Can a vehicle re-enter a planet slowly and not need a lot of sheilding?

Question

Based on the responses from my last question:http://answers.yahoo.com/question/index;_ylt=ArTGALomd0zLpRQZ8eaSzKMBxgt.?qid=20070530073733AA7fTfJ

Could a vehicle(flying car for example) re-enter safely if it just slows down and re-enters slowly;with out the need for as much heat sheilding?

Answer 1

Yes, but doing that would require the impractical.

It is impossible to use a parachute or an improvisation, because the terminal velocity of reentry is just to high. A metallic parachute could be used, but we would then be talking about the said impracticality. And besides, the parachute would then receive the full force of the atmosphere's resistance, and it would need heat shielding.

We could use reverse thrusters, on the other hand, but that would be too wasteful on fuel.

We could device a decent that has a very small angle of reentry, but the air resistance we lost vertically we gain horizontally. For a plan like this, our ship would have to circle the world several times before it finally lands, and that would be just too much of distance, and great distance gives great space for friction to work, so we still would need those sheilding.

Answer 2

Think about the amount of fuel it takes to get something into Orbit. To slow a craft down outside the atmosphere so that it could re-enter without the need for heat shielding would take almost as much.

There is a concept of the space elevator. In this scenario a super tether is anchored to the earth and extends just beyond geo-synchronous orbit. Payloads are lifted into orbit by crawling up the tether and then releasing. The only fuel needed is that which is necessary to move from the release orbit to the desired one. In theory that could work to bring things back. Capture the tether in orbit and then crawl slowly down.

But we do not have the material science to construct a space elevator.

Answer 3

If your vehicle is just going straight up and down, without establishing orbit, then it's certainly possible. In essence, you'd just be parachuting down from high altitude. Crafts like Rutan's SpaceShipOne don't have the kind of shielding that's necessary on the space shuttle, since SpaceShipOne doesn't reach orbital velocity - it essentially just goes straight up and down.

However, if your vehicle has established orbit, it has a velocity of thousands of miles per hour, parallel to the surface of the planet. That lateral velocity has to be reduced to zero before you can land. It's the lateral velocity that causes all the heat when the craft enters the atmosphere - and as a practical matter, you need heat shielding to deal with it.

Theoretically, it would be possible to reduce the lateral velocity to zero before the craft re-enters the earth's atmosphere, but it wouldn't be practical. It's cheaper and easier to just use heat shields and let atmospheric friction do your braking for you.

Answer 4

I think if a ship re-entering orbit were to have something like a helicopter setup and renetered slowly from the get-go then it wouldn't have to be slowed down, but it would still take alot of fuel.

Answer 5

The amount of fuel needed would be unbelievable. You'd have to slow it before it hit the atmosphere and then slowly lower it under power until you could open a parachute or something else to bring it the last 20,000 feet or so.

Answer 6

I don't think it can enter slowly. Gravity accelerates at 9.8metres per second squared. It would require a lot of power to slow the vehicle down against gravity if even possible.

Answer 7

Well it cannot because a vehicle or any object requires a speed of about 8 km/s to escape or for re entry speed less than 8 km/s will not allow any vehicle to enter space or re enter(this speed is specific for earth, varies for other planet)

Answer 8

No! Once gravity gets hold of you it is free fall all the way, you have to go very fast to not get going too fast, there is not enough atmosphere to glide down slowly.

Answer 9

Yes, it is possible.