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