Currently, private sector-led space development utilizing small-lift launch vehicles and satellites is rapidly expanding. The chemical compound hydrazine is generally used as propellant for small rocket engines (called "thrusters") that control the orientation and orbit of such spacecrafts. Hydrazine is easily decomposed by a catalyst and converted into gas, making it easy to control the reaction. However, it is highly toxic and requires special equipment and protective clothing to be handled, and must be strictly controlled.
In response to this, Hiroki Matsunaga invented "Energetic Ionic Liquids" (EILs), which are propellants fueled by ionic liquids, generally regarded as "non-flammable solvents." A heat source was used to demonstrate the ignition of EILs. Compared to hydrazine, EILs prepared by Matsunaga that use ammonium dinitramide as a base agent can not only reduce toxicity, but also theoretically improve thruster performance by about 50%.
Various liquid propellants using energetic substances have been proposed to replace hydrazine, but most of them use water (a combustion inhibitor) or methanol (a volatile toxicant) for liquefaction. The theoretical performance and safety of EILs that do not contain these substances are outstanding. The development of these EILs boasting 50% improvement is a breakthrough, as thruster designs generally have difficulty in improving performance, even by a few percentage points.
Currently, Matsunaga is working with various research institutes and companies to advance basic research on synthesis and ignition. Preparation is underway for prototype space propulsion systems using EILs as propellants and for ground-based combustion tests. Aiming for a space demonstration test within a few years, they are in the process of demonstrating the feasibility of using microreactors, laser ignition, and other new technologies in solving the issues of how to synthesize and ignite EILs safely and efficiently, through small scale tests.
Once a space propulsion system using EILs is established, an ultra-compact propulsion system combining performance, safety, and operability will be realized; far surpassing existing systems. Since EILs can achieve a wide variety of capacities in different combinations, they are expected to be applied to many space missions including nano-satellites, which will greatly accelerate space development.
