Saturday, July 30, 2005

Foam

Most who follow the news know all about the reason that the Space Shuttle Columbia burned up upon re-entry. The reasons behind it are a sad tale of environmental regulations gone bad.

Columbia was doomed about 30 seconds after it took off several years ago. Chunks of foam from the external fuel tank broke or fell off, hit the wing of the orbiter and sealed the fate of our astronauts. The phenomenon of pieces of foam breaking off and hitting the orbiter is nothing new. After every takeoff there were always issues with tiny pieces of foam and other things breaking off and dinging the orbiter. Sometimes the tiles fell off themselves. The stress of takeoff is immense and those things are natural. Remember that something moving at Mach 1 can cause a whole bunch of bad things to happen to whatever it hits.

The extent of the damage starting in mission STS-87 in 1997 (the missions for the Space Shuttle are numbered, and STS stands for space transportation system - the official name for the Space Shuttle) was like nothing that had ever been seen up to that time.

But why now? Why after STS-87? Why after so many takeoffs and landings did the Space Shuttle all of a sudden have so many problems with the damn foam?

You can thank the government of the USA.

In 1987 many industrialized nations including the USA signed the Montreal Protocol. It was amended many times after that. What it says in simple English is that the nations who signed the document will agree to ramp down production of chlorofluorocarbons (CFC's), eventually to zero by Jan. 1, 1996. The science supposedly was that the CFC's, after being released into the atmosphere, damage the ozone layer and would let in more UV radiation, contributing to increased intstances of skin cancer, global warming and melting of the polar ice caps. I don't want to get into a discussion about whether the CFC's actually damage the ozone. The signing countries abided by it and that was that.

Instantly life changed for many people in many industries, including the one that I work in, heating and air conditioning. There are many different CFC's and they were used in manufacturing processes for everything from nylon to refrigerators and air conditioners to socks to de-icing planes sitting on tarmacks in winter. Oh yeah, one more thing a certain CFC was used to make. The CFC called R-11 was used to make foam. Space Shuttle external fuel tank foam.

The R-11 was one of five ingredients of the foam. It was actually not one of the ingredients of the foam itself, rather it was used as a blowing agent. What this does is create millions of bubbles so the foam solution can be "blown" (a better word may be sprayed or applied) in a smooth fashion. The foam is only one inch thick on the Space Shuttle's external fuel tanks so this solution must be applied smoothly. The R-11 facilitated this.

In 1997, NASA decided to become more environmantally friendly. They decided to move from a banned CFC blowing agent to an approved HCFC (hydrochlorofluorocarbon) blowing agent called R-141b. They could have continued using R-11, as any government agency can get a pass on environmental regulations if they really want it. But they didn't. They decided to do the environmentally correct thing and abide by the Montreal Protocol. The rest, as they say, is history. The new foam was more brittle and more broke off of the external fuel tanks than ever before. It was only a matter of time before an accident like Columbia was going to happen.

4 comments:

Anonymous said...

Hello Dan, Its John, As for this foam issue. I believe that they have made a fundemental mistake in the basic design. The foam is needed to insulate the tank while it is on the ground not in flight. Why design the foam to stay on for the liftoff? They end up making so many design concessions to that aspect that must certainly affect its performance in its primary function. Why don't they just make a caccoon that either seperates and is removed just prior to launch or at least falls completely free when the shuttle launches. I'd bet that you could make a pretty cheap system that would require none of the durability requirement from the aerodynamic forces of 13,000 mph winds...

What do you think?

Dan from Madison said...

John,
I don't think there was a fundamental design flaw, rather a big flaw when they redesigned the foam with R-141b. The bitch of it all for me is that they KNEW that the new foam broke off a lot more after STS-87. Right then and there they should have known that one thing and only one thing had changed in the design of the foam - the subsitution of the R-11.

The tanks have to be insulated for flight. After liftoff the external fuel tank is still feeding the boosters and must keep that liquid Hydrogen and Oxygen, shall we say, cool (-423 F and -297 F respectively). So no choice there, it has to come along. Otherwise your theory about leaving it behind would be great.

Bottom line of all this is that I think NASA can and should do better. I can't think of too many industries except space exploration and air travel that use 30 year old technology on a daily basis.

Anonymous said...

Oh Contraire...
The liquid O2 and the liquid H need to be heated before it can burn. I believe that if the temps are stabilized at liftoff, then any heating from the aerodynamic friction can be figured into the equation. What happened here is a vendor sold a bill of goods regarding the insulation and then the design got frozen and then the design guys started inventing potential benefits from the existing solution. One, the liquid fuel tanks have to be insulated while the shuttle is waiting indefinitely for flight after fueling. This requirement should have been satisfied with a terrestrial based system not intended for flight. The aerodynamic heating issues should have been worked into the liquid heating portion of the thermodynamic equation of heating the liquid fuels up to combustion temps. As for the insulation from the heat of the main shuttle engines, well, that consideration is aft of any risk of parts hitting the shuttle. Once again, I believe that this is a case of designs being locked in based on poor engineering. Sort of how the social programs get refunded year after year but that is a different post...
I agree whole heartedly that the freon issue should have not applied to the shuttle. If indeed the old freon worked for the aforementioned application, only a bunch of tree hugger engineers would have put our astronauts safety second and excluded the limited use of a process being phased out over time anyway. Plus, I am quite sure that China and every other viable 21th century competitor would still use the freon if they wanted...

John

Dan from Madison said...

Well, we just have to agree to disagree on some of the points. The boiling point of Hydrogen is negative 423.17 degrees F. The boiling point of Oxygen is negative 297.3 degrees F. So, if we are, in fact going to use a design such as the Space Shuttle that uses liquid fuels the tank must be insulated. The outer boosters of course use solid fuels. The way that the large liquid tank was insulated is obviously the issue here. I personally think it would be impossible to figure the heat from aerodynamic friction into the actual heating equation for the H and the O - every day and in fact every minute the atmosphere changes ever so slightly with the humidity levels, temps, etc. I think the point that we are both trying to make in this comments section is valid - that the Space Shuttle is old and has served it's time.