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Mars Direct Plan

Artificial Gravity



One of the classic myths about a human Mars mission is that the crew will be subjected to long periods of microgravity ("zero-gravity"), and that before the mission, huge amounts of money must be spent on space stations and other projects, so that the effects of microgravity can be studied. The Mars Direct plan employs artificial gravity for the trip through space, which makes this concern invalid. Artificial gravity can be easily created. In traditional rocket launches, all stages of the rocket are abandoned when they burn out. In Mars Direct, the final stage of the rocket is attached to the crew module by a long tether. When the stage runs out of fuel, the tether is unwound, creating a two-body system with a center of mass somewhere along the tether. The system is then rotated around this center of mass, with the burnt-out rocket stage acting as the counter-balance to the crew module.


Mission Sequence



Launch windows to Mars open up approximately every two years, when Earth and Mars are in the correct orientation relative to each other. The Mars Direct plan consists of one launch in the first year, and two launches during every launch window after the first, which keeps humans on Mars almost constantly.

  • YEAR 1
    • An unmanned Earth Return Vehicle (ERV) is launched from Earth on a low-energy trajectory equipped with a reactor for manufacturing propellant. It lands on Mars, and begins making fuel for the trip home
  • YEAR 3
    • A second ERV is launched
    • A manned habitat (HAB) is launched on a faster trajectory, carrying the crew to the landing spot of the first ERV, which will eventually carry them home
  • YEAR 5
    • Another ERV is launched, to replace the one that the last crew traveled home in
    • A second hab is launched, carrying a crew to replace the first

5-year Sequence



Fuel Production



Traditional Mars mission design requires that everything, including rocket fuel for the return trip, be brought from Earth. This increases the mission mass and complexity to the point where the mission can no longer be launched from Earth, and must be assembled in orbit. This was the crippling blow which was dealt to the past designs. The ability to get around this problem is what makes the Mars Direct plan so unique. Rather than bring all the fuel from Earth, why not manufacture the return propellant on the surface of Mars, using Martian resources? The Martian atmosphere consists almost entirely of carbon dioxide, which can be transformed via chemical reactions, along with a small quantity of hydrogen brought from Earth, into rocket fuel. This results in up to 18 kilograms of rocket propellant being produced for every kilogram of hydrogen supplied, lowering the initial mission mass to the point where it could be launched directly from the surface of the Earth. As an added bonus, some of the water and oxygen created by this process can be used for drinking and breathing, again reducing the amount of resources to be brought from Earth. Also, the fuel produced can be used to run equipment, such as manned rovers.

Earth Return Vehicles with associated vehicles



Mission Timeline



The ideal mission timeline requires minimizing time in travel between planets, while maximizing time spent on Mars, so that essential science and exploration can be performed. Reducing the time in flight reduces the mission risk factors, such as lowering stress on spacecraft systems. Scientific return is the purpose of the mission, and so ample time must be allotted on the surface of Mars. The Mars Direct plan utilizes an opposition-class mission, which has a flight time of 150 days, both to and from Mars, and allows for a 550 day stay on the surface before the return launch window opens up. The total mission time is 910 days. Traditional Mars mission timelines spend less time away from Earth, but spend more time in interplanetary space, while minimizing time spent on Mars.

Habitat floor plan



Safety Considerations



The Mars Direct plan has many built-in safety systems, such as the following. What would happen if the crew landed on Mars, only to find that the ERV which had been sent two years earlier had failed to make the return propellant? This is one of the beautiful points about the plan. The ERV is launched two years before the crew, and begins making its propellant immediately upon landing on Mars. When the manufacturing process is complete, the ERV signals to Earth that it is ready. If the fuel production were to fail, the crew would know about it before they were to leave Earth, and so they would not be launched in the first place. Even if something were to go wrong, and it was not known that the ERV had failed, the crew could just use the second ERV which was launched in their own launch window. Now, what happens if something goes wrong in flight, and the crew need to return to Earth before landing on Mars? Would they have to wait for the next launch window to get home? No! Certain orbital trajectories between the planets, known as free-return trajectories, allow the crew to abort the Mars landing, and return to Earth automatically, without expending any extra fuel. The Mars Direct plan uses a two-year free-return, which means that if the crew cannot land on Mars, their trajectory will return them to Earth two years after they left.

Earth Return Vehicles with fuel truck



Launch Vehicle



Since the return propellant is being manufactured on the surface of Mars, the mass needed to be launched from Earth is significantly reduced. While no rocket being made in North America today could launch the mission, there was one in existence 30 years ago! The Saturn V rocket, which launched astronauts to the Moon, has enough power to launch the mission payload directly to Mars. Other designs, including a modified space shuttle set-up have been proposed, but the bottom line is that the technology is available today. Fictional 'Ares' Launch Vehicle


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This document's URL is http://Chapters.MarsSociety.org/toronto/Education/MarsDirect.shtml. 'T'was last updated on Tuesday, 11-Sep-2012 01:03:42 PDT.
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