The Sciences

One Giant Leap for Machine Kind

While human explorers remain stubbornly stuck in Earth orbit, robotic space probes are preparing for the next great age of exploration: drilling, rolling, sailing, and prospecting where nobody has gone before.

By Tim FolgerOct 31, 2011 5:00 AM
Curiosity, NASA's new Mars rover, under construction. A shell of graphite and aluminum will shield the robot's electronics from heat. | NASA/JPL-CALTECH


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The robots are out there, dozens of them, going where their soft-bodied, oxygen-breathing creators can’t or won’t anytime soon. They own space. While a handful of humans hunker down in near-Earth orbit in the International Space Station, an aging craft conceived in the Reagan era, unmanned machines at this very moment are orbiting Mercury, trundling across the sands of Mars, even preparing to leave the confines of the solar system.

The space station is a thing of beauty in its way, the apotheosis of Apollo-style technology. But in terms of scientific achievements it suffers in comparison with NASA’s spaceborne fleet of robots—currently 55 strong—especially given the large funding gap that has always existed between the manned and unmanned space programs. NASA’s budget for 2012 provides about $4.5 billion for robotic space science, versus $8.3 billion for human space exploration, almost $3 billion of which goes to the station alone. And that is the outlay for a NASA without shuttle flights or plans to send people back to the moon.

Noble as human exploration may be, we would know very little about anything in the cosmos much more distant than the moon were it not for robotic explorers. Through them we have learned of lava plains on Venus, a buried ocean on Jupiter’s moon Europa, lakes of methane on Saturn’s moon Titan, and salty geysers on another Saturnian moon, Enceladus. And manned missions? Since the Apollo moon landing of 1969, NASA has mostly confirmed what it knew from the outset, which is that hurtling humans deep into space is expensive, dangerous and, for the foreseeable future, beyond reach. The reality is, when it comes to carrying out serious space science, humans simply can’t compete with spacefaring hardware. And that is probably not going to happen in our lifetime.

Sheltered as we are by Earth’s atmosphere and magnetic field, which deflect lethal radiation from space, we are like coddled children who have never ventured into a tough neighborhood. The space station, orbiting less than 250 miles overhead (about the distance between Boston and Philadelphia) hardly qualifies as a space station at all. It is really more of a not-quite-above-Earth’s-atmosphere station, since it, like the shuttles once did, travels within the thin air of the ionosphere.

Real outer space is hazardous, even for robots. Ed Stone, the project scientist for the astonishingly successful twin Voyager missions that flew past Jupiter, Saturn, Uranus, and Neptune in the late 1970s and 1980s, and are now on their way to the stars, says the Voyagers would not have survived their close encounters with Jupiter had it not been for some advance warning from a previous mission.

That precursor mission, called Pioneer 10, flew past Jupiter in 1973. It did not get as close to Jupiter as the two Voyagers would, but it got near enough to find that the massive planet could wreak havoc on spacecraft. “Pioneer 10 discovered that the radiation environment of Jupiter was much more severe than anyone had expected,” Stone says. “It took us nine months to redo the circuitry on the Voyager spacecraft to make it much less susceptible to radiation effects.”

In just a few hours near Jupiter, Voyagers 1 and 2 absorbed blasts of radiation hundreds of times greater than the lethal dose for humans. And surface conditions on some planets are even more murderous. The early Soviet Venera probes, the first spacecraft to touch down intact on another world, were built like tanks. Even so, they succumbed to Venus’s crushing atmospheric pressure and 900 degree Fahrenheit surface temperatures—hot enough to melt lead—within a couple hours of landing.

The sheer harshness of the environment that begins a few hundred miles above our heads, and the huge distances involved in traveling to other planets, bode poorly for any of us who might dream of establishing human outposts much beyond Mars. “I don’t think the stories of science fiction we read in childhood are ever going to happen,” says John Mather, a Nobel laureate who is now the senior project scientist for the James Webb Space Telescope, the $6.5 billion successor to the Hubble telescope that NASA plans to launch in 2018. “People won’t be rocketing around the solar system. I think we’ll be able to send people throughout the inner solar system, to visit asteroids, comets, and Mars—if we want to. Beyond that,” he says, pausing for a moment, “people are fragile, and we cry when they die. Robots are fragile but we don’t cry when they die.”

Perhaps the demise of some robots should be mourned. Right now, the two Voyager spacecraft are poised at the very edge of the solar system; Voyager 2, the more distant, is nearly 11 billion miles from Earth. The spacecraft have traveled farther than any other objects humanity has made, and they are still sending back data 34 years after their launch. Both Voyagers have reached the outer limits of the heliosphere, an enormous, tenuous bubble of charged particles from the sun that surrounds our solar system.

Instead of the relatively stable environment that was expected at the brink of interstellar space, the Voyagers have encountered what some scientists have described as a “magnetic jacuzzi,” a region where the sun’s magnetic field appears to be ripping apart and reconnecting, forming bubbles millions of miles across. It is a place human explorers will not visit in the foreseeable future, although the data on the flux of cosmic rays (energetic particles from deep space) into the solar system will allow engineers to better gauge the risk to both spacecraft and humans during extended space voyages.

The Voyagers are now so far away that the signals from their 23-watt radio transmitters, powered by a radioactive generator, take more than 12 hours to reach Earth. Sometime within the next five years Voyager 1 will become the first spacecraft to cross the boundary of the heliosphere and enter interstellar space. There it is likely to be buffeted by winds of particles from supernovas that will be colder and denser than the solar wind, though still not as dangerous as Jupiter’s radiation belts. The spacecraft should have several years to explore the new realm. “We have enough electrical power to operate fully until 2020,” says Stone, who has been involved with the Voyagers since their inception.

In the meantime, NASA is planning some 30 new robotic missions to explore cosmic mysteries closer to home. The billion-dollar Solar Probe Plus, tentatively slotted for launch in 2018, would skim the outer atmosphere—or corona—of the sun itself, repeatedly dipping within five solar diameters of the sun’s surface, far closer than any probe has ever approached our star. The spacecraft’s exterior will endure 2600 degree Fahrenheit temperatures, while keeping the craft’s payload at room temperature. “It will work its way in over a period of seven years, getting closer and closer,” says Paul Hertz, chief scientist at NASA’s Scientific Mission Directorate. “Our goal is to find out how the solar wind gets accelerated, and why the corona is even hotter than the surface of the sun.”

NASA’s biggest ambition is the hunt for life and a habitat that can support it. Several planned or proposed missions will specifically explore the question of whether life exists, or once existed, elsewhere in our solar system. In late November, NASA plans to launch a 10-foot-long, six-wheel-drive mobile robot named Curiosity. If all goes well, the $2 billion bot will land on Mars nine months later and begin looking for signs of past or present life in rock and soil samples, all the while immune to the toxic dust, freezing temperatures, and space radiation that would derail human geologists.

Unencumbered by human frailties, Curiosity—like the rovers Spirit and Opportunity, which survived on the Red Planet years longer than expected—will be free to hunt for E.T. “If we find evidence for life on Mars, boy, are we just gonna go wild with speculation about how common it is in the universe,” says Lou Friedman, a former scientist with NASA’s Jet Propulsion Laboratory in Pasadena and cofounder, with Carl Sagan, of the Planetary Society. “Because here we are within a hundred years of the start of the space age and we find life on another world. Wow! That’s one way of looking at it. Another way is, here we are in the solar system with all its variations in planetary environments, and if we don’t find life, that’s going to be a downer.”

What comes after the Mars Science Lab is uncertain. Last March the National Research Council released a 400-page report called the Planetary Decadal Survey, which recommended 25 possible missions for NASA between 2013 and 2022. At the top of the list was the Mars Astrobiology Explorer Cacher, or MAX-C, which would collect soil and rock samples for a later mission that would return them to Earth. Perhaps by then manned missions will have resumed, and NASA might even have at last a solid plan for sending humans to Mars too.

For now, the second-highest priority mission on NASA’s wish list is the Jupiter Europa Orbiter, which would survey the ice-covered moon Europa and the global ocean that seems to lie beneath its frozen surface. If life exists anywhere else in the solar system, it may be in Europa’s ocean, which is estimated to be about 60 miles deep, its waters kept above freezing by the moon’s gravitational interactions with Jupiter.

“We know very little about that ocean,” says Steven Squyres, an astronomer at Cornell University who has been involved with many robotic missions. “We don’t know how thick the ice is, where the thin spots are, or where on the surface you might go to find out what it’s like inside Europa. So the orbiter mission is designed to address some of those questions.”

It now seems likely that mundane terrestrial concerns—the federal budget deficit—will force NASA to postpone the Europa mission indefinitely. “We apparently won’t be doing a Jupiter Europa Orbiter anytime soon,” Hertz says. “That’s a mission I wish we could do. It would be a great one. But with this budget we have to prioritize. Everything we do is great, and some of the things we don’t do would be great too.”

One of the most intriguing of NASA’s possible future missions would involve a visit to Titan, Saturn’s largest moon. The Titan Mare Explorer would be the first mission to explore an extraterrestrial sea, dropping a capsule onto Ligeia Mare, one of Titan’s seas of liquid methane, in 2023. The capsule, built to withstand the –300 degree Fahrenheit temperatures, would float on that oil-black sea for up to three months, looking for organic chemicals that might be similar to the ones that allowed life to begin on Earth.

It is likely that in another decade or two the achievement gap between human and robotic space exploration will have widened only further. By then, robots may even have found evidence for life on Mars or on one of the moons of Jupiter or Saturn. So where does that leave us? Are we destined forever to experience the solar system vicariously through robotic eyes?

“I don’t think we’re at the stage of human evolution where we should give up on going out there,” Lou Friedman says. “To me, there’s a deep and profound connection between unmanned and human exploration. They drive each other. Robotic exploration drives our interest in doing follow-up missions with humans. It may be that in the future we will stay hidebound and let robots explore the universe. But I’m not there yet. I’m a human chauvinist, and I’m rooting for the humans.”

We will follow the robots one day. With heavily shielded spaceships, perhaps we will brave Jupiter’s deadly radiation belts. Maybe we will get to see the moon Io, a hellish world of nonstop sulfur volcanoes, against a backdrop of Jupiter’s enormous colored bands of clouds. But one thing is certain. Wherever we go, whether we are gazing at geysers on Enceladus or tramping the sands of Mars, robots will have been there first.

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