-Z- (Z@Gundam.Com)
Mon, 20 Dec 1999 17:49:18 -0800


At 22:50 12/19/1999 -0500, you wrote:
>-Z- wrote:
>
>> I think that six months to MARS, not the Moon. With that kind of
>> propulsion, you could get to the Moon within a day or so, about half the
>> time of a Hohmann transfer, which takes about 72 hours.
>
>Doh! My typo/flub. At any rate, my point was, wouldnt the propulsion systems
>of the
>Jupiteris or other ships be just as fast?

Only if they were being used in the same way, in either multiple sequential
bursts (like the Orion and Medusa nuclear pulse systems) of continuous
boost. Continuous boost would impose a prohibitive mass ratio due to the
amount of fuel you'd have to carry and expend to sustain the boost. Even a
sequential burst drive would impose a mass ratio penalty, which might be
enough to make it uneconomical for trips within the Earth Sphere. And the
long trip out to Jupiter is to GATHER fuel -- you wouldn't want to expend
any unnecessarily and there's no reason to rush.

In any case, there's no evidence of either in Gundam to date. What we see
in Gundam is the same minimum-energy doubly-tangent Hohmann transfer orbit
used to send Apollo to the Moon. You apply enough acceleration to change
from a Terrestrial orbit to a lunar orbit -- no more, no less -- and coast
the entire distance. Ditto for the return trip. The acceleration and
transit times are fixed, with a variance of a only a few meters per second
delta-V and a few hours transit time.

Speaking of delta-V and transit times, I did some more calculations and
what I found blows a big hole in the notion that Axis was set up "on the
way" to Jupiter or that it served as a way station between Earth and Jupiter.

It takes 6.6 km/sec delta-V to go from Earth orbit to Jupiter orbit or vice
versa. But, as noted earlier, it takes about 9.5 km/sec delta-V to go from
Earth orbit to the asteroid 1Ceres -- nearly half again as much. And
there's a 2.3 km/sec delta-V differential between 1Ceres and Jupiter
orbit. Run the numbers through the mill and we have a transit time of 1.84
years (22 months) from Earth orbit to and from 1Ceres and a transit time of
3.97 years (47.64 months) from 1Ceres to and from Jupiter orbit.

That's right, nearly four years. Jupiter is nearly twice as far from
1Ceres as 1Ceres is from Earth and you're limited to about a fourth of the
boost.

It gets worse.

Remember the synodic period? That's the time between oppositions, the
launch windows for making a Hohmann transfer between two orbiting
bodies. The synodic period between Earth and 1Ceres is 1.28 years (15.36
months), but the synodic period between 1Ceres and Jupiter orbit is (gulp!)
7.56 years (90.72 months)!!!

Not only does it take you four years to make the transit, but you can only
do it once every eight years!

-Z-

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