送交者: steven 于 2006-4-04, 03:28:25:
回答: 倒是SV的动力问题想跟steven讨论一下 由 deadmeat 于 2006-4-04, 02:45:32:
OMS which allows the orbiter to move around, and change orbits. The OMS fuel is hypergolic, not compressed air which cannot provide enough thrust for the orbiter to change orbit. To answer you question, it is easier to think in terms of conservation of energy. Regardless how you do it, for the orbiter, which has both potential energy and kinatic energy, to return to earth, the energy has to be dissipated. Like your down hill car, you can either use break to slow it down, or use engine to slow it down. To slow it down with break, it takes a longer time, and eventaully, you will burn your break.
For shuttle, you want to break the orbiter, you need a thrust, When you have a short but strong burn, your engine experience high heat but short time, and you deaccelerate enough to come in a sharper reentry angle. Or if you has longer but less powerful burn, you take a smooth reentry angle, and you have to keep changing reentry orbits to get back. Now, Your engine experience less intensive heat but for a lot longer time. It is very hard to dissipate that long lasting heat in such a small area, and your engine will have a melt down before you get back down to the low atmosphere layer.
For a sharper angle, the aerobreaking generates high intensive heat, but only for a short time. The heat on the bottom of the orbiter get dissipated through radiation. So in that regard, it is much safter and effective using the current reentry method.