Bush Space Plan Unwise?

From: Arthur P. Smith [mailto:apsmith@...]

> On Mar 12, 2004, at 11:33 AM, Combs, Mike wrote:
> >
> > What orbits were you thinking about?
>
> Depends how long the craft is waiting there for fueling/refueling. If
> it's days, a low orbit like those used for the Apollo rendezvous makes

> some sense; longer waits I would think a somewhat higher orbit, but
not
> necessarily as far as L1.

The logic of the whip-around maneuver is that you're taking fuel which
has lots of potential energy, due to having been pushed "uphill", and
converting much of it to kinetic energy at that burn at the lowest
practical point in the gravity well. So L-1 is favored since that's a
point of relatively high potential energy in the Earth-moon system.
There are other Lagrange points with higher potential energy, but an
advantage of L-1 is that it's relatively easy to slip off the point and
swing back down toward the Earth. Easy as falling off the proverbial
log!

I've had others point out to me that the Earth-Sun L-1 point is a region
of even higher potential energy. But since travel to Earth-moon L-1
would be a matter of a couple of days, while travel to Earth-sun L-1
would be on the order of a couple of weeks, I'd consider the Earth-moon
L-1 point to be a more likely departure point for expeditions leaving
Earth.

> My reasoning here is that the refueling
> vehicle would presumably be reusable also and need extra fuel and time

> to get to and from the higher orbits - though really this is somewhat
> off the top of my head here :-)

I'd agree that we should expect the tanker to be a reusable vehicle, but
I'm envisioning the tanker shuttling between the surface of the moon and
the rendezvous point. In which case the higher Earth orbits are easier
to reach from the moon than the lower ones. One has to find a trade-off
between a point not too difficult to reach from Earth, nor too difficult
to reach from the moon either, since a substantial mass of fuel is
involved. L-1 strikes me as a good compromise.

Regards,

Mike Combs