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This article is from the In-Depth Report Exploring the Red Planet

At Heaven's Gate: 50 Years After Humans First Reached Space, What Frontiers Remain?

Humankind has been confined to Earth's orbital environs for decades, but plans abound for manned missions to deeper reaches of the solar system
Mars panorama from Opportunity rover



NASA/JPL-Caltech/Cornell University

On April 12, 1961, Soviet cosmonaut Yuri Gagarin did something no human had done before. On board the Vostok 1 spacecraft, Gagarin became the first person in space after rocketing into the sky from a launch site in Kazakhstan for a nearly two-hour flight. What is more, Gagarin became the first human to orbit Earth, a feat that the U.S. would not achieve until its third manned spaceflight, John Glenn's three-orbit flight on Friendship 7, February 20, 1962.

Fifty years later, both the space race—and the Cold War of which it was a part—have come to an end. The Soviet Union is no longer, but the Russian space program has become an invaluable partner to NASA's human spaceflight program. Over the past decade more than a dozen countries, including Russia and the U.S., have sent astronauts to the International Space Station, the longest-serving continuously manned orbital outpost in history. Meanwhile, China has built up a formidable program of its own, sending three manned missions into space since 2003.

But human exploration of the solar system has contracted in scope since 1972, when the last set of Apollo astronauts to visit the moon returned to Earth. Whereas the first 10 years following Gagarin's flight were peppered with firsts—notably the pioneering moon missions Apollo 8 and Apollo 11—the last four decades have witnessed little else but trips to and from low Earth orbit.

That ought to change, finally, in the decades to come. Space agencies around the world are planning ambitious missions to the moon and to even farther-flung locales that have never been visited by humankind. No one knows who the next Yuri Gagarin will be, or what flag will adorn his or her spacesuit, but below are a few solar system destinations that might find themselves festooned with fresh footprints in the next 50 years.

The moon
Humankind has landed and walked there before—six times, in fact—but since 1972 the only lunar visitors have been of the robotic variety. The U.S. remains the only nation to send its astronauts to the moon, and for several years it looked as if NASA would be back before anyone else. President George W. Bush proposed in 2004 that NASA return humans to the moon by 2020, but the feasibility of that goal was already waning when President Barack Obama scuttled the moon shot in 2010. Obama chose to scrap the Bush-era moon goal and the spacecraft system that was to enable it in favor of a more flexible strategy toward space exploration using a new deep-space launcher, whose specifics have become a point of contention between NASA and Congress.

Meanwhile, China has been ramping up its lunar exploration program, sending unmanned orbiters to the moon in 2007 and 2010. China has also demonstrated the ability to send its space flyers, sometimes known as taikonauts, into orbit—and officials have said that taikonauts could set foot on the moon by 2025. That timeline seems to mesh with the other leading contender for a lunar return. Along with China and the U.S., Russia is the only nation with a proved ability to send humans into space. The head of the Russian space agency has said that cosmonauts would land on the moon by 2025.

But, as with the plans for a Chinese moon mission—and as NASA is well aware following its abandoned Bush-era plans—many technical challenges stand between the decision to go to the moon and planting a flag on the lunar surface. It remains to be seen which nations, if any, are willing to pursue the expensive, complicated and dangerous goal of a manned moon landing.

Near-Earth asteroids
When Obama steered NASA away from the moon, he directed the space agency toward a manned asteroid landing around 2025 instead. The attractions of such a mission are myriad: For starters, no nation has ever achieved it nor has any nation's astronauts ventured so deep into the solar system. And asteroids are a rich library of scientific information, preserving a record of the chemical conditions that prevailed when the solar system was in its infancy. An asteroid visit might also afford a significant logistical advantage over a moon landing: The much weaker gravitational pull of an asteroid means that a spacecraft could simply rendezvous with it at close range so astronauts could spacewalk to the surface without the need for a full-fledged landing module.

But nothing in space travel is easy, and touching down on an asteroid might be a sight more complicated than a simple rendezvous. Asteroids are often odd-shaped bodies that spin extremely rapidly. Some are little more than rubble piles, and their loose structure combined with weak gravity means that the vicinity of an asteroid might be littered with loosely bound debris.

In any event, such a mission would require NASA to develop a heavy-lift launch system to spring a crew of astronauts out of Earth orbit, and the specs, timeline and cost of such rockets have caused friction between the space agency and Congressional funders.

Mars
Mars looms large as a human destination in sci-fi lore—no surprise, given that it remains unmarred by human boot prints but orbits the sun tantalizingly close to Earth, well within the realm of possible exploration. But that possibility has always been out of reach.

If that changes, it likely won't be for another two decades at the very least. Obama has stated that his goal is to send U.S. astronauts on a round-trip swing past Mars in the 2030s, with a landing on the Red Planet shortly thereafter.

Reaching Mars might require extensive international cooperation—or some creative thinking. Some nations have already joined forces for robotic exploration of the planet or to lay groundwork for a future manned mission. China's first Mars probe, Yinghuo 1, is expected to hitch a ride to the Red Planet as early as this year on a Russian rocket along with Phobos–Grunt, a Russian lander bound for Phobos, one of the two tiny Martian moons.

And Russia has already partnered with the European Space Agency (ESA) to investigate the psychological effects that the prolonged confinement and isolation of a round-trip Mars journey might have on a crew. In an experiment called Mars500, now in progress, six volunteers are spending more than 500 days in an enclosed capsule in Moscow, punctuated by a simulated landing and spacewalk on Mars.

But serious technical challenges and physiological questions remain. (For one, can a human safely endure the dosage of cosmic radiation that comes with such a journey?). And at present, no nation is close to being able to send a manned mission to Mars, let alone return that crew safely.

Enter the creative thinking: Some, including physicist Lawrence Krauss, have proposed that the best way to get to Mars might be to make it a one-way trip. That would greatly reduce the complexity of the mission—no need for a return stage, no need for fuel for the trip home—and cut in half the dangerous cosmic radiation dosage that astronauts would accrue on the interplanetary journey.

Lagrange point
In 2009, after taking office, Obama convened a blue-ribbon panel to review NASA's plans for manned spaceflight. One of that commission's suggestions was a manned mission to a Lagrange point in space, one of five gravitational equilibrium points in the sun–Earth system where gravitational and centrifugal forces balance to create a relatively stable place to essentially hover in a deep-space orbit. (Astronauts would not be able to explore much while spacewalking at a Lagrange point, but it would be an unprecedented voyage into deep space nonetheless.)

One of those points, a spot well beyond the orbit of the moon known as L2, has become a popular destination for unmanned astronomical spacecraft—both NASA and ESA have sent missions there.

The L5 Society, a 1970s group driven by the space-colonization ideas of Princeton University professor Gerard O'Neill, advocated for a human presence at the two most stable Lagrange points, L4 and L5. That dream has not yet become reality but may in the coming decades as humankind ventures beyond low Earth orbit and into ever deeper reaches of the solar system.

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