Question about Earth re-entry and feathering?

Question

I have heard that the SpaceShipOne spaceship used a technique called feathering where the ship slows down during re-entry to reduce the friction with the atmosphere to reduce the heat on the way in. If this concept was applied to where the ship slowed down VERY much, could there be a point where the ship would encounter a negligable amount of heat, and would not need any heat shilding at all? Also, could the intense re-entry G forces be reduced as well?

Answer 1

The maneuver of feathering doesn't reduce heat, but speed. Atmospheric re-entry always builds heat.
The Space Shuttle (upon re-entry) uses a maneuver NASA calls 'pancaking', where the Shuttle's underside is presented to the atmosphere head- on to reduce speed, along with a series of wide "S"- turns, which also help to reduce velocity.
As this speed is reduced more gradually using these techniques, G- forces are thereby minimized.

Answer 2

I am not an aeordynamics expert, but I do know that the density of the atmosphere increases exponentially as you drop down from space. This effectively means that if you are dropping fast, you will more or less "slam into" the atmosphere (transitioning from "no friction" to "a lot of friction" in the space of just a few seconds).

In order to make this transition more gentle, you'd have to drop into the atmosphere at a slower rate. But there's the catch-22: you can't reduce your rate of descent until you actually hit the atmosphere. If I remember right, SpaceShipOne is weightless for something like 6 minutes, which probably means it's falling for at least 3 minutes before it hits the atmosphere. At that rate, it hits the atmosphere at something like 4,000 mph. (My numbers may be all wrong--I have the (excellent) documentary by the Discovery Channel at home, in which they give the real numbers, but I haven't seen it for a while.)

I can imagine a scenario in which the craft "changes shape," so that when it first hits the atmosphere it presents very little surface area so that the friction is minimal; and then very gradually it presents greater surface area so that it slows down sufficiently for touchdown. It seems to me that this is kind of what the "feathering" technique is trying to achieve.

Of course, another possibility would be to use rockets to gradually slow your descent until you're in sufficiently thick atmosphere. I assume the reasons they don't do that are (1) fuel is expensive and heavy; and (2) rocket engines are way more complex than heat shields and therefore more likely to fail (with deadly consequences)

Answer 3

-->If this concept was applied to where the ship slowed down VERY much, could there be a point where the ship would encounter a negligable amount of heat, and would not need any heat shilding at all?

Yes - that was exactly the point of the feathering - the feathered ship had a large amount of drag, which kept it from going fast enough to generate much heat. However, Spaceship One never got going very fast (on its way down) to begin with, and in fact, right at the top of its flight, was hardly moving at all. An orbiting ship doesn't have that luxury - it's going a lot faster, so in order to reenter the way Spaceship One did, it would have to fire retrorockets to slow way down; that would mean it would have to carry that much more fuel right from the start. But carrying more fuel means more weight, and excess weight is a killer in space flight. It's just more practical to design the ship to take the heat.

Answer 4

Nope, there will always be friction no matter how slow you go.