ISEE-3/ICE: The first cometary flyby

Artist's Illustration of ISEE-3/ICE. Credit: NASA

• Launch Date: August 12, 1978
• Launch Site: Launch Complex 17B, Cape Canaveral Florida, United States
• Launch Vehicle: Delta 2914 (no.144/Thor no. 633)
• Mission Type: Flyby
• Targets: 21P/Giacobini-Zinner, Halley's Comet, and Earth's Magnetosphere
• Dimensions: Unavailable
• Mass: 479 Kilograms

The International Sun-Earth Explorer-3 (ISEE-3) was originally intended to collect data on Earth's magetic tail. It was later repurposed to visit two comets.

The Mission

As the name suggests, ISEE-3 was the third mission of its kind. This spacecraft, as well as the first one, were built by NASA, while the second was built by ESA. ISEE-3 was placed in the L1 Lagrange point between the Sun and Earth on November 20, 1078.

After completing its initial scientific goals, scientist proposed to send the spacecraft to investigate the tail of Earth's magnetic field, and then use a lunar gravity assist to send the spacecraft into interplanetary space.

The spacecraft used its thrusters to liberate itself from the L1 point on June 10, 1982. After making new measurments of Earth's magnetic field, the spacecraft was given another new mission. Renamed the International Cometary Explorer (ICE), the spacecraft used 5 complicated gravity assists of the moon to put it on a heliocentric orbit. The spacecraft would then observe the comet 21P/Giacobini-Zinner.

ICE making a gravity assist around the moon. Credit: Solar Walk 2/Orchard

On December 22, 1983, the spacecraft made its last lunar flyby, and headed off for the comet. On September 11, 1985, the spacecraft came within 7,862 kilometres of the comet's nucleus. Data from ICE showed that the comet was a "dirty snowball" as predicted by scientists.

ICE was later redirected to visit Halley's comet, though it didn't get nearly as close as ESA's Giotto spacecraft did. Closest approach on March 28, 1986 was 40.2 million kilometres from the nucleus. NASA terminated operations with ICE on May 5, 1997, but kept the transmitter operational to easily track it.

In 2014, independent engineers and scientist proposed to reactivate the spacecraft, since it would be nearing Earth's sphere of influence that year. The spacecraft still had 5 functioning instruments onboard, and they wanted to put ICE back in orbit around Earth to "resume its original mission."

The project was entirely publicly funded, and NASA signed an agreement in May that year. While the first thruster burn performed nominally, after not being used in 27 years, the second failed. The spacecraft passed by the moon on August 10, 2014, and failed to enter orbit around Earth.

The Targets

Giacobini-Zinner as seen by the Kitt Peak telescope on October 31, 1998. Credit: N.A.Sharp/NOAO/AURA/NSF

• Date Discovered: December 20, 1900
• Designation: 21P/Giacobini-Zinner
• Class: Jupiter-Family Comet [NEO]
• Radius: 1 Kilometre
• Rotational Period: N/A
• Orbital Period: 2392.12 Days (6.55 Years)

  
  
  
  

  Giotto image of Halley's Comet. Credit: Halley Multicolor Camera Team, Giotto Project, ESA

• Date Discovered: December 25, 1758 (was seen for hundreds of years before, but wasn't recognized as the same comet)
• Designation: 1P/Halley
• Class: Halley-Type Comet [NEO]
• Radius: 5.5 Kilometres
• Rotational Period: 2.2 Days
• Orbital Period: 27726.15 Days (75.91 Years)