MS T5 (Sakigake), Planet A (Suisei)

Planet A [ISAS]

Sakigake ('Pioneer') is a test spacecraft similar to Suisei (Planet-A). It flew by Comet 1P/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.

Sakigake carried following instruments:

• Plasma Wave Probe (PWP)
• Magnetometer (IMF)
• Solar Wind Experiment (SOW)

Suisei (the Japanese name meaning `Comet') was launched on August 18, 1985 into heliocentric orbit to fly by Comet 1P/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.

Suisei carried following instruments:

• Ultraviolet Imager (UVI)
• Plasma Experiment (ESP)