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Suisei

Japanese Probe to Halley's Comet
Courtesy of NASA's National Space Science Data Center

Suisei (the Japanese name meaning `Comet') was launched on March 18, 1985, into heliocentric orbit to fly by Comet P/Halley. It is identical to Sakigake apart from its payload: a CCD ultraviolet (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 November 1985, generating up to 6 images/day.

The spacecraft encountered Comet P/Halley at 151,000 kilometers (93,831 miles) on the sunward side during March 8, 1986, suffering only 2 dust impacts. Fifteen burns of Suisei's 3-Newton motors over 5 - 10 April 1987, yielded a 65 meters (213 feet) per second velocity increase for a 60,000 kilometer (37,000-mile) Earth gravity assist swingby on August 20, 1992, although the craft was then lost behind the Sun for the summer. Preliminary tracking indicated a 900,000-kilometer (559,000-mile) flyby had been achieved.

Further orbit corrections will have to be commmanded from Japan's 64 meter (210-foot) Usuda deep space antenna. ISAS decided during 1987 to guide Suisei to a November 24, 1998, encounter with P/Giacobini-Zinner only 5 days before Sakigake's arrival. It will also fly within several million kilometers of Comet P/Tempel-Tuttl on February 28, 1998.

The probe is operated by Japan's Institute of Space and Aeronautical Science (ISAS).

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