A Sort Of Plastic Rocket

While I was searching for the lightest solid made of carbon and hydrogen only, I found the polyethylene. Which is one of the most widely used plastic on earth. It is a very compact form of storing carbon and hydrogen. I read about the solid boosters that utilized these plastics partially. My proposition is a liquid propulsion rocket that uses polyethylene as the fuel.

Low-density polyethylene (LPDE) easily decomposes into methane and ethylene in the presence of UV light and oxygen. Stronger and more transparent high-density polyethylene (HDPE) is more resistant to decomposition. However, it also decomposes.

My rocket design has a liquid oxygen (LOX) tank at the top. Under the LOX tank LDPE will be molded surrounded by the HDPE which is surrounded by the borosilicate glass rocket shell. The idea is to initially decompose LPDE into methane and ethylene with the help of LOX and external UV light (the Sun). The generated gas will then be used by the rocket engine as the fuel. Storing polyethylene as fuel is much simpler and has higher density compared to storing liquid methane inside a pressure tank. Initially, LDPE will be consumed as fuel source and HDPE will serve as the casing for the pressurized gas. Then, HDPE will also decompose as the pressure inside the tank drops. The strength of the borosilicate glass will be enough to withstand the decomposing HDPE. The glass will only be used on the fuel section of the rocket. The remaining of the rocket will be made of aluminum magnesium alloy which adheres perfectly with silicon.

Before the rocket is launched, the LPDE will be directed to external UV light and some LOX will be released to the LPDE section. Once the decomposing gas reach certain pressure, the rocket will be launched. The rocket will be launched such that it would rotate slightly around its axis for a uniform UV exposure. The launches will be conducted at noon for maximum UV light.

Even though, this idea may not work for the first stage of a rocket, modified versions of it can be utilized by the upper stages and on some satellites.