2-to-1 resonant orbit better than Lagrangian points?

Hi, this is interesting.

>
> Monart Pon wrote,
> "(L5 is one of several Lagrangian points that are gravitationally stable located roughly equidistant from both the moon and Earth about 240,000 miles, and is a preferred location for a space settlement.)"
>
> I was reading Heppenheimer's book from the late '70s >on space colonization. He mentions that although L4/L5 >were originally chosen by O'Neill, later analysis >showed that a "2-to-1 resonant orbit" with perigee >100,000 miles and apogee 200,000 miles was preferred. >The reason was that the transfer delta-V from the L2 >collection point to the 2-to-1 resonant orbit was much >more favorable than the transfer energy to the Lagrangian points.
>
> Is this still the scientific consensus regarding the location for a production facility based on a lunar resource/mass driver scenario?
>

The delta-vee difference from Luna to L-4/5 versus the 2:1 resonant orbit is interesting.

To get to the resonant orbit it is easiest to go via
the L-1(?) point (between Earth and the Moon), that is
an apolune of about 40,000 kms. To get to L-4/5 from
Luna requires a lot higher apolune, so is significantly more energy.

One of the main attractions of L-4/5 was at first sight the issue of launch window opportunities. If L-4/5
were points, then there is no launch window and you can launch any time. But alas it is not so----L-4/5 points
are not stable, and the orbits around then have quite long periods, about 89 days (IIRC).

The 2:1 resonant orbit will allow a launch window every lunar month, every 28.x days, which is much more attractive than every 89 days.

Another advantage, there are more launch windows to/from Earth, every 14 days versus 89 days.

The energy from Earth to the 2:1 resonant orbit versus
L-4/5 is about the same, in both cases lunar flyby
would be used, so the intial pergee detlta-vee is
the same.

In short, I like the 2:1 resonant orbit a lot better than L-4/5...it is now my baseline.

Charles F. Radley