FW: MESSENGER visible from w. N.America Aug. 2

From: Dale Ireland (direland@drdale.com)
Date: Sat Jul 10 2004 - 19:29:03 EDT

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     Interesting post from the IOTA group
    Dale Ireland
    -----Original Message-----
    From: David Dunham [mailto:dunham@erols.com] 
    Sent: Thursday, July 08, 2004 10:40 PM
          The MESSENGER spacecraft to Mercury is scheduled to be launched on
    August 2nd, the start of a 12-day launch window.
    The injection into its heliocentric orbit, performed with the Delta rocket
    3rd stage, will be in daylight n.w. of Australia, but the spacecraft will
    then climb rapidly in height and head towards Hawaii.  It will raise almost
    straight up over Hawaii, and then the Earth's rotation will catch up, moving
    the ground track west from there, over Japan, Asia, Europe, etc., gaining
    height and becoming fainter.  But while over Hawaii, it will be relatively
    close in a dark sky, well placed for optical observation from Hawaii and
    western North America.  It is a larger spacecraft than CONTOUR, so I think
    it will be 7th or 8th mag. at this part of the trajectory, around 8h UT of
    August 2 (the geometry will be similar, with similar timing, for the other
    launch dates).  It will be rather fainter as it rises for other locations,
    but maybe still 9th or 10th mag., for Japan and Asia, maybe 11th mag. for
          Jon Giorgini has added the predicted MESSENGER trajectory to the JPL
    Horizons ephemeris generator that you can use to calculate predictions for
    your location at
    You should start the calculations at 7:10 UT of Aug. 2; any earlier and you
    will get an error message because the spacecraft trajectory file starts
    shortly after the expected separation from the spent 3rd stage rocket (you
    might see it, too, nearby) sometime during 7:09 UT.  You can check the
    options that suppress output when the Sun is above the horizon and the
    spacecraft is below it.
    If all goes as planned, observing this will be just for entertainment &
    education; the orbit will be determined well from radiometric tracking, and
    also from radar observations planned from an island in the western Pacific.
    But if there is any problem with contacting the spacecraft during these
    first hours after its launch, then optical observations of it could be
    valuable for determining the trajectory and homing in on the spacecraft with
    the large Deep Space Network antennae.
          MESSENGER will swing by the Earth a year after launch, providing
    another opportunity to observe the spacecraft.
    David Dunham, IOTA & JHU/APL MESSENGER Mission Design Team
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