A shuttle fix I haven't heard proposed...

[Donnie B.]

It now seems pretty likely that the loss of Columbia was due to damage caused by foam insulation falling off the external tank. One thing no one seems to have pointed out is that there have been previous generations of launch vehicles that were immune to this failure mode.

The Saturn V, for example, had cryogenic hydrogen fuel in its second and third stages, but never did a piece of foam fall off. Why? Because the foam was installed inside the fuel tanks rather than outside.

Now I grant you, installing that insulation was an expensive and tricky, labor-intensive process. Large fixtures were built to position and rotate the tanks as workers attached form-fitted blocks of foam by hand, working from the inside. However, it seems to me that the technology of insulating foam has advanced in the last 40 years, as have robotic assembly techniques.

So why is it not possible to manufacture the shuttle's external tank with internal insulation, possibly using sprayed-on, expanding foam? Even if we had to resort to the old installation method, would the extra cost not be justified by the saving of even one orbiter?

[newt]

Apparently, the foam came off the "bipod" support strut(s) attached between the forward lower area of the Shuttle and the tank, where it insulates the strut(s) from the cold temperature of the fuel and prevents ice from forming that could fall off and damage the Shuttle.
Can't remember off the top of my head where, but I read recently that they are considering changing to the use of strut heaters, different metal resistant to the cold temps, or some other configuration.
I think the external application to the tank is partially to resist damage on landing impact in the ocean. Cheers. Newt.

[WHarris]

I think the external application to the tank is partially to resist damage on landing impact in the ocean. Cheers. Newt.

Actually, the main reason is to prevent ice from forming on the external tank. Falling ice can do a lot more damage to the tiles and RCC panels than the foam.

[kucharek]

Another possibility is - as it is done on some launchers - to make the isolation more easily to come off. In most parts it is just needed until launch. I guess the problem would be the sheer amount of stuff coming down on launch.

[Doodler]

Some of the old launch video of the Saturn V showed ice clumps pouring off the sides of the midsection during liftoff. Being a single piece launch vehicle, I am quite certain an ice shower was a pretty insignificant problem, where with a multi-piece operation like the shuttle this would be a huge problem.

[Donnie B.]

Hmmm... I know we discussed this (or something similar) shortly after the Columbia disaster, but...

How about a "boost protective cover", similar to that used on the Apollo CM during launch? Obviously this would entail a large weight penalty for a spacecraft as large as the orbiter, but would it be prohibitive?

[TinFoilHat]

How about a "boost protective cover", similar to that used on the Apollo CM during launch? Obviously this would entail a large weight penalty for a spacecraft as large as the orbiter, but would it be prohibitive?
There's a huge surface to protect. I suspect that it would weigh far too much to be practical, as well as introducing a new potential LOCV situation: failure of the protective cover to cleanly seperate from the orbiter.

I heard that at one point NASA considered building an air-conditioned enclosure around the entire launch pad, to reduce ice buildup.

The real problem is having a huge, fragile reentry shield mounted right up against a large cryogenic tank at launch. There's no way to get away from that without redesigning the entire system, unfortunatly.

[aporetic_r]

Is it possible to change the attitude of the shuttle during its ascent, so that the orbiter is beneath the external tank for a shorter period of time? Obviously there are several variables involved in making this calculation, so I won't even attempt it. But the less time the orbiter is beneath the ET during its ascent, the less we have to worry about anything falling off of the ET or its connection points and onto the orbiter.

Aporetic
www.polisci.wisc.edu/~rdparrish

[Edited for spelling.]

[SAMU]

[quote="TinFoilHat
I heard that at one point NASA considered building an air-conditioned enclosure around the entire launch pad, to reduce ice buildup.

[/quote]

I like the idea of the airconditioned structure around the pad. Actually all you really need is a dehumidified enclosure. It would eliminate the need for insulation at all. How much does all that insulation weigh any how? Couple or tens of tons anyhow, right? And all that saved weight goes straight to more payload. What's a ton of payload cost to launch by the Shuttle? Couple or tens of millions of dollars. Heck, you could rebuild the whole dehumidifying enclosure after every launch at that rate.

[TinFoilHat]

I like the idea of the airconditioned structure around the pad. Actually all you really need is a dehumidified enclosure. It would eliminate the need for insulation at all.
Not quite. You still need some insulation even if ice isn't a worry. With no insulation the surface of the fuel tank would get cold enough to liquefy nitrogen, and heat leaking into the tank during liftoff would cause too much fuel to boil off during ascent. Other conventional cryogenic-fueled boosters have insulation on the inside of the tank walls, despite not needing to prevent ice buildup.

[Kaptain K]

Is it possible to change the attitude of the shuttle during its ascent, so that the orbiter is beneath the external tank for a shorter period of time? Obviously there are several variables involved in making this calculation, so I won't even attempt it. But the less time the orbiter is beneath the ET during its ascent, the less we have to worry about anything falling off of the ET or its connection points and onto the orbiter.

Aporetic
www.polisci.wisc.edu/~rdparrish

[Edited for spelling.]
Attitude is essentially irrelevant. The aerodynamic forces of a multi-hundred kph airstream dwarfs any gravitational forces! 8)

[aporetic_r]

Attitude is essentially irrelevant. The aerodynamic forces of a multi-hundred kph airstream dwarfs any gravitational forces!

What you say makes sense, but I find it difficult to believe that object X stripped from place A has virtually the same chances of hitting place B regardless of the relative positions of A and B, no matter what the speed and/or mass of the craft. While I don't know the exact angle of ascent of the Columbia at the time when the foam struck, it appears to be only a few degrees from vertical, but if the craft had been tilted the same number of degrees in the opposite direction (if, in fact, this is possible during the first few minutes of a shuttle ascent, which I doubt) it seems that the likelihood of such a catastophic strike would have been reduced.

Aporetic
www.polisci.wisc.edu/~rdparrish

[Avatar28]

Attitude is essentially irrelevant. The aerodynamic forces of a multi-hundred kph airstream dwarfs any gravitational forces!

What you say makes sense, but I find it difficult to believe that object X stripped from place A has virtually the same chances of hitting place B regardless of the relative positions of A and B, no matter what the speed and/or mass of the craft. While I don't know the exact angle of ascent of the Columbia at the time when the foam struck, it appears to be only a few degrees from vertical, but if the craft had been tilted the same number of degrees in the opposite direction (if, in fact, this is possible during the first few minutes of a shuttle ascent, which I doubt) it seems that the likelihood of such a catastophic strike would have been reduced.

Aporetic
www.polisci.wisc.edu/~rdparrish

Not really. At those speeds the foam would only be able to drop a few cm at most before impacting the orbiter.

[DALeffler]

Seems to me they need to fix the foam itself: it's not supposed to fall off, yet it has seperated from the ET on all (or almost all) STS launches.

As for not fixing the foam, how about fitting the RCC panels with full area supports underneath them? That's supposably why tiles don't suffer more damage: the wing surface underneath the tiles supports the entire area where the tile is bonded to the wing. The RCC panels are bolted onto the wing leading edge at the corners of the panels with no support underneath them.

Doug.

[TinFoilHat]

As for not fixing the foam, how about fitting the RCC panels with full area supports underneath them? That's supposably why tiles don't suffer more damage: the wing surface underneath the tiles supports the entire area where the tile is bonded to the wing. The RCC panels are bolted onto the wing leading edge at the corners of the panels with no support underneath them.
I'm not sure this would be mechanically possible. The RCC panels get really, really hot during reentry, especially in the unsupported center section. Unlike the tiles, RCC conducts heat well, so you can't rely on it alone to block the heat. The air gap behind the panel, mounting the panel only at the corners with insulated Inconel brackets, and the insulation layers on the front of the leading edge spar all help to keep this heat from leaking through to the wing structure. The tiles are bonded across their full back area with a flexible pad, but unlike the RCC panels the tiles conduct heat very, very poorly, so the support pad never reaches dangerous temperatures.

[Argos]

Is it possible to change the attitude of the shuttle during its ascent, so that the orbiter is beneath the external tank for a shorter period of time

I think that trying to change the attitude would involve an aerodynamic compensation for the characteristic roll the craft does until it balances itself. I believe you could do it with the orbiter´s elevons, in which case you´d be draining energy off the boosters, by adding drag.