Duration: 18 months
Water propulsion has begun to emerge as a sustainable replacement for hydrazine boosting performance by 50% without any of the toxicity. Despite these benefits water propulsion is limited to applications not requiring sustained high thrust due to the need to electrolyse the water before it is used. This means it cannot be used for missions requiring a large continuous deorbit burn, a high delta V capture or a rendezvous manoeuvre.
URA proposes a solution for a sustained thrust hybrid rocket engine based around the high energy reaction of magnesium particles and steam. This concept uses an innovative 3D printed magnesium fuel grain that releases powder to the combustion chamber at a controlled rate, which combined with steam enables a throttleable hybrid rocket engine fed directly with water.
Previous studies by Tokyo University have shown that suspended aluminium & magnesium powder readily reacts with steam, and others have shown a high performance up to 300 seconds of ISP. The main blocker to implementation of these propellants is the ability to provide a controlled flow rate of particulate to the combustion chamber. To date experiments have relied on carrier gases or wires, increasing complexity, reducing reaction efficiency & limiting application to cubesat scales.
URA has found a solution; enabling this propellant combination to be used in rockets of any size up to the kilo-Newton range. Using a design based around established metal binder jet printing a bubble structure is printed into magnesium powder using low melting point adhesives. The bubble structure design creates capsules of magnesium dust that are held captive by an adhesive shell. Steam entering the chamber melts the adhesive at the fuel grain surface releasing the powder into the combustion flow. By controlling the size of the bubbles the fuel grain regression rate & the combustion properties can be controlled. This technique is scalable & opens up a viable route to achieve water based hybrid rockets.
