Overview

“Suisei” (PLANET-A) is a spacecraft developed by the Institute of Space and Astronautical Science (ISAS) along with “Sakigake” (MS-T5) with the aim of participating in an international cooperative exploration plan to observe Halley’s Comet, which will return for the first time in 76 years.
It was launched on August 18, 1985 by an M-3SII rocket from the Kagoshima Space Center (currently Uchinoura Space Center), and its orbit was corrected toward Halley’s Comet on November 14. On March 8, 1986, it approached to within 151,000 km of the side of Halley’s Comet facing the Sun.
The six spacecraft observed Halley’s Comet in cooperation with the previously launched Sakigake of ISAS, Vega 1 and 2 of the Academy of Sciences of the Soviet Union, Giotto of the European Space Agency, and NASA’s ISEE (ICE), and these six spacecraft were dubbed the “Halley Armada.”
It continued to observe the solar wind after that, but on February 22, 1991, it ran out of hydrazine, the fuel needed for ground corrections, and on August 20, 1992, it performed an Earth swing-by and ceased operations.

The satellite had a mass of 140 kg, a cylindrical shape with a diameter of 1.4 m and a height of 0.7 m, and had a 0.8 m diameter elliptical high-gain antenna on top.
It left Earth’s gravitational field and orbited the Sun, approaching Halley’s Comet, at a speed of about 282 days per orbit.

Observation Instruments

Ultraviolet imager (UVI)

UVI is an instrument for observing in the ultraviolet band. It was designed to capture the ultraviolet light emitted from the coma and tail of Halley’s Comet.
It consists of a vacuum ultraviolet telescope mirror lens, an ultraviolet image intensifier, and a 122 x 153 pixel CCD detector, with a field of view of 1.85 x 1.96 degrees, and is capable of not only photometry but also imaging.
The CCD is cooled by radiation cooling and is operated in spin sync shift mode to avoid blurring of images caused by the spacecraft’s rotation during imaging.
UVI analyzes the distribution of gas components and dust on the comet by measuring specific wavelengths of ultraviolet light. Its observational capabilities include the ability to measure the intensity and distribution of ultraviolet light with high precision.

Energy analyser of charged particles (ESP)

ESP is an instrument that analyzes the energies of charged particles around Halley’s Comet. The instrument is used to measure the energy spectrum of ions and electrons in the comet’s tail and coma.
The sensor consists of a sector-shaped collimator with a 5 × 60 degree field of view and a 270 degree spherical electrostatic analyzer with a microchannel plate with five anodes.
The observable energy range is from 30 eV/q to 16 keV/q in 96 steps, which are equally spaced on a logarithmic scale, with an energy resolution of ΔE/E = 0.06.
By detecting the energy of charged particles and analyzing their distribution, ESP will reveal the comet’s physical properties and its interaction with the solar wind.

Achievements

Suisei provided detailed observational data of Halley’s Comet, providing valuable information on the comet’s gas composition, dust distribution, and the energy spectrum of charged particles. This has deepened our understanding of the comet’s physical properties and its interaction with the solar wind. In particular, the data obtained from ultraviolet observations has greatly contributed to the analysis of the comet’s gas composition.