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 Europe. 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 http://ssd.jpl.nasa.gov/cgi-bin/eph 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 ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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