MESSENGER

Trajectory record

Precise trajectory

Sun-centred J2000 states sampled offline from NASA/JPL NAIF SPICE kernels with geometric (NONE) aberration correction, using the official full-mission merged reference trajectory msgr_040803_091031_120401.bsp (JHU APL, produced 2010-01-21) with DE440s furnished last so planetary positions match the committed body ephemerides. This single merged SPK is what the modern archive ships in place of Voyager's per-encounter kernels, so all six gravity-assist flybys - one Earth, two Venus, three Mercury - are searched against it with no dedicated encounter kernel; each declares its own sampleWindowSeconds instead. The kernel's own embedded PDS label and SPKMERGE log (read via SPICE's DAF comment area) show it merges the mission's segment-by-segment navigation reconstructions, recon001 through recon006a, with each of the six flybys landing inside one of them; the file's own name records the merge's coverage as running from launch (2004-08-03) through 2009-10-31 in this delivery, and coverage stops there rather than continuing through the 2011 orbit insertion or 2015 impact this record's events describe: the file's remaining span to 2012-04-01 is orbit-determination prediction layered on top of the reconstructed tour, and extending the record into the multi-year orbital mission is a data change of its own, left uncommitted here, mirroring how Task A7 (New Horizons) committed only the Pluto encounter phase. Computed closest-approach distances agree with APL's own published centre-relative figures (Flyby Information page) to within 0.041 km at every encounter - Earth -0.005 km, Venus 1 -0.019 km, Venus 2 +0.019 km, Mercury 1 +0.006 km, Mercury 2 +0.041 km, Mercury 3 -0.003 km - and the recorded barycentre-to-centre offset is exactly 0.000 km at all six: Mercury and Venus have no moons, so their NAIF barycentre and body-centre coincide, and Earth's committed ephemeris targets the body centre (NAIF 399) rather than the Earth-Moon barycentre (NAIF 3), so this encounter's barycenterNaifId is 399 to match it. The Earth-Moon barycentre does genuinely sit some 4,336-4,942 km from Earth's centre, but because this encounter is measured against the same point the committed Earth ephemeris uses, that offset never enters the check - so the wide allowance lib/trajectory/validate.ts once carried for Earth was removed rather than corrected, and the tight 400 km default applies here instead. Four of the merged segments - the ones covering the second Venus flyby and all three Mercury flybys - carry a caveat in their own comments, and it is stronger than a footnote: each embeds a planetary ephemeris re-fitted locally from the navigation tracking data (named NAVPE001, NAVPE004, NAVPE005 and NAVPE006) and warns explicitly against pairing that segment with DE405, the ephemeris it was fitted from. Each also publishes a table of how far its own fit moved the planets; the largest of the eight figures those four tables give is 6.551 km, for Earth's position at the second Venus flyby, and every one of them is the length of a three-axis difference vector whose components are committed in this record's cited kernel excerpt. This dataset furnishes DE440s regardless, matching the body positions the rest of the catalogue draws - and that substitution was tested rather than assumed harmless. Re-running with DE440s left out entirely, so that each segment answers from its own embedded planets, reproduces the committed closest-approach distance exactly, to 0.000000 km, at all four: two of them carry a direct spacecraft-to-Mercury arc that needs no planetary ephemeris to complete, and the other two resolve through a barycentre sitting exactly where the planet does, since neither Venus nor Mercury has a moon. What the difference tables bound is where a flyby is drawn against the Sun, by at most that 6.551 km; they do not move the closest-approach distances above.

J2000 · Sun-centered · 7724 samples

Coverage: August 3, 2004 to October 31, 2009