Twenty-five years ago today — March 28, 1986 — the ICE spacecraft flew by Comet Halley.
(Artist’s conception of ISEE-3/ICE. NASA image.)
It was initially placed into an elliptical halo orbit about the Lagrangian libration point (L1) 235 Earth radii on the sunward side of the Earth, where it continuously monitored changes in the near-Earth interplanetary medium. In conjunction with the mother and daughter spacecraft, which had eccentric geocentric orbits, this mission explored the coupling and energy transfer processes between the incident solar wind and the Earth’s magnetosphere. In addition, the heliocentric ISEE 3 spacecraft also provided a near-Earth baseline for making cosmic-ray and other planetary measurements for comparison with corresponding measurements from deep-space probes. ISEE 3 was the first spacecraft to use the halo orbit.
After accomplishing its initial mission, ISEE-3 was retasked:
In 1982 ISEE 3 began the magnetotail and comet encounter phases of its mission. A maneuver was conducted on June 10, 1982, to remove the spacecraft from the halo orbit around the L1 point and place it in a transfer orbit involving a series of passages between Earth and the L2 (magnetotail) Lagrangian libration point. After several passes through the Earth’s magnetotail, with gravity assists from lunar flybys in March, April, September and October of 1983, a final close lunar flyby (119.4 km above the moon’s surface) on December 22, 1983, ejected the spacecraft out of the Earth-Moon system and into a heliocentric orbit ahead of the Earth, on a trajectory intercepting that of Comet Giacobini-Zinner. At this time, the spacecraft was renamed International Cometary Explorer (ICE).
In addition to being the first spacecraft to orbit a Lagrangian libration point, ICE was also the first spacecraft to fly past a comet. It flew first by Comet Giacobini-Zinner, and later by Comet Halley.
Interestingly, in 2014 ICE’s orbit will bring it “close enough to Earth that it could be recaptured if a spacecraft were available.” I wonder if that would make a good story ….by