, moisture wouldn't accumulate in the foam and it wouldn't fall off knocking holes in the orbiter.:
Ted
I'd agree with you Ted, but for two points...
IF shuttle was automated and flown unmanned like Buran was 25 YEARS AGO so that no lives would be put at risk for cargo flights, then I could see it continuing as a cargo hauler, especially for the downmass capabilities. Challenger was TOTALLY avoidable and the O-ring problem was well documented on a NUMBER of flights before Challenger's loss; the most severe O-ring failure was on the previous coldest mission ever flown before Challenger, launched at a temperature of 53 degrees IIRC, which was nearly 10 degrees colder than the 'recommended temperatures' in the flight constraints. The launch of Challenger when it was STILL below freezing after a long cold-soak during the night when the booster temperatures were subjected to 20 degree+ weather overnight was reckless and irresponsible.
There was also an issue of a change of the putty used to seal the faces of the booster segments near the joints-- the putty used since the shuttle started flying had asbestos fibers in it, which were outlawed by the EPA and OSHA, and the 'reformulated' putty did not seal as well.
The problems with the foam were also well known before Columbia was lost. Several missions came back with damaged tiles, tiles knocked off, even a hole burned through the aluminum skin of the wing/belly of the shuttle from a foam strike tearing up the tiles. The tiles on the shuttle are amazingly fragile... they're about the same consistency as that freeze-dried "astronaut ice-cream" you can buy at Hobby Lobby and the space center gift shops... it's actually about as soft as styrofoam... I've held a shuttle tile and it's easily dented with your finger, scratched, or crushed. They're SO fragile that if the shuttle launched or landed in a rainstorm, the raindrops would beat the tiles all to pieces like bullets through tissue paper! From what I understand, the problem with the foam is also partially due to a reformulation change in the foam spraying carrier solvent process, which has led to some bonding issues and voids in the foam which can cause problems. I have't read anything about foam problems being caused by trapped moisture due to the foam not being painted. When exposed to the incredibly cold temperatures of the liquid hydrogen inside the tank, the air bubbles inside the foam get colder and colder until the air inside the bubbles actually liquifies, since nitrogen and oxygen liquefy at MUCH higher temperatures than hydrogen! So long as the bubbles are small, it's not much of a problem, because the foam just 'shrinks' a little bit from the volume reduction of the liquified air, which allows the surrounding atmosphere outside the tank to crush the foam down a tiny bit. If the voids are large, however, the volume reduction is substantial, and the liquified air can form a large heavy "drop" inside the foam bubble, and the foam is crushed more by the atmosphere surrounding the tank. At liftoff, the foam begins to heat as the hydrogen is pumped out of the tank, and the atmospheric drag begins to heat the foam up. The foam is also exposed to the shock waves and forces of the slipstream surrounding the tank as it rips through the atmosphere, trying to rip the foam off the tank. The heating can revaporize the liquid air in the foam, which rapidly expands and pushes the foam back out, and if there is a void, it can cause the foam to tear or break away from the tank wall (if there's a bonding issue) and the foam can be ripped away by the force of the slipstream. There has been a substantial effort to mitigate the foam shedding, with incomplete success. Due to the fragile nature of the orbiter's TPS system, this will remain an issue. Even if the foam problem was solved, a bird strike could do at least the same amount of damage if it were in the worst possible spot. Hence, shuttle's safety is compromised and there is very little that can reasonably be done to correct the issue, there is no abort capability until after the SRB's are jettisoned, and the options are limited afterwards. We can and should develop a safer crew vehicle.
Shuttle is also not a particularly great cargo carrier.... it is capable of lifting 25-30 tons to orbit, but the orbiter itself weighs 99 tons, which comes back. An expendable system using the shuttle's parts could be made that would be capable of orbiting about 100 tons. The orbiter is actually the world's heaviest reusable payload fairing when you really look at it. Reusability is a myth, according to Shuttle manager Steve Shannon, as it's been proven that cost-wise, reusability is a wash with expendables. The downmass issue is more a straw-man than anything, because that downmass has never really had much use, especially in the wake of Challenger when the 'satellite recovery, return, and servicing' paradigm went away. IF there were operational orbital industries making computer chips or medications or something, then there WOULD be a call for the downmass, but basically the downmass goes unused most of the time. If NASA were worried about downmass they'd develop a system with that capability. We MAY need it at some point, but not now or in the foreseeable future.
It's a shame that the Orbital Space Plane (OSP) program went away. That was a Dyna-Soar like small reusable space plane mainly for ferrying astronauts to and from orbit, using an expendable EELV booster for liftoff. That would be an excellent 'next step' beyond the shuttle to keep learning about spaceplanes and making developments for a possible future 'shuttle II" at some point in the future, if it were needed and cost-effective. Costwise, the beancounters say it's just as cheap to do expendable capsules as spaceplanes... I guess we'll find out, if we ever get anything actually flying beyond shuttle.
One other point about shuttle-- most of it's systems are state of the art-- for the mid 1970's!!! It's electronics are SO antiquated that most of the flight hardware was being manufactured on dedicated lines whose usefulness for anything else was obsolete and superseded a LONG time ago. Most of the shuttle components at this point are 'one-off's' and with the cancellation of shuttle, sufficient spares and parts were ordered several years ago and the contracts terminated after delivery. When they were talking about a shuttle extension, it was determined that it would be very difficult and expensive to do, because there would be insufficient parts and spares, and since the contracts were terminated a lot of the manufacturing capabilities to produce more have since been scrapped or gone out of business, so it is impossible to obtain more. Developing 'modern' replacements would be EXTREMELY expensive and time consuming, and would require an entire flight certification testing phase for the new part and everything it interacts with, which would be ENORMOUSLY expensive. For good or ill, the decision to scrap the shuttles has been essentially 'irreversible' for a couple years or so already. Not that if say 5 billion magically appeared that it COULDN'T be done, it surely could... it would just be enormously expensive.
We have the capability of developing better cargo rockets than shuttle, that are more reliable, robust, can carry larger payloads, with fewer launch and payload constraints than shuttle has. We already have a couple such rockets in the EELV's, Delta IV and Atlas V. We COULD develop them into a suitable heavy lift vehicle, Atlas V Phase II, but that would cut the in-house NASA people 'out of the loop' on the money, and THAT is what's unacceptable. That, plus ATK wouldn't be selling all those solid rocket boosters, and they have a POWERFUL lobby!
Anyway, shuttle's time is past, for good or ill. Shuttle was intentionally designed to be flown manned (the Russians proved an orbiter COULD be flown unmanned; Buran only flew once, unmanned, and landed safely) mostly to prevent the possibility of manned flight being cancelled back under Nixon when the likes of Walter Mondale and others who wanted to cancel manned flight altogether were making a lot of noise and gaining some traction.
We need to move forward, but making the best use of what we have-- the shuttle ET has gone through the LWT and SLWT (lightweight tank and superlightweight tank) programs and been refined, and would be an excellent tankage for a new core stage. The SRB's, after Challenger, were completely redesigned at the field joints, and have proven to be excellent and very safe boosters in the intervening years and around 100 flights. The SSME is the most powerful and efficient (ISP) hydrogen engine the US has ever fielded, perhaps in the world, and is powerful enough to make a good first stage engine under that new core. They ARE expensive to throw away, but we have 18 of them at the conclusion of the shuttle program, and PWR (Pratt, Whitney, Rocketdyne) has done SOME work and studies that show that an expendable version of SSME COULD be created, and would be no more expensive than an RS-68 Regen, when the amortized costs of the Regen's development program is included in the engine costs. RL-10 has a LONG history of safety and reliability dating back to the beginning of the space age. It's been estimated that at high enough production rates, an RL-10 could cost no more than a helicopter engine! Six RL-10's COULD be used for an EDS/second stage for such a rocket based on the shuttle stack, when coupled with the highly efficient SSME first stage engines.
There ARE easier and more sensible ways than the Ares path NASA management has chosen... OL JR
