This is my first post. Please forgive my ramblings. What got me to join this forum was kind of related to steam rockets, so this mention of them here caught my eye. I have been interested in rockets from birth (born on the day John Glenn went up!). I even built my own weird rocket model that looked more like a flying saucer. (I’ve never thought of flying actual model rockets, I guess because I grew up in NYC and never heard of it being done.) I went as far as sending my resume to try to get into the astronaut program though. (They weren’t hiring, but I kept the nice letter they sent!)
Anyway, after a career as an EE, I found that my old dream didn't die. So, a few years ago, I started looking into the crazy idea of if I could design my own manned rocket. I decided liq. H2/O2 was out of reach for a hobbyist and was looking for a safer alternative. I read about the limits of chemical rockets and that if we were going to explore deeper into space, we would have to look for alternatives. I was keenly interested in the nuclear thermal rocket plans that the US was and is involved in. I see a lot of promise there.
But that got me looking into thermal rockets and I developed, on paper, a thermal rocket that was pretty energy-efficient and can use a variety of propellants. I’ve ‘paper’ designed it using air, to air mixed with water, to water, to helium and even hydrogen. I’ve looked into the materials, cost, and safety and I think it is time to actually build and test.
The trick to make this work was to go away from the big boiler concept and to break down the heating system to "cells". I have calculated having roughly 400 lbs of thrust per cell using water. And the ISP was at best around 295 seconds. Really not that bad. I had a total calculated flight time of about 16 minutes, meaning maybe enough for a SSTO and powered landing! The trick was, because of the cellular design, I switch off cells as the water mass is used up, keeping the same thrust. That way, the power drain goes down and the water use goes down as well. I had calculated the ISP using helium to be about 500 seconds, but not easy to use as a propellant. Using hydrogen comes with its own problems. I can get an ISP of 730 seconds but have the penalty of the mass of storage tanks and complexity of pumps and the danger of cryogenic fuels. But even with that mass penalty, that would allow for about 50 minutes of burn time.
Looking at the history of water being used, those super-heated steam rockets had an Isp of around 40 seconds and only had 6 seconds of thrust. Momentus Space has a water/solar/ plasma rocket that can lift satellites to higher orbits with an ISP of 700 seconds (but low thrust). And there is talk of refueling rockets in space using the water that is everywhere in the solar system using nuclear or solar means for energy and getting ISP's of >200 seconds.
My plan is to build the actual cells and document their performance before proceeding. If they work, I will probably design a personal aircraft using it first, like a manned/unmanned drone. Using lots air and some water, I could get flight times up to an hour. This option will be battery-powered.
As to vertical flight, I’m still not sure how I’ll proceed. I guess I will go the patent route before seeing if I could test since I’d have to divulge its inner workings to get permission and I’d have no IP protection. I’d prefer to test it first to be honest, but I don’t see a way to do it legally.