Back in the late 1960s Wernher von Braun developed an architecture for colonising the Red Planet and the Moon, as a by-product, using Apollo-style boosters and NERVA-style nuclear rockets. Basically the Interplanetary vehicles were composed of three independent components – the Primary Propulsion Modules, the Planetary Mission Modules and the Mars Excursion Modules/Vehicles. A single Interplanetary Vehicle was composed, usually, of 3 PPMs, 1 PMM and 1 MEM, but an extra-PPM would be needed for some mission configurations. This was quite different to an earlier mission architecture which favoured using 4 PPMs, minimum, and an EEV (Earth Entry Vehicle) for direct returns, Apollo-style, to Earth. Von Braun believed that an Orbital Receiving Laboratory, at a 50 person Orbital Operations Centre (“Space Base”), was needed to isolate possible biological samples from Mars – von Braun had discussed the possibility of intelligent Martian life in his literature on Mars from the early 1960s, so he was being consistent.
The heaviest components were the PPMs, as fully fuelled they massed nearly 246 tons each. Each PPM was shrouded in a heavy meteoroid shield and staging components until they fired. They would be launched into orbit via a modified Saturn V, the Saturn V-25 (S)U Earth Launch Vehicle, designed to lift a maximum of 249 tons when the basic core was wrapped in 4 large Solid Rocket Boosters.
Stephen Baxter’s fictional account of a 1986 Mars Expedition, “Voyage”, explodes one such booster configuration in a launch accident in 1981 – due to a flaw in the SRBs, just like the real “Challenger” disaster of 1986. In “Voyage” that launch disaster and a core explosion in the Apollo-N nuclear test causes NASA to adopt chemical propulsion. While that was an option for a single-shot mission, von Braun’s long-term plan was to colonise Mars. Each vehicle was to carry 6 personnel, and two vehicles would carry 12 people to Mars. In one option two MEMs would depart for the surface and place 6 people on the surface, but another option was for a single lander and orbital operations amongst the Martian moons using a Space-Tug, itself capable of missions to both moons.
But eventually more people would need to be based on Mars and to do so specially designed freighters were required. These would carry Base Modules – the surface equivalent of a PMM – and Descent Modules, essentially the lander-half of an MEM. A single freighter could carry four of either at a time, and they would be combined in Mars orbit for delivery to the surface. A single Base Module could accommodate 12 personnel, just like the PMM and the core Space Station module that the PMM was to have evolved from.
On that issue, the Space Station, the original was to have launched in c.1975, to carry the “Skylab” experiment even further, and provide training in long-duration in-space activities for 12 astronauts, male and female. “Apollo” itself was to have finished with Apollo XX in 1975, to be succeeded by the much more powerful Space-Tug. The Space-Tug was to have been launched via a single Saturn-V for 14-day missions to the Lunar Surface with a crew of 3. Eventually a Space Station module was to have been landed using a Space-Tug Propulsion Module and to form the nucleus of a Moon Base. To sustainably operate a Base the Nuclear Shuttle was to have been introduced in 1978 to service the Base, carrying multiple loads of Base Modules, Propulsion Stages and freight modules. Eventually the Base was to be powered via nuclear reactors and/or solar power, depending on the applications.
You can see how the Moon Base was to be a practice run for Mars – power reactors, Nuclear Shuttles and PMM/Base Modules. A very crowded schedule with a first Mars Mission launching in 1981…