Updated 19:45 Eastern with details from briefings.
WASHINGTON – A static fire test of the core phase of the Space Launch System ended early on January 16 when a hydraulic system for one of its four engines reached a “deliberately conservative” limit during testing.
In a January 19 statement, NASA said that the core engine hydraulic system for the core phase “exceeds the predetermined test limits set” for the Green Run test. “As they were programmed, the flight computers automatically ended the test.”
Later that day, during a call with reporters, NASA officials said that the hydraulic reservoir level and hydraulic pressure in the Core Stage Auxiliary Power Unit, or CAPU, for the engine dropped below a range of milliseconds, causing the flight . computer to end the test. The CAPU drives a thrust vector control system used to gimbal the engines, and the problem occurred about one second after a gimbal series started 60 seconds into the test.
It also caused a strike by the CAPU. “The automated software on board turned off CAPU 2 just to secure the system in case of a problem,” John Shannon, vice president and SLS program manager at Boeing, said during the call.
The problem with the hydraulic system was not linked to a serious component failure (MCF) that was reported by test controllers approximately 45 seconds after ignition. NASA said that the MCF actually took place 1.5 seconds after the ignition, and that it was caused by the loss of “one leg of redundancy” in the instrumentation for engine 4. “Test restrictions for hot fire were set to test let this condition continue, because the engine control system still has sufficient redundancy to ensure safe engine operation during the test, ”the agency said.
NASA is still investigating what officials said shortly after the test was a “flash” seen in the vicinity of a thermal protection blanket around engine 4. The blanket showed signs of scorching, but it is expected from standard engine operations and temperature in the engine. section was normal.
The parameters used for the Green Run test were, according to the agency, “deliberately conservative to ensure the safety of the core phase during the test.” NASA officials have previously stressed that they are taking a cautious approach to testing the core phase, as it is flight hardware intended for use during the first SLS launch, Artemis 1.
“We need to remember that the rocket we just tested is the rocket that Orion is going to launch around the Moon,” NASA administrator Jim Bridenstine said at a briefing after the January 16 test. “If we do this test, the risk is that we can not take it, because it is the same vehicle that Orion will drive.”
“Our test parameters show our first approach to safety and were quite conservative. This core phase is a valuable flight article that will bring America back to deep space, ”Shannon said in a statement from the company about the Green Run test. “Our deadline is set to collect data without unnecessarily compromising the system.”
But they acknowledged in the call that they may have been too conservative. The hydraulic system had a reading, a parameter that was perhaps set a little too conservatively, ‘Bridenstine said. “If it had been a true launch, the parameter would not have been set so conservatively and the rocket would have continued.”
“It’s to walk the fine line between making sure for the first time that we use any of these hardware, that we have adequate protection to keep the stage safe, but also to make it work through the test regime,” Shannon said. “There is a judgment to ask how you set the parameters to ensure that the stage remains in a good configuration for a further test or a start.”
NASA has not yet decided whether to conduct a second fire test. In comments before the first test, NASA and Boeing officials said that although the test would take 485 seconds, they would gather most of the information they needed after 250 seconds. However, the engine shutdown occurred after only 67.2 seconds.
NASA said it would review the data collected during the test before deciding whether to conduct a second fire test or send the stage to the Kennedy Space Center for final preparations for the Artemis 1 mission. “You need to understand the risk of exposing the flight core stage to another round of testing, and how it compares the risk to the learning we have to do,” said Kathy Lueders, NASA’s co-administrator for human reconnaissance and operations , said.
One factor, according to Bridenstine, is the graded lifespan of the core stage. He said the stage should be filled nine times with liquid hydrogen and liquid oxygen. This has been done twice so far: a wet dress rehearsal in December and for the test for static fire. A limited amount of propellant was loaded onto the stage for the first attempt at the wet dress rehearsal in early December.
Doing a static fire test again means charging the stage at least once more with propellants. “Every time we do something like that, it takes away one of us nine times we can refuel,” he said. “There are reasons to do a fiery fire, and there are reasons we might not do a hot fire.”
One former NASA official recommended that the agency conduct a second fire test. “My advice is to retest and retrieve complete data – it may take a few weeks, but the schedule is secondary,” tweeted Wayne Hale, former manager of the shuttle program and current chair of the NASA Advisory Board’s Human Exploration and Operations Committee.
John Honeycutt, SLS Program Manager at NASA, said in the call that work to recover the engines after the truncated fire test is underway, either to support a second fire test or to prepare the stage for shipment to KSC . He earlier said it would take 21 to 30 days to get the nuclear phase ready, giving NASA time to review the data and decide if a second arson is needed.
“The data analysis will drive us and let us know whether we are going after the launch or that we are doing an additional fire test,” he said. “We do not yet have a date on which we will be on that decision.”