Re: 1 g acceleration?

Dan Clemmensen (
Sun, 05 Jul 1998 11:26:47 -0400

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.