Propellant: H2O (Filled as liquid. Liquid or solid during storage and use)
Envelope: 95x95x95 mm (ie., 1U with 5mm margin)
Wet Mass: 980 grams
Propellant Load: 250 grams of liquid, pure water
System Power: 6 Watts (Typical flow rate with all thrusters active)
Max System Power: 18 Watts (Maximum flow rate with all thrusters active)
Thermal Draw: 11.5 Watts (Heater on, no thrusters active)
Temperature Range: -25C to +49C (Valves heated to 4C)
Survival Temperature: -40C to 49C
Input Voltage: 5V logic, 12V thrust
Thrust: 17.2 mN (all thrusters active)
Isp: 7,300 sec
Total Impulse: 17,800 Ns
Delta V: 4,620 m/s for 4kg 3U 2,273 m/s for 8kg 6U
Thrust/Power: 2.9 mN/Watt
Thrust/Mass: 17.6 mN/kg
Lifetime: >= 4x propellant load (based on ongoing experiments)
The above values for Thrust, ISP, Power, and Mass Flow are based upon experimental data available under NDA.
The ConstantQ™ family of thrusters use a pulsed electrostatic cycle to enable a variety of Earth-orbiting and deep space missions using water propellant. Test results show water’s vapor pressure and its plasma speciation are especially useful to this operating cycle.
A ConstantQ™ thruster has:
a plasma formation region containing spark electrodes
two exhaust ports, each ringed by acceleration electrodes
a single power supply providing spark and acceleration power
Vapor enters the plasma formation region, expanding and changing pressure on its path towards the exhaust ports. Paschen’s law ensures a spark occurs within the vapor at the point where the supply voltage meets the pressure on the Paschen curve.
Each exhaust port is ringed with high voltage electrodes. One exhaust port’s voltages act to focus and extract positive ions from the plasma. The other affects electrons.
Electrons, being far less massive than ions, leave the plasma before ions, generating thrust from their interaction with the acceleration electrodes. Once outside the thruster, the electrons form a virtual cathode that pulls upon the ions remaining within the thruster.
As the ions leave, thrust is obtained from acceleration electrodes. However, the ions also derive kinetic energy from the virtual cathode, slowing the exhaust electrons and even causing electrons to flow back toward the thruster. This gives an increased acceleration voltage upon the ions, expanding the classic Child-Langmuir limits for space-charge flow rate and thrust density.
As the ions exit the thruster, they meet the returning electrons, neutralizing the plasma. With water vapor, the interface between exiting ions and returning electrons appears as a white-hot sphere 5-8mm outside the ion’s exhaust port. This phenomenon is believed to be due to the presence of multiple ion species with different velocity profiles. In the image below, the two exhaust ports are shown, with the electron port on the left and the ion port on the right. Note the distinctly different exhaust appearances of the two.
A resonance occurs between the incoming gas pressure, spark push back, and plasma drain rate through the exhaust ports (as driven by the supply’s high voltage which can be varied to align with mission Isp). The ConstantQ™ uses a very specific geometry to drive this resonance, minimize wear, reduce power supply complexity, and reduce flight computing demands.
ConstantQ™ thrusters have produced thrust using water vapor, Xenon, Argon, Krypton, Iodine, and air.
Current Pricing: $85,000 USD
Our current batch of M1.4 Thrusters has sold out. Due to market supply chain constraints, the lead time for our next batch of M1.4 Thrusters will be 6 months. Please contact us for contract information, which varies by country.
The M1.4 device uses ConstantQ™ propulsion technology, converting electricity and water vapor into thrust. Thrust is derived from electrostatic acceleration of separated ions and electrons using a combination of classic collisionless flow and electrohydrodynamic (EHD) regimes, all working in a cycle determined by propellant temperature, input power, and device geometry. The operating cycle is self stabilizing and does not require real time active control once initiated, though altering temperature and/or power will alter delivered thrust. The process is self neutralizing and does not require a neutralizer device. Pressures throughout the system generate water vapor through sublimation, avoiding the need for water to boil and tolerating frozen ice as the propellant. Temperature management is achieved with a high-density flat heater on the tank, a valve self-heating feature, and routing of electronics waste heat to minimize freezing of water vapor. Thrust is attained with a wide range of temperatures, including a tank full of frozen water ice.
Water vapor is generated through sublimation that occurs when the system is run below the vapor pressure – a process that does not require water to boil into steam. Water vapor, not liquid water, reaches the thrust heads and is converted into plasma and thrust. Should liquid water get near the thrust heads, it would rapidly sublimate into vapor due to vacuum exposure.
No. The M1.4 naturally operates in pulses with a slight breathing mode around an unstable operating point. Internal capacitors essential to starting the process also prevent instant shutdown as their stored energy continues to feed pulses. As such, impulse bit timing, duration, and thrust are likely not regulated tightly enough for precision pointing of small craft.
The applied equations are based upon an assumption of collisionless particle acceleration which is not fully applicable to this thruster design. The thruster instead operates in a mixture of regimes, some of which include collisions. Within the electrostatic acceleration region, the mean free path is short compared to the exit distance, causing charged particles to have many collisions with neutrals before exiting. The short mean free path means ion velocity never reaches high values, power consumption is lowered (due to that u^2 term in the power equation though with power gains offset by the number of collisions). Collisions do work on neutral gas, compressing and heating, forming a shock wave of higher pressure neutrals with anisotropic pressure and temperature distributions, further lowering the mean free path. The higher pressure gas wave pushes against the exhaust nozzle, giving the majority of the thrust. This is known as electrohydrodynamic (EHD) operation where charged particles are used to drag and compress neutrals.
In the flow rate regime used, there is more thrust per watt and higher Isp compressing neutrals (which are counted in the Isp) with a few charged particles rather than converting and accelerating most of the neutrals. Efficiency drops at higher flow rates where no initial long mean free path region exists after ionization, so the required compression shock wave never forms. At lower rates, the mean free path isn’t long enough to cause compression and indeed power consumption rises.
We have observed the pressure increases and have created a model that well captures the energy coupled into the gas and charged particle acceleration. The model shows the thruster is actually only moderately efficient, though clearly doing well enough to fit the size factor and thrust levels needed by the market. We are currently preparing for very high quality 3rd party thrust measurements to test the model, then will release details of this mixed-regime model under non-disclosure.