Mars Direct
[2] By December 1990, a study to estimate the project's cost determined that long-term expenditure would total approximately 450 billion dollars spread over 20 to 30 years.
[5] While working at Martin Marietta designing interplanetary mission architectures, Robert Zubrin perceived a fundamental flaw in the SEI program.
Zubrin came to understand that if NASA's plan was to fully utilize as many technologies as possible in support of sending the mission to Mars, it would become politically untenable.
[4]Zubrin's alternative to this "Battlestar Galactica" mission strategy (dubbed so by its detractors for the large, nuclear powered spaceships that supposedly resembled the science-fiction spaceship of the same name) involved a longer surface stay, a faster flight-path in the form of a conjunction class mission, in situ resource utilization and craft launched directly from the surface of Earth to Mars as opposed to be being assembled in orbit or by a space-based drydock.
While they focused primarily on more traditional mission architectures, Zubrin began to collaborate with colleague David Baker's[7] extremely simple, stripped-down and robust strategy.
96 tonnes of methane and oxygen would be needed to send the Earth Return Vehicle on a trajectory back home at the conclusion of the surface stay; the rest would be available for Mars rovers.
The Habitat Unit would not be launched until the automated factory aboard the ERV had signaled the successful production of chemicals required for operation on the planet and the return trip to Earth.
During the trip, artificial gravity would be generated by tethering the Habitat Unit to the spent upper stage of the booster, and setting them rotating about a common axis.
The plan involves several launches making use of heavy-lift boosters of similar size to the Saturn V used for the Apollo missions, which would potentially be derived from Space Shuttle components.
The lower deck of the Mars Habitat Unit provides the primary working space for the crew: small laboratory areas for carrying out geology and life science research; storage space for samples, airlocks for reaching the surface of Mars, and a suiting-up area where crew members prepare for surface operations.
Protection from harmful radiation while in space and on the surface of Mars (e.g. from solar flares) would be provided by a dedicated "storm shelter" in the core of the vehicle.
Zubrin remained committed to the strategy, and after parting with David Baker attempted to convince the new NASA administration of Mars Direct's merits in 1992.
[4] After being granted a small research fund at Martin Marietta, Zubrin and his colleagues successfully demonstrated an in-situ propellant generator which achieved an efficiency of 94%.
When subjected to the same cost-analysis as the 90-day report, Mars Semi-Direct was predicted to cost 55 billion dollars over 10 years, capable of fitting into the existing NASA budget.
With the potentially imminent advent of low-cost heavy lift capability, Zubrin has posited a dramatically lower cost human Mars mission using hardware developed by space transport company SpaceX.
In this simpler plan, a crew of two would be sent to Mars by a single Falcon Heavy launch, the Dragon spacecraft acting as their interplanetary cruise habitat.
The problems associated with long-term weightlessness would be addressed in the same manner as the baseline Mars Direct plan, a tether between the Dragon habitat and the TMI (Trans-Mars Injection) stage acting to allow rotation of the craft.
[14] On the surface, the crew would have at their disposal two Dragon spacecraft with inflatable modules as habitats, two ERVs, two Mars ascent vehicles and 8 tonnes of cargo.
