The Continued Journey of the International Cometary Explorer

The Third International Sun-Earth Explorer (ISEE-3) became the first spacecraft to orbit a Lagrangian point (Sun-Earth L₁) in 1978. In a daring extended mission, ISEE-3 was nudged out of its halo orbit to swing by the Moon five times, exploring the geomagnetic tail before being ejected by the last lunar swingby into a heliocentric orbit that reached Comet Giacobini-Zinner in 1985. The spacecraft was renamed the International Cometary Explorer (ICE)¹. A schematic of the multiple swingby trajectory is on the cover of Celestial Mechanics and Dynamical Astronomy. Since 1983, ICE slowly drifted away from the Earth, reached superior conjunction in 1999, and is now drifting towards the Earth, due to arrive in 2014. In 1986, the last maneuvers were performed to target a lunar swingby on August 10, 2014; additional maneuvers with the remaining 150 m/sec spacecraft ΔV capacity were designed to capture it into a highly elliptical Earth orbit².

In September 2008, NASA's Deep Space Network acquired and tracked ICE, showing that the spacecraft's transmitter is working and that its 1990's-era orbit is accurate. A small group is planning for the 2014 return, locating command documentation and hardware for communicating with and maneuvering ICE. Maneuvers of only about 2 m/sec performed anytime from 2010 to 2013 can target either an Earth or lunar (as described in Ref. 2) swingby. Low-ΔV options will be shown where ICE can be returned to a Sun-Earth L₁ halo orbit, or can use multiple Earth swingbys to encounter Comet Wirtanen during its near-Earth apparition in December 2018.

¹Farquhar, R. W., "The Flight of ISEE-3/ICE: Origins, Mission History, and a Legacy", J. Astronaut. Sci. 49, 23-73 (2001).

²Roberts, C. E., Dunham, D. W., and Farquhar, R. W., "The International Cometary Explorer Comet Encounter and Earth-Return Trajectory", Adv. Astronaut. Sci. 69, 709-725 (1989).