Giotto Earth flyby - orbital data

Ed Cannon (ecannon@mail.utexas.edu)
Thu, 24 Jun 1999 03:37:25 -0500

Below is some authoritative information on the Giotto flyby.  It
apparently will be quite a challenge to observe.  Maybe some of
our south Atlantic colleagues will give it a go!  I'll have to
hope for a chance to see Cassini.

Ed Cannon - ecannon@mail.utexas.edu - Austin, Texas, USA

] ... Giotto will once again fly past the Earth on 1 July 1999,
] travelling at a speed of about 3.5 km/sec. The closest distance
] is uncertain, the current best estimate being about 220,000 km
] (just over half the Earth-Moon distance). This will occur at
] around 02.40 UTC (GMT) on 1 July. No attempt will be made to
] reawaken the sleeping spacecraft, but observers in the Southern
] Hemisphere may be able to detect it with large telescopes.
]
] The trajectory relative to the Earth will be almost perpendicular
] to the equator. 15 hours before closest approach (perigee),
] Giotto will be within one degree of the South Pole direction.
] Although the spacecraft will be flying northwards, the Earth's
] rotation will cause Giotto's apparent motion to be mainly
] westwards. At perigee, it is expected to be vertically above the
] South Atlantic, between Tristan da Cunha and South Georgia. It
] will then fly over southern South America as it recedes from the
] Earth. It will cross over the equator 16 hours after perigee.
]
] The swingby is expected to slightly change the orbit, making it a
] little more circular and more inclined. Giotto will continue to
] orbit the Sun for the foreseeable future, completing approximately
] eight revolutions for every nine made by the Earth.
]
] The 1999 Return to Earth: Predicted Orbital Elements.
]
] Giotto's orbital elements with respect to the ecliptic are:
] Semi-major axis - 1.0827 AU. (period 1.127 years)
] Eccentricity - 0.081274.
] Inclination - 5.5353 deg.
] Longitude of ascending node - 279.111 deg.
] Argument of perihelion - 313.2221 deg.
] True anomaly - 339.4604 deg.
]
] Best estimates for the flyby with respect to the equator are:
] Time at perigee - 1999/07/01.11141 (TDB)
] Geocentric distance at perigee - 225,430 km.
] Hyperbolic excess velocity - 3.48 km/s.
] Inclination - 90.38 deg.
] Right ascension of ascending node - 294.69 deg.
] Argument of perigee - 314.09 deg.
] Sub-satellite longitude at perigee - 337.39 deg. East.
] Sub-satellite latitude at perigee - 45.79 deg. South.
] (TDB = Barycentric Dynamical Time, formerly Ephemeris Time)
]