Discovery is ready. Is NASA?
Published on Jun 18, 2006 at 4:49 pm.
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Filed under NASA, space exploration, space shuttle.
Recently, July 1 was set as the target date for Discovery’s next flight, the first shuttle flight in about a year. The orbiter has been mated with its external fuel tank, and the solid rocket boosters are attached. The shuttle sits atop its mobile launch platform, and its been moved into position for final launch preparations. The astronauts are trained and ready to go. Mission Control is ready to go. The payload is ready to go. All that is needed is for the liquid hydrogen and liquid oxygen to be loaded aboard the external tank, and Discovery is go for launch. All systems are go. Bus is NASA ready?
Some NASA engineers and safety officers remain apprehensive about the launch, and a few even recommend postponing launch. The issue is with the foam on the external tank. Foam issues go back to the first few shuttle launches. The external fuel tank holds liquid hydrogen and liquid oxygen. These are crygenic fluids. Under atmospheric pressure, hydrogen boils at -253 C (-423 F) and oxygen boils at -183 C (-297 F). Under pressure, these boiling points are higher, but you can’t put too much pressure into the shuttle’s tanks. Quite a bit of insulation, and other means are used to keep these fluids cold. However, there is some heat leakage. Portions of the external tank get cold. Fact of life. Deal with it. Well, the external tank is coated in a foam insulation to minimize heat flow into the tank and to keep ice from forming on the outside of the tank. Ice will form. It is inevitable. The shuttle launches from the Florida coast. It is humid. So, when you have a very cold surface in high humidity, you get ice. Fact of life. But, you can’t have too much ice on the tank. For one thing, it adds mass that makes lifting off into the proper orbit tougher. Secondly, the ice will tend to fall off. Ice falling off at supersonic speeds and slamming into the orbiter can severely damage it. The external tank is HUGE. So, the foam is applied in a spray on process. The first few shuttle flights had an overcoat of protective paint on top of the foam. NASA engineers decided that the paint was not really necessary, and that the foam is hard enough and durable enough to handle being exposed to the elements for several months — sufficient time for a launch. However, from early in the shuttle program, there has been a problem with ice and foam falling off. Most of these bits of ice and foam fall of harmlessly. Some strike the orbiter. Early in the shuttle program, a study focussed on the possibility of damage from these strikes. This study found that there was a very real possibility that a sufficiently large piece of ice or foam could produce sufficient damage to result in loss of the orbiter. Still, NASA had issues with ice and foam. In the late 1990’s, the way that the foam was applied was changed to be more environmentally friendly. Unfortunately, this seemed to result in more foam issues. Finally, two flights before the ill fated last flight of Columbia, a very large piece of foam fell off after launch and struck a support holding one of the solid rocket boosters. The strut was severely damaged, but it did not give way. Had it done so, and it may have almost done so, then the shuttle would have gone wildly out of control in a catastropic accident that would have most certainly meant loss of the craft and crew. Inexplicably, this incident received a rather low rating in terms of inflight events. All previous large foam shedding events had been classified as inflight anomalies, a category of incident that would put a hold on future flights until they could sort things out. This one was almost swept under the rug. Speculation has been that this was done because NASA was under increasing pressure to finish the International Space Station, which was way over budget and very behind schedule. So, two more flights followed, including the Columbia flight in which a similar large piece of foam feel from the same area. This time the foam struck the leading edge of the orbiter’s wing, damaging the orbiter in a manner that would ultimately lead to the loss of the Columbia upon reentry over Texas at the end of the mission. Again, under pressure to not make waves for later flights, NASA managers were debating what to do about the foam strike. Some engineers were asking for Air Force surveillance satellites to look at the shuttle to see if they could see the damage. The request was even made of the Air Force, but then cancelled when a NASA lead engineer found that the request had been made by one of her subordinates without going through her first (while she was out of the office). This turf battle was only one of the problems that faced Columbia. She also led a committee that was to study the incident. According to the earlier documents from the studies in the early days of the shuttle program, strikes by foam or ice could result in major damage to the orbiter, so this strike should have been classified as, at least, an inflight anomaly, and perhaps even given even more attention. Instead, the committee debated about wording in the original document, finally deciding to remove the word “foam” in the phrase “foam or ice”, and thus since the incident procedure only related to ice strikes instead of foam strikes, the matter was solved. Yeah, right. Typical government reasoning. We all know what happened next.
So, now we are about to launch another shuttle. After extensive tests, redesign of some of the problem foam areas, and more planning on contingency procedures for foam and ice impacts, another mission flew last year — with more foam shedding. As long as we have foam on the external tank, there will be foam shedding. Perhaps again painting the tanks with some protective overcoat would help, but that would add weight (one reason it was left off in the first place). A new type of foam might help, but I doubt it. Tougher foam would, in fact, produce its own problems if it were to fall off and strike the orbiter. We just need to accept that foam will shed unless we have something over it.
In a feel good measure, a tile repair procedure is now available for small repairs in orbit. This is actually a good idea, but such a procedure might not have helped with the sort of damage to Columbia. This is like the feel good sort of crew escape mechanism put in place after the Challenger accident. That, too, would only work under specific circumstances that would likely not occur.
So, does that mean that we should not fly the shuttle until it is 100% safe? Well if that were the plan, it would never fly again. No launch system is 100% safe. All will fail if launched enough times. The Saturn V rockets were among the best in terms of rockets without failures, but only a few were ever launched. In the early days of space flight, though, people understood the risks. After all, with the Mercury missions, astronauts flew into orbit atop Atlas rockets, which blew up about half of the time that they were launched! The Redstone rockets that lifted the first two Mercury missions into space in suborbital jaunts were better, but still not 100% successful. NASA was so convinced that the rockets were dangerous that they installed rockets on a small tower atop the astronaut’s capsule. This escape tower’s rockets were just powerful enough to yank the capsule off of the missile in the event that it went out of control or exploded (That it would yank the capsule off of a perfectly good rocket was tested, but whether this would really work to save the astronaut in an emergency was never really proven.). The Gemini capsules had ejection seats for the astronauts. Apollo again went back to the escape tower safety system. Columbia had ejection seats fitted for the first few shuttle missions. Then, they were removed. Somehow, NASA forgot that spaceflight was dangerous. At the time of the Challenger accident, NASA administrators were claiming a phenominal safety figure of only one failure per 10,000 flights expected. No launch system has ever had that safety factor. Even commercial aircraft can’t realistically expect that sort of record. A more careful study done after Challenger showed a probable loss of vehicle accident with a frequency of about one per 50 to one per 100 flights. That is what we got. Columbia was the second such accident in well over 100 flights. Following Challenger, NASA was criticized for not taking the dangers of spaceflight seriously, for being a slave to schedules and calendars rather than listening to engineers and rocket scientists. Things got better, but they went back the way they were. The same criticisms hold of the NASA culture at the time of the Columbia accident.
So, what about now? Have things changed? According the the newspaper article that I read, the Discovery is being launched on schedule, despite foam concerns, because of scheduling issues with the International Space Station. Yep. Lots of change there. The possibility of damage on launch, though, is not being ignored. If the orbiter is severely damaged, then it can remain docked at the ISS until a rescue mission could be launched. But, I have questions. Can NASA get another shuttle ready for launch to get to the ISS? Would NASA risk another shuttle with the same foam issues at work? What would happen if NASA were to lose another orbiter? Most of the NASA administrators state that such a loss would be the end of the shuttle program. So, is it really smart to have only one vehicle to get to orbit? Yeah, we’ve got the Soyuz, but do we want to rely on just that? Of course not. But, there is little funding for a replacement to the shuttle. I think that we need to sit back and realize that space flight is dangerous. The astronauts know this. They know that they are risking their lives to go into space. Climbing mountains is dangerous, and people die doing so. But, there are still mountain climbers. People die in boating accidents around where I live every holiday weekend. But, no one is proposing closing the lakes to boaters. We should try to make the shuttle the safest that we can. But, there is only so much that can be done given the design of the system and the budget constraints. In fact, budget constraints are why the shuttle is the way that it is in the first place. The shuttle has a 98% success rating. That is spectacular for a launch system. We need to understand that. There is about a 2% chance of losing a shuttle on each mission. That isn’t much, but it isn’t zero. If we fly enough shuttles, we’ll lose another one. That shouldn’t be the end of the US manned space program. Instead, we should grieve, figure out what went wrong, do our best to make sure that it doesn’t happen again, and go forward.
So, Discovery is ready to fly. Is NASA? I’m not so sure.
-Astroprof
