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Sakigake & Suisei
Spacecraft Sakigake Suisei
Country Japan Japan
Mission Comet Halley Flyby Comet Halley Flyby
Launch Date January 7, 1985 August 18, 1985
Launch Vehicle Mu-3SII Mu-3SII
Spacecraft Mass 138.1 kg 139.5 kg
Key Dates Mar 11, 1986 - Comet Halley Flyby Mar 8, 1986 - Comet Halley Flyby
End of Mission 1998? 1991
Comments First Japanese Deep Space Probe Second Japanese Deep Space Probe

sakigake_s.jpg On January 7, 1985, Japan launched a spacecraft originally known as MS-T5 which was then renamed to Sakigake (Japanese word for "Pioneer"). Sakigake was Japan's first ever deep space probe and its mission was to measure the solar wind and magnetic field as it flew by Halley's Comet. Sakigake was identical to its twin, Suisei, except for its instrument payload. Sakigake carried no imaging instruments. On March 11, 1986, Sakigake made its closest approach to Halley's Comet at a distance of 6.99 million km. Sakigake discovered that the solar wind was affected by the comet's presence at the 6.99 million km distance, but this result conflicted with Suisei's measurement of 420,000 km. Shortly after its closest approach, Sakigake served as a reference spacecraft for Giotto's encounter which helped eliminate Earth atmospheric interference with Giotto's radio signals.

suisei_s.jpg Suisei was Japan's second deep space mission to study Comet Halley. Suisei, meaning "Comet" in Japanese, was identical to Sakigake except for its instrument load. Launched on August 18, 1985, Suisei began observation of Comet Halley in November 1985. The spacecraft returned up to six UV images a day of the comet. Just prior to its closest approach on March 8, 1986, the UV instrument was switched off and the the solar wind experiment was turned on. Cometary water, carbon monoxide and carbon dioxide ions were detected. During closest approach, Suisei was hit by two dust particles which slightly changed the spin axis and spin period of the spacecraft. After the encounter, Suisei continued to monitor Comet Halley, and detected two major and four minor outbursts from the comet as it rotated.

Sakigake is still active and is expected to survive well into the 1990's. Since the Halley's Comet flyby, Sakigake has made a number of Earth flybys with the last occuring on July 3, 1995. However, almost no fuel remains after the last flyby, and it is now no longer possible to send Sakigake to comet Giacobini-Zinner in 1998.

Suisei was planned for a comet Giacobini-Zinner encouter in November 1998. However, the mission ended when Suisei ran out of propellant on February 22, 1991. The spacecraft shut itself off and hasn't been heard from since.


Ron Baalke, STARDUST Webmaster, ron@jpl.nasa.gov
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