Propellant, commonly known as fuel, is the key to the development of aerospace technology. Traditional aerospace propellants such as hydrazine fuels, although they can produce strong thrust, are highly toxic and have certain risks in storage, transportation and use. Electric power propulsion requires higher power support and puts forward high requirements for energy supply. The emergence of water-fuel thrusters is expected to become a new driving force for future aerospace exploration.

  Recently, a US aerospace startup announced the successful testing of the world's first water-fuel plasma thruster. During testing, the thruster showed certain performance advantages. It only requires 1.5 watts of power to achieve stable thrust for 5 minutes, with a thrust of 37.5 milliNewtons and a specific impulse of 4800 seconds, which is about 10 times that of hydrazine-type thrusters. Its size is only 10 cubic centimeters and can be adapted to 1U cubic satellites (that is, small satellites with a weight of 1 kg and a volume of 10 cm x 10 cm x 10 cm) and various microsatellites. In terms of technological innovation, the company ionizes water molecules into plasma through low-voltage electric fields, and then uses electromagnetic fields to accelerate the spraying to generate thrust. This method achieves zero toxicity and easy storage of propellants. The thruster is suitable for long-term on-orbit maintenance tasks for low-orbit satellites, and can also power small detectors to perform long-range deep space exploration missions.

  Coincidentally. A Japanese startup is working with an Italian company to conduct in-orbit testing of a 1U cubic star's water ion propeller in June and October 2025. The thruster integrates water ion propulsion and electric propulsion technologies, taking into account efficiency and flexibility. Due to its modular design, it can be adapted to different small satellites. This test mainly verifies the technical reliability of the thruster in space debris evasion and satellite sustainable deorbit.

  The emergence of water-fuel thrusters will have a multifaceted impact in the commercial aerospace field. On the one hand, water has significant advantages as fuel. Water is extremely low and is almost negligible compared to tens of thousands of dollars per kilogram of hydrazine fuel. On the other hand, water does not require special protection and storage, which can greatly reduce the risks and costs of fuel storage and transportation. In addition, low-power water-fuel thrusters help reduce the volume of satellite power systems and reduce the weight of the entire satellite, thereby reducing the launch cost.

  Water-fuel thrusters bring more possibilities to space missions. For the giant constellation project under construction, the use of water-fueled thrusters helps to extend the life of the satellite, reduce the frequency of network replenishment, and improve the stability and service quality of the constellation satellites. In the past, due to fuel mass and thruster power, some deep space exploration missions were difficult for startups to achieve. The low power consumption and high specific impulse characteristics of water-fuel thrusters make small space exploration agencies expected to carry out deep space exploration tasks such as asteroid sampling at a lower cost.

  Although water fuel thrusters show many advantages, they are still facing some technical challenges. Its thrust is small, only 1/10 of that of hydrazine fuel thrusters, and cannot meet the needs of spacecraft emergency orbital changes and other missions, thus limiting the scope of application. In addition, water will produce trace amounts of hydrogen and oxygen during the electrolysis process, and long-term operation may cause corrosion to the reaction chamber materials, affecting the service life and performance stability of the thruster.

  As an emerging technology in the field of space power, water fuel thrusters have brought new opportunities and changes to the development of commercial aerospace with their safety, low cost and low power consumption. The development of this technology has also brought new variables to the competition and cooperation of various countries in the aerospace field, and is worthy of continuous attention and in-depth research.

[Editor in charge: Gao Qiang]