From: Ted Molczan (
Date: Sat Jul 31 2004 - 01:26:37 EDT

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    Brian Webb asked:
    > Does anyone have the TLEs for MESSENGER? I'd like to plot the 
    > spacecraft's position against the star background so I can 
    > find it visually.
    Assuming launch on Monday 2004 Aug 02 at 06:16:11 UTC, this will be its
    approximate parking orbit:
    1 73000U 73000A   04215.26401620  .00000000  00000-0  00000-0 0    06
    2 73000  32.4400 204.0000 0000100   0.0000 117.0000 16.40200000    04
    From lift-off to the start of its manoeuvres to leave Earth orbit, it will pass
    over oceans, except for a brief pass over South Africa, well after local
    JPL Horizons already contains Messenger's orbital data, and will generate
    ephemerides for any period beginning 2004 Aug 02 at 07:10 UTC, about 2 min after
    third stage burnout: 
    Note that it will not generate an ephemeris if you start the time span earlier
    than the above time.
    The ephemeris does not estimate the spacecraft's visual magnitude; however, I
    have derived the following formula, for use with data provided by the ephemeris:
    mag =  32.47 + 5 * log10("delta") + 0.01 * ("S-T-O" - 90)
    where:  "delta" = Target apparent range ("delta"). Units: AU
            "S-T-O" = Sun-Target-Observer angle; target's apparent PHASE ANGLE as
    seen at observer's location at print time.           
                      Units: DEGREES
    The formula is based on an estimated standard magnitude of 6.6 (1000 km, phase
    angle 90 deg), based on the spacecraft's approximate dimensions: 2.5 m long, 2 m
    Ted Molczan
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