From: Dan Clemmensen (Dan@Clemmensen.ShireNet.com)
Date: Sun Jul 05 1998 - 09:26:47 MDT
Hara Ra wrote:
>
> >> I guess my real question is, according to the people on the
> >> ship, does it appear to take more and more energy to maintain a
> >> constant 1 g acceleration experience or is this only true in the
> >> space/time frame of the people on earth? So, according to the people
> >> on the ship, you can accelerate at 1 g forever right?
>
> Depends on frame of reference. Aboard the ship, the power required rises
> indefinitely, as does the perceived velocity relative to the universe due
> to time dilation and space contraction. On Earth, you simply grow more
> massive and keep approaching C, with an eventually constant power requirement.
>
I don't think that's correct. In the ship reference frame, The ship gets no
heavier, and therefore needs the same power as measured in its frame to maintain
the 1 g accel as measured in its frame. I think the relevant formula is f=ma.
In the earth frame, the ship is expending the same energy over a longer time and
is pushing a heavier ship. Its accel is therefore lower in this frame,
asymptotically approaching 0 g as v approaches c.
The practical problem is the source of energy and reaction mass. If you try to
carry your reaction mass, you'll need an unreasonable amount, even with a
matter/antimatter drive, which is the theoretical best for a reaction drive.
ke=.5mv^2 is the energy you need to accelerate mass m to velocity v, but
e=mc^2 is the energy available in mass m, assuming all of it can be converted to
acceleration. But, you also need energy to carry the mass you will use later.
This is a losing propsition: read "The Physics of Star Trek" for a full
and fun treatment.
You can try to get around this by using a ram scoop, using a yet-to-be-developed
technology to sweep interstellar hydrogen from your path into your engines. This
is a bit tricky: don't try this at home. Read Poul Anderson's "Tau Zero" for a
good SF treatment of this.
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