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Suisei (the Japanese name meaning `Comet') was launched on August 18, 1985 into heliocentric orbit to fly by Comet P/Halley. It is identical to Sakigake apart from its payload: a CCD UV imaging system and a solar wind instrument. The main objective of the mission was to take UV images of the hydrogen corona for about 30 days before and after Comet Halley's descending crossing of the ecliptic plane. Solar wind parameters were measured for a much longer time period. The spacecraft is spin-stabilized at two different rates (5 and 0.2 rpm). Hydrazine thrusters are used for attitude and velocity control; star and sun sensors are for attitude control; and a mechanically despun off-set parabolic dish is used for long range communication. Suisei began UV observations in Nov. 1985, generating up to 6 images/day. The spacecraft encountered Comet P/Halley at 151,000 km on sunward side during March 8, 1986, suffering only 2 dust impacts. Fifteen burns of Suisei's 3 N motors over 5--10th of April 1987 yielded a 65 m/s velocity increase for a 60,000 km Earth gravity assist swingby on August 20, 1992, although the craft was then lost behind the Sun for the summer. The hydrazine was depleted on 22 February 1991. Preliminary tracking indicated a 900,000 km flyby had been achieved. ISAS had decided during 1987 to guide Suisei to a Nov. 24, 1998 encounter with P/Giacobini-Zinner, but due to depletion of the hydrazine, this, as well as plans to fly within several million kilometers of Comet P/Tempel-Tuttle on Feb. 28, 1998 has been cancelled.

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

Alternate Names

  • Planet-A
  • Comet
  • 15967

Facts in Brief

Launch Date: 1985-08-18
Launch Vehicle: M-3SII
Launch Site: Uchinoura Space Center, Japan
Mass: 139.5 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
Dr. Mikio ShimizuProject ScientistInstitute of Space and Aeronautical Science 
Prof. Kunio HiraoProject ManagerInstitute of Space and Aeronautical Science 

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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