International Cometary Explorer Totally Explained

Everything about The International Cometary Explorer totally explained

The International Cometary Explorer (ICE) spacecraft was originally known as International Sun/Earth Explorer 3 (ISEE-3) satellite, launched August 12, 1978. It was part of the ISEE (International Sun-Earth Explorer) international cooperative program between NASA and ESA to study the interaction between the Earth's magnetic field and the solar wind. The program used three spacecraft, a mother/daughter pair (ISEE 1 and ISEE 2) and a heliocentric spacecraft (ISEE 3, later renamed ICE). ICE was the first spacecraft to use this type of "halo" orbit. It was later sent to visit Comet Giacobini-Zinner and Comet Halley, and was the first spacecraft to visit more than one comet.

Original mission: International Sun/Earth Explorer 3 (ISEE-3)

ISEE-3 originally operated in a "halo" orbit about the L₁ Sun-Earth Lagrangian point. It was the first artificial object placed at a so-called "libration point", proving that such a suspension between gravitational fields was possible.
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.

The Explorer-class heliocentric spacecraft, International Sun-Earth Explorer 3, was part of the mother/daughter/heliocentric mission (ISEE 1, 2, and 3). The three spacecraft carried a number of complementary instruments for making measurements of plasmas, energetic particles, waves, and fields.
This heliocentric spacecraft had a spin axis normal to the ecliptic plane and a spin rate of about 20 rpm. It was initially placed into an elliptical halo orbit about the L₁ libration point 235 Earth radii (approximately 1.5 million km, or 932,000 miles) on the sunward side of the Earth, where it continuously monitored changes in the near-Earth interplanetary medium.

Second mission: International Cometary Explorer

On June 10, 1982, after completing its original mission, ISEE-3 was repurposed. It was renamed the International Cometary Explorer (ICE). The primary scientific objective of ICE was to study the interaction between the solar wind and a cometary atmosphere. After a successful thruster burn to knock it loose from its halo orbit on September 1 of that year, it used the instability of the Earth/Moon and Earth/Sun Lagrange points, making a series of lunar orbits over the next 15 months. Its last and closest pass over the Moon, on December 22, 1983, was a mere 119.4 km above the moon's surface. By the beginning of 1984, ICE was in heliocentric orbit.

Giacobini-Zinner encounter

After ejection out of the Earth-Moon system, ICE entered a heliocentric orbit ahead of the Earth on a trajectory intercepting that of Comet Giacobini-Zinner. On 11 September, 1985, the craft passed through the plasma tail of Comet Giacobini-Zinner. Due to the nature of its original mission, ICE carried no cameras. It instead carried instruments for measurements of energetic particles, waves, plasmas, and fields.

Halley encounter

ICE transited between the Sun and Comet Halley in late March 1986, when other spacecraft (Giotto, Vega 1 and 2, Suisei and Sakigake) were also in the vicinity of Comet Halley on their early March comet rendezvous missions (see Halley Armada). ICE became the first spacecraft to directly investigate two comets.

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 with only a low duty cycle, with some support being provided by the Ulysses project for data analysis. Two years later, termination of operations of ICE/ISEE3 was authorized May 5, 1997.

End of mission

Termination of operations of ICE/ISEE3 was authorized May 5, 1997.
The ISEE-3/ICE downlink bit rate was nominally 2048 bit/s during the early part of the mission, and 1024 bit/s during the Giacobini-Zinner comet encounter. The bit rate then successively dropped to 512 bit/s (on 1985-12-09), 256 bit/s (on 1987-01-05), 128 bit/s (on 1989-01-24) and finally to 64 bit/s (on 1991-12-27).
As of 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 degree. It may be possible to capture the spacecraft in 2014, when it again makes a close approach to Earth. If the craft is recovered, it has already been donated by NASA to the Smithsonian Institution.

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