: NASA says the shutdown was triggered by test parameters that were designed to be conservative, to ensure the safety of the core stage during the test.
During a maneuver that was meant to simulate how the engine would pivot as the SLS core stage ascended, a hydraulic system associated with the auxiliary power unit for Engine 2 exceeded its pre-set pressure limits for the test. That’s what triggered the shutdown, NASA said.
“If this scenario occurred during a flight, the rocket would have continued to fly using the remaining CAPUs [core-stage auxiliary power units] to power the thrust vector control systems for the engines,” NASA said in a status update.
NASA said the shutdown sequence had nothing to do with the major component failure, or MCF, that was reported on Engine 4. That issue was characterized as an erroneous reading that resulted in a loss of redundancy for the engine control system’s instrumentation system.
Honeycutt referred to a “flash” around Engine 4, and NASA said engineers were continuing to investigate that report. But an inspection of the engine showed that the thermal insulation blankets did their job.
Mission managers are still assessing whether another hot-fire engine test will be required. During a Jan. 19 teleconference, Bridenstine told journalists that the value of repeating the test will have be weighed against the additional wear and tear on the multibillion-dollar rocket.
He said the SLS’ cryogenic propellant tanks were designed to weather nine cycles of filling, chilling and emptying. “Every time we do something like that, it takes away one of our nine times that it can tank,” Bridenstiue said.
Kathy Lueders, NASA’s associate administrator for human exploration and operations, said “we are still shooting for a launch this year.” But she acknowledged that the snag in the Green Run test could make it harder to stick to that schedule.
“It would obviously take out some of the margin that we had. … As you know, things don’t always go beautifully,” she said.
Update for 5 p.m. PT Jan. 21: NASA clarified the game plan for future core stage testing in a blog posting, and it turns out that there’s not as much of a limitation on tanking cycles as Bridenstine thought.
Nine cycles of propellant tank pressurization had been allotted for Green Run testing at Stennis Space Center, but another 13 cycles are being reserved for the period after the tests in Mississippi are completed. That could include the cycles for a wet dress rehearsal on the Florida launch pad, for multiple launch attempts, and for any other activities that require propellant loading and tank pressurization.
Bottom line is that NASA is budgeting seven more tanking cycles for tests at Stennis, which should be ample.
As of Jan. 21, NASA still hasn’t decided whether to try another full-duration, four-engine firing at Stennis. That decision will be based on further inspection of the core stage hardware and further analysis of the data collected during the shortened Jan. 16 test firing.
Whatever happens, Bridenstine won’t be involved in the decision. He left his post as NASA administrator when Joe Biden became president on Jan. 20. Steve Jurczyk, who was an associate administrator under Bridenstine, has taken the helm as acting NASA adminstrator.