From the time Sputnik first orbited Earth in 1957 to the fall of the Soviet Union 34 years later, Western cooperation in manned spaceflight was cemented by a common ideology and a common foe. Its capstone was the International Space Station.
But today, the United States and Europe, which built the space station, have reached a crossroads as they search for ways to put astronauts on Mars. One path could lead to tighter cooperation, not only between the US and Europe, but also with Russia, China, and other nations interested in manned spaceflight. The other path could lead to an international space race in which the US may find itself still in the lead but increasingly isolated.
The choice could determine how aggressively the world carries out its next round of human space exploration.
Already, efforts at international cooperation are off to a shaky start, suggests Joan Johnson-Freese, a specialist in space and international security at the US Naval War College in Newport, R.I. She notes that President Bush announced in January his moon-and-Mars plan as a done deal and appointed a commission to lay out options for implementing it. Yet none of the potential partners was brought in at the outset, she says.
"Everybody is posturing and rethinking their positions," Dr. Johnson-Freese observes. "The Europeans are beginning to say: 'What are our options?' And there are options. We're not the only game in town" when it comes to launching people into space.
While nations pursue human spaceflight for reasons of national prestige - "No one ever held a parade for a robot," Johnson-Freese says - they're also driven by the fundamental scientific questions that researchers say can be answered only by humans armed with geologists' hammers, drilling rigs, and labs too sophisticated to be wrapped within a robotic rover.
Recent results from the Red Planet have only served to whet their appetites. Over the past two months, the US rover Opportunity has uncovered virtually irrefutable geologic evidence that the Martian surface once hosted bodies of water that could have been suitable habitats for simple life forms.
Perhaps just as intriguing, Europe's Mars Express orbiter reportedly has uncovered preliminary evidence that methane is a tiny but persistent component of the Martian atmosphere.
Without some source to replenish the gas, it would vanish - broken up by the sun's intense radiation. The source could be volcanic. But researchers have yet to see evidence of current volcanic or hydrothermal activity that could account for the methane. Or it could represent the holy grail of Mars exploration: life in the form of microbes living deep beneath a crust porous enough to let their waste methane escape. Researchers are busy trying to confirm the observation and ensure that the initial result wasn't a fluke.
For its part, Europe's project at this point consists of a variety of studies to lay out a vision for human spaceflight that could lead to a European astronaut setting foot on Mars by 2030, explains Franco Ongaro, who heads the effort, known as the Aurora program.
The program, approved in 2002, gave the European Space Agency (ESA) a two-year head start.
It is "meant to prepare Europe's participation in an international endeavor," he says. At such time as Europe is invited to the table to discuss the shape of an international manned moon-Mars program, it will have a range of sophisticated options to lay on the table.
Aurora's blueprint is broadly similar to the plan outlined by the Bush administration. It includes research on Earth aimed at developing power and propulsion systems, and designing habitat modules and life-support systems, and a range of other technologies. It envisions a set of robotic missions - including a Mars orbiter-and-rover package in 2009, a mission to bring back samples in 2011, and demonstrations of ascent and descent modules in 2013.
Mid-level contacts between ESA, and Russia, the US, China, and Japan, have taken place throughout the Aurora process so far, Dr. Ongaro notes, adding that a team from Russia was in the US this week to review ideas for the manned portion of the effort. He says that once the Aldridge Commission presents its report to Mr. Bush and the US begins to convert the recommendations into plans, "this will make it easier to sit down and compare notes" with NASA.
When asked about scenarios that could prompt the Europeans to look for partners elsewhere, he replies: "I really don't see any real meaning to doing that. I'm a strong believer in space exploration as a step beyond the 'the race.' To me the first woman or man on Mars would be perceived as just that. It wouldn't be a European, an American, or an Indian."
Yet others note that Aurora is taking place within the framework of a larger European effort to begin asserting its technological autonomy. Europe, Russia, and Asia see space exploration as indispensable to economic development and as a steppingstone to a high-tech, information economy, analysts say, although they don't discount its national-security uses, which the US emphasizes. And partnerships beyond the US are high on the agenda.
Europe, for example, is establishing its own global, civilian, satellite-navigation system. Last year, China agreed to invest at least $236 million in the project. China, which recently orbited and safely retrieved its first "taikonaut," is reported to be preparing a 5,170-pound satellite for launch to the moon in 2007, to be followed by an unmanned lander 2010.
Meanwhile, under a recent agreement, Russian Soyuz rockets - arguably the most reliable in the world - will begin launching from ESA's space center in Guyana in 2006. The Soyuz craft have served as the workhorse of Russia's manned spaceflight efforts.
In this broader context, Aurora "attests to Europe's willingness to step into a vacuum in US policy" regarding human exploration of the solar system, says Ray Williamson, a research professor at George Washington University's Space Policy Institute in Washington, D.C.
No one has yet produced a credible cost estimate for an international effort to send humans back to the moon and to Mars, analysts say. Yet they add that it's clear no one nation or space agency could shoulder the cost alone. Moreover, benefits from true partnerships stretch beyond cost to include sustained commitment from participating nations.
The US has taken the lead in trimming back the timetable and objectives for the space station because of rising costs and a smaller shuttle fleet following the loss of the orbiter Columbia and its crew early last year. But without international participation, several analysts agree, the project might not have gotten as far as it did.
"It's sobering that in the past 20 years, NASA has not been able to manage a single large project" to completion beyond the space station, says ESA's Ongaro, ticking off a list of projects that have fallen by the wayside. Time after time, the space station might have floundered in Congress were it not for the international commitments with key allies - who in many cases had long ago committed the money to complete their pieces of the project.
If the space station represents humanity's halting first steps at cooperation in manned spaceflight, a number of specialists are working to define cooperation for the 21st century.
The International Academy of Astronautics is finishing a report outlining a range of approaches for cooperation on future space-exploration activities, says James Zimmerman, who for 12 years served as NASA's representative in Europe and currently heads a space-policy consulting firm in McLean, Va.
One possibility would be to establish an international body outside the United Nations framework, but modeled after ESA, that would coordinate an international moon-Mars effort, says Kevin Madders, a space policy consultant in Brussels.
Since 1958, NASA policy has forbidden the agency to go down what he terms this more "organic" road to cooperation in manned spaceflight, he says. "You've got to have a very good reason to change that track. Taking on the moon and Mars could provide such a reason."