Project: ICE cube thruster
imperial.ac.uk
imperial.ac.uk
Design, fabrication and test of the iridium catalysed electrolysis (ICE) thrusters (2023) https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.884942
Experimentally Demonstrating the Feasibility of Water as a Multimode Electric-Chemical Propellant (2022) https://www.researchgate.net/publication/362036633_Experimen...
[edit] Quick research shows that no, that's not right! But the article says "feed the gases into a thruster." Are they burning them at that point?
Water gets you dense, room-temperature propellent storage. Big solar panels give you lots of excess power. Converting small amounts of water into gas as it's needed and then burning it means you don't need to plan to store cryogenic liquid hydrogen.
Recombination of hydrogen/oxygen gives you flame temperatures far north of >3,000 K. This is probably the simplest way to "just heat the water", in this temperature range. I imagine a "conventional" 3,000 K heat exchanger (for example, electric-resistive) would be very difficult to engineer.
(Those also exist, and you can look up "resistojet" to find alternative approaches to compare against. As best as I can tell, those tend to operate at much lower temperatures; and the high-performing ones use hydrazines as their (mono)propellant, boosting the final temperature by exothermic chemical decomposition. I might have misunderstood the literature).
There must be some simplicity factor that makes the circuits we use on the ground unfit to space. Because people build 3000K heaters all the time (usually arc-based, but also, a light-bulb is one).
When the Oxygen and Hydrogen are burned from this engine, they should recombine into water.
If we fired an engine like this in space toward a "sail", would it be possible to produce a craft long enough and with a system attached to the aft that could re-collect the water for reuse?
Possibly by having stiff wires that use the surface tension of the water to stickily grab on as the craft moves forward?
You mean like an air boat [1]? Using a sail just makes it less efficient when self powered.
It wouldn't work like that in space because there is no working fluid (air) against which to push - which is what the fan is doing, whether it's using a sail or not. Conservation of momentum would eliminate any propulsion if the propellant is recollected.
For propellent-less drives, I would be looking at light-sails or mag-sails, rather than trying to collect and unburn the trillions of water molecules your engine is scattering across the vacuum of space.
I don't think that the boat experiment is a good analogue, though, as it seems the engine would be pushing with more force in the backward direction than could be harnessed in the forward direction.
It still seems like there could be a possible way to re-collect the water for further use as propellant in a vacuum once you have harnessed the energy from it's combustion. Essentially using solar to propel your craft and then reclaiming the raw propellant (water) so that it can be separated again.