NASA Says Today’s Fuel Leak Was Three To Four Times Above Fire Hazard Limit 

NASA-SLS-SEPTEMBER-2022
The SLS rocket is pictured just as NASA called off its launch attempt earlier today. Image: NASA

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After battling for hours with a hydrogen leak that forced it to stop its second launch attempt of the Space Launch System (SLS) rocket, officials from the National Aeronautics and Space Administration (NASA) have decided to roll back the rocket to the vehicle assembly building. NASA's second launch attempt was scheduled for a window that opened in the afternoon Eastern Time today, but two and a half hours before launch, the launch director Ms. Charlie Blackwell-Thompson agreed to scrub the mission after her team recommended her a no-go. Their recommendation came after multiple attempts to stop the leak failed, and the teams proceeded to empty the rocket of its fuel and oxidizer soon after the scrub.

The announcement came during a media teleconference that NASA held earlier today, with agency officials explaining the reasons behind the scrub and highlighting the way forward.

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NASA Will Decide Whether To Repair SLS On The Launch Pad Or Roll It Back To Vehicle Assembly Building

NASA administrator Senator Bill Nelson opened the conference and reiterated that before its launch, the Space Shuttle was sent back to the vehicle assembly building twenty times. He stressed that "we do not launch until we think it's right", and that the decision was the launch team's to make with safety being the top concern behind any decision.

NASA's associate administrator for exploration systems development Mr. Jim Free explained the current situation and confirmed that there will be no more launches this month. The next launch period, which begins in mid-October, will be decided upon later and teams will be ready to decide by Monday. NASA will also accommodate its upcoming fifth crewed launch to the International Space Station (Crew-5) that is scheduled to take place with SpaceX.

He added that:

We don't go into these tests lightly. We don't just say hey we think, we hope this is gonna work. The confidence to do another launch attempt today was born out of the fact that we understood the hydrogen leaks that we had on Monday. Those are different than the leak we had today. In terms of scale,  one was in the same place, but today was a different signature. And we understood the engine issue. So we were confident coming into today, but as the administrator said we're not going to launch until we're ready which means we're going to step through these things.

NASA's Jim Free explains what's next for the Artemis 1 launch. Image: NASA

Delving into the technical details, NASA's Artemis mission manager Mr. Mike Sarafin explained what the teams did up to the scrub and what the teams will do next. He shared that teams are working through a fault tree analysis to explain why a leak of this magnitude was not there on Monday and they were analyzing additional controls to ensure an overpressure event that led to today's scrub does not take place again.

Just prior to the cryogenic loading operation the team was working through a chill down. And then, there was an inadvertent pressurization of the hydrogen transfer line that the pressure exceeded what we, what we had planned, which was about twenty pounds per square inch, it got up to about sixty pounds per square inch. And the flight hardware itself, we know is fine, we did not exceed the maximum design pressure, but there's a chance that the soft goods, or the seal in the quick disconnect at the eight inch quick disconnect saw some effects from that. But it's too early to tell exactly whether that was the cause of the hydrogen leak that we had today. We do know is that we saw a large leak, at the eight inch quick disconnect today and that leak started when we went from the slow fill to the fast fill. This particular quick disconnect did not have a problem of this magnitude on Monday. We did see a small leak, but we did not see one of this magnitude. It was characterized as a large leak by our operations team.

The team tried three times to resolve the leak, and all three times we saw a large leak. And as was discussed previously, if you can thermally stabilize both sides of the quick disconnect, we have a ground side and a flight side and that is where the fluid flow occurs through. If you can chill that down and ensure that there's no differential temperature across that interface, sometimes the leaks can seal themselves or heal themselves. So the teams attempted that, they attempted to essentially reseat the leak by increasing the pressure in there and that was not successful. So initially the team declared the scrub at 11:17 eastern time, and then went into vehicle safing and drain the cryo.

The SLS on NASA's Crawler transporter as part of the rocket's June 2022 wet dress rehearsal. Image: Ben Smegelsky/NASA

The liquid oxygen is currently off the vehicle, and liquid hydrogen at least when we were in the mission management team meeting was still onboard the vehicle and they were in process of draining it and it should be off by now or very close to it. The team will get into what they call the inserting which is they put gaseous nitrogen in there so as not to condense water vapor in the tank area and then they'll swap over to air. What that does is it allows us to get the tanks back up to ambient conditions and then for us to gain access. In the scrub meeting that we had at 2L30 eastern, we talked about three options.

The first option was to simply de-mate and re-mate the umbilical at the pad hoping that the soft goods would seal the leak up but our confidence level given the size of the leak that we saw today was fairly low that that would solve the problem. The team leaned towards a removal and replacement of the soft good in the quick disconnect and the options were basically to do it at the pad or do it back in the vehicle assembly building. And either of these options did not preserve our ability to fly before the end of this launch period which expires on the sixth. So the team is developing a series of schedule options and we're going to hear about those early next week. The schedule options include removal and replacement of the soft goods on the disconnect at the pad, followed by a cryo test - that is the only cryo test to ensure that we do not have a further issue with respect to leaks at the temperatures that we need to fill the vehicle on day of launch. The other option is to roll back and remove and replace the quick disconnect soft goods in the vehicle assembly building. There's a risk versus restraint. Doing at the pad you're exposed to the environmental conditions. We need to build an environmental enclosure to do that. We do it in the vehicle assembly building, the vehicle assembly building is the environmental enclosure. However, we cannot test this quick disconnect at the VAB at cryogenic temperature, we can only do it at ambient temperatures.

The NASA officials during the conference earlier today.

So we're working through those options, the team it's too early to say but they're working through a fault tree analysis as to why we did not see a leak of this magnitude on Monday but we're seeing it of this magnitude at today's attempt. And then also looking at the chill down procedure to look at additional controls such that we don't have a reoccurrence of the inadvertent overpressure that we had earlier today. All that said, we've talked about it before, this is an incredibly hard business.

This is an initial test flight of this vehicle. As was said by administrator Nelson, we're gonna fly when we're ready. And as part of this initial test flight, we're learning the vehicle, we're learning how to operate the vehicle and we're learning all of the things required to get us ready to fly and we've demonstrated a large number of those things, not only through wet dress and some of the other ground tests that we've had but we, we're still earning as we go again to get this vehicle off safely. So our focus is on understanding the problem, developing solutions in terms of schedule but also risk versus risk impacts and we'll follow up next week when we have those options fleshed out further.

The SLS rocket is visible in the backdrop of a sunrise at NASA's KSC during its first launch attempt earlier this week. Image: NASA

Depending on the work left, it will now take several weeks before the rocket it is ready to fly again. A key constraint is the flight terminal system, which runs on batteries that are not rated to last more than 25 days. These batteries can only be changed at the vehicle assembly building.

NASA will use its fault tree analysis to decide whether to tinker with the umbilical cord on the pad or in its vehicle assembly building. Engineers have to be careful when removing the cord as by doing so they might lose crucial data that could point them in the right direction to discovering the reason behind today's fault.

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The hydrogen concentration was at least two to three times higher than 4%, with 4% being the flammability limit, or the fire hazard limit - making it clear why NASA did not launch today. The seal on the quick disconnect arm will be inspected for foreign object debris or simple damage, and Mr. Sarafin explained that a leak similar to the one today is typically resolved through a simple replacement.

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