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A Propulsion System With A Water-Based Propellant

Hydro Moves

Terran Orbital built and launched the Pathfinder Technology Demonstrator (PTD) 1 spacecraft on behalf of NASA, the first in a series of missions that will test the operation of a variety of novel CubeSat technologies in low-Earth orbit, providing significant enhancements to the performance of these small and effective spacecraft. Over the course of multiple planned PTD missions, the successful demonstration of new subsystem technologies will increase small spacecraft capabilities enabling direct infusion into a wider range of future science and exploration missions.​

The PTD missions utilize a Terran Orbital Corporation’s state-of-the-artMKII Avionics platform. The 6-unit (6U) spacecraft, named Trestles, is common to all PTD missions and easily accommodates different technology payloads being demonstrated without the need to redesign the spacecraft each time completely. In addition to providing the spacecraft, Terran Orbital also serves as the integrator for each technology payload into its respective spacecraft and performs in-orbit mission operations from the Terran Orbital mission operations center after each launch.​​

The PTD-1 mission launched on January 24, 2021, to demonstrate the Hydros-C propulsion system with a water-based propellant developed through a public-private partnership with Tethers Unlimited, Inc., of Bothell, Washington. Carrying approximately one pint of water in a flexible bladder contained within a metal vessel aboard the CubeSat, the propulsion system separates water into hydrogen and oxygen propellants by applying an electric current through the water. The propulsion system uses power provided by the spacecraft’s solar arrays to operate the miniature water electrolysis system. The demonstration tested propulsion performance through programmed thrust events, which change spacecraft velocity and altitude executed by the hydrogen and oxygen-fueled combustion. This propulsion system provides higher thrust compared to other propulsion technologies while requiring lower power input. The data collected during this flight demonstration will be incorporated in future Hydros-C and its larger Hydros-M systems. The Hydros-M system is planned for several missions, including NASA Science Mission Directorate’s Polarimeter to UNify the Corona and Heliosphere (PUNCH) mission. PTD-1 is the first mission to demonstrate a water-based electrolysis propulsion system on any type of spacecraft.




Technology Demonstration


NASA Ames Research Center


6U Satellite

Launch Date

January 24, 2021

Launch Vehicle

Space X Falcon 9

Mission Length


Mission Completion


Space X Falcon 9

Falcon 9 is a rocket that can carry cargo and humans into Earth’s orbit, even reaching the International Space Station (ISS). It is produced by American aerospace company SpaceX. Technically, it is a partially reusable, medium lift launch vehicle.

The rocket has two stages. The first (booster) stage carries the second stage and payload to a certain altitude, after which the second stage lifts the payload to its ultimate destination. The rocket evolved through several versions. V1.0 flew from 2010–2013, V1.1 flew from 2013–2016, while V1.2 Full Thrust first launched in 2015, encompassing the Block 5 Full Thrust variant, flying since May 2018.

The booster is capable of landing vertically to facilitate reuse. This feat was first achieved on flight 20 in December 2015. Since then, SpaceX has successfully landed boosters over 100 times. Individual boosters have flown as many as thirteen flights. Both stages are powered by SpaceX Merlin engines, using cryogenic liquid oxygen and rocket-grade kerosene (RP-1) as propellants.

The heaviest payloads flown to geostationary transfer orbit (GTO) were Intelsat 35e carrying 6,761 kg (14,905 lb), and Telstar 19V with 7,075 kg (15,598 lb). The former was launched into an advantageous super-synchronous transfer orbit, while the latter achieved a lower-energy GTO achieving an apogee well below the geostationary altitude.

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