Mars Direct

Mars Direct

Mars Direct is a proposal for a manned mission to Mars. Proponents of the scheme have claimed it to be both cost-effective and that it can be conducted with current technology. It was originally detailed in a research paper by NASA engineers Robert Zubrin and David Baker in 1990, and later expanded upon in Zubrin's 1996 book The Case for Mars. It now serves as a staple of Zubrin's speaking engagements and general advocacy as head of the Mars Society, an organization devoted to the colonization of Mars.



The plan involves several launches. Proponents of Mars Direct have suggested that the heavy-lift boosters required would be no larger than the Saturn V used for the Apollo missions, and could potentially be derived from Space Shuttle components.

The first flight would bring an unmanned Earth Return Vehicle to the red planet, with a supply of hydrogen, a chemical plant and a small nuclear reactor. Once there, a series of chemical reactions (the Sabatier reaction coupled with electrolysis) would be used to combine a small amount of hydrogen (8 tons) carried by the Earth Return Vehicle with the carbon dioxide of the Martian atmosphere to create up to 112 tonnes of methane and oxygen. 96 tonnes of these would be needed to return the Earth Return Vehicle to Earth at the end of the mission, the rest would be available for Mars rovers. Proponents of the scheme have suggested that this process would take approximately ten months to complete.

Some 26 months after the Earth Return Vehicle is originally launched from Earth, a second vehicle, the "Mars Habitat Unit", would be launched to coincide with a low-energy transfer window to Mars, and would carry a crew of four astronauts. This would not be launched until the automated factory had signaled the successful production of the chemicals. This vehicle would take some six months to reach Mars. During the trip, supporters of Mars Direct have suggested that artificial gravity could be generated by tying the spent upper stage of the booster to the Habitat Unit, and setting them both rotating about a common axis.

On reaching Mars, the upper stage would be jettisoned, with the Habitat Unit aerobraking into Mars orbit before soft-landing in proximity to the Earth Return Vehicle. Precise landing would be supported by a radar beacon started by the first lander. Once on Mars, the crew would spend 18 months on the surface, carrying out a range of scientific research, aided by a small rover vehicle carried aboard their Mars Habitat Unit, and powered by the methane produced by the Earth Return Vehicle. To return, they would use the Earth Return Vehicle, leaving the Mars Habitat Unit for the possible use of subsequent explorers. The propulsion stage of the Earth Return Vehicle would be used as a counterweight to generate artificial gravity for the trip back.


The Mars Direct proposal includes a component for an Earth Return Vehicle (ERV) and a Mars Habitat Unit (MHU).

Earth Return Vehicle

The Earth Return Vehicle is a two-stage vehicle. The upper stage comprises the living accommodation for the crew during their six-month return trip to Earth from Mars. The lower stage contains the vehicle's rocket engines and a small chemical production plant.

Round trip payload
Crew compartment 7,100 kg
Reaction control system 400 kg
Biconic brake 2,450 kg
Stage 1 (dry) 6,330 kg
Stage 2 (dry) 1,770 kg
Mars-bound payload
Hydrogen for propellant production 5,810 kg
SP-100 Reactor 4,500 kg
Earth-bound payload
Crew 450 kg
Suits 300 kg
Consumables (dry food) 2,000 kg
Soil Samples 150 kg
Stage 1 propulsion system
Usable propellant (methane / oxygen) 70,160 kg
Dry mass 8,850 kg
Total engine thrust 85,237 kgf (835.89 kN)
Specific impulse 373 s (3.65 kN·s/kg)
Stage 2 propulsion system
Usable propellant (methane / oxygen) 25,000 kg
Dry mass 2,560 kg
Total engine thrust 9,059 kgf (88.84 kN)
Specific impulse 373 s (3.65 kN·s/kg)

Mars Habitat Unit

The Mars Habitat Unit is a 2- or 3-deck vehicle providing a comprehensive living and working environment for a Mars crew. In addition to individual sleeping quarters which provide a degree of privacy for each of the crew and a place for personal effects, the Mars Habitat Unit includes a communal living area, a small galley, exercise area, and hygiene facilities with closed-circle water purification. 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. Proponents of the design have argued that protection from harmful radiation while in space and on the surface of Mars (e.g. from solar flares) is provided by a dedicated "storm shelter" in the core of the vehicle.

The Mars Habitat Unit would also include a small pressurized rover that is stored in the lower deck area and assembled on the surface of Mars. Powered by a methane engine, it is designed to extend the range over which astronauts can explore the surface of Mars out to 320 km.

Since it was first proposed as a part of Mars Direct, the Mars Habitat Unit has been adopted by NASA as a part of their Mars Design Reference Mission, which utilizes two Mars Habitat Units - one of which flies to Mars unmanned, providing a dedicated laboratory facility on Mars, together with the capacity to carry a larger rover vehicle. The second Mars Habitat Unit flies to Mars with the crew, its interior given over completely to living and storage space.

To prove the viability of the Mars Habitat Unit, the Mars Society has implemented the Mars Analogue Research Station Program (MARS), which has established a number of prototype Mars Habitat Units around the world.

Round Trip Payload Tonnes
Main Structure 8.52
Decks 6.00
Airlock / Radiation Shelter 1.82
Airlock Doors 0.40
Interior Fittings  
Walls 0.30
Furniture 0.50
Science Equipment 1.00
Exercise and Health 0.20
Plumbing and Lighting 1.00
Replacement Air (3 charges) 0.81
Solar Panels 0.25
Life Support System 4.00
Consumables for Crew 11.76
Crew of 6 0.45
Personal Effects 0.70
Spacesuits 0.30
Pressurised Rover 2.00
Deployed Surface Science 0.40
Contingency 5.00


Since Mars Direct was initially conceived, it has undergone regular review and development by Zubrin himself, the Mars Society, NASA, Stanford University and others.

Zubrin and Weaver developed a modified version of Mars Direct, called Mars Semi-Direct, in response to some specific criticisms.[1] This mission consists of three spacecraft and includes a "Mars Ascent Vehicle" (MAV). The ERV remains in Mars orbit for the return journey, while the unmanned MAV lands and manufactures propellants for the ascent back up to Mars orbit. The Mars Semi-Direct architecture has been used as the basis of a number of studies, including the NASA Design Reference Missions.

The NASA model, referred to as the Design Reference Mission, currently on version 5.0, calls for a significant upgrade in hardware (at least 3 launches per mission, rather than two), and sends the ERV to Mars fully fuelled, parking it in orbit above the planet for subsequent rendezvous with the MAV.

The Mars Society and Stanford studies retain the original 2-vehicle mission profile of Mars Direct, but increase the crew size to six.

Mars Society Australia developed their own four-person Mars Oz reference mission, based on Mars Semi-Direct. This study uses horizontally landing, bent biconic shaped modules, and relies on solar power and chemical propulsion throughout,[2] where Mars Direct and the DRMs used nuclear reactors for surface power and, in the case of the DRMs for propulsion as well. The Mars Oz reference mission also differs in assuming, based on space station experience, that spin gravity will not be required.

The Mars Society has argued the viability of the Mars Habitat Unit concept through their Mars Analogue Research Station program. These are two or three decked vertical cylinders ~8 m in diameter and 8 m high. Mars Society Australia plans to build its own station based on the Mars Oz design.[3] The Mars Oz design features a horizontal cylinder 4.7 m in diameter and 18 m long, with a tapered nose. A second similar module will function as a garage and power and logistics module.

Mars Direct was featured on a Discovery Channel programs Mars: The Next Frontier in which issues were discussed surrounding NASA funding of the project, and on Mars Underground, where the plan is discussed more in-depth.


A modified proposal, "Mars for Less", was developed by Grant Bonin, and has been adopted as the design reference mission for a new umbrella group of advocates, the MarsDrive consortium. The design retains most of the essential features of Mars Direct, but uses multiple medium-lift rocket launchers that are commercially available today (such as the Ariane V or the Delta rocket) to launch the crew vehicles, and their propulsion, separately, and mate them in orbit. By doing so, the multi-billion dollar development cost of a new launch vehicle is avoided.

A modified proposal, called "Mars to Stay", involves not returning the first immigrant/explorers immediately, or ever. Dean Unick has suggested the cost of sending a four or six person team is one fifth to one tenth the cost of returning that same four or six person team. A quite complete lab can be sent and landed for less than the cost of sending back even 50 kilos of rocks. Twenty or more persons can be sent for the cost of returning four.[4]

In fiction

  • Both Mars Direct and Mars for Less concepts figure prominently in Brian Enke's 2004 novel, Shadows of Medusa.
  • A Mars Direct scheme is used in Robert M. Blevins' 2005 novel The 13th Day of Christmas.

See also


  1. ^ R. Zubrin and D. Weaver "Practical methods for near-term piloted Mars missions". AIAA93-2089,29th AIAA/ASME Joint Propulsion Conference, Monterrey CA, United States, June 28-30th, 1993
  2. ^ D.Willson and J.D.A Clarke "A Practical Architecture for Exploration-Focused Manned Mars Missions Using Chemical Propulsion, Solar Power Generation and In-Situ Resource Utilisation." Proceedings of the 6th Australian Space Science Conference,p.186-211, 2006
  3. ^ Mars Society Australia Mars-Oz web site
  4. ^ Aldrin: Mars Pioneers Should Not Return to Earth
Further reading

External links

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