International Cometary Explorer

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Operator NASA, ESA
Mission type Earth/Moon L1 libration point orbiter (ISEE-3), Giacobini-Zinner & Halley's Comet (ICE)
Launch date August 12, 1978
Launch vehicle Delta 2914
Satellite of Sun
COSPAR ID 1978-079A
Mass 390 kg
Orbital elements
Eccentricity .05
Inclination .1°
Apoapsis 1.03 AU
Periapsis .93 AU
Orbital period 355 d

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 ESRO/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 orbit spacecraft (ISEE-3, later renamed ICE).

ISEE-3 was the first spacecraft to be placed in a halo orbit at one of Earth-Sun Lagrangian points (L1). It was later (as ICE) sent to visit Comet Giacobini-Zinner and became the first spacecraft to do so by flying through a comet's tail passing the nucleus at a distance of approximately 7800 km.[1] ICE was not equipped with cameras.

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

The ISEE-3, (later ICE), undergoing testing and evaluation.

ISEE-3 originally operated in a halo orbit about the L1 Sun-Earth Lagrangian point, 235 Earth radii above the surface (about 1.5 million km, or 924,000 miles). 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.

ISEE-3 was spun at 20 rpm, with a rotational axis in line with the ecliptic, to keep it properly oriented for its experiments and solar power generation.

Second mission: International Cometary Explorer[edit]

ICE mission
Top-down view of the orbit of ISEE-3(ICE) relative to the inner solar system.

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[edit]

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[edit]

ICE transited between the Sun and Comet Halley in late March 1986, when other spacecraft (Giotto, Vega 1 and 2, Suisei and Sakigake) were in the vicinity of Comet Halley on their early March comet rendezvous missions (see Halley Armada). ICE flew through the tail and its minimum distance to the comet nucleus was 28 million km[2] (for comparison the Earth's minimum distance to Comet Halley in 1910 was 20.8 million km[3]).

Heliospheric mission[edit]

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.

End of mission[edit]

On May 5, 1997, NASA ended the ICE mission, and ordered the probe shut down, with only a carrier signal left operating.

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 December 9, 1985), 256 bit/s (on January 5, 1987), 128 bit/s (on January 24, 1989) and finally to 64 bit/s (on December 27, 1991).

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.[4]

Further contact[edit]

In 1999, NASA made brief contact with ICE to verify its carrier signal.

On September 18, 2008, NASA, with the help of KinetX, located ICE using the Deep Space Network after discovering that it had not been powered off after the 1999 contact. A status check revealed that all but one of its 13 experiments were still functioning, and it still has enough propellant for 150 m/s of Δv. NASA scientists considered reusing the probe to observe more comets in 2017 or 2018.[5] Such a mission, however, would delay any attempt to capture the spacecraft until the 2040s.

ICE's current trajectory will bring it close to Earth in August 2014. [4] On February 4, 2014, the Goddard Space Flight Center announced that the Deep Space Network equipment necessary to transmit signals to the spacecraft had been decommissioned in 1999, and that replacing it was not economically feasible.[6] But an 18-meter satellite dish at the Johns Hopkins Applied Physics Laboratory does still have the right hardware, and NASA gave them approval to try to achieve contact. If they can get it to change its orbit by late May or early June, it could use the moon's gravity to get back into a halo orbit from which it could once again perform its original mission. This is the only realistic chance to do that.[7]

ISEE 1 and ISEE 2[edit]

ISEE 1 and ISEE 2 were launched on October 22, 1977 from Cape Canaveral by a Delta rocket, and both re-entered on September 26, 1987.[8]


  • von Rosenvinge, Tycho T.; Brandt, John C.; Farquhar, Robert W. (18 April 1986). "The International Cometary Explorer Mission to Comet Giacobini-Zinner". Science 232 (4748): 353–356. Bibcode:1986Sci...232..353V. doi:10.1126/science.232.4748.353. 
  • Oglivie, K.W.; Durney, A.; von Rosenvinge, T. (July 1978). "Descriptions of Experimental Investigations and Instruments for the ISEE Spacecraft". IEEE Transactions on Geoscience Electronics. GE-16 (3): 151–153. doi:10.1109/TGE.1978.294535. 
  • [9]


  1. ^ Stelzried, C1.; Efron, L.; Ellis, J. (July–September 1986). "Halley Comet Missions" (PDF). NASA. pp. 241–242. 
  2. ^ Paul Murdin, ed. (2001). "International Cometary Explorer (ICE)". Encyclopedia of Astronomy and Astrophysics. Bristol: Institute of Physics Publishing. doi:10.1888/0333750888/4650. 
  3. ^ Reddy, Francis. "Comets - How bright will it be?". 
  4. ^ a b ISEE-3/ICE - International Sun-Earth Explorer 3 - International Cometary Explorer
  5. ^ Lakdawalla, Emily (October 3, 2008). "It's Alive!". The Planetary Science Weblog. 
  6. ^ Lakdawalla, Emily (February 7, 2014). "ICE/ISEE-3 to return to an Earth no longer capable of speaking to it". The Planetary Science Weblog. 
  7. ^ Greenfieldboyce, Nell (March 18, 2014). "Space Thief Or Hero? One Man's Quest To Reawaken An Old Friend". NPR. 
  8. ^ ISEE 2, NSSDC ID: 1977-102B
  9. ^ Birmingham, T. J. (1998). Comet Encounters. Compiled from Papers published in the Journal of Geophysical Research and Geophysical Research Letters. Washington, DC.: American Geophysical Union. 

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