“Public expectations should have been set lower,” according to notes of the meeting by a participant that were obtained by The Washington Post. In the end, NASA got 100 percent of the data it needed for only 15 of the 23 test objectives, after the engines fired for just 67.2 seconds instead of the full eight minutes as planned.
The truncated test has again raised questions about the SLS program, which is already years behind schedule and billions of dollars over budget. It remains unclear how the shortened test will affect NASA’s original plans to try to launch the SLS for the first time later this year. Though the program to build the rocket started 10 years ago, Saturday was the first time NASA ignited all four of the RS-25 engines while attached to the rocket’s core, or primary, stage.
In a blog post Tuesday, NASA said the premature end of the test came after sensors detected a problem with the hydraulic system that steers the rocket by moving the engines during flight.
But that issue would not have affected an actual launch because the space agency had set “intentionally conservative” limits to protect the rocket while it was bolted down to the test stand, the agency said. In a news conference late Tuesday afternoon, John Honeycutt, NASA’s SLS program manager, said that was in part because the core stage used in the test would be the same hardware used in flying the mission.
“If this scenario occurred during a flight, the rocket would have continued to fly using the remaining” units that power the engine movement, NASA said in the blog post.
In the private briefing, officials provided more detail, saying that the movement of the engines, known as “gimbaling,” was “much more vigorous” than previous gimbal tests in which the engines were not ignited, according to the notes of the participant, who spoke on the condition of anonymity because the person was not authorized to speak publicly. As a result, the hydraulic pressure dropped below the limit and triggered the engine shutdown.
In addition to the problem with the hydraulic system, NASA said in its blog post there was a sensor reading that indicated a “major component failure.” That was not related to the engine shutdown and involved an instrumentation problem that NASA said it would resolve “before the next use of the core stage.” Despite the sensor reading, the test continued “because the engine control system still has sufficient redundancy to ensure safe engine operation during the test,” NASA said.
But in the private briefing, officials said the warning would have triggered an abort of an actual launch “just as it would have stopped a [Space] Shuttle launch,” according to the briefing participant’s notes. “You want to launch with full redundancy.”
During the news conference, Jeff Zotti, the RS-25 program manager for Aerojet Rocketdyne, confirmed that if the controller “had detected the failed sensor before liftoff we would have paused and fixed the sensor.”
After the test, NASA officials also said they noticed a “flash” around one of the engines. On Tuesday, the agency said that the “temperatures in the core stage engine section were normal” and that the thermal blankets used to protect the engines from the extreme heat “did their job and protected the rocket.”
In the private briefing, officials said there were no “indications of any leaks or fire.” If another test is required, it would take between three and four weeks to prepare, they said.
Despite the truncated test, NASA said in its blog that the rocket’s hardware “is in excellent condition” and that “all four engines performed as expected,” reaching their “full power” by producing 1.6 million pounds of thrust during the test at NASA’s Stennis Space Center in Mississippi.
Still, the agency — and Boeing, the prime contractor on the rocket stage — continue to investigate the problems encountered during the test and have not yet decided if the test will need to be repeated or if the core stage can be shipped to the Kennedy Space Center next month as scheduled.
After the test on Saturday, NASA Administrator Jim Bridenstine said that despite the early shutdown, the agency “got lots of data that we’re going to go through and be able to sort through and get to a point where we can make determinations as to whether or not launching in 2021 is a possibility or not.”
The RS-25 engines are left over from the Space Shuttle program, which ended in 2011. NASA and Boeing officials had noted that to indicate engineers were very familiar with the engines and were confident the systems would perform as expected. NASA even put out a dramatic video hyping the test and the upcoming missions to the moon it would enable.
“We have a lot of experience with some of this hardware and the engines being as mature as they are gives us high confidence that we can do one hot fire and be ready to go,” John Shannon, Boeing’s SLS program manager, had told reporters before the test.