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Originally Posted by Mikko
kirjoitti:
Mitch wrote:
Should this not allow for much greater payloads to be
carried since less fuel is needed to get up to 30,000 ft?
Not *much* greater payloads.
There is an improvement. The spacecraft can be smaller, or deliver a
slightly larger payload, or get into orbit in a single bound.
But 30,000ft and, say, 600mph isn't much of a boost. It's a long, long,
long way from orbit. The difficulty of getting to orbit is better
described by "17500 miles per hour" than any figure of altitude.
Why is that speed needed?
Only thing I can think is, that since earths gravity effects the craft
whole time, the longer it takes, the more gravity will "drag back" the
craft?
But also gravity gets smaller when you get more away from the earth?
How high does one have to go to have only half of gravity?
What if someone built a 30,000 ft high tube, similar to magnetic trains
- electrical magnets around it. Then you could just put metallic
cargo inside - without any engine or fuel, and shoot it up. The tube
would have to be high enough that there is no air where the cargo comes
out, and maybe part of the tube would have to be a vacuum.
Propably not something to do today, but still lot shorter than the
"space-lift", and it would give near 100 % payload.
(you could mix magnetic cargo with-non magnetic)
And maybe design some kind of shell that can used as "package" to shoot
cargo up, and then used as walls for space station or building in other
planet.
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Why is the velocity needed? Well, the answer is quite simple...if you fly straight UP, you fall straight down. Orbiting is simply the fine art of falling and never hitting the ground. If you want to get into an actual orbit, you need to have sufficient velocity that you fall around the planet, not back into it.
With no atmosphere (say the moon) can be orbited at a relatively low altitude, and due to the low gravity, requires significantly less velocity to orbit it. to orbit the earth successfully, you need to get above the atmosphere (much more than 30,000 ft - that's only six miles high). The effects of atmospheric drag on a spacecraft taper off, the further you go from the surface, but appreciable atmospheric effects can still be felt at 100 kilometers altitude.
At 17,500 mph, you are successfully falling around the planet.
Now on to your other idea... A magnetic rail gun. A good idea for a number of reasons. For example, you can inject the acceleration thru externally applied thrust (rather than burning fuel carried with you) The down side to this is that if the rail gun is within the atmosphere, you have the friction of all that air. Not particularly useful for use on the Earth's surface, but a VERY good way to accelerate payloads from for example the surface of the Moon.