The Mars Direct Architecture
The Mars Direct plan involves two launches. The first is an unmanned flight, containing an unfueled methane/oxygen engine and the ERV for launching off the Martian surface, liquid hydrogen, a nuclear reactor that works with the methane/oxygen engine, a set of compressors, a chemical processing unit, and the scientific rovers. During the next two to three years propellant is being formed from the CO2 on Mars. On Earth, two more spacecrafts are launched. One is like the one launched before, the other is a craft containing a crew of four, with supplies for three years, a ground rover, and landing gear. In this model, artificial gravity is provided by spinning at 1 rpm. The craft lands at the same site as the fully fueled ERV.
There should be no problem with the surface rendezvous. The site has been explored for two years prior to manned touchdown by machines. The ERV will also be able to beam a signal to the incoming craft directing it. If, for some reason, the craft lands away from the ERV, the land rover in the hab module can take the crew there. If not, the crew can take off in the ERV that they brought with them, otherwise the craft will begin to fuel itself for another manned mission due to land in another few years to continue the exploration of Mars.
With fuel save for ground missions, about 22,000 ground kilometers can be traveled by ground vehicles in the 1.5 years of surface-stay. All personnel stays on the Martian surface, giving them shielding from cosmic radiation and natural gravity.
The Mars Direct launch vehicle is much like any other craft launched from Earth, with solid rocket boosters to escape Earth’s gravity that separate after burning.
Artificial gravity is obtained by spinning the two parts of the module
connected with a tether. One part contains the crew habitat while the other
is the burnt-out heavy lift launch vehicle (HRV) used during the launch
from Earth. In this model, the tether is 1500 meters long and rotates at
1 rpm, giving a pull of 0.38 Earth-G (which is equal to one Mars-G). The
tether would consist of six flat-woven braids with interconnecting cords
every meter. By using this, three braids can snap before the remaining
three would be overstressed and fail as well (though the spin could be
decreased to prevent the overstraining of the remaining braids). Maneuvers
are achieved by firing thrusters along the line of the tether or parallel
to the vector of the spinning system so that the spin rate, and therefore
gravity, is not affected. See Artificial Gravity.