-Z- (Z@Gundam.Com)
Sun, 19 Dec 1999 14:49:50 -0800


At 13:26 12/19/1999 -0500, you wrote:
>Here's another question: How often does the Jupiteris or Jupiter Energy
>Fleet (there's more than the Jupiteris?) come back to the Earthsphere?
>Is it once a year or something?

If the name "Thousandth Jupiter" isn't hyperbole, there are at least a
thousand of them by UC 0123.

Going through the timeline, I can't determine the transit time to and from
Jupiter because I can only find departure and arrival dates, but not
both. Time to dig out the old ephemeris and crunch some numbers.

In the real world, you must achieve a change in velocity (delta-V) of 6.6
km per second to go from Earth orbit to Jupiter orbit. That's assuming a
minimum-energy Hohmann-type transfer orbit, such as we see used throughout
the Earth Sphere, and a gravity slingshot around the Moon.

In order to use a Hohmann orbit, you must start and finish with origin and
destination precisely opposite the Sun. You can't just boom out whenever
you want, but must wait for the right geometry, otherwise your delta-V goes
up and up to impossible values. For an Earth-to-Jupiter run, you get a
launch window once each synodic period, the time it takes both planets to
go around the Sun and come back to the same relative positions. For a
Hohmann orbit, the two planets must be in opposition and the synodic period
for such oppositions is 1.09 years. You can, of course, launch a ship from
Jupiter to Earth at the same time you launch one from Earth to Jupiter, but
you can only launch once a year, tops.

The transit time itself works out to 2.7 years, so the ship that's launched
from Jupiter the same day that you send one out won't get here until midway
between your second and third outbound launch. For Scirocco's Jupitoris to
arrive in the Earth Sphere on 29 April 0087, it must've been launched circa
August or September 0084 -- just a few months after the Titans came to power.

Someone on the Z Gundam staff did their homework on this. They have the
Axis asteroid beginning it's journey to the Earth Sphere on 6 February 0086
and arriving on 2 October 0087. Not knowing where Axis might actually have
been situated in the Asteroid Belt, I looked up the figures for
1Ceres. The transit time works out to 1.84 years, which is damned close to
the transit time given for Axis. And the synodic period is 1.28 years, so
the launch could take place as scheduled. The delta-V is actually higher
than for an Earth-Jupiter run, about 9.5 to 9.8 km/sec.

The same or very near values would also apply to moving 3Juno from the
Asteroid Belt to the Earth Sphere to become Luna-II....

-Z-

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