Re: Lunar Geosynch orbit question !

From: B Magnus B{ckstr|m (
Date: Wed Jun 27 2001 - 23:54:01 PDT

  • Next message: Tony Beresford: "Re: Lunar Geosynch orbit question !"

    On Wed, 27 Jun 2001, Rick Baldridge wrote:
    > Jim King wrote:
    > > Since the Moon always keeps the same face towards the Earth wouldn't a
    > > "lunasynch" sat be at the L2 Earth-Moon Lagrange point?
    > Not quite.  L2 Lagrange point is on a LINE with the Sun and the Earth,
    > further out than the Earth, with the Moon's orbit well inside.  L2 does NOT
    > follow the Moon, therefore, it does NOT stay in-sync with the "far side" of
    > the Moon. (Although since L2 is downsteam of the Moon and the Earth, it DOES
    > see mostly the "dark" side of the Moon with some small phase being possible,
    > and ALWAYS the dark side of the Earth!)  The Moon is only downstream AND
    > in-line with the Sun and Earth at Full Moon. (For purists, I won't get more
    > technical than that!)
    > > Anybody know the distance from the Moon of the Earth-Moon L2?  Would a sat
    > > Earth-Moon L2 ever be visible from the Earth?
    > L2 is 1.5 million kilometers from Earth, away from the Sun side, according
    But, just as the Sun-Earth system has Lagrangian points, so does the
    Earth-Moon system!  Thus there is a point some distance beyond the moon
    (as seen from the Earth) at which a spacecraft could "stay put" in the
    Earth-Moon frame. The spacecraft would be perpetually watching the far
    (rather than dark!) side of the moon.
    Communicating with that spacecraft might be a problem; or, what with the
    moon being in the way, Earth-Moon L2 might be perfect for a radio 
    astronomy mission -- free from this planet's electromagnetic spam ;-)
    // Magnus
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