This device helps vent gas that boils off from the liquidoxygentank, and also bathes the top of the tank in warmed nitrogen to prevent ice from forming.
这个装置有助于排除液氧燃料箱蒸发的气体，并且它还可以用加温氮气笼罩箱顶，以防结冰。
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The insulating foam prevents ice from forming on the tank when it is filled with 500,000 gallons (1.9 million liters) of supercold liquid hydrogen and liquid oxygen before liftoff.
Cameras and an inspection team spotted the bat clinging to the side of Discovery?s 15-story external tank as it was being fueled with propellant ? super-cold liquid hydrogen and liquid oxygen.