Re: Fictional Apollo 18(+) Missions

From: Henry Spencer (henry_at_spsystems.net)
Date: 11/30/04 

Date: Tue, 30 Nov 2004 20:30:45 GMT

In article <32773f53.0411292053.1c594540@posting.google.com>,
TVDad Jim <jim@tvdads.com> wrote:
>> To a first approximation, you can reach any lunar-orbit inclination for
>> about the same cost, provided you don't insist on getting there on a
>> free-return trajectory...
>
>Again, I'm not good at the math here, but I thought there were
>opportunities at the La Grange Point #1 where Apollo could adjust the
>inclination angle somewhat.

The Apollos didn't pass through the L1 point, actually.

The usual mental model of the situation -- spacecraft zooms out to
intercept a nearly-stationary Moon -- is *wrong*. It's actually more
accurate to think of the spacecraft, nearly stationary at the apogee of a
highly elliptical transfer orbit, being overtaken by the fast-moving Moon.

That being the case, whether the spacecraft passes over the lunar equator
(where an LOI burn gives an equatorial orbit), or a lunar pole (where an
LOI burn gives a polar orbit), or something in between, is a matter of
quite small adjustments in exactly where the transfer orbit's apogee is
and exactly when you get there. Only when you start studying the details
quite carefully do modest cost differences appear. 

-- 
"Think outside the box -- the box isn't our friend."    |   Henry Spencer
                                -- George Herbert       | henry@spsystems.net

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