Cold Gas Propulsion for Small Satellites

Steam TunaCan Thruster

As the space industry shifts toward more compact and agile platforms, selecting the right small satellite propulsion system has become a critical mission-design decision. Among the various technologies available, cold gas propulsion for small satellites remains one of the most reliable and widely adopted solutions due to its inherent simplicity and safety. By utilizing the controlled expansion of a pressurized gas to generate thrust, these systems offer a low-complexity alternative to more power-intensive electric propulsion, making them an ideal choice for the growing CubeSat and SmallSat markets.

Propulsion is essential for today’s small satellite operations. They enable:

  • Collision avoidance
  • Constellation management
  • Orbital maneuvers
  • Deorbiting
  • Station keeping
  • Attitude control

There are various propulsion systems available for small satellites. Cold gas propulsion systems are one of them. And it is one of the simplest and most reliable solutions.

What Is Cold Gas Propulsion?

Cold gas propulsion generates thrust without heating the propellant. It relies on the expansion of pressurized gas.

The system consists of:

  • Propellant tank (high-pressure storage)
  • Filter
  • Valve system
  • Nozzle

The propellant is stored under high pressure. It flows through the valve into the nozzle. Thrust is produced when the gas expands. The thrust generated is proportional to the pressure inside the tank.

Since there is no heater, the system doesn’t add thermal energy to the working fluid. Instead, it converts stored pressure energy into kinetic energy at the nozzle exit.

System Layout

Basic construction includes a tank, solenoid valve, and nozzle.

The pressure is reduced before the propellant reaches the thruster, allowing controlled and repeatable pulses.

Cold Gas vs. Electrothermal Propulsion

The primary difference between cold gas and electrothermal propulsion lies in the heater.

An electrothermal propulsion system includes:

  • Heat exchanger
  • Electric heater

In this type of system, the propellant (for example, water) is heated before expansion. Increasing temperature increases exhaust velocity and improves specific impulse.

When the heater and heat exchanger are removed, the system effectively becomes a cold gas thruster.

Performance Trade-Off

Cold gas systems do not add thermal energy. That is why their performance is typically 2–3 times lower compared to electrothermal systems.

However, there are certain benefits to eliminating the heater:

  • Lower electrical power demand
  • Reduced component count
  • Higher overall reliability
  • Simpler integration

In some missions, this simplicity is more valuable than peak efficiency.

Propellants Used in Cold Gas Systems

Cold gas propulsion requires propellants that can operate without additional heating.

Compressed gases:

  • Nitrogen (N₂)
  • Hydrogen (H₂)
  • Argon (Ar)
  • Helium (He)

Liquids stored at saturation conditions:

  • Nitrous oxide (N₂O)
  • Propane
  • Ethane
  • Carbon dioxide (CO₂)

Water is not suitable for cold gas mode. Without heating, it evaporates too slowly to generate meaningful thrust. That is why water-based propulsion systems operate in electrothermal mode.

Cold Gas Propulsion Limitations

The system is simple, but it has several important drawbacks:

  1.  Lower Specific Impulse
    Compared to electrothermal or electric propulsion systems, cold gas engines deliver significantly lower efficiency.

  2. High-Pressure Storage Requirements
    The system uses high-pressure tanks, which require rigorous leak testing and safety validation.

  3. System Complexity in Gas Handling
    While the thrust generation principle is simple, the storage and regulation of high-pressure gas involves regulators, valves, sensors, and safety components that must operate reliably in space.

Cold gas propulsion represents one of the most mature and reliable propulsion technologies available for small satellites. By relying solely on stored pressure energy, it eliminates the need for heaters and complex thermal subsystems.

While its specific impulse is lower than electrothermal alternatives, its robustness, simplicity, and operational predictability ensure that cold gas propulsion continues to play an important role. As noted in the NASA State-of-the-Art for Small Satellite Propulsion Systems, these systems remain a baseline for SmallSat missions due to their high reliability and low integration risk.

Comparison: Cold Gas vs. Electrothermal Propulsion

Feature
Cold Gas Propulsion
Electrothermal Propulsion
Heating Mechanism
No heater; relies on expansion of pressurized gas.
Includes an electric heater and heat exchanger.
Performance (Specific Impulse)
Typically 2–3 times lower efficiency.
Higher exhaust velocity and improved specific impulse.
Power Consumption
Lower electrical power demand.
Higher power required to operate the heating system.
System Complexity
Simpler with fewer components (no thermal subsystems).
More complex due to added heaters and heat exchangers.
Reliability
Higher overall reliability due to simplicity.
Slightly reduced due to more components and thermal stress.
Common Propellants
Nitrogen, Hydrogen, Argon, Helium, CO₂.
Water (requires heating to evaporate and generate thrust).

The primary difference between cold gas and electrothermal propulsion is that cold gas systems lack a heater, making them simpler and more reliable, while electrothermal systems offer 2-3 times higher performance by heating the propellant.

About SteamJet Space Systems

SteamJet Space Systems is a leading UK-based provider of high-performance satellite propulsion solutions. We specialise in water-based thrusters designed specifically for CubeSats and Small Satellites (SmallSats), with a strong focus on water-based thruster safety.

By pioneering the use of green propellants and intelligent thermal engineering, SteamJet enables complex LEO (Low Earth Orbit) manoeuvres — including orbital maintenance, collision avoidance, and de-orbiting — without the risks associated with toxic hydrazine or high-pressure cold gas systems, advancing green propulsion for space missions.

Steamjet Propulsion Technology

Our modular systems are engineered for seamless integration and maximum safety compliance:

Discover how SteamJet’s sustainable space propulsion innovations are providing the safety and reliability required for the next generation of crewed and robotic missions. Contact our engineering team (link) for technical specifications and ICDs.

Electrothermal Propulsion Testing for SteamJet Thrusters

Steam TunaCan electrothermal propulsion thruster

Understanding how heat moves through an electrothermal propulsion system is critical when the thruster is mounted directly onto a spacecraft. We conducted a detailed thermal mapping campaign to evaluate operational behaviour. A new thermal imaging camera was used during this test.

Electrothermal propulsion thruster thermal mapping

Nozzle and Heat Exchanger Performance

The protective top cover was removed and we could capture the thermal distribution across the thruster during operation.

Measurements demonstrated that the heat exchanger does indeed heat up — the temperature on the surface facing space exceeds 300 °C. At the same time, the temperature on the contact surfaces located closer to the attachment point and the engine body is significantly lower — around 40 °C.

This confirmed that our thermal modelling accurately represents real operational conditions.

Steam TunaCan electrothermal propulsion thruster for CubeSats
Steam TunaCan electrothermal propulsion thruster for CubeSats

Thermal Impact on the Spacecraft Interface

One of the key elements of this campaign was to understand how heat propagates toward the spacecraft.

The base of the thruster, meaning the surface used to mount the unit to the satellite, showed minimal temperature variation. During the operation the temperature changes remained within approximately 1°C.

Additionally, the contact surfaces located closer to the engine structure but not directly exposed to the hot section stabilized around 40°C, well within acceptable limits.

The results of the thermal mapping campaign confirm that SteamJet thruster doesn’t pose a thermal overheating risk to the satellite.

About SteamJet Space Systems

SteamJet Space Systems is a leading UK-based provider of high-performance satellite propulsion solutions. We specialise in water-based thrusters designed specifically for CubeSats and Small Satellites (SmallSats), with a strong focus on water-based thruster safety.

By pioneering the use of green propellants and intelligent thermal engineering, SteamJet enables complex LEO (Low Earth Orbit) manoeuvres — including orbital maintenance, collision avoidance, and de-orbiting — without the risks associated with toxic hydrazine or high-pressure cold gas systems, advancing green propulsion for space missions.

Steamjet Propulsion Technology

Our modular systems are engineered for seamless integration and maximum safety compliance:

Steam TunaCan Thruster: A compact, high-efficiency solution for 1U-3U CubeSats.

Steam Thruster One: Scalable propulsion for larger SmallSat constellations.

Discover how SteamJet’s sustainable space propulsion innovations are providing the safety and reliability required for the next generation of crewed and robotic missions. Contact our engineering team for technical specifications and ICDs.

Artemis II Mission: Water Propulsion for Crewed Spaceflight

SteamJet water propulsion system for NASA’s Artemis II CubeSat mission

SteamJet water propulsion is being demonstrated during NASA’s Artemis II mission, setting a new safety benchmark for CubeSat operations on crewed spaceflight. Artemis II is an upcoming lunar spaceflight mission led by NASA. The launch date is currently set for March, 2026. Since Apollo 17 in 1972, Artemis II is the first manned mission beyond low Earth orbit.

Four astronauts will perform a lunar flyby aboard the Space Launch System. The spacecraft will fly around the far side of the Moon, reaching a closest approach of approximately 6,513 km. During the mission, the crew will monitor the spacecraft, study the effects of deep-space travel, and make trajectory corrections as required.

Safety Requirements for Crewed Missions

Every crewed space mission must meet strict safety requirements to ensure crew safety. This means that all systems must include redundancy so that no single failure can lead to the loss of the crew.

That is why the mission allows zero tolerance for propulsion risk. Secondary payload must comply with high safety standards and undergo strict testing procedures.

K-Rad Cube Satellite Mission Challenge

The K-Rad Cube satellite, developed by South Korean company NaraSpace, will fly aboard NASA’s Artemis II mission. After it is deployed into a highly elliptical orbit the satellite will face a challenge. Its first perigee is within Earth’s upper atmosphere. Without orbital correction, the satellite will be lost.

The K-Rad Cube satellite will perform an orbital correction using the SteamJet Thruster One propulsion system. The thruster had to be configured to operate safely during a prolonged burn, with all systems remaining stable and functioning smoothly for approximately 12 hours.

SteamJet Thruster One Water Propulsion System

SteamJet Thruster One is a water-based propulsion system making it safe for crewed missions because there are no additional risks such as with high-pressure tanks and hazardous materials. On top of that, this system allows for diverse mission applications, ensures advanced performance and operational flexibility.

Qualification and Acceptance Testing

SteamJet Thruster One went through rigorous testing procedures in order to qualify for NASA manned mission standards.  As a part of mission qualification our team performed fuel tank burst pressure testing to confirm that the pressurised tank meets the Design Burst Pressure requirement defined in ANSI/AIAA S-080A-2018, Section 10.4.10. Furthermore, SteamJet engineers completed an acceptance test campaign compliant with industry standards, covering functional, vibration dynamic, thermal vacuum, and leak-rate testing.

During this mission, SteamJet water-based propulsion can demonstrate its capabilities in high-stakes, real-world conditions. The thruster will execute a high-thrust, high-precision maneuver once limited to chemical systems.

Pushing the Boundaries of Green Water Propulsion

Before the Artemis II mission, Cubesats required chemical propulsion to operate in these challenging conditions. Chemical propulsion is costly, toxic and complex in terms of operations. On top of that, it presents additional risks for the crewed mission. SteamJet water-based propulsion technology offers a safe and scalable solution for deep-space and high-energy orbit missions without added hazards.

This mission proves that sustainable propulsion can handle demanding orbits, opening the door for future CubeSats to take on complex missions without sacrificing safety or environmental responsibility.

About SteamJet Space Systems

SteamJet Space Systems is a leading UK-based provider of high-performance satellite propulsion solutions. We specialise in water-based thrusters designed specifically for CubeSats and Small Satellites (SmallSats), with a strong focus on water-based thruster safety.

By pioneering the use of green propellants and intelligent thermal engineering, SteamJet enables complex LEO (Low Earth Orbit) manoeuvres — including orbital maintenance, collision avoidance, and de-orbiting — without the risks associated with toxic hydrazine or high-pressure cold gas systems, advancing green propulsion for space missions.

Steamjet Propulsion Technology

Our modular systems are engineered for seamless integration and maximum safety compliance:

Discover how SteamJet’s sustainable space propulsion innovations are providing the safety and reliability required for the next generation of crewed and robotic missions. Contact our engineering team for technical specifications and ICDs.

SteamJet Thruster One: Testing and Flight Readiness for Artemis II Mission

SteamJet Thruster One

SteamJet Thruster One will perform an orbit correction for South Korea’s K-Rad Cube satellite during the upcoming Artemis II mission. South Korean NaraSpace designed and built the K-Rad Cube satellite for NASA’s historic Artemis II mission, the first crewed lunar mission in over 50 years.

Once deployed into a highly elliptical orbit, the satellite will face an immediate challenge because its first perigee passes through Earth’s upper atmosphere. SteamJet Thruster One will provide the orbital correction required to prevent the satellite’s re-entry into the atmosphere.

Before any mission, SteamJet thrusters undergo a meticulous testing process to guarantee performance and reliability. Fuel tank burst pressure testing was also completed to meet the elevated safety standards required for the crewed Artemis II mission.

In addition to burst testing, engineers conducted acceptance testing on the SteamJet Thruster One for Artemis II, following established industry practices. Acceptance test campaign consists of several phases:

  • Functional test
  • Vibration dynamic test
  • Thermal vacuum test
  • Leak rate

Functional test

Functional testing verifies the thruster’s performance in all operational modes. The flight profile details all settings relevant for in-orbit operation aboard the satellite. For the Artemis II mission there are two main operational modes: commissioning and thrust.

The commissioning mode is the first operational state activated post-launch. It purges residual gases from the fuel lines.

For the Artemis II mission the thruster was optimized to deliver high thrust, operating nearly in continuous mode. This configuration ensures the mission objective is met, raising the orbit perigee to over 180 km during the first orbit.

An impulse of 240 Ns was generated in order to accomplish this goal. The test consisted of a sequence of cycles that included thrust generation, heating without firing and system health checks.  The manoeuvre was split in two parts, with a cooling period in between.

Telemetry data of a firing block:

Telemetry data of a firing block

The results of the overall functional thrust mode test are as follows:

  • Water Tanks initial condition: 350g of water on each tank at a pressure of 3.4 atm
  • Water consumed: 167.0 g
  • Total Impulse: 240 – 260 Ns
  • Thrust: 15 – 17 mN
  • Test duration: 11h 25m (including cool down period)

Vibration dynamic test

During the vibration dynamic test, engineers simulate operational conditions to ensure all components meet quality standards.

The vibration stand main specifications were the following:

Parameter
Value
Stand
ETS_L620M.std
Maximum payload weight [kg]
300.0
Reduced mass of the moving system [kg]
6.0
Operating frequency range [Hz]
3.00 – 3500.00
Buoyancy force [N]
6000.00
Maximum speed [m/s]
1.80
Maximum movement [mm]
25.00
Maximum acceleration [m/s2]
980.00

Thruster mounting for vibrations testing along X,Y,Z:

Thruster mounting for vibrations testing

During and after vibration dynamic testing, all thruster parameters remained within normal limits and met specifications.

Thermal vacuum test

The main goal of the thermal vacuum test is to check that the thruster performs and survives extreme temperatures encountered in space. Additionally, the test reveals any hidden issues early, reducing the chance of problems during the first hours of flight.

Engineers successfully completed all functional checks at the different dwell temperatures. The total mass loss during Thermal Vacuum was 0.7g, or 0.059 %, which confirms that the integrity of the thruster is maintained.

Leak rate

After the thermal vacuum test, engineers measured the leak rate. The thruster was fuelled and left for 20 hours in vacuum conditions while monitoring pressure and temperature values. Engineers detected no leaks during this 20-hour period.

Thruster telemetry during leak rate test:

Thruster telemetry during leak rate test

Conclusion

SteamJet Thruster One has successfully completed all testing required for the Artemis II mission. Functional, vibration, thermal vacuum, and leak rate tests confirmed that the thruster performs reliably in all operational modes, maintains its integrity under extreme conditions, and meets mission requirements. With verified performance and no detected leaks, the thruster is fully flight-ready to perform the critical orbital correction for the K-Rad Cube satellite.

About SteamJet Space Systems

SteamJet Space Systems is a leading UK-based provider of high-performance satellite propulsion solutions. We specialize in water-based thrusters designed specifically for CubeSats and Small Satellites (SmallSats), with a strong focus on water-based thruster safety.

By pioneering the use of green propellants and intelligent thermal engineering, SteamJet enables complex LEO (Low Earth Orbit) maneuvers — including orbital maintenance, collision avoidance, and de-orbiting — without the risks of toxic hydrazine or high-pressure cold gas systems. This approach advances green propulsion for space missions.

Steamjet Propulsion Technology

Our modular systems are engineered for seamless integration and maximum safety compliance:

Steam TunaCan Thruster: A compact, high-efficiency solution for 1U-3U CubeSats.

Steam Thruster One: Scalable propulsion for larger SmallSat constellations.

Discover how SteamJet’s sustainable space propulsion innovations are providing the safety and reliability required for the next generation of crewed and robotic missions. Contact our engineering team for technical specifications and ICDs.