ISEE-3/ICE

By Marty McDowell/NASA

The International Sun-Earth Explorer 3 (ISEE-3) spacecraft was one of three spacecraft (ISEE 1, 2 & 3) whose purpose was to study the solar wind and the solar-Earth relationship at the boundaries of the Earth's magnetosphere. In 1981, it was proposed that ISEE-3 be rerouted towards a comet. To that point, the mission was not intended to study comets. After a series maneuvers and flybys of the moon, ISEE-3 encountered Comet Giacobini-Zinner in 1985 and provide distance observations of Comet Halley in 1986.

Launched on August 12, 1978, ISEE-3's first mission was to use instruments for making measurements of plasmas, energetic particles, waves, and fields to measure the solar wind. On June 10, 1982 the first of maneuvers necessary to move the spacecraft in position to meet the comet began which moved the spacecraft out of its halo orbit where it had been for nearly four years. Fifteen complicated maneuvers that would make the average teenage Atari Asteroids champion envious were required (this included five lunar flybys!). The fifth and final lunar flyby on December 22, 1983, passed a mere 119 kilometers above the Moon's surface not far from the Apollo 11 landing site. The craft and mission was renamed ICE (International Cometary Explorer) to reflect the new mission goals. 

By June 5, 1985, the spacecraft had been maneuvered to within 27,000 kilometers behind Comet Giacobini-Zinner. This allowed the craft's fields and particles instruments to sample the comet's tail. For the first time ever, measurements of a comet from the comet were made as the first ions were detect on September 11 (which is also the date of its closest approach - a mere 7,862 kilometers). This craft did not include a camera among its instruments, so the first close-up pictures of a comet would not appear for another year. The spacecraft found a region of interacting cometary and solar wind ions, and encountered a comet plasma tail about 25,000 km wide. Water and carbon monoxide ions were also identified, confirming what astronomers had long confirmed. A comet is a "dirty snowball" - dust and ice.

It Takes a Licking and Keeps on Ticking

The venerable spacecraft did not have any protection against the high-velocity dust and was expected to suffer significant damage. The damage was minimal as the rate of one dust impacts per second was significantly below estimates.

The Only U.S. Observations of Halley

In 1986, ICE made distant observations of Comet Halley on the sunward side of the comet. Because of the cancellation of projects due to the Challenger tragedy, these observations were the only made by the U.S. from space of the comet. At its closest approach, it drifted by at a distance of 31M kilometers from the comet on March 28, 1986. Contrast this with the 9,900 kilometer distance of the Soviet Vega 1 craft, and you get a picture of how out of the running the Americans were in the pursuit of Comet Halley.

Lassie, Come Home

In the year 2014, the ICE spacecraft will be close enough to Earth that it might be captured. This would allow scientists and engineers to analyze its exterior for dust impacts. Who knows? You might even be able to bid on it on eBay. (Actually, NASA has already committed to donate the spacecraft to the Smithsonian Institute for display should it be recovered.)

Source: NASA.

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Space References (Videos):
Cosmos. PBS, 2000.
Stephen Hawking's Universe. PBS, 1997.
Hyperspace. BBC, 2002.
Life Beyond Earth PBS, 1999.
The Planets. BBC, 1999.
Understanding The Universe. A&E, 1996.