The Mars Direct concept for a human mission to Mars has been vigorously championed since 1990 by engineer Robert Zubrin, who developed it with fellow Martin Marietta Corporation engineer David Baker. The National Aeronautics and Space Administration (NASA) estimated in 1993 that its plan for Mars exploration, which is called the Design Reference Mission and drew heavily on the Mars Direct approach, could make human footsteps on Mars possible by as early as 2009.
A Clever Synthesis
Mars Direct originated in a Martin Marietta-sponsored effort to develop plans for U.S. President George H. W. Bush's Space Exploration Initiative (1989-1993), which aimed to return humans to the Moon and land the first astronauts on Mars by 2019. Bush's initiative failed because of excessive cost and lack of political support, but it provided an opportunity to revive many old Moon and Mars exploration ideas. Mars Direct, for example, is a cost-saving synthesis of concepts dating back to the 1950s.
Old concepts in Mars Direct include manufacturing propellants on Mars for the trip home to Earth; splitting the expedition between cargo and crew spacecraft; and a 500-day stay on Mars for the first expedition. The last idea allows the crew to wait for Mars and Earth to move into positions in their orbits around the Sun and enable a propellant-saving low-energy voyage back to Earth. In 1989 NASA's Space Exploration Initiative Mars plan was expected to cost about $400 billion. According to Zubrin's 1990 estimate, Mars Direct might cost a quarter as much.
The Mars Direct Plan
In their earliest Mars Direct papers, Zubrin and Baker described a Mars expedition kicking off in December 1996. A giant Ares rocket consisting of a space shuttle external tank with four attached space shuttle main engines and two shuttle advanced solid rocket boosters would lift off from Kennedy Space Center in Florida. Atop the external tank would sit a rocket stage and a 40-ton automated cargo lander covered by a streamlined shroud. The cargo lander would include an aerobrake heat shield, a descent stage, an Earth-return vehicle (ERV), a propellant factory, 5.8 tons of liquid hydrogen, and a nuclear reactor on a robot truck. The Ares rocket would launch the cargo lander onto a direct course to Mars without assembly in Earth orbit—hence the name Mars Direct.
The 1996-launched cargo lander would land on Mars, then the robot truck would trundle away to safely position the nuclear reactor in a crater. The reactor would then activate to generate electrical power for compressors. These would draw in Martian air to manufacture propellant for the ERV.
The propellant factory would use the Sabatier Process first proposed for use on Mars in 1978 by engineers Robert Ash, William Dowler, and Giulio Varsi at NASA's Jet Propulsion Laboratory. Liquid hydrogen feed-stock would be exposed to Martian atmospheric carbon dioxide in the presence of a catalyst , producing liquid methane and water. The methane would be stored and the water split using electricity to yield oxygen and more hydrogen. The oxygen would be stored and the hydrogen recycled to manufacture more water and methane. In a year this process would manufacture 107 tons of methane and oxygen propellants.
In January 1999 two more Ares rockets would lift off. One would carry a cargo lander identical to the one already on Mars; the other, a drum-shaped, 38-ton piloted spacecraft 8.4 meters (27.5 feet) wide and 4.9 meters (16 feet) tall. Its top floor would house the four-person crew, while its bottom floor would carry cargo, including a Mars rover. The Ares rockets would launch the two spacecraft directly onto six-month transfer paths to Mars.
The 1999-piloted spacecraft would land near the cargo lander launched in 1996. The 1999 cargo lander, meanwhile, would land 800 kilometers (500 miles) from the 1996 cargo lander and begin making fuel for the second crew, which would leave Earth in 2001.
Eleven of the 107 tons of propellants manufactured by the 1996 cargo lander's propellant factory would fuel the rover. The explorers would undertake long traverses, thoroughly studying and recording the characteristics of the region around their landing site. The rover might traverse a total of 16,000 kilometers (10,000 miles) during the explorers' 500-day Mars surface stay.
As Earth and Mars move into position, the 1999 expedition crew would board the 1996 ERV. Rocket engines burning the methane and oxygen propellants manufactured from the Martian atmosphere would place it on direct course for Earth. After six months in the ERV, the crew would reenter Earth's atmosphere and perform a parachute landing.
The most significant difference between Mars Direct and NASA's 1993 Design Reference Mission was the division of ERV functions between two vehicles. In the judgment of many, the Mars Direct ERV was too small to house four astronauts during a six-month return from Mars. It provided about as much room as a phone booth for each crew member. In NASA's plan, therefore, the crew would use a small Mars ascent vehicle to reach Mars orbit. Once there, they would dock with an orbiting ERV.
The 2001 expedition crew would land near the 1999 cargo lander, and the 2001 cargo lander would land 800 kilometers (500 miles) away and make propellants for the 2003 expedition. The 2003 crew would land by the 2001 cargo lander; meanwhile the 2003 cargo lander would touch down 500 miles away and make propellants for the 2005 crew; and so on. After several expeditions, a network of Mars bases would be established. "Just as towns in the western U.S. grew up around forts and outposts," wrote Zubrin and Baker, "future Martian towns would spread out from some of these bases. As information returns about each site, future missions might return to the more hospitable ones and larger bases would begin to form." (Zubrin and Baker 1990, p. 41).
see also Human Missions to Mars (volume 3); Living on Other Worlds (volume 4); Mars Bases (volume 4); Mars Missions (volume 4); Natural Resources (volume 4); Power, Methods of Generating (volume 4); Resource Utilization (volume 4); Zubrin, Robert (volume 4).
David S. F. Portree
Hoffman, Stephen J., and David I. Kaplan, eds. Human Exploration of Mars: The Reference Mission of the NASA Mars Exploration Study Team. Houston, TX: NASA Lyndon B. Johnson Space Center, 1997.
Portree, David S. F. Humans to Mars: Fifty Years of Mission Planning, 1950-2000. Washington, DC: NASA History Office, 2001.
Zubrin, Robert. "The Economic Viability of Mars Colonization."Journal of the British Interplanetary Society 48, no. 10 (1995):407-414.
Zubrin, Robert, and David Baker. "Humans to Mars in 1999."Aerospace America 28, no. 8 (1990):30-32, 41.
Hoffman, Stephen J., and David I. Kaplan, eds. Human Exploration of Mars: The Reference Mission of the NASA Mars Exploration Study Team. 1997. National Aeronautics and Space Administration, Lyndon B. Johnson Space Center. <http://www-sn.jsc.nasa.gov/PlanetaryMissions/EXLibrary/docs/MarsRef/contents.htm>.
Portree, David S. F. Humans to Mars: Fifty Years of Mission Planning, 1950-2000. 2001. <http://members.aol.com/dsfportree/explore.htm>.
"Mars Direct." Space Sciences. . Encyclopedia.com. (September 22, 2018). http://www.encyclopedia.com/science/news-wires-white-papers-and-books/mars-direct
"Mars Direct." Space Sciences. . Retrieved September 22, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/news-wires-white-papers-and-books/mars-direct
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American Aerospace Engineer 1952-
Robert Maynard Zubrin is an aerospace engineer credited for revolutionizing plans for the human exploration of Mars. After an early career as a teacher, Zubrin went to graduate school in the mid-1980s, earning a doctorate in nuclear engineering from the University of Washington.
As an engineer for the aerospace firm Martin Marietta (now Lockheed Martin) starting in the late 1980s, Zubrin worked on projects ranging from a nuclear rocket engine to a spaceplane. His best-known work at the company, however, was the development of "Mars Direct," a new architecture for human missions to Mars that would rely on the resources available on Mars to reduce their cost. Mars Direct attracted the attention of the National Aeronautics and Space Administration, which incorporated aspects of the proposal into its Mars mission plans.
Zubrin also coauthored a popular book about Mars Direct,The Case for Mars (1996). Zubrin used the success of the book as a springboard in 1998 for creating the Mars Society, a membership organization that promotes the human exploration of Mars. Zubrin serves as president of the society, which has supported a number of research projects designed to further technology needed for future Mars missions. Zubrin also founded Pioneer Astronautics, a small aerospace firm in Colorado he created after leaving Lockheed Martin in 1996.
see also Human Missions to Mars (volume 3); Mars (volume 2); Mars Bases (volume 4); Mars Direct (volume 4).
Zubrin, Robert. Entering Space: Creating a Spacefaring Civilization. New York: JeremyP. Tarcher/Putnam, 1999.
——. First Landing. New York: Ace Books, 2001.
Zubrin, Robert, with Richard Wagner. The Case for Mars: The Plan to Settle the Red Planet and Why We Must. New York: Free Press, 1996.
"Zubrin, Robert." Space Sciences. . Encyclopedia.com. (September 22, 2018). http://www.encyclopedia.com/science/news-wires-white-papers-and-books/zubrin-robert
"Zubrin, Robert." Space Sciences. . Retrieved September 22, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/news-wires-white-papers-and-books/zubrin-robert