Getting into orbit?

Question

I know that a rocket has to achieve about 27,000mph to ecape into orbit. But would not it be possible to go slowly vertically into orbit by just over coming gravity. Gravity reduces as you get higher.

Answer 1

Actually its about 17500 mph.

What you're talking about won't work--for two reasons. The first is that the orbital velocity has to be lateral--meaning if you draw a line straignt up from the earth's surface, your direction has to be at right angles to that line. If you are going at the right speed for your altitude (and high enough to be above the atmosphere, fof course, you'll be in orbit--the earth's gravity is still pulling you down, but the curvature of the earth means that the "ground" below falls away at exactly the same rate, so you just go around in a circle without getting any closer to the earth.

But as you describe it, you'd just be going straight up, not around the earth. The other reason is that it takes more energy to go higher. By the time you got high enough for the orbital veloicity to decrease enough to matter (and it does get less as you go up, you're right there) you'd have expended a lot more fuel than if you go into a lower orbit.

BTW--you don't want to do this slowly--you want to do it as fast aas possible. The reason is that until you do reach orbit you have to keep expending fuel to hold the spacecraft up against the force of gravity as welll as accelerate. Thelonger that takes, the more fule you have to expend.

Answer 2

There is an escape velocity, it is 11 meters per second. that's the escape velocity from the earths gravity, you can go up slowly but you wont really escape from the gravity, just get higher and higher until gravity gets too weak. But you cant get up in a balloon, because the gas in the balloon is lighter than the air an in the space there is no air, so the upward thrust wont work, due to the lack of air. the reason of needing a rocket is that there is a point with no air, when jets and balloon gases cant work, and a rocket needs no air.

Answer 3

The reason for this speed is that it is the speed where the *centrifugal force of the orbit is equal to the force of gravity, so that it takes no additional fuel to maintain that altitude.

If you go slower, then you must either constantly expend energy to counteract the force of gravity, or else you will not maintain the altitude (fall back to Earth).

If gravity didn't reduce as you got higher, the orbital velocity would be even higher than it already is.

*(I know there's no such thing as centrifugal force in physics, but explaining centripetal acceleration would make it a confusing answer to most readers)

Answer 4

To completely escape Earth's gravitational pull, starting from the surface of the Earth, an object must be launched with an initial velocity greater than or equal to what is known as the "escape velocity". Earth's escape velocity is 11.2 km/s.
If an object were launched up into the air at this speed, it would never fall back down.

But the escape velocity only refers to an un-powered object's initial speed (it assumes no further addition of energy along its route) and assumes the object was launched from the planet's surface, not some distance above it.
If the object was launched from 100 miles up, the necessary escape velocity would be reduced.
If the object was a rocket that could continue thrusting itself after it took up, it could forever leave Earth, even by traveling at much slower speeds.

To calculate the escape velocity for a given object (which you are trying to escape) of mass M, and starting distance from the masses center of mass, r,
v_e = sqrt (2*G*M / r)
Where v_e is the escape velocity, G is the universal gravitational constant (= 6.67 E-11 N m^2 / kg^2).

Answer 5

That figure of 27,000 mph has been calculated taking into account that gravity diminishes with distance to the center of the Earth. That value is obtained applying the laws of mechanics and the law of gravitation of Newton. So there is no a way for trickeries.
The energy to escape (or the speed) does not depend on the specific way followed by the rocket, it just depend on the distance from the Earth.
I aplogize for my bad English.

Answer 6

You need 17,500 MPH sideways, or parallel to the Earth's surface, to stay in a low orbit, but the higher you are, the less speed you need.

You need to start at 25,000 MPH to escape completely. That speed can be in any direction, straight up works just fine. As you climb higher and higher, you slow down more and more, so that as you pass the Moon you are going less than 5,000 MPH. It is like throwing a rock up. The rock goes up, slowing down all the time, stops, falls back, speeding up all the time, until it hits the ground. The harder you throw it, the higher it goes. If you throw it up at 25,000 it goes up fast enough that its slowing speed is just matched by the rate at which gravity gets weaker, and it never falls back again. Throw it faster than 25,000 MPH, and it just escapes with extra speed.

Answer 7

You have to recall that gravitational forces reduce by 1 over r squared. Since earth's radius is roughly 7000 miles, even at 7000 miles into space, the gravity is still 1/4 what it is here. You'd be burning loads of fuel with your suggestion.

Answer 8

There is also friction between the rocket and the air molecules which would slow down or even stop the rocket.

Answer 9

Yeah, all you need is a bunch of balloons to float into orbit.

Answer 10

Yeah, all you need is a bunch of balloons to float into orbit.