Engineers outlined on the conference call that the data behind the glitch has been collected and is now being analyzed.
NASA officials also explained some of the differences between the SLS and the space shuttle and other reasons that might have affected the event to cancel Monday’s launch.
Sensor glitch could cause Monday’s Artemis I launch to be canceled
On the conference call, NASA’s SLS program manager John Honeycutt said the reason engineers didn’t perform the critical engine bleed start test during the rocket’s first wet rehearsal earlier this year was a hydrogen leak. The cause of the leak was resolved by Monday, and while engineers did initially find some leaks, the vehicle was successfully refueled and then made its way to a test where hydrogen was flowed into the rocket’s engines to cool them before liftoff .
The result of this test is that hydrogen removes heat from the engines, each with its own bleed system. The system is similar to the one on the space shuttle, however the key difference between the two is that after the hydrogen heats up and removes the heat from the engines, it flows back into the spacecraft’s fuel tanks. For SLS, on the other hand, the warm hydrogen left the spacecraft through a ground vent instead.
Honeycutt said the location of the third engine – most likely the one behind the edge ball – was unlikely to have contributed to the failure. He added that NASA is checking the temperature sensors to make sure they are working properly, and that the sensors are not flight instruments — instead, they are designed to develop flight instruments.
Honeycutt still believes that once the hydrogen begins to flow from the tower and from the vents to the ground, the fuel flow is satisfactory. Later, the official added: “I think you know that we understand the physics of how hydrogen behaves, it’s not how the sensor behaves, it’s not inconsistent with the physics. So we’re going to look at all the other things we have. data and use that data to make informed decisions about whether we’re cooling down all our engines.”
NASA has tested all of these engines at its facility in Stennis, but in those tests, the cooling of the engines started earlier, the engines weren’t intended to be as cold as they were in Monday’s run, and Stennis’ sensors were more sensitive. Those are the only differences between the Stennis heat run and Monday’s launch attempt, and the reason NASA decided to wait for Monday’s launch test is that a full hydrogen tank would provide better conditions for the test. The test stand at Stennis has a smaller hydrogen exhaust pipe, while the SLS’ exhaust system was redesigned after the rocket’s green run tests.
After Monday’s operation, NASA now plans to begin deflation testing about 30 to 45 minutes earlier on Saturday, confirmed by Artemis I flight director Charlie Blackwell-Thompson. The rocket’s engines will also be at ambient temperature on Saturday, according to Honeycutt.
As of now, NASA engineers are evaluating data collected from the rocket after Monday’s wipe. Although the launch was canceled, they continued to evaluate the rocket as it was still filled with ultracold liquid hydrogen and oxygen, data that is currently being analyzed and explained to the SLS program leaders.
If Saturday’s launch attempt goes well, the weather is the sole cause of the delay, and the team will be able to turn the vehicle around within 48 hours. The probability of violation is now 60%, but the nature of the cloud cover makes accurate predictions uncertain.
In Monday’s attempt, the engine was targeted to be cooled to a temperature of 40 degrees Fahrenheit — about 400 degrees Fahrenheit. With Honeycutt blowing straight, engines one, two, and four were about -410 degrees Fahrenheit, while engine three was about -380 degrees Fahrenheit. At an earlier meeting, a NASA official had misquoted the target temperature as 4 degrees Fahrenheit.
Since replacing any potentially faulty sensors would require NASA to miss the launch window, NASA is not planning to take this action for now. Instead, the agency will try to work within the data displayed by the sensors. Saturday’s launch window will open at 2:17 p.m. ET Saturday.