SLS Green Run static light interrupted by “deliberately conservative” test limits



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Updated at 7:45 p.m. EST, with briefing details.

WASHINGTON – A static fire test of the center stage of the space launch system ended in early January 16 when a hydraulic system for one of its four engines hit an “intentionally conservative” limit during the test.

In a Jan. 19 statement, NASA said the hydraulic system for Engine 2 on the main stage “exceeded the preset test limits that had been set” for the Green Run test. “As they were programmed to do so, the flight computers automatically ended the test.”

Later that same day, during a call with reporters, NASA officials said the hydraulic tank level and hydraulic pressure in the Core Stage Auxiliary Power Unit, or CAPU, for that engine are fell below the limits over “a series of milliseconds”, triggering the flight. computer to complete the test. This CAPU drives a thrust vector control system used to card the motors, and the problem occurred about one second after starting a gimbal sequence 60 seconds after starting the test.

This also triggered the closure of this CAPU. “The automated software on board shut down CAPU 2 just to secure the system if something went wrong” with the unit itself, John Shannon, Boeing vice president and SLS program manager, said on the call.

The hydraulic system problem was not related to a major component failure (MCF) reported by test controllers approximately 45 seconds after ignition. NASA said the MCF actually took place 1.5 seconds after ignition, and was caused by the loss of a “redundancy leg” in the engine 4 instrumentation. “Testing constraints for the hot fire were set to allow the test to proceed under this condition, because the engine control system still has sufficient redundancy to ensure safe operation of the engine during the test, ”the agency said.

NASA is still investigating what officials said shortly after the test was a “lightning bolt” seen near a thermal protection blanket around the 4 engine. The blanket showed signs of scorching, but this was expected. standard engine operation and temperatures in the engine. section were normal.

The settings used for the Green Run test, the agency said, were “intentionally careful to ensure the safety of the center stage during the test.” NASA officials have previously stressed that they are taking a cautious approach to testing the main stage as it is flight hardware, intended for use on SLS’s first launch, Artemis 1.

“We have to remember that the rocket we just tested is the rocket that will launch Orion around the moon,” NASA administrator Jim Bridenstine said in a post-test briefing on Jan. 16. “When we do this test, there is a risk that we cannot take because it is the same vehicle that will be piloting Orion.”

“Our test parameters demonstrate our safety-oriented approach and were appropriately conservative. This fundamental step is a valuable flight item that will bring America back to deep space, ”Shannon said in a company statement regarding the Green Run test. “Our red line limits have been set to allow data collection without unnecessary risk to the system.”

But they acknowledged in the appeal that perhaps they had been too conservative. The hydraulic system “had a reading, a parameter, that maybe was set a little too carefully,” Bridenstine said. “If this had been a real launch, this parameter wouldn’t have been set so carefully and the rocket would have continued.”

“It’s about crossing the fine line between ensuring, for the first time that we are using one of these devices, that we have sufficient protection to keep the stage in a safe configuration, but also to let it run for a while. the test diet, ”Shannon said. “This is a matter of judgment as to how you set these parameters to make sure the scene stays in a good setup for another test or launch.”

NASA has not yet decided whether it will conduct a second hotfire test. In comments before the first test, NASA and Boeing officials said if the test was to last 485 seconds, they would collect most of the data they needed after 250 seconds. However, the engine shutdown took place after only 67.2 seconds.

NASA said it wanted to review the data collected during the test before deciding to conduct a second hot test or ship the scene to the Kennedy Space Center for final preparations for the Artemis 1 mission. “You have to understand. the risk of exposing the main stage of flight to another round of testing, and how can that risk be offset by the learning we have to do, ”said Kathy Lueders, NASA associate administrator for the exploration and human operations.

One factor, Bridenstine said, is the rated life of the center stage. He said the stage is designed to be nine times filled with liquid hydrogen and liquid oxygen propellants. This has been done twice so far: a wet dress rehearsal in December and for the static fire test. A limited amount of thruster was loaded onto the stage for the first wet dress rehearsal attempt in early December.

Doing another static fire test means loading the stage with thrusters at least once more. “Every time we do something like that, it takes away one of our nine times we can tank,” he said. “There are reasons to do a full duration hotfire, and there are reasons why we might not do a full duration hotfire.”

A former NASA official recommended that the agency conduct a second hot test. “My advice would be to retest and get full data – may take a few weeks, but the timing is secondary,” tweeted Wayne Hale, former director of the shuttle program and current chair of the NASA Advisory Council’s Human Exploration and Exploitation Committee.

John Honeycutt, head of the SLS program at NASA, said in the call that work to recycle the engines after the truncated hotfire test is underway, either to support a second hotfire test or to prepare the scene. for shipment to KSC. He previously said it would take 21 to 30 days to prepare the main stage, which would give NASA time to review the data and decide whether a second hotfire was needed.

“The data analysis is going to motivate us and inform our decision as to whether to go ahead with the launch or if we do an additional hot test,” he said. “We do not yet have a date when we will be at this decision point.”



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