A critical test shot of NASA’s Mississippi lunar rocket ended just 67 seconds after it began on Saturday, shortly before a planned eight-minute burn that was to pave the way for the space agency’s final shipment of the rocket’s core stage at the Kennedy Space Center in Florida the start preparations.
The Boeing-built SLS core stage ignited its four Aerojet Rocketdyne RS-25 engines for the first time on Saturday at 5:27 p.m. EST (4:27 p.m. CST; 2227 GMT) to prevent combustion likely to last longer than would last eight minutes, the culmination of a year-long series of checkouts at the Stennis Space Center in southern Mississippi.
The 98-meter-high SLS core stage, which was attached to the huge B-2 test stand in Stennis, was throttled to full power after the four main engines had ignited every 120 milliseconds.
The thrusters that were left over from the space shuttle program built up to 1.6 million pounds of thrust. That makes Saturday’s hot-fire test the strongest rocket fire at the Stennis Space Center since NASA tested the Apollo-era Saturn 5 moon rocket on the same stand in the 1960s.
After the RS-25 engines had come to life for a little over a minute and produced a ground-shaking thunder, they switched off at the command of the missile’s on-board computer system, which detected an unspecified fault in one of the engines.
Engineers tracked the cause of the engine’s premature shutdown on Saturday night, but NASA officials had few details on what could have sparked the early end of the test fire.
“I know that not everyone is as happy as we could be because we wanted eight minutes of hot fire and we had more than a minute,” said NASA administrator Jim Bridenstine.
Ahead of Saturday’s test fire, NASA officials said preparations for the first test flight of the Space Launch System in late 2021 are on the right track. It wasn’t immediately how Saturday’s early SLS engine shutdown might affect that schedule, although it will certainly add more risk.
“We have a lot of data to go through and sort through to get to a point where we can decide whether or not to start in 2021,” Bridenstine said. “While today wasn’t everything we hoped for, it was an important day.”
The outgoing NASA chief, who will leave his post on Wednesday with the end of the Trump administration, said the engineers had gathered vital data on the rocket’s performance despite the engine shutdown. The Space Launch System is an important part of NASA’s Artemis program, which aims to bring astronauts back to the moon for the first time since 1972.
The SLS will launch NASA’s Orion crew capsule to send astronauts close to the moon. NASA plans to build a mini space station that will serve as a research outpost and waypoint for crews traveling between the earth and the lunar surface. The Orion spacecraft will connect to a descent ship in lunar orbit, where astronauts float in the lander to get to the lunar surface.
Here is a replay of the initial Hotfire test of the core stage of the Space Launch System, interrupted in a scheduled eight-minute shot just over a minute.
– Spaceflight Now (@SpaceflightNow) January 16, 2021
The first SLS test flight, known as Artemis 1, will launch an Orion spacecraft to orbit the moon without astronauts. A second SLS / Orion flight around the moon in 2023 will have three astronauts and a Canadian crew member.
The Trump administration’s goal of a human landing on the moon’s south pole by the end of 2024 is rapidly dwindling. The schedule has been aggressive from the moment Vice President Mike Pence announced the 2024 lunar landing target in 2019. However, Congress failed to provide the funds NASA needed to develop human-rated lunar landers to meet the schedule, which raised further doubts about the 2024 deadline.
Space policy experts believe the Biden administration is unlikely to meet the target for a moon landing by 2024, but may make slower efforts to get U.S. astronauts back to the moon.
The space launch system has been repeatedly delayed since the program was announced in 2011, missing the targets for its debut in 2017, 2018, 2019 and 2020. NASA spent more than $ 18 billion on the SLS program from 2011 to September 30, 2020.
“This is a program that is important to the United States of America, it is important to our leadership in the world, it is important to us to go to the moon and go fast,” said Bridenstine on Saturday, adding, that the purpose for The Artemis program goes beyond science.
“It’s about an instrument of diplomacy. It’s about American leadership. It’s about exploration, ”he said.
Having all four RS-25 engines fired at the same time was “a win in itself,” said Bridenstine. The engines flew three times each with the space shuttle.
During the development of the Saturn 5 moon rocket and space shuttle, NASA fired test items in Stennis to validate the propulsion system design. To save money, the first fully-fledged SLS core level serves both as a test item and as a flight unit. NASA officials said they were extra careful with the stage because it is supposed to fly after all.
“This is not a failure,” said Bridenstine. “This is a test … we will make adjustments and go to the moon.”
Based on an analysis of the video and audio broadcast on NASA TV, the first sign of problems came during the abbreviated SLS hot fire test about 50 seconds after the engine was ignited when an engineer on the test team declared an “MCF” or a “major” component failure ” on engine no.4.
“Copy this, but we’re still running, we still have four good engines, right?” The test leader answered on a communication network.
“Yes, copy that,” said a member of the test team.
Shortly after the MCF call, about 67 seconds after the engine started, the video showed that the core phase engines appeared to be in a shutdown sequence. Oral confirmation of the engine shutdown came a few seconds later from a member of the test team.
“There has been some discussion about an ‘FID’ on Engine 4, our terminology for fault identification, followed shortly by an MCF, which is a major component fault,” NASA SLS program manager John Honeycutt said at a press conference for some Hours after the test. “I don’t know much more about it than you do at this point. Every parameter that went wrong on the motor can send this error ID. “
The engines shut down about a minute after the test program began, about the same time the RS-25s were programmed to throttle back to 95% thrust before reverting to full power at 109% of rated power. At the same time, the motors should be swiveled with hydraulic cardan rings.
“So there is a lot of momentum going on at this point,” said Honeycutt. “As we were about to initiate the gimbal (or), we saw a small lightning bolt at the interface of Motor 4’s thermal blanket.
“At this point … the engine controller has sent the data to the core stage controller to shut down the vehicle,” Honeycutt said. “The team achieved a lot today, we learned a lot about the vehicle, we loaded the vehicle, we wrung out our pressure system, we conditioned the engines and we have about 60 seconds for the RS-25.”
John Shannon, Boeing’s SLS program manager, said before the test shot teams wanted at least 250 seconds of runtime on the core stage before moving on from the hot fire. At this point in the test, the engines would have been throttled and brought back to full thrust and performed two gimbal profiles, including a sweep at about T + plus 2 minutes and 30 seconds, to check the structural response to engine movement.
“We have been saying all along that we want to get at least 250 seconds, but I think we need to do our careful work and look at the data we have gathered to make sure we have a good plan for the future.” Honeycutt said.
Bridenstine said Saturday it was too early to be sure whether engineers will need to do another hot fire test in the core phase or whether turning off the engine early will delay the first start of the SLS test, known as Artemis 1 the Mission, until 2022 should.
“It depends on what the anomaly was and how difficult it will be to fix,” Bridenstine said. “And we still have a lot to learn to find out. I think it might very well be that it is easy to fix and we could feel safe going down to the cape and then sticking to the schedule. It is also true that we could find a challenge that will take more time to complete. “
NASA could have delivered the SLS core stage to the Kennedy Space Center before the end of February if the test fire had gone perfectly on Saturday, and positioned the stage for stacking with two solid rocket boosters, an upper stage, and the Orion spacecraft. Assuming NASA officials decide to repeat the hot fire test, February is the earliest that another test fire could occur.
It takes three to four weeks to dry out the RS-25 engines, do inspections, and prepare the core phase for a second hot fire test, assuming managers decide to do another test, Honeycutt said. This turnaround time does not affect how long it may take repairs to complete to fix the problem caused by the Saturday’s untimely end of the hot fire test.
Each of the four RS-25 engines that were fired on Saturday flew on NASA’s space shuttle fleet. The engines were launched in 1998 on 21 shuttle missions.
NASA has spare RS-25s in case engineers need to replace any of the engines on the first SLS core stage. Ground teams at Stennis could swap engines with the rig-mounted missile, officials said.
“We need to fully understand the problem and do a core phase and engine assessment to make sure we understand the problem and know what to fix or fix if it needs to be fixed,” Honeycutt said on Saturday evening.
The only damage to the missile observed after Saturday’s test fire was on the thermal blanket near engine # 4, where teams noticed the lightning just before the engine shut down, Honeycutt said.
When asked if the data analyzed so far suggests engineers need to make major changes to the core phase, Honeycutt said, “What I’ve seen so far about the performance of the hardware during the wet dress rehearsals we conducted, during today’s hot fire and the limited amount of images I’ve seen so far, I don’t think we’re considering a significant design change. “
Email the author.
Follow Stephen Clark on Twitter: @ StephenClark1.