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The reason there's ice buildup on the Shuttle tanks is because it takes a long time to fill them with Liquid H2 and Liquid O2, both at cryogenic temperatures. Water vapor from the air freezes on the insulated but still very cold surface of the tank.
| The ice breaks off when the shuttle is doing perhaps 500 or 1000 mph, and it's like a rock when it hits the delicate surface of the Tiles. These are designed without much tensile strength; all the effort is in being a thermal shield. Getting hit by a brick (equivalent to ice falling at 1000 mph) is not in the plan. So why not stop the ice buildup in the first place? NASA has spent hundreds of millions (literally) redesigning the tanks, when they might have thought of controlling the atmosphere around the shuttle while it's being filled in the first place. A lot of the ice buildup is just water-ice, and can be lessened by a controlled humidity environment. Sure, there are issues with this approach, but it's got to be easier to deal with than just allowing the ice to slough off and hoping for the best! Temperature- and humidity- control of the gantry area might cost perhaps $10M, to build a low-humidity enclosure, or blanket the ship with hydroscopic chemicals that lower ambient humidity. The original disaster was due to arrogance about the O-Rings response to temperature (they don't seal when the material is too cold); the second disaster was due to arrogance about the heat shield tiles. And don't ask why the O-Rings were needed in the first place, it was a political decision to spread the work around to get political support. The tiles are catalogued after each mission in a database; you can't imagine how serious the issue is, sometimes one burns a third of the way through, it's a big thing. Engineers know the heat distribution on reentry; what they cannot do is effect tile replacement in space, it's a complicated, intricate process requiring curing the epoxy-like glue in a controlled atmosphere. Ice. Why allow it in the first place? No one thought of that, among these bozo bureaucrats? Nasa inspects ice buildup, does not prevent it |
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