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Sakigake Mission to Comets

Mission Type: Flyby
Launch Vehicle: Mu-3S-II (No. 1)
Launch Site: Kagoshima Space Center, Japan
Spacecraft Mass: 138.1 kg
Spacecraft Instruments: 1) solar wind ion detector; 2) plasma wave probe and 3) magnetometer
Spacecraft Dimensions: Outer drum: 70 cm high, 140 cm diameter
Spacecraft Power: 1750 solar cells with a 2 A-hr nickel-cadmium battery
Maximum Power: 100 W
S-Band Data Rate: 64 bps at closest approach
Maximum Data Rate: 64 bps
Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, Monographs in Aerospace History No. 24, by Asif A. Siddiqi

National Space Science Data Center,

Solar System Log by Andrew Wilson, published 1987 by Jane's Publishing Co. Ltd.

The MS-T5 spacecraft was the first deep-space vehicle launched by any country apart from the Soviet Union and the United States (the two German Helios probes had been launched by NASA). Japan's goal was to launch a single modest probe to fly past Comet Halley. The country's Institute of Space and Astronautical Sciences (ISAS) launched this test spacecraft, nearly identical to Suisei, the actual vehicle launched later, to prove out the technologies and operations of the actual mission. A new Japanese launch vehicle, the Mu-3S-II, propelled the spin-stabilized spacecraft into space. After launch, the spacecraft was renamed "Sakigake," which means "pioneer" in Japanese.

Following two course corrections on 10 January and 14 February 1985, Sakigake was sent on a long-range encounter (about 7.6 million kilometers) with Halley. The spacecraft served as a reference vehicle to permit scientists to eliminate Earth atmospheric and ionospheric contributions to the variations in Giotto's transmissions from within the coma. The spacecraft's closest approach to Halley was at 04:18 UT on 11 March 1986, when it was 6.99 million kilometers from the comet. Sakigake found that the solar wind appeared to be disturbed by the comet at that distance. Previously, it had been thought that the range of a comet's influence on the solar wind was only 1 million km. (Sakigake's near-twin, Suisei, found the range to be only 420,000 km.)

Nearly six years after the Halley encounter, Sakigake flew by Earth on 8 January 1992 at a range of 88,790 kilometers. After two more distant flybys through Earth's magnetic tail (in June 1993 and July 1994), Sakigake maintained weekly contact with the ground until telemetry was lost on 15 November 1995, although the ground continued to receive a beacon signal until all contact was terminated on 7 January 1999.

Future mission planning had included a 23.6 km/s, 10,000 km flyby of Comet P/Honda-Mrkos-Pajdusakova on 3 February 1996 (approaching the nucleus along the tail) some 0.17 AU from the Sun, and a 14 million km passage of Comet P/Giacobini-Zinner on 29 November 1998.

Key Dates
7 Jan 1985:  Launch (19:26 UT)
11 Mar 1986:  Comet Halley Flyby
Status: Successful
Fast Facts
Sakigake Facts Sakigake was the first deep space mission launched by any country other than the United States and the Soviet Union.

The spacecraft was nearly identical to the Japanese Suisei spacecraft launched eight months later.

Sakigake means pioneer in Japanese.
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Last Updated: 1 Dec 2010