Nuclear Mars Retriever

Planetary missions, especially the ones requiring a return trip need advanced propulsion technologies. I am in favor of the ones utilizing nuclear reactors instead of chemical reactions. I propose a hybrid reactor to achieve this goal. A combination of Pressurized water reactor and Advanced gas-cooled reactor. The basis will be a pressurized water reactor which has the smallest footprint. The cooling will be done using carbon dioxide like in advanced gas reactors.

The first stage of the rocket carrying the Mars Retriever will be a traditional liquid propulsion rocket. The Mars Retriever will be the second stage utilizing a nuclear propulsion. The second stage will be composed of stacked dry ice containing spherical tanks. The controlled nuclear reactor would heat up the carbon dioxide gas to generate the thrust for the rocket. As the Mars Retriever travels, the depleted tanks will be ejected to reduce the weight until the last tank. The remaining dry ice in the tank will be used to safely descent the Retriever on Mars surface. Then the nuclear reactor will be used as an electric generator. Carbon dioxide captured from the Mars atmosphere will be used for this purpose. As a result the Retriever will have plenty of electricity to conduct its sample retrieving mission including much deeper sample gathering. The Retriever will also serve as the central charging and communication base for the small explorers that it carried on board.

Earth–Mars cyclers (cycler is a trajectory that encounters two or more bodies regularly. Once the orbit is established, no propulsion is required to shuttle between the two) occur almost every two years. Therefore, the Retriever would conduct its exploration mission within that time frame. In the meanwhile, the Mars Retriever will use its electricity to fill the dry ice tank with carbon dioxide from the Mars atmosphere. Even with partially filled tanks the Retriever will take off and fly to other locations to explore much larger area with a single mission. On final location, the tank will be fully loaded to take off and start the return journey. When the tank depletes during return journey, the Retriever will release the sample capsule that carries the samples. The capsule will use ion thrusters to complete the mission back to Earth.