The Fourth Stage

Since the beginning of space exploration, humanity could only send surface explorers to Mars with few exceptions. Main reason for that is the time it takes for a payload to reach the planets. We need to increase the payload’s average speed during its long voyage. In my planetary rocket design, I dedicated the fourth stage for that. This stage needs to generate high thrust like the previous stages.

An option can be to have a liquid methane engine to generate high thrust. For this task, a highly efficient but small engine can be developed. As a result, the thrust would be generated over a longer duration and the rocket would not be stressed by high g-forces.

Another option would be to use ion thrusters. However, a special engine needs to be developed to generate enough thrust for the heavy rocket. The gasses used in ion thrusters are quite expensive and supplying large volumes to satisfy the thrust requirement can be quite expensive. Additionally, ion thrusters require electricity for the thrust. While travelling away from the sun, not much electricity can be generated and protruding solar panels may not be reliable.

My proposal is a rocket stage filled with dry ice and Plutonium 238 heated nozzles. The idea is to convert small portions of dry ice into carbon dioxide and eject it from a tiny nozzle. The details are shown on the diagram. A Pu 238 tube with tiny holes on its sides would be used to heat the dry ice and pressurize it to generate thrust. The tube would be initially covered by an insulator low melting plastic that leaves no residue. This shield would prevent the dry ice from premature melting. The delay is the duration for the lower stages to complete their duties. Once the insulation melts away by the heat of the isotope, the rocket would start generating thrust. This is a much simpler and reliable design compared to the rest. Utilizing heat generated by radioactive decay gives the stage high ISP. The carbon dioxide gas would be exhausted from a tiny hole to accumulate higher pressure inside. This also increase the duration of the thrust generated.

The stage would be covered by a detachable heat shield. This shield would keep the dry ice cold during the atmospheric escape. Once the rocket is in LEO, the shield would be released to reduce weight. The released shield would than burn away in the atmosphere.

This simple stage can be cascaded to generate even more thrust.