[runciblespoon]

"the solid rocket boosters ignited and somewhere in the right booster, a 0.280-inch-wide O-ring failed due to the cold."

The 'solid rocket boosters' being constructed in segments because they had to be transported by rail from Utah. They had to be constructed in that state as part of the deal to get the politicians to vote in the finances.

[Rebelgecko]

I think that's an oversimplification of a complicated issue. It's certainly possible that the NASA administrator chose to go with Morton Thiokol to keep congressmen from Utah happy, but as far as I know there's no proof that there was any "deal", and there's plenty of technical reasons to go with a segmented design (although there's tradeoffs).

One of the bidders on the contract actually wanted to make a monolithic SRB, but that brings a new set of problems and limitations, especially at large sizes (you can look up the Aerojet 260" for some more info).

The shuttle SRBs were built in 7 segments, some of which were joined together at the factory. The multisegment design was based on the flight-proven Titan SRBs, which supposedly would help with R&D costs. However manufacturing constraints (if the SRB just used the Titan design and scaled it up, they'd need bigger hunks of metal than anyone was casting at the time) and design tweaks led to changes that degraded O-Ring performance and potentially kept both primary and secondary O-rings from being properly seated. There was really a whole confluence of things that went wrong, and a lot of missed opportunities to fix any one of the issues that led to O-ring failure.

Plenty of people still use segmented SRBs today, especially for their modularity. The (first version) of the SLS boosters are based on the shuttle design, with extra segments stuck added on.

[jedberg]

I see what you're getting at, but the separate construction and transport was not the issue here. The O ring was a necessary pressure valve, but it failed because the cold made it brittle.

The bigger issue here was the politics between Nasa and it's contractors. The contractors told them that the launch would be dangerous at the temperature, but they were ignored.

[robryk]

> The O ring was a necessary pressure valve (...)

Do I understand correctly that you're saying that the O-ring would be necessary even if the SRBs were constructed as a single long tube, instead of segments that are assembled together?

If so, would you mind expanding on that? I was under the impression that the only reason the whole O-ring and caulking of the joints was necessary was the existence of the joints.

[jedberg]

I'm not a rocket scientist so I might be wrong, but I'm pretty sure the O ring would be required no matter how it was constructed.

[0xffff2]

Why do you think that? As the person you replied to said, the only reason the O-ring is there at all is to seal the joint between the sections. If the join't didn't exist, there would be no reason at all for there to be a rubber ring embedded in the structure.

[jedberg]

Because that spot on the SRB is a flex joint to allow some movement of the nozzle as the engine fires. The joint isn't there because of transportation or other reasons.

[askvictor]

I'm no rocket scientist either, but happened to be reading in depth about SRBs in general and Challenger in particular, and my understanding is: the joint in question was a field joint, to be assembled in the field, as opposed to factory joints which were assembled in the factory. The construction of these joints were different (asbestos insulation vs O-rings). The differing design is due to transportation and logistics.

[robryk]

That spot was the "aft field joint" according to wikipedia. According to the diagram linked[1] that is distinct from the case-to-nozzle joint.

[1] https://science.ksc.nasa.gov/shuttle/technology/sts-newsref/...

[oh_sigh]

And if the politicians didn't vote to build the SRBs in Utah, then maybe there would be no SRB at all, which is a good method to prevent deaths from SRBs.

[0xffff2]

Okay... how is that relevant to my comment at all?

[gmiller123456]

>The O ring was a necessary pressure valve

Do you have a reference for this? Seems very intriguing to me. To me it seems the last thing you would want, under any circumstances would be to have hot gases coming out anywhere near the hydrogen tank and you'd make every effort to contain any overpressure until it exited beyond the hydrogen tank.

[Pica_soO]

At such projects, everybody is constantly mumbling about what all could go wrong, its just legally relevant background noise- not actually "sticking" out warnings pointing at a particular point of failure.

[kop316]

I'm sorry, You completely mischaracterize what happened that morning. The contractor responsible for the solid rocket booster flat out said "do not fly this love morning". NASA actually went to his supervisor and for his supervisor to sign off on the flight (the particular contractor who refused to sign off said " that was the single smartest decision of his life").

The following is a link to his book, but I actually heard a presentation from him.

https://www.amazon.com/Truth-Lies-Rings-Challenger-Disaster/...

[colechristensen]

You seem to be implying that a root cause of the accident was the political spreading around of construction.

Rockets are incredibly complex machines, you could use this sort of post hoc reasoning to find cause and blame for any anomaly by saying such a part could have been done differently. You couldn't ever use this reasoning to make design decisions that prevented accidents.

[jcranendonk]

What it really comes down to is that the Challenger exploded due to man's folly in exploring outer space. /s

[cortesoft]

I mean, was the alternative to construct them on site? Is that what would have happened if not for the political pressure? It seems likely that they would have been manufactured SOMEWHERE requiring transport, no matter what.

[erik_seaberg]

Could have used a ship; that's how they delivered the larger Saturn V stages from New Orleans and Seal Beach to Cape Kennedy.

[Rebelgecko]

Would not be practical for a Vandenberg launch (which was a shuttle requirement that was never taken advantage of)

[0xffff2]

To clarify, there are many places where the boosters could have been manufactured and transported by ship. The shuttle SRB's where manufactured in Utah, where transportation by ship is impractical.

[Symmetry]

For example, SpaceX builds all their rockets in LA and transports them by truck to the launch site. With their next, bigger, rocket they'll send them by ship.

Blue Origin is planning to build their big rockets in Florida near the launch site.

[madrox]

The post hoc ergo propter hoc going on in this comment and its responses are wild.

The O-ring failed because it was a bad O-ring, and no one in positions that matters appreciated it was a bad O-ring. Politicizing it into a witch hunt to make congress look bad doesn't do anyone favors. It just feeds existing rage.

[CamperBob2]

Didn't the O-ring fail because it was used outside its specifications? My recollection is a bit hazy but it seems that it was more of a political problem than an engineering problem.

[Rebelgecko]

To slightly oversimplify, it wasn't beyond spec, the spec for the part just wasn't really defined. The conversation the night before launch went something like this:

Contractor: "We don't want to launch, we're worried about how the cold will affect the O-ring"

NASA: "Do you have any data showing that the O-rings will fail at 50°F?"

Contractor: "No, but we don't have any data showing that they won't fail at 50°F"

NASA: "We launched when it was cold before and nothing went wrong" (The coldest launch before Challenger was successful, although both of the SRBs had badly charred O-rings)

Contractor: "Once, and there is circumstantial evidence that the O-rings had issues on that launch. (managers kicks engineers out of the room). We're not telling you not to launch."

That said, the hardness of the O-rings wasn't the only issue (at least, by itself it may not have caused the Challenger to explode). There was some putty around the O-rings that had problems. It was known to let water in, and the night before the launch it rained and was cold enough that the water that got in next to the O-rings could've frozen and kept them from maintaining their seal. There were primary and secondary O-rings, but the secondary O-rings didn't really give good redundancy.

[b1c837696ba28b]

There is a book, "Challenger: A Major Malfunction: A True Story of Politics, Greed, and the Wrong Stuff". There is also Feynman's report. Recommended reading!

[greglindahl]

Segmented SRBs are used on Ariane 5 and Northrop Grumman's upcoming Omega rocket, while Vega, Vega-C, and Ariane 6 will use a single-segment SRB. It's a choice that was dictated by politics for the Shuttle, but it's also a choice that can be made for other reasons, like a smaller composite segment using a cheaper tool (Omega and the Boeing 787 fuselage tube).

[TeMPOraL]

In general, "need to be segmented for transport" is not necessarily a political thing. Russians have the Proton rocket which looks as if it had boosters bolted to it, where in fact those are parts of the first stage. I heard recently that the reason for this design is precisely because if those side parts were internal, the rocket wouldn't fit on a railcar.