In November/December 2013, during the Falcon 9 Flight 7 (SES-8) processing flow, SpaceX managed to get the vehicle onto the pad and attempted to launch a few times without success. Either a scrub was called or the flight computers decided to automatically terminate the countdown prior to liftoff.

During the second launch attempt "a slower-than-expected increase in pressure" (source) was seen on the first stage engines, and an abort was called by the flight computers at T-0.

It's worth noting that this was later found to be due to contamination of the pyrophoric TEA-TEB ignition fluid, with Musk stating:

So there was some oxygen that inadvertently got in the TEA-TEB tank. Could have just been atmospheric oxygen that got in when the tank was refilled, or could have been a bit of oxygen that flowed back in from a previous engine test. That would then react with the TEA-TEB in the tank and reduce its concentration, so that the tank then contained a mix of TEA-TEB and combustion products.

In other words, it was like they expected 180 proof TEA-TEB but only got 100 proof. The fire in the engines was monitored and was less than the launch computer expected, so it shut the engines down rather than proceeding to full thrust.


On the day of launch though, Musk simply stated on Twitter:

We called manual abort. Better to be paranoid and wrong. Bringing rocket down to borescope engines ...

(Twitter Post)

What exactly does "borescoping an engine" involve though? How long would this process take? What would they be able to determine with this test that they couldn't by simply looking at flight computer data?

  • 4
    $\begingroup$ The quote discussing the TEA-TEB was not from Musk. It was from Ben Brockert, a rocketry expert who does not work for SpaceX. What he describes is accurate, but should be attributed correctly. $\endgroup$ – pericynthion Mar 31 '15 at 17:45

I imagine that borescoping allows them to get a look at the inside of the engine's combustion chamber without having to disassemble it. If the problem was physical damage or obstruction to the injectors, for example, this could be visually detected.

In this case, it likely wouldn't have shown the contamination of the ignition fluid; it would rule out some possibilities pretty quickly.

  • $\begingroup$ So if it couldn't determine the problem in this instance, what are some of the "other possibilities" you mention? are injector obstructions/other issues all that common that boroscoping is a common task when dealing with rocket engines? $\endgroup$ – ReactingToAngularVues Mar 30 '15 at 20:13
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    $\begingroup$ I think it's just that borescoping could be done super quickly relative to any other physical inspection because it doesn't require anything to be taken apart, so it's got relatively high troubleshooting value for the effort put in. I'm not a real rocket scientist; I don't know what the likely culprits for this kind of failure would be, but borescoping could rule out any gross defects/damage in the engine bell, throat, combustion chamber, and injectors. Think of a doctor looking down your throat with a tongue depressor prior to recommending exploratory surgery. $\endgroup$ – Russell Borogove Mar 30 '15 at 20:21
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    $\begingroup$ Agreed that it can done relatively quckly, but in most cases you do have to open things up, test ports or whatever, and any time you open up a propulsion system, you're setting yourself up for leak checks, etc. when you are done. $\endgroup$ – Organic Marble Mar 30 '15 at 20:30
  • $\begingroup$ D'oh! I was only really thinking about going up the engine bell into the chamber, yet somehow my answer still basically applies when extended to going through test ports into other sections of the plumbing. Thanks. $\endgroup$ – Russell Borogove Mar 30 '15 at 21:10

Imagine a colonoscopy for a rocket engine. You go in with a flexible light pipe that has a camera on the end. (Engine is nicely sedated, usually).

It looks around, cuts out any polyps it sees, oh I mean obstructions.

So if a valve failed to open/close, they can see that without taking it all apart.


Borescoping is nothing other than optical inspection of the engines and plumbing from inside. The purpose is usually to look for debris and/or damage in the fluid ducts.

I don't think "how long" can be answered because there are too many variables: what is the purpose, does it succeed, what is the configuration, what is the equipment. On STS it was a non-trivial task.

The telemetry might suggest, for example, blockage due to debris, but boroscoping can confirm it.

  • $\begingroup$ Sorry if it seems like I'm moving the goalposts here, but would this have allowed them to definitively have determined the root cause of the problem in this instance (impure TEA-TEB)? What debris would you expect? I really wouldn't anticipate to see anything stuck to the chamber walls. $\endgroup$ – ReactingToAngularVues Mar 30 '15 at 20:11
  • $\begingroup$ Just for those who have never seen a boroscope, you can buy them from here. Not an advert - I just found them by googling! $\endgroup$ – Brian Tompsett - 汤莱恩 Mar 30 '15 at 20:14
  • $\begingroup$ On STS they did routine inspections to see if there was debris in the propellant feedlines. If debris was found, and it met certain criteria, they had to go after it with flexible grabbing tools. Many, many meetings ensued to determine whether those criteria were met. Here's a story when one such inspection got into the press: cbsnews.com/network/news/space/home/spacenews/files/… $\endgroup$ – Organic Marble Mar 30 '15 at 20:19
  • $\begingroup$ Here's another story about when they found metal in the prop lines. spaceflightnow.com/shuttle/sts121/060217ceit I have been looking for pictures but I can't find any in the open literature. $\endgroup$ – Organic Marble Mar 30 '15 at 20:25

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