A Fourth Orbiter Is Set to Join Mars Exploration Team

Since 1960, humans have tried 35 times to send missions to Mars. Depending on how you count, as many as 21 have failed. Spacecraft blew up on launch, never left Earth's orbit, crashed into the Martian surface, missed going into orbit and zoomed off into space, inexplicably shut down or simply disappeared.

"Mars is hard, and Mars is unpredictable," said Jim Graf of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Mars doesn't treat you very well."

Despite this record, Mars today has three satellites orbiting overhead, two rovers crawling around its surface -- and it appears destined to have an operating, robotic "human presence" in the neighborhood indefinitely.

The plan is to solve the mystery of how a world apparently once wet and warm turned into the chill, windblown wilderness that is Mars today. "We want to know whether it was habitable, whether life got started and, if it did, how it evolved," said geologist Raymond E. Arvidson of Washington University in St. Louis, who reviews the Mars program for NASA.

This Friday afternoon, barring a catastrophe like those that have doomed four missions in the past eight years, NASA's Mars Reconnaissance Orbiter will begin the rocket burn that will put it in orbit as the planet's fourth working satellite.

This is not a slam dunk. For a nail-biting half-hour during and after this process, the spacecraft will be out of contact behind Mars, while project manager Graf and the rest of the mission team wait to find out whether the planet has captured the new satellite or shot it back into space, never to return.

"We're on the money right now," Graf said at a recent news conference as the orbiter began its final approach. "But we are getting into the dangerous portion of the mission. A lot can go wrong, and if we don't succeed, we will fly right by the planet."

But win or lose, the human presence will endure. Functioning spacecraft have been on station at Mars since 1997, with new missions planned for launch in 2007, 2009 and beyond. And if humans ever actually land there to fulfill President Bush's "Vision for Space Exploration," they will have benefited from decades of research detailing such aspects as radiation hazards and the likeliest places to mine water ice.

"The missions we're doing for the next 10 years are pathfinders," said Arvidson, who chairs NASA's Mars Exploration Program Analysis Group. "We're doing the robotic precursor work -- picking out the best sites where humans on the surface can do the detailed studies."

At the dawn of the space age 50 years ago, many people still had the idea that Mars might be a habitable planet, not as threatening as the Mars of H.G. Wells's "The War of the Worlds" but a place that might harbor advanced life forms. "We were still making maps with canals on them," Arvidson recalled.

That archetype was dashed in 1965 when the flyby of the Mariner 4 spacecraft showed a barren, crater-pocked surface like Earth's moon. But over time, patient exploration revealed a much more complex landscape -- one perhaps sculpted in the past by flowing water.

Mars's three currently operating satellites -- NASA's Mars Global Surveyor, which arrived in 1997, NASA's Mars Odyssey and the European Space Agency's Mars Express -- developed this theory, and in 2004 the Mars rover Opportunity confirmed it by identifying sedimentary rock laid down in what had been a set of ancient lake beds.