DRM - Space Transportation
The space transportation system to be employed in a manned mission to Mars of a trans-Mars injection (TMI) stage, a biconic aerobrake, a descent stage, an ascent stage, an Earth return stage to be launched from Martian orbit, and an Earth crew capture vehicle similar to those used in the Apollo missions.
The following is a description of the components of this system:
Trans-Mars Injection Stage (TMI)
The TMI stage designed for the Mars DRM uses nuclear thermal propulsion and is virtually the same for both manned and unmanned missions. The only difference between the stages used for both missions is its thrust.
The TMI stage used in human missions uses four 15,000 lb. thrust NERVA derivative (NDR) engines, which have an Isp of 900 seconds. Also, this stage incorporates a shadow shield between the NDR engine and the LH2 tank that protects the crew radiation build up in the engine.
In contrast, the TMI stage of cargo missions only uses three NDR engines and does not have a shadow shield. This less powerful stage places the cargo on a minimum energy trajectory.
Mars Orbit Capture and Descent Stage
The Mars orbit capture as well as the most of the descent maneuver is carried out using a single biconic aeroshell.
The descent stage uses four RL10-class engines, which were modified to burn LOX/CH4, for the post-aerocapture burn and for the final 500m/se. of descent before landing on the surface of Mars. This vehicle is capable of landing approximately 65 metric tons of cargo on unmanned missions.
The ascent vehicle is composed of the ascent stage and the ascent crew module.
The ascent stage is delivered on the surface with its propellant tanks empty. The descent vehicle that delivers it also carries several tanks of seed hydrogen to be used in the in situ production of the 30 metric tons of propellant, LOX/CH4. The ascent vehicle is propelled by two RL10-class engines, which were modified to burn LOX/CH4.
The ascent crew module is called the Earth Crew Capture Vehicle (ECCV). The ECCV is similar to the Apollo Command Module and it is used for entry into Earth’s atmosphere besides departure from the Martian surface.
Earth Return Vehicle
The Earth return vehicle is composed of the trans-Earth injection (TEI) stage, the Earth-return transit habitat, and the ECCV. The TEI stage is delivered to Mars fully fueled four years before the crew’s actual return trip. Like both the ascent and the descent stages, the TEI uses RL10-class engines, which were modified to burn LOX/CH4. Attached to this stage is the return habitat, which is an effective duplicate to the one used by the crew during their trip to Mars.