From: spike66 (spike66@attbi.com)
Date: Sun Jul 14 2002 - 22:56:41 MDT
Robert J. Bradbury wrote:
>On Sun, 14 Jul 2002, Technotranscendence wrote:
>
>>On Sunday, July 14, 2002 11:27 AM Robert J. Bradbury
>>bradbury@aeiveos.com wrote:
>>
>>>It turns out Spike is pretty much correct.
>>>
>>How could this be?:)
>>
This could be. {8-]
>>I know, it shocks me too. The idea of such a mind out
>>running around on a motorcycle in the middle of MidCal
>>seems like such a waste.
>>
Ah yes, but you see, it isnt a waste, because the equations needed
to calculate delta vees are verrry simple, simple indeed. In fact, there
surely is software avialable somewhere, analogous to Mike Lorrey's
flight configuration package (what's it called?) that one could get to
figure out things like what it would take to haul a space shuttle to the
moon. I have a sort of intuition about these things from having done
jillions of calcs and thinking about orbits.
I was asked if there are some shortcuts to estimating orbit mechanics,
I believe Damien asked. In fact there is. I did not need to even take
out a piece of paper to estimate a billion dollars to take a shuttle to
the moon. I figured thus:
The delta vee required to achieve escape velocity is square root of 2
times the minimal orbit velocity. We know that minimum orbit velocity
is about 8 km/sec, so you would need over 3 km/sec to get out to the
moon, which is *almost* far enough to require escape velocity to get
out there. Exhaust velocity is about 4.5 km/sec in vacuum, so to get
over 3 km/sec, you would need nearly as much fuel as payload.
You already know that to acheive exhaust velocity with a payload,
you need about 61% fuel, (1-1/e). So I knew that an orbitter is
about 100 megagrams, and it could hoist about 30 megagrams, so
it would take about 3 shuttle loads of fuel to haul it out to the moon,
so about a gigadollar US.
I estimated this in less than 10 seconds from hearing the idea. Of
course it is much more impressive to see the stunt done in person
in real time. So next Extroschmooze, pull something like this on
me so I can reproduce it. spike
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