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I wonder if a rocket that uses electricity from internal batteries to heat water in its tanks to high pressure would be able to use that pressure to take off. Is it possible?

I've researched here and outside on this subject, but I didn't feel the issue was resolved. In none of the questions I looked at, someone considered the rocket carrying water in its tanks and gradually heating that water, turning it into steam, during the flight to maintain the pressure needed for the flight.

I believe this method is much better than building a rocket with all the pressure inside it before launch. Using electricity from batteries also seems a better idea than using any other type of fuel for heating. And it's less risky than using nuclear power.

When I think about this type of rocket, powered by water and electricity, I imagine it's just a matter of engineering. It would be as difficult to build it as any other rocket, yet it looks much cheaper and more environmentally friendly.

Am I right? And would it be possible to build such a rocket?

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No, it is impossible. A conventional rocket with liquid fuel and liquid oxidizer uses these propellants to produce hot gas under high pressure as well as a reaction mass.

The force needed to lift the rocket is the result of the exhaust of the reaction mass with very high velocity.

If you use liquid hydrogen and oxygen, the exhaust is very, very hot water too.

If you use water and batteries to heat it, you use only the water as reaction mass but not the mass of the batteries. But the batteries will weigh much more than the water that could be heated with them. The hot steam will be much colder than the combustion product of hydrogen and oxygen. The rocket will be so heavy it will never take off.

Batteries are very bad water heaters, that is why there are no battery operated water cookers for camping.

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    $\begingroup$ I was going to add that there are faster ways to heat water with lithium batteries, but those methods still makes them very bad water heaters. $\endgroup$
    – pipe
    Jan 15, 2022 at 21:02
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    $\begingroup$ It's all about energy density, really. The batteries we have are not good enough (by a large factor), but if we found a way to construct batteries with fifty times higher density, that would be similar to rocket fuel, which leaves the not-doubling-as-reaction-mass problem. Make them two hundred times as good and it would indeed become a matter of engineering. $\endgroup$
    – Michael Borgwardt
    Jan 15, 2022 at 21:41
  • $\begingroup$ +1. Does the same rationale also apply to in-orbit thrusters, such as a water resistor-jet? What, if anything, might make that a better prospect? $\endgroup$
    – Puffin
    Jan 15, 2022 at 22:25
  • $\begingroup$ Solar cells can deliver a very large amount of energy over their lifetime, but they can't deliver much power. So, a solar-electric steam rocket can deliver a lot of impulse, but it can't deliver it in a hurry (thrust is low). $\endgroup$
    – John Doty
    Jan 15, 2022 at 22:45
  • $\begingroup$ RCS thrusters are typically used intermittently with a very low duty cycle, so would be a decent application for a resistojet using water propellant and a battery that is kept charged using solar power. If you're making major changes to your orbit, though, you'd be better off without the batteries (and their mass) and operating lower power (and lower mass) thrusters directly from solar panels...if you're patient enough. $\endgroup$
    – Christopher James Huff
    Jan 16, 2022 at 2:14
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I wonder if a rocket that uses electricity from internal batteries to heat water in its tanks to high pressure would be able to use that pressure to take off. Is it possible?

I guess technically it could get off the ground, but it wouldn't be able to get into space. The energy density of rocket fuel is massively larger than batteries. Moreover, rocket fuel serves both as fuel and reaction mass. A fundamental difference between rockets and other uses of batteries, such as cars, is that rockets have to carry their own reaction mass, while cars use the ground as their reaction mass. This means that they have to be very efficient in their use of reaction mass. And while a car being inefficient can be solved by simply carrying more fuel, piling more fuel onto a rocket just makes it heavier and makes it need more fuel and reaction mass. Past a certain level of inefficiency, you get into a fatal loop of more fuel needing more fuel which needs more fuel, and you can't get to space no matter how much more you pile on.

I believe this method is much better than building a rocket with all the pressure inside it before launch.

Why? When we pressurize fuel before putting in the rocket, we use Earth-bound energy sources, which means that we don't have to take those energy sources with us. If we're adding pressure midflight, we have to take the fuel to do so with us, and we need fuel to lift that fuel off the ground, and we get back to the issue I mentioned before.

Using electricity from batteries also seems a better idea than using any other type of fuel for heating.

Why?

When I think about this type of rocket, powered by water and electricity, I imagine it's just a matter of engineering.

Not really. It's also a matter of physics. A battery works by having chemical reactions produce ions that produce electricity. It makes more sense to have chemical reactions directly producing energy, and rocket fuel reacting with oxygen is one of the most energetic chemical reactions there is.

It would be as difficult to build it as any other rocket, yet it looks much cheaper and more environmentally friendly.

Batteries are much more expensive than gasoline. The reason batteries are more environmentally friendly is that the chemical reactions that power them are much more reversible than the ones involved in burning hydrocarbons, and so while hydrocarbons are basically single-use, batteries can be recharged. If we had a good way of turning carbon dioxide and water into gasoline, gasoline engines would be more environmentally friendly than electric cars. For the most part, a rocket is single-use no matter how it's powered, so you lose the major upside.

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