Mars Direct

Did You Know?

• Baker pitched Mars Direct at the Marshall Spaceflight Center in April 1990, where reception was very positive, and the plan later received a standing ovation at the National Space Society.
• Zubrin and his colleagues demonstrated an in-situ propellant generator that achieved 94% efficiency, with no chemical engineers involved in the development.
• Mars to Stay proposals suggest sending immigrants without immediate return, potentially costing one fifth to one tenth of a return mission.

History

On July 20, 1989, US President George H. W. Bush announced the Space Exploration Initiative (SEI), which included long-term plans for a human mission to Mars. A study completed by December 1990 estimated the project would cost about 450 billion dollars over 20 to 30 years, leading to hostile Congressional reaction and denial of funding within a year. Dan Goldin became NASA Administrator on April 1, 1992, and abandoned near-term human exploration beyond Earth orbit in favor of a "faster, better, cheaper" robotic strategy. While at Martin Marietta, Robert Zubrin identified a fundamental flaw in the SEI program: its plan to use as many technologies as possible made it politically untenable. Zubrin described this approach as the opposite of correct engineering. His alternative, dubbed Mars Direct, rejected the "Battlestar Galactica" mission strategy of large nuclear-powered spaceships. Instead, it featured a longer surface stay, a conjunction-class flight path, in situ resource utilization, and direct launches from Earth to Mars without orbital assembly. After management approval, a 12-man team at Marietta worked on mission details, but Zubrin collaborated with David Baker on a simpler, stripped-down strategy focused on using local resources and traveling light.

Mission scenario

An uncrewed Earth Return Vehicle (ERV) is launched first, carrying an automated factory that produces methane and oxygen from Martian resources. About 96 tonnes of these propellants are needed for the return trip; the remainder fuels rovers. Fuel production takes roughly ten months. Some 26 months after the ERV launch, a Mars Habitat Unit carrying a crew of four is launched on a six-month low-energy trajectory to Mars. The Habitat Unit is not launched until the factory confirms successful propellant production. During transit, artificial gravity is generated by tethering the Habitat Unit to the spent upper stage and rotating them to produce 1 g. Upon arrival, the upper stage is jettisoned, and the Habitat Unit aerobrakes into Mars orbit before landing near the ERV, guided by a radar beacon. The crew spends 18 months on the surface conducting research, aided by a small rover powered by methane from the ERV. For return, the crew uses the ERV, leaving the Habitat Unit for future explorers. Follow-up missions are dispatched every two years, ensuring a redundant ERV is always on the surface for emergency use; in such a scenario, the crew would travel hundreds of kilometers to the other ERV in a long-range vehicle.

Components

The Mars Direct proposal includes a heavy-lift launch vehicle called Ares, an Earth Return Vehicle (ERV), and a Mars Habitat Unit (MHU). Ares would be similar in size to the Saturn V, derived from Space Shuttle components, using Advanced Solid Rocket Boosters, a modified external tank, and a new LOX/LH2 third stage for trans-Mars injection. It could place 121 tonnes into a 300 km circular orbit and boost 47 tonnes toward Mars. The ERV is a two-stage vehicle: the upper stage provides living quarters for the six-month return trip, while the lower stage contains rocket engines and a small chemical production plant. The MHU is a two- or three-deck vehicle with individual sleeping quarters, a communal living area, galley, exercise area, and closed-cycle water purification. Its lower deck houses laboratory areas, storage, airlocks, and a suiting-up area. Radiation protection is provided by a dedicated storm shelter in the vehicle's core. The MHU also carries a small pressurized rover, stored in the lower deck and assembled on the surface, powered by a methane engine and designed for exploration up to 320 km. Since Mars Direct, NASA has adopted the MHU for its Mars Design Reference Mission, using two units: one uncrewed for laboratory work and a larger rover, and one crewed for living and storage.

Revisions

Since its initial conception, Mars Direct has undergone regular review by Zubrin, the Mars Society, NASA, Stanford University, and others. Zubrin and Weaver developed a modified version called Mars Semi-Direct in response to criticisms. This architecture uses three spacecraft, including a Mars Ascent Vehicle (MAV) that lands uncrewed and produces propellants for ascent to Mars orbit, while the ERV remains in orbit for the return journey. Mars Semi-Direct became the basis of NASA's Design Reference Mission 1.0, replacing the Space Exploration Initiative. When cost-analyzed similarly to the 90-day report, it was predicted to cost 55 billion dollars over 10 years, fitting within the existing NASA budget. As of September 1, 2012, the NASA Design Reference Mission (version 5.0) calls for at least three launches per mission, sends the ERV fully fueled to Mars orbit, and has the MAV rendezvous with it. With the advent of low-cost heavy lift capability, Zubrin has proposed a simpler plan using SpaceX hardware: a crew of two sent by a single Falcon Heavy launch, with the Dragon spacecraft as the interplanetary habitat and inflatable modules for extra space. Artificial gravity would be generated by tethering the Dragon to the TMI stage. Research at NASA Ames has shown a robotic Dragon could perform a fully propulsive landing on Mars. On the surface, the crew would have two Dragons with inflatable modules, two ERVs, two MAVs, and 8 tonnes of cargo.