International Cometary Explorer

History

The International Cometary Explorer (ICE) was a NASA spacecraft originally launched on 12 August 1978 as International Sun-Earth Explorer-3 (ISEE-3). It was the third spacecraft of the International Sun-Earth Explorer program, a cooperative NASA and European effort to study interactions between the solar wind and Earth's magnetic environment.

ISEE-3 became the first spacecraft placed in a halo orbit around the Sun-Earth L1 Lagrange point. After completing its primary mission, NASA redirected the spacecraft through Earth's magnetotail and then toward Comet 21P/Giacobini-Zinner. Following its departure from the Earth-Moon system, it was redesignated the International Cometary Explorer.

On 11 September 1985, ICE became the first spacecraft to encounter a comet, passing through the plasma tail of Comet 21P/Giacobini-Zinner. It later made distant observations of Halley's Comet and remained in heliocentric orbit after completion of its principal scientific missions.

ISEE-3 mission

The International Sun-Earth Explorer program consisted of three spacecraft. ISEE-3 was intended to investigate energetic particles, electric and magnetic fields, plasma, and the solar wind. The spacecraft carried 14 scientific instruments, including equipment for measuring the solar wind, cosmic rays, X-rays, and gamma rays. It carried no cameras.

ISEE-3 operated around the Sun-Earth L1 point approximately 1.5 million km (930,000 mi) from Earth. It entered its L1 halo orbit on 20 November 1978 and became the first artificial object placed into an orbit around a libration point. The spacecraft spent about three years performing its original scientific mission.

Retargeting to a comet

After the primary mission, NASA scientists developed a plan to reuse ISEE-3 for additional research. On 10 June 1982, the spacecraft performed a maneuver that removed it from its L1 halo orbit. Its subsequent trajectory included passages through Earth's magnetotail, fifteen propulsive maneuvers, and five lunar gravity assists.

The final and closest lunar encounter occurred on 22 December 1983, when the spacecraft passed approximately 119.4 km (74.2 mi) above the Moon. This sequence expelled it from the Earth-Moon system into heliocentric orbit and placed it on a trajectory toward Comet 21P/Giacobini-Zinner. The spacecraft was then redesignated International Cometary Explorer.

Comet encounters

ICE reached Comet 21P/Giacobini-Zinner on 11 September 1985. It passed through the comet's plasma tail at a distance of approximately 7,800 km from the nucleus; the source account gives a closest distance of 7,862 km (4,885 mi). Measurements from the encounter provided detailed information about the interaction between the solar wind and the cometary environment. The mission made ICE the first spacecraft to study a comet at close range.

On 28 March 1986, ICE also observed Halley's Comet from a much greater distance. The spacecraft passed about 40 million km (25 million mi) from Halley and collected additional measurements of the cometary environment.

Later mission and 2014 recovery attempt

NASA ended routine ICE mission operations during the 1990s. The supplied sources differ on the precise milestone: one account states that NASA shut down the mission in 1995, while another states that routine contact was suspended in 1997, followed by brief status checks in 1999 and 2008.

Interest in the spacecraft returned in 2014 when an independent group organized the ISEE-3 Reboot Project. Two-way communication was reestablished on 29 May 2014. The group raised funds through crowdfunding and attempted to alter the spacecraft's trajectory as it returned to the vicinity of Earth.

On 2 July 2014, the team successfully fired the spacecraft's thrusters for the first time since 1987. Subsequent propulsion attempts failed, reportedly because of insufficient nitrogen pressure in the propulsion system. ICE passed the Moon and continued in heliocentric orbit. Contact with the spacecraft was lost on 16 September 2014. The supplied account states that it is expected to approach Earth again around 2031.

Design

ICE was a spin-stabilized spacecraft with a barrel-like cylindrical body covered by solar cells. Four long antennas extended from the spacecraft around its circumference. The complete antenna span was approximately 91 m (299 ft). The spacecraft rotated at 19.76 revolutions per minute about an axis perpendicular to the ecliptic, supporting experiment orientation, solar-power generation, and communications with Earth.

The spacecraft had a dry mass of approximately 390 kg (860 lb) and nominal electrical power generation of 173 W. Its scientific payload was designed to measure particles, plasma, waves, electric and magnetic fields, and high-energy radiation rather than to produce optical imagery.

Scientific instruments

ISEE-3 carried 14 scientific instruments. The instrument complement included a solar-wind detector and equipment for studying energetic particles, cosmic rays, X-rays, gamma rays, plasma, and electromagnetic fields. The same basic scientific payload enabled the spacecraft to investigate both the Sun-Earth environment and the plasma conditions associated with comets.

Operational history

The spacecraft's operational life comprised several distinct scientific phases. As ISEE-3, it studied the Sun-Earth environment from the L1 region. It was subsequently redirected through Earth's magnetotail and into heliocentric orbit. As ICE, it conducted the first spacecraft encounter with a comet at Giacobini-Zinner in 1985 and later observed Halley's Comet in 1986.

Its 2014 recovery demonstrated that communications and some spacecraft functions remained available decades after launch, although the attempt to return ICE to a more useful orbit was unsuccessful. Further information about the mission is available from the Space.com mission history and the International Cometary Explorer reference.

Variants

• International Sun-Earth Explorer-3 (ISEE-3): Original designation for the spacecraft during its Sun-Earth and Lagrange-point research mission.
• International Cometary Explorer (ICE): Redesignation adopted after ISEE-3 was redirected from its original mission toward Comet 21P/Giacobini-Zinner.

Operators

• NASA: Built and operated ISEE-3 as part of the cooperative International Sun-Earth Explorer program and subsequently redirected the spacecraft for the ICE comet mission. European organizations participated in the wider ISEE program and scientific cooperation.

Specifications (International Cometary Explorer)

General characteristics

• Type: Scientific deep-space spacecraft
• Original designation: International Sun-Earth Explorer-3 (ISEE-3)
• Launch date: 12 August 1978
• Dry mass: 390 kg (860 lb)
• Configuration: Barrel-like cylindrical, spin-stabilized spacecraft with body-mounted solar cells
• Antenna span: Approximately 91 m (299 ft)
• Spin rate: 19.76 rpm
• Nominal electrical power: 173 W

Scientific payload

• Scientific instruments: 14
• Measurements: Energetic particles, plasma, waves, electric and magnetic fields, solar wind, cosmic rays, X-rays, and gamma rays
• Imaging equipment: No cameras

Mission milestones

• L1 halo-orbit entry: 20 November 1978
• Closest lunar pass during retargeting: 119.4 km (74.2 mi), 22 December 1983
• Giacobini-Zinner encounter: 11 September 1985
• Giacobini-Zinner closest distance: Approximately 7,800 km; one supplied account specifies 7,862 km (4,885 mi)
• Halley's Comet observation: 28 March 1986 at approximately 40 million km (25 million mi)