What is "sakigake"

, known before launch as MS-T5, was Japan's first interplanetary spacecraft, and the first deep space probe to be launched by any country other than the USA or the Soviet Union. It aimed to demonstrate the performance of the new launch vehicle, test the schemes of the first escape from the Earth gravitation for Japan on engineering basis, and observe space plasma and magnetic field in interplanetary space. Sakigake was also supposed to get references for scientists. Early measurements would be used to improve the mission of the Suisei probe several months later.

Sakigake was developed by the Institute of Space and Astronautical Science for the National Space Development Agency (both of which are now part of the Japanese Aerospace Exploration Agency, or JAXA). It became a part of the Halley Armada together with Suisei, the Soviet/ French Vega probes, the ESA Giotto and the NASA International Cometary Explorer, to explore Halley's Comet during its 1986 sojourn through the inner solar system.