The International Cometary Explorer (ICE) spacecraft, designed and launched as the International Sun-Earth Explorer-3 (ISEE-3) satellite, was launched on 12 August 1978 into a heliocentric orbit. It was one of three spacecraft, along with the mother/daughter pair of ISEE-1 and ISEE-2, built for the International Sun-Earth Explorer (ISEE) program, a joint effort by NASA and ESRO/ESA to study the interaction between the Earth's magnetic field and the solar wind. ISEE-3 was the first spacecraft to be placed in a halo orbit at the L1 Earth–Sun Lagrange point. Renamed ICE, it became the first spacecraft to visit a comet, passing through the plasma tail of comet Giacobini-Zinner within about 7,800 km (4,800 mi) of the nucleus on 11 September 1985. NASA suspended routine contact with ISEE-3 in 1997 and made brief status checks in 1999 and 2008. On 29 May 2014, two-way communication with the spacecraft was reestablished by the ISEE-3 Reboot Project, an unofficial group, with support from the Skycorp company and SpaceRef Interactive. On 2 July 2014, they fired the thrusters for the first time since 1987. However, later firings of the thrusters failed, apparently due to a lack of nitrogen pressure in the fuel tanks. The project team initiated an alternative plan to use the spacecraft to "collect scientific data and send it back to Earth", but on 16 September 2014, contact with the probe was lost.
Original mission: International Sun/Earth Explorer 3 (ISEE-3)
ISEE-3 carries no cameras; instead, its instruments measure energetic particles, waves, plasmas, and fields. ISEE-3 originally operated in a halo orbit about the L1 Sun-Earth Lagrange point, 235 Earth radii above the surface (about 1,500,000 km (930,000 mi). It was the first artificial object placed at a so-called "libration point", entering orbit there on 20 November 1978, proving that such a suspension between gravitational fields was possible. It rotates at 19.76 rpm about an axis perpendicular to the ecliptic, to keep it oriented for its experiments, to generate solar power and to communicate with Earth. The purposes of the mission were:
to investigate solar-terrestrial relationships at the outermost boundaries of the Earth's magnetosphere; to examine in detail the structure of the solar wind near the Earth and the shock wave that forms the interface between the solar wind and Earth's magnetosphere; to investigate motions of and mechanisms operating in the plasma sheets; and, to continue the investigation of cosmic rays and solar flare emissions in the interplanetary region near 1 AU.
Second mission: International Cometary Explorer When NASA rejected space probe mission to Halley’s Comet, Frederick L. Scarf of TRW, with a help of NASA's Robert W. Farquhar, found a way to bypass bureaucracy "to gain control of an orbiting research satellite that had already outlived its usefulness". ISEE-3 was sent from its L1 point to the comet Giacobini-Zinner in September 1985; Scarf himself told the reporter: “We stole it [the satellite]”. The probe proved that the comet "sends out shock waves as it passes through space". ISEE-3 became the first space probe that studied a comet. After completing its original mission, ISEE-3 was re-tasked to study the interaction between the solar wind and a cometary atmosphere. On 10 June 1982, the spacecraft performed a maneuver which removed it from its halo orbit around the L1 point and placed it in a transfer orbit. This involved a series of passages between Earth and the Sun-Earth L2 Lagrange point, through the Earth's magnetotail. Fifteen propulsive maneuvers and five lunar gravity assists resulted in the spacecraft being ejected from the Earth-Moon system and into a heliocentric orbit. Its last and closest pass over the Moon, on 22 December 1983, was only 119.4 km (74.2 mi) above the lunar surface; following this pass, the spacecraft was re-designated as the International Cometary Explorer (ICE).
Giacobini-Zinner encounter Its new orbit put it ahead of the Earth on a trajectory to intercept comet Giacobini-Zinner. On 11 September 1985, the craft passed through the comet's plasma tail. ICE did a flyby of the comet nucleus at a distance of 7,800 km (4,800 mi) of the nucleus on 11 September 1985.
Halley encounter ICE transited between the Sun and Comet Halley in late March 1986, when other spacecraft were near the comet on their early-March comet rendezvous missions. (This "Halley Armada" included Giotto, Vega 1 and 2, Suisei and Sakigake.) ICE flew through the tail; its minimum distance to the comet nucleus was 28×10^6 km (17×10^6 mi). For comparison, Earth's minimum distance to Comet Halley in 1910 was 20.8×10^6 km (12.9×10^6 mi).
Heliospheric mission An update to the ICE mission was approved by NASA in 1991. It defines a heliospheric mission for ICE consisting of investigations of coronal mass ejections in coordination with ground-based observations, continued cosmic ray studies, and the Ulysses probe. By May 1995, ICE was being operated under a low-duty cycle, with some data-analysis support from the Ulysses project.
End of mission On 5 May 1997, NASA ended the ICE mission, leaving only a carrier signal operating. The ISEE-3/ICE downlink bit rate was nominally 2048 bits per second during the early part of the mission, and 1024 bit/s during the 21P/Giacobini–Zinner comet encounter. The bit rate then successively dropped to 512 bit/s (on 9 December 1985), 256 bit/s (on 5 January 1987), 128 bit/s (on 24 January 1989) and finally to 64 bit/s (on 27 December 1991). Though still in space, NASA donated the craft to the Smithsonian Museum. By January 1990, ICE was in a 355-day heliocentric orbit with an aphelion of 1.03 AU, a perihelion of 0.93 AU and an inclination of 0.1°.
Further contact In 1999, NASA made brief contact with ICE to verify its carrier signal. On 18 September 2008, NASA, with the help of KinetX, located ICE using the NASA Deep Space Network after discovering that it had not been powered off after the 1999 contact. A status check revealed that 12 of its 13 experiments were still functioning, and it still had enough propellant for 150 m/s (490 ft/s) of Δv. It was determined to be possible to reactivate the spacecraft in 2014, when it again made a close approach to Earth, and scientists discussed reusing the probe to observe more comets in 2017 or 2018.
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