Rocket for Human Mission to Mars

I am not a fan of sending humans to Mars when very capable robots exist for such tasks. Human mission requires several times larger rocket compared to a sample retriever robotic mission. The solution to a human mission is a scalable rocket design. A rocket with approximately the same dimensions as a lunar mission cannot achieve this. I opted for reduction in efficiency in order to scale up the design. The final design would be comparable in dimension with a tanker ship.

The rocket I propose will have 5 or more stages. Based on Saturn V rocket design, each stage’s gross mass is approximately 3.8 times its payload. Therefore, adding more stages to a rocket increases its gross mass exponentially. With my proposed rocket design this ratio may go lower. The rocket will generate thrust by carbon dioxide’s critical pressure. Liquid carbon dioxide will be warmed to its critical point, 31 °C, by the radioactive decay of nuclear waste Strontium-90. The rocket will not have a combustion chamber but a pressure chamber to generate thrust. The radioactive material with large surface area will be placed inside the pressure chamber to heat the pumped in liquid carbon dioxide. Carbon dioxide will be pumped at high pressure using turbopumps powered thermodynamically by the temperature difference between the liquid carbon dioxide and the decaying radioactive material. Low temperature operation will reduce the weight and cost of the engine and the nozzle. The propellant tank will also be lighter and cheaper than a liquid propulsion rocket’s tank.

Carbon dioxide has the highest vapor pressure of all the gasses. It has a critical temperature of 31° C and a critical pressure of 73.8 bar. Rocketdyne F-1 (Saturn V engine) has a chamber pressure of 70 bar and SpaceX Raptor engine has a chamber pressure of 350 bar. These numbers show that; engine efficiency is one think overall rocket performance is another. F1 engine completed many high-energy space missions successfully compared to more efficient counterpart which still has a long way to go.

My much simpler rocket design allows it to be built at much larger scales. It’s engine’s simplicity allows much larger engines to be build. Larger diameter would allow more engines to be placed on its bottom to increase the thrust. The first stage of the rocket will utilize additional solid boosters to assist take off. The rocket’s trajectory will be vertical to increase its distance from Earth as quickly as possible. Coupled with more stages, the rocket will achieve much higher speeds compared to Apollo missions. This will reduce the round-trip duration and increase the success rate of the mission.

I will discuss the details of the rocket and the Mars Stage on my next articles.