Overview

“Sakigake” (MS-T5) is a spacecraft developed by the Institute of Space and Astronautical Science (ISAS) along with “Suisei” (PLANET-A) for the purpose of participating in an international cooperative exploration plan to observe Halley’s Comet, which will return for the first time in 76 years.
Prior to the Suisei, it was launched on January 7, 1985 by the M-3SII rocket from the Kagoshima Space Center (currently the Uchinoura Space Center).
The missions included confirming the rocket’s flight performance, achieving Japan’s first interplanetary orbit, generating and determining the orbit required for launch into a solar orbit, communicating over extremely long distances, and controlling and determining attitude.
Sakigake itself was also equipped with scientific observation equipment and took part in the Halley’s Comet observation mission along with Suisei, which was launched on August 19, 1985, and probes from Europe, America, and Russia.
It made its closest approach to Halley’s Comet on March 11, 1986, and observed the solar wind magnetic field, plasma activity, and solar wind plasma waves near Halley’s Comet. It continued to observe solar wind plasma waves for 14 years until it ceased operations in 1999.

The satellite was cylindrical, with a mass of 138 kg, a diameter of 1.4 m, and a height of 0.7 m, and had an antenna on top.
After leaving the Earth’s gravitational field, it orbited the Sun, approaching Halley’s Comet, at a speed of about 282 days per orbit.

Observation Instruments

Plasma wave probe (PWP)

PWP is an instrument that observes plasma waves in the low frequency band (LF) of 30 - 195 kHz. The purpose of this instrument is to detect plasma waves generated by shock waves passing through the cometary coma.
The PWP observation data shows many ascending and descending types of emissions, which are thought to be plasma waves generated by shock waves in the cometary coma.

Interplanetary magnetic field measurement (IMF)

IMF is an instrument that continuously records the magnetic field in interplanetary space using a three-axis ring-core sensor.
IMF observational data was used to understand the cause of disturbances in the ion tail of a comet.

Solar wind ion detector (SOW)

SOW uses the spin of the craft to measure the bulk velocity of solar wind ions, plasma flow direction, ion density, and ion temperature with Faraday cup-type sensors.
The instrument observed the general structure of the solar wind in detail during the year before its closest approach to the comet.
SOW observational data provided important information for understanding the interaction of the comet’s coma with the solar wind.

Achivements

Sakigake is Japan’s first space probe to achieve interplanetary orbit.
The observational data suggested that disturbances in the comet’s ion tail are caused by the high-speed solar wind. It also confirmed the presence of plasma waves in the comet’s coma and showed that they may be stimulated by shock waves.
These results provided important clues for a deeper understanding of the interaction between comets and the solar wind.