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With the Crew-6 mission successfully lifting off from the Kennedy Space Center today, SpaceX shared more details about the scrub on Monday just moments before liftoff. NASA's Crew-6 mission was planned initially for liftoff early morning on Monday, but the mission was postponed as SpaceX engineers could not confirm that the ignition fluid for the rocket was successfully making its way out of the rocket as part of pre-flight procedures. At today's post-launch press conference, SpaceX's senior director for human spaceflight shared more details about the fault and how his company fixed the issue before today's successful launch.

SpaceX's NASA Crew-6 Launch Was Delayed Due To Clogged Ignition Fluid Filter

SpaceX's Falcon 9 rocket uses triethylaluminum-triethylborane (TEA-TEB) to light up the Merlin engines on its rockets. As part of the preflight procedures, this fluid is pumped through the system to ensure no gas bubbles are inside when the system is fired up for the flight.

SpaceX's Benji Reed gave a detailed explanation for the fault during today's press conference, as he explained that engineers were uncertain if the ignition fluid was successfully making its way into the tank during the procedures. He shared that:

We flow to make sure that there's enough of this TEA-TEB going into the engines when it's time to ignite them. We flow it up to the interface of the rocket, up to the interface of the engines to basically get all the gas out of the system. It's for like when you replace your brakes and you have to bleed the brake line system to make sure you got all the air bubbles out of the lines. Your want to make sure you just have brake fluid, it's the same idea. We want to bleed the line so we have any gas out of the system, and we're sure we have exactly enough TEA-TEB, the correct amount of TEA-TEB to ignite the engines right when it's time.

So during the count on Sunday night, we were watching as we do all of the different data, all the different signatures of information, as we call them, coming in from the rocket and the ground system. And one piece of data looked a little bit funny, one of the signatures looked a little funny. Which was how much TEA-TEB is coming back into the catch tank. So coming out. So when you're bleeding in the TEA-TEB to the rocket interface, you're pushing the air out, or the gas out, but you also want to make sure you're bringing the TEA-TEB back to a catch tank and you want to see how much you're catching in that tank on the way out.

The green glow from the TEA-TEB ignition of the Merlin engine on SpaceX's Falcon 9 second stage as part of the NASA Crew-6 launch earlier today. Image: NASA

And we weren't getting clear data compared to what we would expect to see the amount of TEA-TEB coming into that tank. And that gave us pause for concern. At that point in the count, there was within an hour but still we had most of that hour to go. We had a very clean board, overall clean count. The teams weren't working other issues of anything significant, and so we were looking at, we said well we can go ahead and work this issue and try to understand it a little bit better

And, so they did that. All of the engineers, in the back room, this was the key operators were looking at that and assessing, okay, are we okay? Are we really are we sure that we're not getting enough TEA-TEB into that catch tank or not. At the end of the day we couldn't be absolutely sure that we had enough TEA-TEB, enough of this ignition fluid, bled up to the interface of the rocket to make sure that we would get that consistent, exactly timed ignition that we need across all nine engines. So we scrubbed the launch because we needed to make sure we have that in place.

Then in the interim, so after we scrubbed launch, we got into the system, and we discovered that there was a filter that was clogged. And just like most fluid systems that you have, in your house or your car, or in rockets, in ground systems, we've got filters. And this particular filter was clogged and that's why we weren't getting enough TEA-TEB into the catch tank.

The SpaceX Dragon docks with the ISS as part of the Crew-5 mission in October 2022. Image: NASA

Mr. Reed also shared details about an abnormal reading from a sensor on the Crew Dragon's hooks. There are twelve hooks on the spaceship, out of which six are used to hold its nose cone and all are used to dock to the space station. These 12 hooks have three sensors each, called limit switches. The sensors generate information to convey the status of the hooks to the teams to let them determine whether they are opening, open, closing or are closed.

According to the SpaceX executive, one of these switches is sending incorrect data, so the system transferred all the hooks to the backup motors. After the shift, all the clamps worked fine. So SpaceX has decided to ignore data from the errant switch and use the primary motors. Mr. Reed confirmed that this poses no risk to the crew for either docking or departing from the space station.

As far as the filter is concerned, it was clogged due to oxidization that resulted from regular maintenance. Air entered the system during maintenance after one of the system's fluids was changed. This led to some material's oxidation, which blocked the filter and the resulting incorrect catch tank readings.