I'm kind of lost trying to understand this. Wouldn't make more sense to just heat the water directly and make a steam thruster? What does the electrolizing step gain? (They claim not to store the gases, so it can't be decoupling the steps.)
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).
Interesting. Resistorjets seem to be all over the place.
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).
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.
Or more like using water as a form of capacitor, since electrolysis only require voltage and can be run at any power, whereas thrust is something where you want immediate demand of power
I really hate being pedantic here, but it's ultimately using mass for thrust instead of being a pure photon rocket (which arguably is also expelling energy which has mass but in this particular case you're expelling momentum - and probably causing smarter people than me to groan in exasperation at my description).
There is an almost unbelievable experiment where a fan is used to blow into a sail attached to a boat and it shows that you can propel a boat using a fan that is mounted on the boat itself. It's a bit mind bending.
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 can propel a boat using a fan that is mounted on the boat itself
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.
The wind from the fan on the boat was just bouncing off the sail. It would be more efficient to just take down the sail, point the fan aft and turn it on.
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.
The thought was to re-collect the propellant for reuse in an environment where you cannot easily replenish it, once you have harnessed the energy from burning the components of that propellant.
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.
But what happens when the boat speed matches the propeller airspeed? Wouldn’t sucking the air from the ground and deflecting to a variable angle allow for higher top speed until you are power-limited (as opposed to gearing limited)?
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...