Illustration by Chesley Bonestell, reproduced courtesy of Bonestell LLC

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An illustration of spaceships hovering above Mars.

Illustration by Chesley Bonestell, reproduced courtesy of Bonestell LLC

Mars Missions: A Time Line of Success and Failure

Dennis Tito isn't the first to propose a manned mission to Mars.

Humans have been thinking about visiting Mars—or being visited by Martians—for more than a century. On Wednesday, a group funded by businessman Dennis Tito announced its intention to launch a manned flyby mission to Mars in 2018.

Our awareness of Mars dates back millennia, while our modern picture of the red planet emerged in the 1870s, when Italian astronomer Giovanni Schiaparelli claimed to see networks of channels (canali) through his telescope. The Italian word, mistranslated into English as "canals," helped inspire American astronomer Percival Lowell to observe Mars for decades and create detailed maps of a Martian canal system.

Lowell's work popularized the idea of Mars as a dry and dying world with canals constructed by an advanced civilization carrying life-giving water from the polar ice caps. (Related: The Psychology of Deep Space Travel.)

This romantic vision helped spur novels like War of the Worlds by H. G. Wells. But in the 20th century, Wells's fantastic sci-fi world of heat-ray-wielding Martian invaders gave way to scientific research on how humans might actually visit the red planet.

German rocket pioneer Wernher von Braun was the first to develop a practical plan for a Martian journey. In the early 1950s, while working for the U.S. government, he proposed a massive expedition involving ten 4000-ton spaceships and 70 crew members.

The envisioned Mars trip reflected von Braun's grand dream of winged shuttle rocket fleets, a giant orbiting space station, and a moon base. Beginning in 1952, Collier's magazine published eight articles on this futuristic goal, hiring artists to bring von Braun's plans to life. ("Meet One of Mars Rover Curiosity's Earthbound Twins.")

Working with von Braun, Walt Disney produced a series of television specials dramatizing human trips to orbit, the moon, and finally Mars. Cereal manufacturers introduced toy models of this proposed Martian space fleet.

More than half a century on, the dream that compelled so many Americans still seems, to many, to be just that: a dream.

So why hasn't Martian travel happened yet?

Technology and cost have been the two big sticking points.

Von Braun's plan, for its part, overlooked many barriers—prolonged effects of weightlessness, radiation from solar flares—and was grounded in a poor understanding of Mars, whose thin atmosphere makes it a far more hostile place than he knew.

The costs involved to solve such problems are immense, helping prevent Mars travel so far. But Von Braun's proposals have given rise to more than a thousand schemes from governments, companies, and private groups to reach the red planet. The NASA publication Humans to Mars, written by David S.F. Portree, chronicles these efforts. Here are highlights:

1962: Project EMPIRE. A series of studies by NASA and outside aerospace contractors, Project EMPIRE proposed a Mars flyby using the same 500-day orbit as the planned 2018 Inspiration Mars trip. The flyby was designed to allow astronauts to gain more information about the planet and return to Earth. Later plans envisioned an enormous rocket called Nova—larger than the Saturn V moon rocket—to boost five 450-foot-long (137-meter-long) ships to orbit, carrying a total of 15 crew members to Mars for an extended stay. This and other early plans assumed large manned ships would slow down by skimming off the surface of a thick Martian atmosphere, saving huge amounts of fuel.

1964: Mariner 4. This unmanned probe, the first to reach Mars, revealed a planet with a far thinner atmosphere and higher radiation levels than expected. Lowell's canals and an ancient Martian civilization were missing. Mariner revealed that human travel to Mars would be hazardous and that automated probes might perform many observations more cheaply.

1966: JAG. This plan for a 1976 mission proposed using a nuclear-powered rocket carrying four humans on a flyby around Mars. On approach, an automated probe would descend to the planet's surface, collect soil samples, then quickly rocket up to a manned ship zooming overhead. The crew would return to Earth after a 667-day voyage. Soaring Vietnam War costs killed the project, although the automated lander eventually developed into the unmanned Viking missions that successfully touched down on Mars in 1976.

1969: Post-Apollo. Hoping to exploit the first moon landing, NASA proposed an ambitious follow-on program, pitched in part by Wernher von Braun and echoing his original vision: a winged shuttle, a space station, and a large human expedition to Mars. Faced with Vietnam War costs and waning public interest in space following the moon landing, the plan was rejected, though then President Richard Nixon approved development of the space shuttle. In the following decades, unmanned craft successfully visited Mercury, Mars, Jupiter, Saturn, Uranus, and Neptune.

1989: Space Exploration Initiative. Developed during the first Bush Administration, the plan provided a framework to complete the space station, set up a lunar outpost, and mount a Mars expedition around 2010. Cost estimates soared to over $500 billion, dooming the effort.

2004: Vision for Space Exploration. This plan, hatched during the second Bush Administration, called for using technology developed for the Apollo and shuttle programs to construct a new crew vehicle, booster rocket, and heavy-lift rocket to return to the moon as early as 2015. New technologies and approaches tested on the moon, the thinking went, would lead to human trips to Mars around 2030. Most of the program was canceled for cost reasons.

2012: Red Dragon. Developed by Elon Musk's Space Exploration company, this plan proposes to send an automated "Dragon" vehicle to land on Mars in 2018, paving the way for an eventual human landing.

2013: Inspiration Mars. Proposed by Dennis Tito, the first space tourist, the idea is to seize on an unusual 2018 planetary alignment to send a male and female astronaut on a 500-day flyby around Mars. The National Geographic Society is exploring the idea of partnering with Tito's group.