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Sakigake ('Pioneer') is a test spacecraft similar to Suisei (Planet-A). 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.

Spacecraft image for illustrative purposes - not necessarily in the public domain.

Alternate Names

  • MS-T5
  • Pioneer
  • 15464

Facts in Brief

Launch Date: 1985-01-08
Launch Vehicle: M-3SII
Launch Site: Uchinoura Space Center, Japan
Mass: 138.1 kg
Nominal Power: 100.0 W

Funding Agency

  • Institute of Space and Aeronautical Science, U of Tokyo (Japan)


  • Planetary Science
  • Space Physics

Additional Information

Questions or comments about this spacecraft can be directed to: Dr. David R. Williams.



NameRoleOriginal AffiliationE-mail
Prof. Kunio HiraoProject ManagerInstitute of Space and Aeronautical Science 
Prof. Hiroshi OyaProject ScientistUniversity of

Selected References

Scarf, F. L., The 1985-86 spacecraft missions to comets Giacobini-Zinner and Halley, In -- Advances in Space Plasma Physics, Ed. B. Buti, 22-32, World Scientific Publ. Co., 1985.

Hirao, K., and T. Itoh, The Planet-A Halley encounters, Nature, 321, No. 6067, 294-297, May 1986.

Reinhard, R., Space missions to Halley's comet and international cooperation, In--Comet Halley Investigations, Results, Interpretations Volume 1: Organization, Plasma, Gas, edited by J. W. Mason, Ellis Horwood Ltd, Chichester, England, 1990.

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