Comment by MaulingMonkey
2 days ago
> They didn't need more unmanned testing to find the issue; they needed to stop ignoring it.
Should such testing have been needed? No.
Was such testing needed, given NASA's political pressures and management? Maybe. Unmanned testing in similar conditions before putting humans on it might've resulted in a nice explosion without loss of life that would've been much harder to ignore than "the hypothesizing of those worrywart engineers," and might've provided the necessary ammunition to resist said political pressures.
> Unmanned testing in similar conditions before putting humans on it might've resulted in a nice explosion without loss of life that would've been much harder to ignore
The loss of the Challenger was the 25th manned orbital mission. So we can expect that it might have taken 25 unmanned missions to cause a similar loss of vehicle. But what would those 25 unmanned missions have been doing? There just wasn't 25 unmanned missions' worth of things to find out. That's also far more unmanned missions than were flown on any previous NASA space program before manned flights began.
Even leaving the above aside, if it would have been politically possible to even fly that many unmanned missions, it would have been politically possible to ground the Shuttle even after manned missions started based on the obvious signs of problems with the SRB joint O-rings. There were, IIRC, at least a dozen previous manned flights which showed issues. There were also good critiques of the design available at the time--which, in the kind of political environment you're imagining, would have been listened to. That design might not even have made it into the final Shuttle when it was flown.
In short, I don't see your alternative scenario as plausible, because the very things that would have been required to make it possible would also have made it unnecessary.
Record low launch temperatures are exactly the kind of boundary pushing conditions that would warrant unmanned testing in a way that not all of those previous 25 would have been. Then again, so was the first launch, and that was manned.
> I don't see your alternative scenario as plausible
Valid.
> Record low launch temperatures
Were not necessary to show problems with the SRB joint O-rings. There had been previous problems noted on flights at temperatures up to 75 degrees F. And the Thiokol engineers had test stand data showing that the O-rings were not fully sealing the joint even at 100 degrees F. Any rational assessment of the data would have concluded that the joint was unacceptably risky at any temperature.
It might have been true that a flight at 29 degrees F (the estimated O-ring temperature at the Challenger launch) was a little more unacceptably risky than a flight at a higher temperature. But that was actually a relatively minor point. The reason the Thiokol engineers focused on the low temperature the night before the Challenger launch was not because they had a solid case, or even a reasonable suspicion, that launching at that cold a temperature was too risky as compared with launching at higher temperatures. It was because NASA had already ignored much better arguments that they had advanced previously, and they were trying to find something, anything, to get NASA to stop at least some launches, given that they knew NASA was not going to stop all launches for political reasons.
And just to round off this issue, other SRB joint designs have been well known since, I believe, the 1960s, that do not have the issue the Shuttle SRBs had, and can be launched just fine at temperatures much colder than 29 F (for example, a launch from Siberia in the winter). So it's not even the case that SRB launches at such cold temperatures were unknown or not well understood prior to the Challenger launch. The Shuttle design simply was braindead in this respect (for political reasons).
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> So we can expect that it might have taken 25 unmanned missions to cause a similar loss of vehicle.
That doesn't follow. If those were unmanned test flights pushing the vehicle limits you can't just assume they would have gone as they actually did.
> If those were unmanned test flights pushing the vehicle limits
As far as the launch to orbit, which was the flight phase when Challenger was lost, every Shuttle flight pushed the vehicle to its limits. That was unavoidable. There was no way to do a launch that was any more stressful than the actual launches were.
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