whay arent we doin other planets any more

whay not investing in the future of other fathers
as they say, goen for instance to other planets
and mars, with men in spacecrafts

not just becus it is easy, but becus it is dificult, and
we bulive that the men of earth shud comit themself
makin comitments

where are all that space travel they bull****ed us in
tha near past?

In sci.physics.relativity, heckuva

wrote
on 28 Jan 2006 14:45:54 -0800
. com:
whay arent we doin other planets any more

whay not investing in the future of other fathers
as they say, goen for instance to other planets
and mars, with men in spacecrafts

not just becus it is easy, but becus it is dificult, and
we bulive that the men of earth shud comit themself
makin comitments

where are all that space travel they bull****ed us in
tha near past?


The best I can do is 32 or so years to visit a star 8
light-years away (say, Sirius), and that's with some
*very* optimistic assumptions.

Assume, for the nonce, that we do have an Ultimate Engine,
with v_e = 0.115 c, and using Newtonian physics. (At this
v_e the error isn't too bad.) We want to get to Sirius,
which is 8 light-years away, in 32 years. (We also want
to actually land there, which has some ramifications
fuel-wise.)

Tsiolkovsky to the rescue. Well, sort of; in any event
v_f = v_i + v_e * log(M_i/M_f). (There's an alternative
definition in Relativistic space, which I'd have to
look up, though someone did post it not too many days ago.)

..25 = 0 + .115 * log(M_i/M_f)
log(M_i/M_f) = .25 / .115 = 2.174
M_i = M_f * 8.793.

Bear in mind that this is acceleration. Deceleration requires
more fuel; in that case M_i = M_f * (8.793)^2 = 77.31 . Or,
put another way, the spacecraft is going to have to be 98.7% fuel.

The good news: at 0.25c relativistic effects will shave about
1 year off the journey. Also, the engine needn't be all that
powerful -- just have a very good v_e. One might even enjoy
normal gravity (9.805 N/kg) for about 3 months.

The bad news: there's no real good way for them to get back. :-)
Also, the destination system will get peppered with rocket parts,
if one assumes a multistage design with detachable fuel tanks.

And then there's the actual design of the Engine. I'm assuming
that it is possible to combine 4 protons using the equation:

4p = 2He4 + 25MeV

(a *very* questionable assumption, as Uncle Al pointed out
when I originally proposed this Engine) then propelling
the helium nucleus out the rear. Since an alpha particle
has 3727.37917 MeV I get a gamma correction factor of

(3727.37917 + 25) / 3727.37917 = 1.0067071

which corresponds to a v of .116 c.

This is arguably the best we can ever do; one can get
a higher v_e by ejecting protons or even electrons but
the helium becomes an issue.

With contemporary rockets v_e = 30000 m/s for an ion thruster
(a la Deep Space 1) or 10^-4 c; a VASIMR rocket might get
10^-3 c. Assuming M_i = M_f * 30 (a more reasonable assumption
given contemporary construction), and a VASIMR rocket, we get

v_f = 1/2 * 300000 * log(30) = 510180 m/s = 1.7018 * 10^-3 c

or a transit time of about 4700 years.

http://en.wikipedia.org/wiki/Specific_impulse

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