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These Explorer-class heliocentric spacecraft were part of the mother/daughter/heliocentric mission (ISEE 1, 2, and 3). The purposes of the mission were: (1) to investigate solar-terrestrial relationships at the outermost boundaries of the Earth's magnetosphere; (2) 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; (3) to investigate motions of and mechanisms operating in the plasma sheets; and, (4) to continue the investigation of cosmic rays and solar flare emissions in the interplanetary region near 1 AU. The three spacecraft carried a number of complementary instruments for making measurements of plasmas, energetic particles, waves, and fields. The mission thus extended the investigations of previous IMP spacecraft. The launch of three coordinated spacecraft in this mission permitted the separation of spatial and temporal effects. 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 Lagrangian librations point (L1) 235 Earth radii on the sunward side of the Earth, where it continuously monitored changes in the near-Earth interplanetary medium. In conjunction with the mother and daughter spacecraft, which had eccentric geocentric orbits, this mission explored the coupling and energy transfer processes between the incident solar wind and the Earth's magnetosphere. In addition, the heliocentric ISEE 3 spacecraft also provided a near-Earth baseline for making cosmic-ray and other planetary measurements for comparison with corresponding measurements from deep-space probes. ISEE 3 was the first spacecraft to use the halo orbit. In 1982 ISEE 3 conducted a series of maneuvers that resulted in it being ejected out of the Earth-Moon system and into a heliocentric orbit ahead of the Earth, on a trajectory intercepting that of Comet Giacobini-Zinner. At this time, the spacecraft was renamed International Cometary Explorer (ICE). The primary scientific objective of ICE was to study the interaction between the solar wind and a cometary atmosphere. The spacecraft traversed the plasma tail of Comet Giacobini-Zinner and made in situ measurements of particles, fields, and waves. It also transited between the Sun and Comet Halley, when other spacecraft (Giotto, Planet-A, MS-T5, VEGA) were also in the vicinity of Comet Halley on their comet rendezvous missions. ICE became the first spacecraft to directly investigate two comets. Tracking and telemetry support have been provided by the DSN (Deep Space Network). The ISEE bit rate was nominally 2048 bps during the early part of the mission, and 1024 bps during the Giacobini-Zinner comet encounter. An update to the ICE mission was approved by NASA headquarters in 1991. It defined a Heliospheric mission for ICE consisting of investigations of coronal mass ejections in coordination with ground-based observations, continued cosmic ray studies, and special period observations such as when ICE and Ulysses were on the same solar radial line. Termination of operations of ISEE 3 was authorized May 5, 1997. Typical orbit: 341 x 454923 km, 9 deg inclinaton. ISEE Chronology
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