The Japanese space program () has cumulatively launched 384 spacecraft since 1970, the fifth most of any nation. It is currently operated by JAXA, formed from a 2003 merger of the Institute of Space and Astronautical Science (ISAS), National Space Development Agency of Japan (NASDA), and National Aerospace Laboratory of Japan. In recent years, Japanese space policy has been shaped by the US-Japan alliance and intensifying great power competition.
JAXA deployed the SELENE lunar orbiter and the SLIM lander and rovers. Hayabusa achieved the world's first asteroid sample return in 2010; Hayabusa2 deployed the first rovers on an asteroid. Akatsuki studied Venus from orbit from 2015 to 2024. IKAROS was its largest solar sail research mission. BepiColombo, jointly launched with the European Space Agency in 2018, is a Mercury flyby and orbiter mission. Martian Moons eXploration is planned to launch in December 2026 and conduct the first sample return from Phobos.
JAXA operates the medium-lift H3 rocket, from Tanegashima Space Center, and small-lift Epsilon family, from Uchinoura. JAXA is one of five agencies operating the International Space Station (ISS). Japan constructed Kibō, its largest module, and regularly resupplies the station with the HTV-X cargo spacecraft, and the H-II Transfer Vehicle from 2009 to 2025. Since 1992, Japan's Astronaut Corps has flown eleven astronauts aboard Space Shuttle, Soyuz, and Dragon 2 crafts, primarily to the ISS.
History After World War II, many aeronautical engineers lost their jobs as aircraft development was banned under the US Occupation of Japan. In 1951 the San Francisco Peace Treaty once again allowed the development of aviation technology. Following this, Professor Hideo Itokawa of Tokyo University established an aviation research group at the Institute of Industrial Science at the university. That group succeeded in horizontally launching the Pencil Rocket on 12 April 1955 in Kokubunji, Tokyo. The rocket was long and had a diameter of .
The Pencil Rocket was the first experiment of its kind in Japan. Initially, the focus was on the development of rocket-powered aircraft, not space exploration. However, following Japan's participation in the International Geophysical Year, the focus of the rocket project shifted towards space engineering.
Early development Iterations of the Pencil Rocket eventually increased in size to such a degree that experimentation within Kokubunji was deemed too dangerous. Therefore, the launch site was moved to Michikawa Beach in Akita Prefecture. Following the Pencil Rocket, the larger Baby Rocket was developed, which reached an altitude of . After the Baby Rocket, two further rocket projects were carried out: a rockoon-type rocket launched from a balloon and a ground-launched rocket. The development of a rockoon turned out to be too difficult, and that experiment was eventually halted. Among several versions of ground-launched rocket prototypes, the Kappa rocket was one of the most successful, gradually reaching higher altitudes. Due to inadequate funding, the rockets were handmade and the tracking radar was operated manually. Production was based on trial and error.
In 1958, the Kappa 6 rocket reached an altitude of and the collected data allowed Japan to participate in the International Geophysical Year. In 1960, the Kappa 8 rocket exceeded an altitude of . The development of larger rockets necessitated a launch site with a large downrange. The old site in Akita Prefecture, which bordered the narrow Sea of Japan, was deemed insufficient for this purpose and a new launch site on the Pacific coast was created, this time at Uchinoura in Kagoshima Prefecture.
Launch of Ohsumi
In the 1960s, Japanese space research and development was primarily focused on satellite delivery systems. A preliminary plan was made to develop successors to the Kappa rockets, known as Lambda rockets, intended for satellite delivery. The Science and Technology Agency then concentrated its studies of Kappa launches on collecting technical data to help the new rockets reach higher altitudes.
In 1963, the government began a gradual increase in spending on space development. That year, the Science and Technology Agency restructured the National Aeronautical Laboratory (NAL) into the National Aerospace Laboratory. The new NAL was to be the center for research on space technology. However, it soon became clear that the NAL had insufficient resources to develop both aeronautical and space technology simultaneously. As a result, in 1964, the Science and Technology Agency was split, with NAL to work only on aviation technology, and a newly created Space Development Promotion Headquarters to handle space technology.
In 1964, at the urging of Hideo Itokawa, the University of Tokyo established the Institute of Space and Astronautical Science. Although development on the Lambda rockets proceeded slowly, there were incremental improvements over the next couple of years; such as the new capability to reach an altitude of , getting closer to that required for the launch of a satellite. At this time, however, political issues delayed development. There was, for instance, a controversy involving rocket guidance technologies, which some considered a military, not civilian, matter. Further aggravation was caused by the continued failure of the Lambda initiative, which lost four rockets in orbit. The failure was reportedly caused by a shock (from the sudden combustion of residual fuel) resulting in parts colliding.
The first successful Japanese satellite launch occurred on 11 February 1970 with the launch of the Ohsumi by an unguided L-4S rocket No. 5. The launch of Ohsumi was an important demonstration of technological cooperation with the United States, particularly in the development of high efficiency batteries that did not lose power at high temperatures.
Successful development
In 1969, the Space Development Promotion Headquarters was reorganized as the National Space Development Agency, which was a separate agency from ISAS. Each of the agencies was developing their own rockets independently. NASDA, for example, was focused on rockets to launch larger satellites with practical and commercial applications, while ISAS launched smaller scientific satellites.
After the agency reorganization, Japan started to develop more precise rockets in the 1970s. Although the first M-4S rocket failed, the next versions of it succeeded in launching three satellites in orbit. They became the foundation of the Mu rocket family. Afterwards, the Mu rockets were changed from four stages to three stages to simplify the system, and additional enhancements were made to the M-3C version. All stages were able to work with the M-3S rockets, and this technology resulted in successful satellite launches, reaching higher altitudes each time.
Engineering Test Satellite Tansei and many other scientific satellites were launched by these rockets. Atmospheric observation satellites such as Kyokko and Ohzora and X-ray astronomy satellites such as Hakucho and Hinotori were also active at this time. ISAS's development of the M-3SII rocket reached its completion. The rocket was the first solid-propellant rocket of its kind, and left Earth's gravity carrying the Halley Armada satellites Sakigake and Suisei. M-3SII established the technology for the satellites that were being launched one after another.
The M-V rocket, a larger solid-propellant rocket, made an appearance in 1997. ISAS reported to the government that it would not be technically possible to increase the diameter of the rocket to more than 1.4m in the next 10 years. This was because NASDA had decided on this size and the National Assembly had imposed further restrictions on top of it, making it difficult to increase the size.NASDA initially planned to develop its own indigenous solid-fuel launch vehicle known as the "Q rocket." However, because of the pressing need for practical and commercial rockets, the Japan-U.S. space agreement was signed and technology from the United States was introduced. Utilizing the American Delta rocket's first stage liquid fuel engine, Japan began the plan of installing the LE-3 during its second stage of development with liquid rockets. With that, the N-I rocket had been developed. However, the liquid rocket's orbital payload capacity was low, and the ability to manufacture satellites was not as strong as the United States's. Because of that, more technology was transferred from the United States in 1977 and the geostationary meteorological satellite Himawari 1 was launched using an American rocket. The satellites Sakura and Yuri were later also launched by American rockets. The N-I rocket used technology acquired from manufacturing technology and management techniques only, but by frequently keeping records, NASDA gradually acquired more technology and the rate of satellite production in Japan has increased since the Himawari 2.
Since then, in order to meet the demands of larger satellites, NASDA started the development of the N-II rocket, the successor to the N-I rocket. The second stage changed to knock-down kit. The nearly 300 kg Himawari 2 was able to be put into geostationary orbit. These rockets made use of United States's Delta rocket's licensed production and the U.S. component's knockdown production, so the vehicles themselves were of high quality. However, when parts such as the satellite's apogee kick motor wore down, information on how to improve them was very difficult to obtain. Imported components from the United States were black box systems, which Japanese engineers were not allowed to inspect. Thus, it became necessary for Japan to independently develop the entire rocket, and domestic development had begun. The newly developed H-I rocket made use of the liquid fuel LE-5 rocket engine in the second stage. The LE-5 was characterized by its use of high-efficiency liquid hydrogen and oxygen propellant and the ability to re-ignite, which made it more capable than the N-II upper stage. The H-I rocket was able to launch objects exceeding 500 kg into geostationary orbit.
The rockets NASDA produced were used to launch many commercial satellites, the rapidly increasing number of communication satellites and broadcasting satellites, weather satellites, and so on. Nine H-I rockets were manufactured, all of which have been successfully launched. This was the first time Japan had successfully launched multiple satellites simultaneously.
Japan did not develop the technology for crewed space flight. Mamoru Mohri, in cooperation with NASA, was originally scheduled to be the first Japanese to go into space in 1990 but due to circumstances with the Shuttle, Toyohiro Akiyama, a civilian, became the first Japanese national to go into space aboard the Soyuz TM-11. Mohri eventually flew on STS-47 in 1992.
Large-scale rockets and related challenges