Reusable spacecraft are attracting global attention. Until recently, launching a single-use rocket was the norm. But using the same vehicle multiple times by having it return to Earth after each mission reduces the launch costs significantly. The U.S. leads in reusable spaceship technology, and Japan is also entering the fray.
Japan has attempted to develop a reusable rocket in the past. The initiative ended in 2003. After 17 years, Japan is resuming work.
Japan’s development plan has two stages: (1) the experimental launch of a 7-meter-long test vehicle, “RV-X,” which would ascend 100 meters and land in Akita Prefecture this autumn; and (2) the development of “CALLISTO” (13.5 meters long), which is closer to a real spacecraft. Japan will jointly develop CALLISTO with France and Germany. In a test launch scheduled for French Guiana in FY 2022, CALLISTO is expected to ascend 40 kilometers into the sky. “We are very keen to succeed,” says JAXA Unit Chief Koichi Okita, “Especially because this will be an important step toward low-cost rocket launches.”
The key to succeeding in this project is the development of an engine that is both sensitive and durable. During takeoff, the rocket uses full propulsion, but landing requires only 40% propulsion. Furthermore, fine maneuvering is necessary until the rocket lands on Earth. Reignition must not be done until last minute before landing to save fuel.
The reusable rockets require a special fuel tank as well. In the case of CALLISTO, the rocket makes a half turn in the sky before heading home. In the middle of this process, there is a possibility that the ship’s system will cease to take in liquid fuel and, as a result, go up in flames. A special mechanism for CALLISTO’s fuel tank is being developed to prevent this from happening. In addition, engineers must install an automatic guiding system with a positioning mechanism to enable a safe landing.
Space X has not patented its main technologies for reusable rockets because patenting would open up the technologies to competitors who are willing to pay a price for the license. “We just have no idea what kind of technology is involved,” admits Shinji Ishimoto, leader of JAXA’s CALLISTO team,
France plans to introduce a reusable rocket jointly with Arianespace, a space industry leader. China and India are also interested in reusable vehicles. “Reusable spaceships may be the mainstream going forward. We would like to acquire the necessary technologies needed to put reusable vehicles into practical use,” Ishimoto says. (Abridged)