Orbital Transfer Vehicle

NASA has selected companies to study lower-cost ways to launch spacecraft to difficult-to-reach orbits. I would like to propose my own design based on my Mars Rocket Lower Stage idea. The idea is to utilize the high vapor pressure of carbon dioxide to attain high efficiency thrust using much simpler mechanisms. Unlike the Mars Lower Stage, the Orbital Transfer Vehicle will produce thrust in pulses.

The idea is very simple. Fill a cold pressure chamber with a predetermined amount of liquid carbon dioxide while the exhaust valve is closed. Then, close the input valve and start heating up the gas. When the pressure inside the pressure chamber reaches a certain pressure, open up the output valve which would generate the thrust. The output valve will remain open until the pressure inside the chamber drops to a certain level. Then, the output valve will be closed and the remaining gas will build up pressure again. This cycle will continue until the pressure drops considerably. Then, all remaining gas will be ejected. After that, new liquid carbon dioxide will be filled inside the chamber and the cycle will repeat. In classical liquid propulsion rockets, this process is continuous and turbopump are used to keep the pressure high and the heat is generated by combustion. This requires a complex and heavy engine. However, it may be enough to produce short powerful thrust pulses for some orbital transfers. Unlike ion thrusters, my method would produce very high thrust. For example, the combustion chamber of Raptor engine is 350 bar. If the pressure chamber of my proposal reaches those pressures, it may produce such high thrust for a short period of time. It is the most efficient way of turning the stored propellent into maximum thrust.

The heat source for my engine can be either solar panels or Plutonium 238. The liquid carbon dioxide can be pumped into the pressure chamber using an electric pump. Even pressure inside the propellent tank may be enough for pumping because the thrust is not continuous.

The overall objective of my idea is to store high density propellant, liquid carbon dioxide, inside a relatively light weight tank. Then release parts of this liquid as high-pressure gas in pulses. The temperature of the exhausted gas would be much lower than the liquid rockets. Therefore, aerospike nozzle can be utilized which saves a lot of space in vacuum. Maneuvering will be achieved by small side exhausts instead of gimbled nozzle. Simple design will reduce the failure rate for long missions and allow more room for the propellant.