[pdonis]

I don't think so, because both losses were due to bad management decisions under irrational political pressure, not any lack of engineering knowledge that more unmanned testing could have provided.

Challenger was lost because NASA ignored a critical flight risk with the SRB joint O-rings. And by "ignored", I mean "documented that the risk existed, that it could result in loss of vehicle and loss of lives of the crew, and then waived the risk so the Shuttle could keep flying instead of being grounded until the issue was fixed". They didn't need more unmanned testing to find the issue; they needed to stop ignoring it. But that was politically unacceptable since it would have meant grounding the Shuttle until the issue was fixed.

Columbia was lost because NASA ignored the risks of tile damage due to their belief that it couldn't be fixed anyway once the Shuttle was in orbit. But that meant NASA also devoted no effort to eliminating the risk of tile damage by fixing the issue that caused it. Which again would have been politically unacceptable since it would have meant grounding the Shuttle until the issue was fixed.

[panick21]

Wrong. Both were lost because of a fundamentally BAD ARCHITECTURE. And that architecture was bad because the NASA engineers who designed it, had never designed anything like it before and were never able to test or evaluate any of their assumptions.

Columbia would not have been lost if the Shuttle was top stacked, instead of side stacked.

Challenger would not have been lost if not for the use of solid rockets to launch humans.

Both of these design decisions were done to reduce development effort.

[pdonis]

> Wrong.

No, I'm not wrong. We're both right. Yes, the original decisions on the Shuttle design were braindead. But even given that, the decisions to ignore clear red flags from Shuttle missions were also braindead.

[panick21]

Agree. But I think that Shuttle didn't do intermediate tests of these things is part of the reason it never lived up to its potential. During development they lost fact of what they tried to achieve in the first place.

They sacrificed what worked for potential, but tried to take far to big of a step.

I would argue, if you design something that has so many potential pitfalls and so many operational constraints, and so many drivers that make it incredibly expensive and slow, it is understandable why they started overlooking red flags. They would have barley ever lunched at all if they had not overlooked red flags.

[MaulingMonkey]

> 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.

[pdonis]

> 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.

[MaulingMonkey]

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.

[pdonis]

> 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).

[Zardoz84]

I should point out that the Buran launched and took earth, with bad conditions, completely automated. It's sad how it ended.

[zardo]

> 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.

[pdonis]

> 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.

[zardo]

You can push the environmental conditions of the launch e.g. winds and temperatures.

[pdonis]

See my response to Mauling Monkey upthread on why the cold temperature of the Challenger launch actually wasn't the major issue it was made out to be.

Note also my comments there about other SRB designs that were known well before the Shuttle and the range of temperatures they could launch in. Those designs were used on many unmanned flights for years before the Shuttle was even designed. So in this respect, the unmanned test work had already been done. The Shuttle designers just refused to take advantage of all that knowledge for braindead political reasons.