[OT] I've created a /. Monster

**Cyde Weys** · #1 June 23rd 04 posted to talk.origins,sci.physics

Dale wrote:

"dkomo" wrote in message
...

Dale wrote:

"dkomo" wrote in message
...

Thomas H. Faller wrote:

[...]

So trying to escape the earth's gravity at less than escape velocity

requires

very large power sources.

Good grief, haven't we heard about conservation of energy? It takes the
same amount of energy to escape the earth's gravity whether you do it at
1 m/s or 25,000 mph. That means you use the same amount of fuel either

way.

Look at this way. If you go up slowly you burn fuel more slowly over a
longer time period. If you go up fast you burn fuel rapidly over a
shorter time period. Either way, you end burning the same amount of

fuel.

No, if you go up slowly, you burn fuel at pretty much the same rate as

if

you go up rapidly, but it takes more time, therefore you burn more fuel.

What? If you burn fuel at a slow rate, you generate less thrust,
produce less acceleration, and therefore you go up more slowly. If you
burn fuel at a fast rate, you generate more thrust, produce more
acceleration, and therefore you go up faster.

As long as you're fighting gravity, you have to burn fuel at a certain rate
just to hover. It's pretty complicated to explain fully, but just take a
look at the limits. If you have just enough thrust to hover, you could be
burning fuel at some given rate forever and never get anywhere. If you don't
have enough thrust even to hover, you'll come to a rest on the Earth's
surface.

If you burned a little extra, say enough to accelerate at 1 m/s^2 you could
achieve orbital velocity in 123 seconds. Well, actually, that's against a
constant gravity, but let's just leave it at that for now. It's also
assuming a constant mass, when of course, the mass would decrease as fuel
was expended, and thus the acceleration would increase over time.

But anyway, if you burned enough to accelerate at 10 m/s^2, you'd achieve
orbital velocity in 39 seconds. Now let's say that accelerating at 1 m/s^2
against Earth's gravity costs 1.1 times as much fuel as hovering, and that
accelerating at 10 m/s^2 takes 2 times as much fuel as hovering. If that's
true, and I'm not sure if it is, then it will take 1.7 times as much fuel to
go the slow way as it does to go the fast way.

Thanks Dale. I think we've finally offered enough evidence now to clear
up dkomo's misconceptions.

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