Research and Development of Space Propulsion System from Earth to Space and Beyond
Feb. 8, 2024 | Aerospace Project Research Associate, ISAS people
TABATA Kuniyoshi / DESTINY+ Project Team, ISAS
Research Summary
My research interests include space transportation and propulsion systems, which connect the Earth to space and deep space beyond the Moon, with the goal of expanding space utilization and the zone of human existence.
Until two years ago, as a graduate student, I was conducting research on "Microwave Rocket," which is able to connect the Earth and space at an extremely low cost. Microwave Rocket *1 uses air as its propellant and converts microwave energy supplied from the ground into thrust impulse, which means that this technology requires no on-board propellant. It can therefore transport many people and necessary equipment to space. Moreover, the vehicle itself can be manufactured at a low cost because of the lack of turbopumps. When realized, such systems will enable the construction of large space structures such as space solar power systems (SSPS), which can be used as a new renewable energy source. As one effort contributing to sustainable development goals (SDGs), Microwave Rocket has great social impact and consequently, I was invited to appear on television as a young researcher during my first year of a doctoral student. Just as Prof. Hideo Itokawa, the father of Japanese rocket development, started with the research on "pencil rocket" and finally, a large M-V rocket has been competed, I would like to plant and nurture the seeds of future technologies such as Microwave Rocket.
After receiving my Ph.D., I moved to the Institute of Space and Astronautical Science (ISAS) of JAXA to develop engines not only for traveling from the Earth to space, but also for traveling into deep space. The ISAS environment is outstanding, with professionals of science, engineering, and academia collaborating enthusiastically to reveal the mysteries of space science. Another important benefit is that I can engage earnestly in specific projects there with many talented researchers. I am in charge of the development of the DESTINY+ (Fig.1) *2 ion engine system (IES) *3, and of the IES operation on HAYABUSA2# *4. The "μ10" ion engine (Fig. 2) represents one type of electric propulsion. Although it can generate thrust only as strong as a person's exhalation through the nose, it consumes only 1/10 times as much propellant as chemical propulsion. Therefore, it can achieve a large delta-V by continuous operation over a long period of time. Reflecting the latest research findings, the DESTINY+ thrust has been increased to about 1.5 times that of HAYABUSA. During development testing, a large vacuum chamber is used to maintain sufficient vacuum even when two ion engines are operated simultaneously. The most recent test to operate the ion engine with the power supply IPPU*5 has also been completed. The vacuum chamber used here has been inherited from the HAYABUSA ion engine’s endurance test. I feel particularly fortunate to be in a blessed environment that allows me to use the high-performance experimental facilities prepared by our predecessors and preserved for our use.
While developing the spacecraft, I am also improving the ion engine for future space exploration. For exploration beyond Jupiter, an even more propellant-efficient engine than the current μ10 must be developed. In general, thrust is determined by multiplying the propellant’s mass to be exhausted by the exhaust velocity. Electric propulsion is remarkably propellant-efficient because the exhaust velocity can be increased using electricity. Therefore, I am currently working on "μ10HIsp" *6, which increases the voltage to 5 times higher than conventional μ10 (corresponding to 75,000 volts), and consequently increasing the exhaust velocity to about 2.5 times higher than that achieved by μ10 (25 times higher than chemical propulsion). The principle is quite simple, but the high voltage causes the ions in the plasma*7 to bombard the engine’s inner walls with high energy, leading to performance degradation. We must maintain large thrust and low propellant consumption considering the lifetime of the spacecraft. Therefore, I am in the process of trial and error to ascertain whether this can be achieved with minimum design modifications. In fact, through a series of tests that I have worked on in the development of the DESTINY+ ion engine, the causes of the performance degradation and recovery methods are being elucidated gradually. I expect that the findings will also be effective for μ10HIsp, for which performance degradation is more severe.
Finally, ISAS provides an environment in which I can learn about spacecraft development and immediately feedback that knowledge to my research activities. The experience here will contribute to my growth as an engineering researcher who should always be aware of practical applications. With the research skills I have acquired here, I would like to make efforts to become a researcher who is able and confident to lead future Japanese space exploration programs.
Terminologies
- *1 Microwave Rocket : In the early 2000s, Prof. Kimiya Komurasaki's group at the University of Tokyo demonstrated the world's first prototype of microwave-beamed energy propulsion (BEP), by which a 100 g vehicle was launched to a height of approximately 2 m.
- *2 DESTINY+ : Acronym representing the spacecraft "Demonstration and Experiment of Space Technology for INterplanetary voYage with Phaethon fLyby and dUst Science", to be launched in FY2024. From low Earth orbit (LEO), the spacecraft will increase its altitude gradually by continually operating four ion engines to move into interplanetary space and explore the asteroid Phaethon, which is considered to be the parent body of the Geminid meteor shower. This, the world's first mission to leave Earth's orbit for deep space using electric propulsion, will open a world of low-cost and more frequent deep space exploration.
- *3 HAYABUSA2# : HAYABUSA2 SHARP. SHARP is an acronym for the “Small Hazardous Asteroid Reconnaissance Probe.” After delivering a capsule containing samples in December 2020, it has continued its space flight to the next target celestial body as an extended mission.
- *4 IES : Ion engine system that includes an ion thruster’s head, a power supply unit, a thruster control unit, etc.
- *5 IPPU : Acronym of IES Power Processing Unit used to drive an ion engine.
- *6 μ10HIsp : Name for an ion engine μ10 with even lower propellant consumption. Isp denotes the specific impulse, a measure of propellant consumption. Higher (High) specific impulse (Isp) indicates lower propellant consumption.
- *7 Plasma : A fourth state consisting of ions, electrons, and neutral particles. This state can be created by applying electrical, thermal, or optical energy to a gas. μ10 produces plasma by resonance between microwaves and electrons in a strong magnetic field.