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Key Dates:

  • 01.07.85 Launch (19:26 UT)
  • 03.11.86 Comet Halley Flyby
  • Status: Mission Complete

Scientific Instruments:

  1. Solar wind ion monitor (SOW)
  2. Plasma wave monitor (PWP)
  3. Magnetometer for solar wind and interplanetary space (IMF)

Fast 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.

Mission Results:

The Sakigake mission received its name after launch and was originally called MS-T5. Sakigake was the first deep space spacecraft 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 stated goal was "Verification of rocket's flight performance, orbit in interplanetary space of test explorer for the first time in Japan, planning and determination of orbit in interplanetary space necessary for launch into heliocentric orbit, ultra-far distance communications, control and determination of altitude, etc."

It flew by Comet P/Halley on its sunward side at a distance of about 7 million kilometers on March 11, 1986. It carried three instruments to measure plasma wave spectra, solar wind ions, and interplanetary magnetic fields, all of which worked normally. The spacecraft was spin-stabilized at two different rates (5 and 0.2 rpm). It was equipped with hydrazine thrusters for attitude and velocity control, star and sun sensors for attitude determination, and a mechanically despun off-set parabolic dish for long-range communication. Sakigake made an Earth swingby on January 8, 1992. The closest approach was at 23h08m47s (JST, = UTC+9h) with a geocentric distance of 88,997 km. This was the first planet-swingby for a Japanese spacecraft. During the approach, Sakigake observed the geotail. A geotail passage occurred at 290 Re on 14 June 1993 before ISTP's multi-spacecraft investigation of that region. The second Earth swingby was on June 14, 1993 at 40 Re, and the third on October 28, 1994 at 86 Re. Almost no hydrazine remains so no further maneuvers were accomplished. Telemetry contact was lost on 15 November 1995 at a distance of 106 million km. Future mission planning had included a 23.6 km/s, 10,000 km flyby of Comet P/Honda-Mrkos-Pajdusakova on Feb 3, 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 Nov 29, 1998.

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 distance 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.

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