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Is there an advantage to orbital flight? Why couldn't an orbiting craft stop orbiting before reentry and return to the atmosphere like SS1?
In order to stop orbiting, they have to slow down from very high speed, and that requires getting rid of a huge amount of kinetic energy. In the case of the shuttle, capsules, etc, that energy is just turned into heat by the atmospheric drag. If you want to avoid that heating, you need to slow down in a different way. The only other choice is to use an engine burn, and that is hugely expensive because it means that you have to lift a lot of extra fuel into orbit along with your payload. In fact, it takes as much fuel to slow down as it takes to get into orbit in the first place (unless you get rid of some mass by tossing out a satellite). But carrying that extra "deorbit" fuel means that your original load on the launch pad has to be much much bigger too. It is better to just let the atmosphere slow you down.
Yeah, thermodynamically irreversible processes like friction and shockwaves turn kinetic energy into thermal energy, and in this case the atmosphere is heated to a plasma by the vehicle's motion relative to the atmosphere. (Mainly at the leading edges where the shock waves are, I think) So, you can attribute it to friction if you like. But the interaction between the vehicle and the gas/plasma is the heating mechanism. Once the atmosphere is heated at the leading edge, it flows back past the rest of the vehicle. I believe there is a thin layer of relatively cool gas in between the tiles and the hottest plasma. (It has been cooled by giving up some of its heat to the cooler surface of the vehicle. When there is a disruption of the flow (like when tiles are damaged on a shuttle) the resulting increase in turbulence can increase the transport of heat through this cooler layer and cause problems.
If you could slow down higher up, then, yes, that would be good, but it is hard to do without causing heating because you have to push on the atmosphere somehow in order to do it. You could use an engine burn, of course, but that is very expensive and that means that you had to take extra fuel into orbit with you, which means that you could have had a bigger useful payload instead.
I read somebody's explanation of why a winged reentry is inferior to a capsule and heat shield, and I bought his arguement, but I cannot remember it I'm afraid.
Any aerospace engineers in the know want to comment?
Well, I am not an expert in reentry, but I'll take a crack at your question. I think the important thing is not maximum heating, but rather some integral of heating over time. If the shuttle or other vehicle entered more gradually, it may be that it would actually reach a higher temperature because it would have more time to soak up the heat from the plasma around it. No matter how well you insulate something, eventually it has to reach practically the same temperature as its surroundings. You hope to get on the ground long before that happens.
Wings are heavy and delicate, and it would be hard to imagine that they could be large enough to significantly lift the craft at high altitude and lower speed and still survive the heating. (The heavier the wings are, the more kinetic energy you need to dissipate to slow down--and the more heating you get.) IMHO wings are a dumb thing to carry into space with you. Lifting bodies are better.
What happens if the number you generate using your alogorithm happens to be the CC number of an actual Visa customer? Don't you cause them some undeserved headaches?
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You may choose between advertising for Sony and counting on my bajillion-per-day lurker page views to make money yourselves. Another "story" like this and I'm history.
Is there an advantage to orbital flight? Why couldn't an orbiting craft stop orbiting before reentry and return to the atmosphere like SS1? In order to stop orbiting, they have to slow down from very high speed, and that requires getting rid of a huge amount of kinetic energy. In the case of the shuttle, capsules, etc, that energy is just turned into heat by the atmospheric drag. If you want to avoid that heating, you need to slow down in a different way. The only other choice is to use an engine burn, and that is hugely expensive because it means that you have to lift a lot of extra fuel into orbit along with your payload. In fact, it takes as much fuel to slow down as it takes to get into orbit in the first place (unless you get rid of some mass by tossing out a satellite). But carrying that extra "deorbit" fuel means that your original load on the launch pad has to be much much bigger too. It is better to just let the atmosphere slow you down.
Yeah, thermodynamically irreversible processes like friction and shockwaves turn kinetic energy into thermal energy, and in this case the atmosphere is heated to a plasma by the vehicle's motion relative to the atmosphere. (Mainly at the leading edges where the shock waves are, I think) So, you can attribute it to friction if you like. But the interaction between the vehicle and the gas/plasma is the heating mechanism. Once the atmosphere is heated at the leading edge, it flows back past the rest of the vehicle. I believe there is a thin layer of relatively cool gas in between the tiles and the hottest plasma. (It has been cooled by giving up some of its heat to the cooler surface of the vehicle. When there is a disruption of the flow (like when tiles are damaged on a shuttle) the resulting increase in turbulence can increase the transport of heat through this cooler layer and cause problems. If you could slow down higher up, then, yes, that would be good, but it is hard to do without causing heating because you have to push on the atmosphere somehow in order to do it. You could use an engine burn, of course, but that is very expensive and that means that you had to take extra fuel into orbit with you, which means that you could have had a bigger useful payload instead. I read somebody's explanation of why a winged reentry is inferior to a capsule and heat shield, and I bought his arguement, but I cannot remember it I'm afraid.
Any aerospace engineers in the know want to comment?
Well, I am not an expert in reentry, but I'll take a crack at your question. I think the important thing is not maximum heating, but rather some integral of heating over time. If the shuttle or other vehicle entered more gradually, it may be that it would actually reach a higher temperature because it would have more time to soak up the heat from the plasma around it. No matter how well you insulate something, eventually it has to reach practically the same temperature as its surroundings. You hope to get on the ground long before that happens.
Wings are heavy and delicate, and it would be hard to imagine that they could be large enough to significantly lift the craft at high altitude and lower speed and still survive the heating. (The heavier the wings are, the more kinetic energy you need to dissipate to slow down--and the more heating you get.) IMHO wings are a dumb thing to carry into space with you. Lifting bodies are better.
What happens if the number you generate using your alogorithm happens to be the CC number of an actual Visa customer? Don't you cause them some undeserved headaches?