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Atmospheric re-entry from orbit seems such a violent affair with tons of speed and energy having to be shed, which necessitates heat shields and what not.
I do understand that the velocity of the craft has to slow down to de-orbit but does it have to be done in such a rapid fashion?
Is it possible for a slower deorbit that doesn't require a heat shield? What would this take? Larger wings on the orbital craft? Big engines? Large parachutes?orbit
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If you are not going to use atmospheric re-entry the only other option is to use engines to slow down, and that would be incredibly expensive.
Imagine if you wanted to land on a body with 1G but no atmosphere, from LEO. Only a rocket will get you down safely in this case. In order to land from LEO you would need a rocket as big as the one that put you up there in the first place. To put a rocket that size up there would require a significant number of launches. It would be fabulously expensive to do it that way when the atmosphere lets us do it practically for free.
Anyway, it's not actually a problem in the first place - atmospheric re-entry is not particularly violent compared to launch, both are between 3-5G for most human rated systems. It's not a problem that needs solving.
When de-orbiting, all the horizontal velocity needs to be transferred into another form of energy. In a normal reentry it is converted to heat. If a much larger aerodynamic surface is used, the heat is dispersed over a larger area. There have been suggestions to use balloons (called a Ballute) to increase surface area for reentry. In a very shallow angle or skip reentry, the heat is dispersed over longer time. A space plane can do this. Retro rocket landings on earth could avoid reentry heat, but it would probably require atomic rockets to have enough energy.
Larger parachutes would not help. At the speed from the orbit, large (and also small!) parachutes would be destroyed at the upper edge of the atmosphere. Parachutes may be used only if the craft is slowed down by the heat shield to subsonic speed, about 0.2 km/s. But the speed in the orbit is much higher, about 7.8 km/s, therefore more than 97 % of the initial speed must be decelerated without parachutes.
