Re: Wishing I could visit the Southern Ocean...

From: Alan Pickup (
Date: Fri Feb 11 2000 - 15:03:10 PST

  • Next message: Stephen D LaLumondiere: "Picosat observations"

    (I think that) Ed Cannon wrote...
    >Molniya 1-64                                     20184 x 92 km
    >1 15977U 85074A   00040.65654808  .01782425 -50777-5  27938-3 0   612
    >2 15977  61.8758 170.3507 6082369 259.5424  31.7975  4.09062855 51348
    >I'd kind of like to see a fair-sized object whose apogee is
    >20000km pass through the zenith at a height of 92 km!  However,
    >I suppose that it might not be very shiny by the time its
    >perigee is that low....
    A word of warning about the "apogee x perigee" heights appearing in the
    "line zero" of some elsets (such as those in the elset files I
    maintain). These heights are computed via from the mean motion and
    eccentricity in a convenient but simplistic way that takes no account of
    the Earth's oblateness. In fact, they are the heights of the satellite
    at its apogee and perigee measured above a sphere of the Earth's
    equatorial radius. Since this Molniya (like most other Molniyas) has its
    perigee near southern apex (its most southerly point), the actual height
    above ground at the perigee is more like 108 km than the 92 km given,
    and it is the 108 km that needs to be used when considering the
    atmospheric drag it will be experiencing.
    There should also be a second health warning relating to the accuracy of
    the implied perigee heights for such eccentric objects. It is not
    unusual to see wild swings of 10-20 km in the perigee, simply because of
    errors in fitting an orbit to observations made. presumably, closer to
    apogee than perigee. For example, only a few hours after posting the
    above elset, SpaceCom issued the following one suggesting (in error) an
    even deeper perigee...
    Molniya 1-64                                     20073 x 67 km
    1 15977U 85074A   00041.38692267  .01871734  00000-0  64408-4 0   629
    2 15977  61.8761 170.0957 6081430 259.5125  30.8419  4.11601382 51377
    The elsets issued since then show perigee "heights" in the range from 94
    to 98 km.
     Alan Pickup | COSPAR 2707:  55d53m48.7s N  3d11m51.2s W   156m asl
     Edinburgh   | Tel: +44 (0)131 477 9144     Fax: +44 (0)870 0520750
     Scotland    | SatEvo page:
    Unsubscribe from SeeSat-L by sending a message with 'unsubscribe'
    in the SUBJECT to

    This archive was generated by hypermail 2b29 : Fri Feb 11 2000 - 15:07:41 PST