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Revolutionizing Satellite Propulsion: The Advantages and Challenges of Water-Based Propulsion

Satellites are essential for modern life. They provide us with communication, navigation, weather forecasting, and much more. But satellites need to be able to maneuver in space, and that requires propulsion.


Traditionally, satellite propulsion has been based on chemical rockets. These rockets are powerful, but they are also expensive and produce harmful exhaust. In recent years, there has been a growing interest in water-based propulsion as a more sustainable and cost-effective alternative.


Water-based propulsion is an emerging technology that is revolutionizing satellite propulsion. This technology uses water or a mixture of water and a propellant to generate thrust and propel the satellite. In this article, we will discuss the advantages and challenges of water-based propulsion and why it is a promising technology for future space missions.

For a deeper understanding of Satellite propulsion and applications please visit: Comprehensive Guide to Satellite Propulsion: Technologies, Applications, and Future Trends

Advantages of Water-Based Propulsion

Water-based propulsion has several advantages over traditional chemical propulsion. One of the most significant advantages is that water is a clean and abundant resource. This means that water-based propulsion is more environmentally friendly than chemical propulsion because it doesn’t release toxic chemicals into the environment.


Another advantage of water-based propulsion is its high specific impulse. The specific impulse is a measure of the efficiency of a rocket engine, and water-based propulsion has a higher specific impulse than traditional chemical propulsion. This means that water-based propulsion requires less fuel to achieve the same amount of thrust as chemical propulsion. As a result, satellites using water-based propulsion can carry more payload and operate for a longer time.


Water-based propulsion systems are also simpler and more reliable than chemical propulsion systems. Water-based propulsion systems have fewer moving parts, and they don’t require the same level of maintenance as chemical propulsion systems. This makes water-based propulsion systems less prone to failure and more cost-effective to operate.

Challenges of Water-Based Propulsion

Despite these advantages, there are also some challenges associated with water-based propulsion. One challenge is that water is not as dense as rocket fuel, so it requires more volume to store the same amount of energy. This can make water-based propulsion systems more bulky and difficult to integrate into satellites.


There is also a challenge due to the energy required to split water into hydrogen and oxygen. This process is called electrolysis and requires a significant amount of energy. This can be a challenge for small satellites with limited power budgets.


Another challenge is that water-based propulsion systems are not as powerful as chemical rockets. This means that they may not be suitable for all types of satellite missions. However, for many missions, water-based propulsion is a viable option that offers a number of advantages over traditional chemical rockets.


Another challenge is the complexity of designing and manufacturing water-based propulsion systems. Water-based propulsion systems require specialized materials and manufacturing processes, which can increase the cost of development and production.


Demonstrations and Advancements

Pale Blue successfully operates its water-based propulsion system in orbit

Pale Blue succeeded in operating the water vapor propulsion system (resistojet) in low earth orbit. Pale Blue’s propulsion system was installed on “EYE,” a nano-satellite for STAR SPHERE Project, and tested for the first time in space. Going forward, the company will innovate and expand the commercial use of its water-based propulsion systems for small satellites.


Some innovative features of the resistojet system include holding the water at a relatively low pressure and allowing it to vaporize at relatively low temperatures. It’s obvious that lots of thought had gone into the design, and now all that effort has been validated with a successful mission.


Pale Blue’s water-based propulsion system aboard “EYE” was launched by SpaceX on January 3rd 2023 and has been currently orbiting earth in LEO. The propulsion system operated for approximately 2 minutes on March 3rd 2023, and the company confirmed successful thrust from the obtained data.


STAR SPHERE Project, led by Sony Group Corporation, is planning to roll out a space photography service in 2023. The satellite will use Pale Blue’s thruster to enter the target orbit before service launch.


“Pale Blue successfully developed and operated its water-based thruster, and with this, the company takes a huge step forward towards orbit insertion for STAR SPHERE Project,” said Jun Asakawa, CEO and Co-Founder of Pale Blue. “We feel a strong significance in this project, which creates new values through the perspective of space and provides opportunities to learn about the Earth and its environment. We will continue technological innovation to create mobility capabilities that are core to the space industry and pioneer the expansion of human possibility.”


The product specifications of Pale Blue’s water thruster aboard “EYE”

– Size: 9.0cm x 12.1cm x 12.1cm

– Wet mass: 1.4 kg

– Power: 22 W (typical / ground testing)

– Thrust: 5.6 mN (typical / ground testing)


But the company isn’t going to stop there. They’re working on another type of water-based thruster that is more like an ion thruster than a simple jet mechanism. In this configuration, the water is atomized via a microwave plasma source and ejected out the back of the propulsion system, similar to a typical ion thruster. However, several patented technologies also go into this system, including the plasma generating system and the design of the vaporization chamber.


Little nozzles could propel nano satellites

Researchers have developed a new type of micropropulsion system for miniature satellites (called CubeSats) that uses tiny nozzles that release precise bursts of water vapor to maneuver the spacecraft. Water is also a very clean propellant, reducing risk of contamination of sensitive instruments by the backflow from thruster plumes.


The new system, called a Film-Evaporation MEMS Tunable Array, or FEMTA thruster, uses capillaries small enough to harness the microscopic properties of water. Because the capillaries are only about 10 micrometers in diameter, the surface tension of the fluid keeps it from flowing out, even in the vacuum of space. Activating small heaters located near the ends of the capillaries creates water vapor and provides thrust. In this way, the capillaries become valves that can be turned on and off by activating the heaters. The technology is similar to an inkjet printer, which uses heaters to push out droplets of ink.


“There have been substantial improvements made in micropropulsion technologies, but further reductions in mass, volume, and power are necessary for integration with small spacecraft,” Alexeenko says. The FEMTA technology is a micro-electromechanical system, or a MEMS, which are tiny machines that contain components measured on the scale of microns, or millionths of a meter. The thruster demonstrated a thrust-to-power ratio of 230 micronewtons per watt for impulses lasting 80 seconds.


“This is a very low power,” Alexeenko says. “We demonstrate that one 180-degree rotation can be performed in less than a minute and requires less than a quarter watt, showing that FEMTA is a viable method for attitude control of CubeSats.” The FEMTA thrusters are microscale nozzles manufactured on silicon wafers using nanofabrication techniques common in industry. The model was tested in a large vacuum chamber. Although the researchers used four thrusters, which allow the satellite to rotate on a single axis, a fully functional satellite would require 12 thrusters for 3-axis rotation.



Future of Water-Based Propulsion

Despite these challenges, water-based propulsion is a promising technology for future space missions. Researchers are exploring ways to improve the efficiency of water-based propulsion systems and reduce their cost. One approach is to use alternative fuels such as ammonia or methanol, which can reduce the amount of energy required for propulsion.


Another approach is to use solar power to generate the energy needed for electrolysis. This would eliminate the need for onboard batteries and reduce the overall weight of the satellite.


Water-based propulsion is an emerging technology that has the potential to revolutionize satellite propulsion. Its high specific impulse, environmental friendliness, and reliability make it a promising technology for future space missions. While there are some challenges that need to be addressed, ongoing research is focused on improving the efficiency and reliability of water-based propulsion systems. As a result, we can expect to see more satellites using water-based propulsion in the future.

About Rajesh Uppal

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