Re: ISS Misses Moon - not by much!

From: Bjoern Gimle (
Date: Mon Jun 04 2001 - 03:22:05 PDT

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    > Such a trip would certainly be worth the effort, but it's a formidable
    > job to calculate such an opportunity. It is possible to calculate the
    > "shadow" track of a satellite, i.e. the track on the ground connecting
    > all the locations from which the satellite would appear to cross the
    > Moon's disk. That would have to be done for all the Iridiums, and one
    > would also have to check all along the track if a flare occurs.
    Not necessarily. If you are not prepared to travel more than a few hundred
    km, the problem is fairly linear. Just like the "shadow" track, the flare
    track is linear (and almost parallell). In 200 km, the Iridiums rotate less
    than two degrees, so the flares move at most four degrees in RA/dec. Moon's
    motion and its parallax are neglible. Just find any flare within a few
    degrees of the Moon, and run IridFlar for one location N and one S of yours.
    The flare positions off one Iridium plane move quite slowly from day to day.
    Taking a broader view, ignoring Earth topography and working in an
    Earth-fixed inertial coordinate system, the flares from one Iridium PLANE
    are essentially THREE parallell lines on the surface, and three lines on the
    celestial sphere!
    -- (office)                         --
    -- (home) --
    -- COSPAR 5919, MALMA,    59.2576 N, 18.6172 E, 23 m         --
    -- COSPAR 5918, HAMMARBY, 59.2985 N, 18.1045 E, 44 m         --
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    This archive was generated by hypermail 2b29 : Mon Jun 04 2001 - 03:47:46 PDT