In this study, Water micro-propulsion system AQUARIUS (AQUA ResIstojet propUlsion System) is proposed for 6U CubeSat: EQUULEUS to explore the deep space. AQUARIUS uses storable, safe and non-toxic propellant: water, which allows for downsizing of whole propulsion system to 2U and storing 1.2 kg water. Liquid propellant storage allows design of all propulsion systems below 100 kPa. The waste heat of communication components is reused to cover high latent heat of water. AQUARIUS has 4.0 mN and specific impulse of 70 s by less than 20 W power consumption. Breadboard model was designed and tested successfully. Engineering model is under developments and operations by using whole systems of EQUULEUS. AQUARIUS will be equipped with EQUULEUS scheduled to be launched in 2019 by SLS (Space Launch System)
