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Momentus Space

Momentus Space

Momentus is a YC Summer 2018 batch company developing the in-space rockets powered by water plasma engines and based in Santa Clara, CA

Momentus Space was founded by space entrepreneur Mikhail Kokorich and his partner Lev Khasis in Santa Clara in 2017. Momentus was originally born out of discussions with satellite operators seeking more affordable space transportation. Momentus is developing in-space propulsion systems powered by microwave electro-thermal (MET) water plasma engines. Momentus Space is the first in-space transportation services company built around high performance water plasma rocket propulsion. Momentus’ water plasma propulsions systems use water which is cheap, non-toxic, and considered safe, and easy to work with. Water based propulsion could provide a path to breaking the ties of space industries to the Earth by allowing resupply from asteroids.

 Artist's conception of the Momentus Ardoride Orbital Transfer Vehicle
Microwave Electro-Thermal Propulsion (METs)

Momentus Space is based on over 30 years of university research funded by NASA and the US Air Force. Momentus Space also has several new patent pending. Momentus Space microwave electrothermal water propulsion systems use one third the propellant as chemical propulsion systems and delivers payloads three times faster than solar electric ion propulsion.

METs are plasma-based electrothermal devices that use Joule heating of a partially ionized gas to heat un-ionized propellant which is then ejected through a converging-diverging nozzle to create thrust in the same manner as chemical rockets. The thruster body itself is a microwave resonant cavity that allows for microwave breakdown of virtually any gas-state propellant. Momentus is developing an MET system that uses water as the propellant in a highly localized region just upstream of the rocket throat. A combination of solar array power and batteries (depending on duty cycle) provides the energy necessary for operation. For their high power systems, the microwave power to drive the system is generated by magnetrons, which are the highest known efficiency means of producing radiation from electric power and are highly mature in the terrestrial food preparation and materials processing industries.

Previous academic research and Momentus' own in-house development efforts have shown that by carefully injecting the propellant gas with vortex inducing swirl, the gas discharge can be confined on centerline, where the microwave intensity is greatest, thereby inducing a strong radial profile in the gas temperature. Electron temperatures on centerline in the discharge can be as high as 15,000 to 20,000 Kelvin allowing heating of the centerline gas to several thousand Kelvin while the boundary layer temperature of the gas that is in contact with the thruster throat can be within the long life temperature constrains of refractory metals.

Momentus' analysis and review of extant literature suggests that at achievable temperatures, specific impulse can approach 1,000s due to extremely high survivable bulk gas temperature and thermal dissociation of the water molecules to the atomic state. The following figure shows key design features of a Microwave ElectroThermal (MET) thruster showing the TM011 Mode Field Pattern in the resonant cavity. This cavity mode provides power coupling and positions the discharge in an optimal location upstream of the nozzle.

Key design features of a Microwave Electro-Thermal (MET) thruster showing the TM011 Mode Field Pattern in the Resonant Cavity.

The next figure shows how molecular dissociation of water serves to increase specific impulse at a given temperature beyond that which would be expected at 18 gImol for water by reducing the average molecular weight. The figure shows a plot of frozen flow, fractional dissociation, and thermal efficiency versus chamber temperature for an expansion ratio of 100:1 with water propellant as modeled in TDK, a two-dimensional kinetic code maintained by Sierra Engineering for combustion simulation. An 8,000K chamber temperature yields a specific impulse of about 750s.

Specific impulse (frozen flow), fractional disassociation, and chamber enthalpy to jet efficiency versus temperature for water propellant.

S-band MET Thruster in the lab.

The figure on the right shows an image of an S-Band (2.45 GHz) MET operating in the Momentus laboratory using water propellant at a power Level of 3 kW.

Water as a propellant

Choice of propellant is a primary cost driver, due to chemical properties, handling requirements, storage conditions, and many other factors including the following:

  • Safe and nontoxic to reduce labor facility costs to build, test propulsion systems and eliminates concern of contamination for ride share payloads.
  • Dense, easy to store and handle at standard pressure and temperature - to eliminate the need for high pressure storage and feed system which in turn enhances safety, reduces tankage mass, and reduces orbital debris risk in case of operational mishap.
  • Inexpensive - Although at current satellite prices propellant costs itself are typically a small fraction of total system cost. As the system cost comes down, more expensive propellants will be an high fraction of total system cost.
  • High in low atomic mass elements as is needed to serve as effective radiation shielding material to allow for synergy in structure design by using the propellant storage tank as both structure and shielding, and
  • Available on the asteroids and planetary surfaces as a form of future proofing against eventual in-situ resource utilization technology and as a way to enable, resupply in space from locally available resources.

Based on these criteria, water is a proposed ideal propellant which is why Momentus selected to focus on water based MET as their core technology.

Products and Services

As shown in the folling roadmap diagram, with Momentus' first orbital flight demonstration planned to be ready for launch in 2019, Momentus technology roadmap starts with the Zeal™ and Vigor™ technologies that they are adapting for flight. Momentus will be ready to start taking orders for small sat transportation services in Earth orbit for launch in 2020 or later with their Ardoride™ and Vigoride™ SmallSat space tugs. By 2021 Momentus plan to have Fervoride™ ready which is a high performance space tug designed to deliver a new generation of GEO sats. Momentus' roadmap includes Valoride™ a large scale space tug designed to support space manufacturing, asteroid mining and resupply for space hotels. Valoride™ is Momentus' proposed workhorse transportation service that ferries equipment and supplies throughout cislunar space and between LEO, GEO, and the asteroids.

Current roadmap of Momentus Propulsion System and Orbital Transfer Vehicle (OTV) Development, along with potential applications.


April 1, 2020
Momentus to launch IRIS-A, a mission for NCKU space laboratory.
July 26, 2019
Momentus wins a NASA iTech Award.
July 2019
Momentus Space raises a $25,500,000 series A round from ACE & Company, Drake Management, Lerner Enterprises, Liquid 2 Ventures, Mountain Nazca, Prime Movers Lab, Quiet Capital, University of Wyoming Foundation and Y Combinator.
November 14, 2018
Momentus announces $8.3M in Seed Funding.
November 2018
Momentus Space raises a $8,300,000 seed round from Andy Atherton, Ben Davenport, Benjamin McCann, Fort Ventures, Kingsley Advani, Liquid 2 Ventures, Mountain Nazca, One Way Ventures, Prime Movers Lab and Y Combinator.

Funding Rounds



Further Resources


Direct Thrust Measurements of an 8-GHz Microwave Electrothermal Thruster

Jeffrey R. Hopkins, Michael M. Micci, Sven G. Bilén, Senior Member, IEEE, and Silvio G. Chianese

Report on recent experimental results.

History and current status of the microwave electrothermal thruster,

D. E. Clemens, M. M. Micci, and S. G. Bilén

Progress in Propulsion Physics, Torus Press, 2009, pp.425-438

Review of work to 2009.

Momentus - CEO John Rood


August 2, 2021

Momentus- Vigoride


October 5, 2020

Propelling deep space flight with a new fuel source, Momentus prepares for liftoff

Jonathan Shieber



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