"Fly down" type reentry possible?

[squeaky024]

Hello all!

I'm wondering if it is possible for a spaceplane to do a different type of reentry and just "fly down" instead of violently burning through the atmosphere. Flying down meaning you slowly reduce your speed, possibly over several orbits, and eventually glide down to a landing. I am asking this if its possible in a real life (or just KSP/orbiter/other simulators) and I am wondering if it would be possible to do this with the goal avoiding the usual heating (and thus less heatshielding needed if at all) during a standard ballistic or space shuttle type reentry profile.

[magnemoe]

Atmosphere is to thin up in the high attitude where the burning going on for this to be possible. Try it in KSP and you see the problem.

Note that an light probe with an inflatable heat shield can get an gentle reentry because of the huge surface to mass area.

[Pyotor Gagarin]

I believe this was a thing back in the Werner Von Braun days. The idea then was to have large wings to give the spacecraft a very low ballistic coefficient just like you're talking about. I think the consensus was that the mass cost of the extra wing area was more than you would save on thermal protection. There's still going to be a LOT of energy to dissipate, so "slow-baking" your ship may not be preferable to a quick reentry burn.

Edited April 30, 2013 by Pyotor Gagarin

[Pyotor Gagarin]

It's worth noting, that even though long-winged space gliders may not be fashionable anymore, inflatable ballutes, and even "space blimps" may still see the light of day. Gentle reentry is definitely a possibility.

[Rune]

Yeah, but then you have to have a system to keep your craft cool without using ablatives. Which means radiators, and a lot of coolant. The same amount of energy has to be absorbed and dissipated, only you can't burn your heatshield to do so. Plus, when you slow down in orbit, you fall, so you have to counteract with lift. Turns out that is difficult to do in such thin air. Also, yeah, the height of your reentry is a factor of your ballistic coefficient, Skylon would reenter far higher than the shuttle, because it is bigger and lighter. It would also stay on reentry regime far longer.

Rune. Burning away ceramics takes a huge amount of energy, while heating people to death takes very little in comparison.

[squeaky024]

Okay guys thanks for the replies, I haven't had a chance to try it myself but I was just thinking "what if I just fly down?" The thin air makes sense, no matter how fast you're going you can't get enough lift to get into more normal flight instead of orbital type trajectories. Also it would be hard to shield from heating on only the nose and leading edges of the wings too

[Moach]

the main thing to consider with performing such a maneuver, is that reentry orbits are usually eccentric ones, with only the periapsis putting it's "toes in the water"...

so it would not be a smooth glide but rather a gentle 'skip' - then lather, rinse, repeat until you get low enough to manage to avoid coming up back out again

unfortunately (for me, at least thus far) what usually happens is that on this 'final' pass, you are still going rather fast - and end up pulling more G's than perhaps you'd be comfortable with enough to still call it a 'smooth glide'

another alternative that comes to mind, would be to maneuver the craft upside down upon first entering the atmosphere so you get just the right amount of negative lift to pull your ApA down inside the atmosphere - this would indeed require some VERY fine flying - and quite a shallow approach to begin with

i fear that in the end, the requirements for performing such a tricky maneuver on the craft would be greater than those imposed by blunting it against the atmosphere and having it do the traditional "coast 'n toast"

another thing to consider is that to generate useful lift at such high altitudes, you need a LOT of speed - it would be similar to the kind a flying that a spaceplane would face during hypersonic ascent.... and thus, it still burns!

then remember, having a large surface area to distribute the heat load is better for your health than pinning it all on the nose of the ship - so even though more 'down-to-earth' aerodynamics would suggest otherwise, you'll find it's actually easier to be blunt than sleek up there

cheers!

Edited May 1, 2013 by Moach

[drakesdoom]

I don't think it would transfer to real life but I think it is worth noting that a decent burn to slow down to safe speeds before reentry does not use much fuel at all if in a very low orbit already. I have done this with the deadly reentry mod only need to slow down long enough for the shoots to open.