Subject:
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Re: Spacecraft propulsion (was: Ship Power Core)
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Newsgroups:
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lugnet.space
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Date:
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Sun, 23 Jan 2000 19:46:28 GMT
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Viewed:
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1482 times
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John J. Ladasky Jr.:
> And the best guess is that the peak exhaust velocity of the best ion
> engine we will ever design will be about 200 km/sec. This is not even
> 1/1,000th the speed of light, and the nearest star is 4.3 light-years
> away. Even an ion engine isn't enough. The acceleration to maximum
> velocity, by itself, would take on the order of 33 years. The rest of
> the journey would take 6,500 years.
I think you have some miscalculations there.
Assuming that the reaction mass is 99% of the total initial
mass of the vessel, and that the peak exhaust velocity is
2*10^5 m/s, the peak velocity of the vessel will be
4.6*10^5 m/s, which results in a transit time of 2,801 years
(excluding acceleration).
An acceleration time of 33 years at each end of the journey
corresponds to a reaction mass ejection of 10^-7 M_ship/s.
These calculations were done without any concern for the
problems near light speed or the drag in "empty" space.
The main equation is:
V_max = V_reaction * ln (M_start / M_transit)
Where M_transit^2 = M_start * M_end.
Play well,
Jacob (at the Niels Bohr Institute in Copenhagen ;-)
------------------------------------------------------------
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Message is in Reply To:
 | | Spacecraft propulsion (was: Ship Power Core)
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| Hi there, You've got to love these fantasy-tech discussions that spring out of the desire to model spaceships in Lego! To all of you who have posted pictures: love your designs. They have the no-nonsense look of real machines. (...) O.K., Tobias, (...) (25 years ago, 16-Dec-99, to lugnet.space)
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