SEVEN SCIENTISTS: AN EDGE OBSEQUY FOR THE ASTRONAUTS OF SPACE SHUTTLE COLUMBIA
Amidst all the self serving rhetoric, I think Edge should contribute its own obsequy. The people who died were scientists. Whatever else they may have believed in, their goal was to learn and to explore.
The Crew of the Space Shuttle Columbia
Rick D. Husband
William C. McCool
Michael P. Anderson
David M. Brown
Laurel Blair Salton Clark
Reality Club Discussion
In 1999 I produced two PBS documentaries that were meant to be the start of a major TV series following the design and construction of the International Space Station, which would, of course, have included the increasingly frequent shuttle flights which were an integral part of the programme. During the production, we filmed Rick Husband as he and his crew wrestled with a problem-laden simulation of a sudden return to launch-site. That time they succeeded without disaster. "We hung in there," he said after they came out of the simulator, "and got it on the ground safely and it all worked out fine."
Like many of the astronauts, there was only one thing Rick had ever wanted to be: "I've wanted to be an astronaut since I was about four years old," he told us. "So when the space programme first started up, I was right there planted in front of the T.V. for every one of the launches and for the whole time growing up. Whenever somebody asked me what I wanted to do, I told them I wanted to be an astronaut."
The irony was that by the time the Space Station project got under way, not very many people shared Rick's childhood enthusiasm. Interest waned with the routineness of largely flawless shuttle launches, and the ignorance of most of the public about the scientific benefits for space exploration, shown by the frequency with which NASA Public Affairs people tried to get the words 'possible cure for cancer' into the descriptions of experiments on crystals, cells, or mice.
The lack of public interest led to regular cutbacks in expenditure and over-reliance on 20-year old technology, while the US annual expenditure on lipstick went up and up. One trivial by-product of this was PBS's decision not to fund further documentaries on a project which couldn't garner enough viewers to justify further funding, while Frontier House pulled in the viewers to its ersatz excitements. Even Martin Rees, a long time believer in the merits of unmanned as against manned exploration, reveals that, as a human being he's in favour of sending people into space.
But I think he's wrong to argue that costs should come down. Maybe eventually, as they always do when a technology reaches maturity, but not yet, when there is so much still to be learnt about the hostile operating conditions for manned spacecraft. It seems to me that whatever President Bush's speechwriter scribbles for him to say in his first reaction to the disaster, there's no reason to think that manned spaceflight can continue without a mature, long-term, and expensive plan that is ring-fenced from the whims of Congress and public fashion. And how likely is that from a nation that killed the Superconducting Supercollider but is quite happy to waste billions on a war in Iraq?
I recall attending a lecture given, back in the 1960s, by John Glenn, the first American to go into orbit. A questioner asked him what went through his mind while he was crouched in the rocket nose-cone, awaiting blastoff. He wryly replied "I was thinking that the rocket had twenty thousand components, and each was made by the lowest bidder".
Glenn was aware of the risk he was taking—so surely, would have been the astronauts who perished in Columbia. But their fate injects a dose of reality: space travel is not a routine exercise. We need to ask—as we do of any pioneering venture—whether the goals of manned spaceflight are inspiring or valuable enough to justify the hazards involved.
The Shuttle's 98 percent success record—two disasters in just over a hundred flights—is actually rather good by space standards. Must unmanned rockets have a worse record. (The French Ariane V rocket had two catastrophic failures in less than a dozen flights).
We don't yet know whether last week's accident could have been avoided by better maintenance. I suspect it could. But even with optimal precautions, the risks of going into space will remain high compared to those that most of us willingly and routinely accept.
Publicly-funded astronauts are, in a sense, acting on our behalf. We feel uneasy about civilians bearing such risks, when the issues aren't of life or death urgency, but primarily science or exploration. Nonetheless, some individuals—wealthy amateur mountaineers who join guided parties to climb Everest, or test pilots—willingly do things that are at least as dangerous as a Shuttle flight.
When I am asked about the case for sending people into space, my answer is that as a scientist I'm against it, but as a human being I'm in favour. Practical activities in space—for communications, science, weather forecasting and navigation)—are better (and far more cheaply) carried out by computers and robots. I am nonetheless an enthusiast for space exploration as a long-range adventure for (at least a few) humans .
The next humans to walk on the Moon may be Chinese—only China seems to have the resources, the dirigiste government, and the willingness to undertake a risky Apollo-style programme. I hope Americans or Europeans will sometime venture to the Moon and beyond, but this will be in a very different style, and with different motives..
The kind of vibrant manned programme that I'd one day like to see will require changes in techniques and style. First, costs must come down. Second, there must be an overt acceptance that the enterprise is dangerous.
A role model for the future astronaut is not a NASA employee, nor even a military test pilot, but someone more in the mould of Steve Fossett, the wealthy "serial adventurer" who, after several expensive failures, succeeded in his solo round-the-world balloon flight. He has a craving for arduous challenges, and is now trying to beat altitude and endurance records for gliders. In each venture, Fossett must knowingly accept accepts a risk of at least 1 percent. Were he to come to a sad end, we would mourn a brave and resourceful man, but there would not be a national trauma. We would know that he willingly too the risks, and it was perhaps the way he wanted to go. Future expeditions to the Moon and beyond will only, I think be politically and financially feasible if they are spearheaded by individuals prepared to accept high risks, and perhaps even privately funded.
Dennis Tito and Mark Shuttleworth each spent 20 million dollars in return for a week in the International Space Station. A line-up of others was willing to follow them, even at that price. Such people won't, in the long run, restrict themselves to the role of passengers passively circling the Earth: they will yearn to go further.
Manned expeditions into deep space may one day be fundable by private consortia. Larry Ellison, who bankrolled a yachting challenge for the Americas Cup would already have the resources to initiate a cut-price project to take humans beyond Earth orbit.
The intrepid voyagers who set out from Europe in the 15th and 16th century to explore the then-open frontiers of our own world were mainly bankrolled by monarchs, in the hope of recouping exotic merchandise or colonising new territory. Some later expeditions, for instance Captain Cook's three 18th century voyages to the South Seas, were publicly funded, their mission being to survey new territory, discover new plants, and make astronomical measurements. For some early explorers—generally the most foolhardy of all—the enterprise was primarily a challenge and adventure: the motivation of present-day mountaineers, balloonists, round-the-world sailors and the like.
The first travellers to Mars (maybe thirty years from now), or the first long-term denizens of a lunar base, could be impelled by this same mix of motives. They would confront hostile environments: nowhere in our Solar system offers an environment even as clement as the Antarctic or the deep ocean. However, no space travellers would be venturing into the unknown to the extent that the great terrestrial navigators were: those early pioneers had far less foreknowledge of what they might encounter in the regions where ancient cartographers wrote "here be dragons". Nor would space travellers be denied contact with home, any more than explorers and lone sailors now are. There would admittedly be about a 30 minute turnaround for messages to and from Mars, because it takes that long for a radio signal to traverse the hundreds of millions of miles distance. But that is as nothing compared to the isolation of traditional explorers.
The stakes will be high for space explorers: they will be opening up entire new worlds, Maybe some would accept—as many Europeans willingly did when they set out for the New World—that there would be no return. A Martian base would develop more quickly if those constructing it were content with one way tickets.
The mountaineers George Mallory and Andrew Irvine both perished on Mount Everest in 1924, during a celebrated early attempt to reach its summit. A stone tablet in Irvine's memory bears a text from Pericles's famous funeral oration (in Hobbes's translation) .
"They are most rightly reputed valiant who perfectly understand what is dangerous and what is easy, but are not thereby diverted from adventuring".
This sentiment, I believe, would have resonated with the Columbia astronauts. In future decades, if humans venture to the Moon and beyond, they will have to go in this same spirit.
I once met an American scientist (in Tucson) who claimed he trained (secretly) for a one way journey to the moon. The program was deemed politically unacceptable, and scrapped. There may be some interesting history to this.
I've been dwelling on George's suggestion of a one way manned voyage to Mars. I think George is right that it has the potential to capture the world's attention as nothing ever has done—science, religion, sex, adventure, reality tv, all rolled into one. The child of Shakespeare, Newton, Darwin, Freud and Einstein. Why don't we make this an Edge project? John Brockman has the best of all address books. Edge could make it happen!
When I think of the "Columbia", I still think of the 213-ton "Columbia Rediviva," launched in Plymouth, Massachussetts in 1787, in which Captain Robert Gray explored the Northwest Coast. There could be no better monument to the crew of the recent Columbia than to make their sacrifice a decisive turning point in truly expanding Earth's biology, technology, and biotechnology out into the solar system.
There's no shortage of ways to to go about this. Here's my (non-original) suggestion.
Let the new "Columbia Rediviva" (Columbia Revived) be a ship built to deliver seven human beings on a (for the time being) one-way voyage to Mars. We all know that technically, the hard part is getting back. But if we could get seven people there, the world would unite as one in sending these first colonists all possible support, and, eventually, developing the infrastructure that might allow people to go back and forth.
Beyond The Shuttle
A friend at NASA's Marshall Space flight Center in Huntsville, Alabama told me today that all his engineer friends were working on their resumes. After the Challenger disaster, NASA dithered for 2.5 years before using the shuttle again. How long this time?
Quite probably, a year—if ever. This second wreck calls into question the entire shuttle program. Voices already are calling for a wholly new approach. The shuttle has the worst safety record of any launch vehicle, and is the most expensive, costing half a billion dollars per mission.
And we now contemplate a war in Iraq that depends on our technical prowess. I doubt that Americans will be moved to doubt our military, just because an advanced spacecraft fell out of a clear blue sky. We are tougher than we may look—and more resolute. The country is reasonably united, and yet again the president has responded with the right sense of gravity. He does disaster well.
Still, it is a good time to reassess. Early results from the telemetry and the huge debris field suggest that the thermal tiles failed. One amateur observer saw something blowing off the shuttle as it passed over California, possibly red-hot tiles. We know that a piece of foam blew off the fuel tanks at launch, striking the shuttle's left wing, a location that seems implicated in the heating spike that the telemetry recorded just before the craft began to slew and tumble.
Reentry is a tricky negotiation between gravity and aerodynamics. Controlling descent angle is important to reduce mechanical and thermal stress on the spacecraft, and an error in the on-board computers can allow the angle to get so steep that the craft breaks apart. (Multiple computers should reduce the risk, but that has not saved computer-run aircraft like the SAAB 39 Gripen from the occasional crash.)
Whatever the fault, tiles or computers or human error, the crash occurred at what many engineers thought was the most dangerous portion of a shuttle's flight. This is not a fluke; the system was vulnerable, and it failed yet again.
Perhaps the only good thing about this disaster is that it will prompt NASA to rethink the design of manned spacecraft from first principles. Foremost is that the more complex a spacecraft is, the more things can go wrong.
The safest manned descent module was also the simplest: the Soviet "sharik" descent capsule, which was used by Vostok and Voskhod craft, and also in many unmanned missions since. It was just a sphere with the center of gravity on the side with the thickest ablative thermal shielding, so it was self-stabilising. Even if the retrorockets failed to separate, it could re-enter safely.
Simple ballistic craft that do not fly are also (relatively) simple. With a spaceplane like the shuttle, however, you are not only committed to a complex shape, you are also committed to using brittle ceramic materials for thermal shielding. The first item on NASA's agenda will be to revisit the tiles issue.
The ceramic tiles not only make overhaul very time-consuming and expensive—specialists affix each tile by hand, managing to do a few per day, and there are thousands— they are also literally impossible to check for inner defects. Unlike metal components, you cannot test them for small cracks that may cause failure.
One way around this is to use many small ceramic tiles, so the spacecraft can survive losing individual tiles. But if several adjacent tiles are lost, it will cause catastrophic failure during reentry. Maybe that happened; it is consistent with what we know now (or are likely to know for several months).
A second line of defense is to have the crew in a detachable unit that can land safely. This would be straightforward in a ballistic craft, but with an aerodynamic spaceplane it is difficult to squeeze such a unit into the nose. On the B-58 bomber the crew had small individual pods that enabled them to eject safely at supersonic speeds, but the weight penalty ruled out this option for the shuttle.
Ideally, you need a descent module that can take a lot of punishment. But a big spaceplane would get impossibly heavy if it was stressed for this. This is another argument for small sixties-era crew capsules.
Ironically, the Soviet "Buran" shuttle could lift loads to orbit without any crew at all, and might make a viable alternative to the US shuttle. But the only remaining craft got badly damaged when a corroded hangar roof fell down on it last year—a symbol of the Russian program's decay.
The safest manned spacecraft built was also among the cheapest and simplest. The lunar lander used pressurized tanks, eliminating the need for turbo pumps, and the fuel and oxidizer self-ignited when mixed, making the engine very reliable.
NASA considered mass-producing similar, simple rockets in the sixties as an option to make space flight cheaper. Political considerations favored the more spectacular spaceplane solution. To date, this decision has killed two shuttle crews and cost billions.
In the end, the next months will try NASA as never before. It has tried to convince its public that going into space is safe, when it is not. Once is an accident, twice is a defect.
The shuttle's justification these days has been its role in supporting a space station that now does little science. The station runs with the minimum crew of three, to save money while forgetting science. The Russian Soyez vehicle could cycle crews and probably will be used to bring down the three up there now.
The station program can limp along for a few years with two flights a year, to cycle crews every half year and not abandon the station entirely. A Russian Proton rocket can continue to boost the station up as its orbit decays from atmospheric friction, as we now do routinely.
This can go on until NASA can decide what to do. Its habit is not to be truly decisive, but now its back is to the wall. It must confront the big question:
What is the American destiny in space? The station is not a destination; it is a tool. But for what?
NASA has played up the station as "a stepping-stone to the planets" — but it cannot perform the two experiments we know must be done before any manned ventures beyond Low Earth Orbit begin.
These are, first, development of a true closed biosphere in low or zero gravity. The station recycles only urine; otherwise, it is camping in space, not truly living there.
Second, we must develop centrifugal gravity. Decades of trials show clearly that zero-g is very bad for us. The Russians who set the endurance records in space have never fully recovered. Going to Mars demands that crews arrive after the half year journey able to walk, at least. No crew returning from space after half a year ever have, even for weeks afterward. So we must get more data, between one gravity and none. Mars has 0.38 g; how will we perform there? Nobody knows.
Spinning a habitat at the other end of a cable, counter-balanced by a dead mass like a missile upper stage, is the obvious first way to try intermediate gravities. The International Space Station has tried very few innovations, and certainly nothing as fruitful as a centrifugal experiment. Until a livelier spirit animates the official space program, the tough jobs of getting into orbit cheaply, and living there self sufficiently, will probably have to be done by private interests who can angle a profit from it. But not right away.
This is an historic moment, one of great opportunity. NASA can either rise to the challenge and scrap the shuttle, or just muddle along. An intermediate path would use the shuttles on a reduced schedule, while developing a big booster capable of hauling up the big loads needed to build more onto the station. This would be cost-effective and smart.
The past Director of NASA said to me a few years ago that he thought the agency had about a decade to prove itself. Around 2010 the Baby Boomers will start to retire and the Federal budget will come under greater pressure. Space could go into a slow, agonizing withering. He thought this was a distinct possibility if NASA did no more than fly around in cycles over our heads. "It has to go somewhere else," he said.
The obvious target that has huge scientific possibility is Mars. Did life arise there, and does it persist beneath the bleak surface? No robot remotely within our capability can descend down a thermal vent or drill and find an answer. Only humans are qualified to do the science necessary, on the spot.
A Mars expedition would be the grandest exploit open to the the 21st Century. It would take about 2.5 years, every day closely monitored by a huge Earthside audience and fraught with peril.
This is what we should be doing. Such an adventure would resonate with a world beset by wars and woes. It has a grandeur appropriate to the advanced nations, who should do it together.
The first step will be getting away from the poor, clunky shuttle, a beast designed 30 years ago and visibly failing now. How we respond to the challenge of this failure will tell the tale for decades to come, and may become a marking metaphor for the entire century.
As well, the engineers at NASA would be overjoyed to have a larger prospect before them, something better than patching up an aging shuttle that, in the end, was going nowhere.
The most fitting salute I can imagine for the Columbia seven would be a continued—indeed expanded, in scope if not in budget—space programme; but not a continuation of the space programme America has today.
Most people who believe that expanding the shared human world beyond the planet of its birth is a good idea have a sad belief that if they give up the shuttle there will never be another manned programme. There is a strange dissonance between the grandeur of the vision and the insistence that its survival depends on never giving up on the programme as it is today.
It's time to resolve that dissonance by providing human spaceflight with a mission other than its own continuation (which has been the de facto mission since Nixon approved the programme) and re-inventing the programme in the context of that mission. I think solar system exploration should be the mission; an ambitious robotic and human partnership with the human side focused, at least to begin with, on Mars. Understanding the earth and its life as a system that has developed—and will continue to develop—over history is a crucial goal for the twentieth century. Learning the history of a similar but different possibly-once-living world could be crucial to that.
So if I was President Bush I would reaffirm my commitment to space by mothballing the last three shuttles and the station (after finding the best way to boost it into a century-stable orbit). I'd then use the annual $6 billion thus saved for a serious solar-system exploration programme. Under that heading I would put: the design of a heavy lift vehicle in the Energia-plus/Saturn V class, capable of launching very large payloads to earth orbit and substantial ones to Mars; a production facility capable of producing those rockets at a rate of two or so a year; development work with others (eg Europe, Russia, India, Japan) on vehicles that would use that capacity for Mars missions along the lines of those that Robert Zubrin has proposed, though not necessarily with exactly that profile; and safe space nuclear power and advanced ion engines to make use of that power, initially to do some impressive robot missions but with planned growth to allow eventual use for manned missions.
I'd use this material for a series of humans-to-Mars precursor missions in which robots would go to Mars and humans would start off practising things nearer to earth. The robot missions would increase knowledge of relevant environmental conditions (for example, set up a weather network) and also demonstrate necessary technologies such as in-situ fuel production using a reactor. The human program would use launched-in-one-piece Skylab-type spacecraft to check out the unknowns about Mars flight. I think relatively short duration Skylab type missions specifically designed to do this represent a significant advantage over the use of today's long-duration space station. Such missions, unlike today's station, could test simulated gravity systems, both systems using centrifuges on board for individual exercise and those that require spinning entire spacecraft on a tether. They would also serve as testbeds for the development of flight hardware for the cruise and landing parts of a Mars mission. And they offer a way of parcelling out the effort between different nations, with different units built in different places. (On international cooperation, and Nick Humphrey's mention of the meaninglessness of borders in space, I'm reminded of the exchange between two astronauts in Niven and Pournelle's "Lucifer's Hammer": "'So you can't see the international borders from space and everyone tries to make a big point of it. If we keep that up, you know what'll happen?' Rock laughed 'Yeah. Everyone's gonna start painting their borders in neon orange a mile wide'")
These Skylab type craft might be used for some beyond-earth-orbit missions, as well as in orbit tests. One such mission might be a near earth asteroid rendezvous and subsequent testing of a low-thrust long-lifetime engine to change the asteroids course, as suggested by Piet Hut and the B612 Foundation. Another might be a trip to Mars orbit, where the crew could do some intensive service work with robots tele-operated in real time but wouldn't have to function outside microgravity. Then start the landings, going to sites that the robots have shown to be interesting that will repay detailed fieldwork. On the timing I'm thinking roughly ten years of development and ten years of trying things out with people in orbit before we start doing the Mars stuff, but with a permanently crewed Mars base developed fairly quickly thereafter (ie in the third decade). That's my feeling for the sort of rate at which a $6 billion (plus non American funds) programme might progress happily.
A programme like this would require no shuttles. It could get by with Soyuz capsules and, later, more advanced landing capsules. And so I would not rush into the development of a replacement shuttle. Instead I'd fly a variety of prototypes for orbital space planes. We need to try a lot more technologies, philosophies and designs in real conditions before even thinking about locking in to a concept for a new reusable TSTO or SSTO machine. But I would make this a considerably lower priority than solar system exploration. We can do the most exciting stuff without it.
It's possible that the USAF will want a manned spaceplane of its own—among other things, the men in blue suits may find the idea of Chinese astronauts being able to go up and rendezvous with US satellites unchecked a little disturbing. If the USAF wants something soon, then let them develop it to their own specifications and out of their own budget; many of the compromises that made the shuttle so complex and vulnerable came from USAF requirements. If such a spaceplane then becomes useful for the solar system programme, then I'm sure they would let us borrow a coupleŠ
If the airforce builds a spaceplane, though, that does not necessarily mean that NASA should do all the other stuff. The shuttle programme is so central to NASA that a post-shuttle restart might make a new organisation desirable; I'd be interested to hear what others think on that.
The Scottish science fiction writer Ken MacLeod provided this epitaph in the wake of the Columbia:
Husband, McCool, Anderson, Brown, Chawla, Clark, Ramon.
Komarov, Grissom, White, Chaffee, Dobrovolsky, Volkov, Patsayev,
Resnick, Scobee, Smith, McNair, McAuliffe, Jarvis, Onizuka.
These names will be written under other skies.
It's a beautiful thought. But the other skies are not going to be reached any time soon through a continued shuttle programme.
What Lies Behind our Desire to Venture into Space?
The leap into Space witnessed in our time, with its triumphs and tragedies, will remain part of the permanent memory of mankind, alongside the historic memory of the great journeys of adventure and discovery that formerly found expression in epic form. People in the distant future may, in their own way and using their own media, be describing our attempts to transcend our physical dependence on the earth somewhat as we still are singing Homer's song to relive the voyage of Odysseus beyond the boundaries of the ancient world.
I venture two brief speculations. The first is that, in retrospect, the exploration of the solar system, and beyond, by means of earth-launched physical instruments, was prepared for by a series of equally daring, mental launchings into space. Science and space have in fact been Siamese twins from the start: Space has been the foremost laboratory of the scientific imagination—from the pre-Socratics who toyed with the question of the limits of space, to Aristotle and his followers for whom the cosmos was not only finite but relatively small, to Kepler who could envisage something like the law of conservation of momentum by thinking about mutually attracting and colliding bodies in far-distant space, to Galileo for whom space was not yet Euclidean but warped, and on to Newton and the modern period.
In a sense, the space age really started not with Sputnik I, but with those early explorers of the mind's own space, who, launching their imaginative conceptions, prepared the ground for launching our hardware. There are several candidates for a designation of the father of the space age. My own preference is a philosopher, mathematician, cosmologist, and cardinal of the church, Nicholas of Cusa. (Appropriately, a crater on the moon has been named after him.) A good description of his work is in Alexander Koyré's great book, From the Closed World to the Infinite Universe. Nicholas of Cusa, who lived from 1401 to 1464, was one of the first who tried to break out of the geocentric, anthropocentric, finite, and hierarchically sequenced world of antiquity, a world bounded by the walls of the heavenly spheres. He glimpsed the dizzying potential of space and entertained a very different universe: open, unbounded, without natural subordination of any one part to any other, filled with identical laws and with essentially interchangeable components. Technically, his step is called the "infinitization of the cosmos," an idea so new then that it was ignored by Nicholas of Cusa's contemporary, Copernicus, who thought the world was contained within a sphere of about 20,000 earth radii.
But Nicholas of Cusa saw the consequences of his vision: In an immeasurable universe, where there is no limiting point or center, all motion is relative, and the earth and all other bodies may be considered in motion. The earth then joins the ranks of the noble stars. He even imagined that the stars may also be endowed with life forms. Most of his readers recoiled in horror and vertigo, except Giordano Bruno, who embraced these ideas, and who, by being burned at the stake in 1600 for such heresies, became (so to speak) the first space casualty. Thereafter, however, Nicholas' ideas became more and more influential.
Nicolas of Cusa was a prominent person, but we know all too little about him. Though we happily have his book with the modest title On Learned Ignorance, which I like to think started the space age some 560 years ago, the reputedly most adventurous of his scientific-philosophical writings have been lost to history.
My first speculation, looking back, brings me to the second, looking forward. Who, in the long run, will tell our story? Who will be the future Homers to sing of our time, and where will they get their information? Will the future students of our attempts at exploring have reliable information, more reliable than we have about our predecessors? Who is now concerned with preparing accounts that can withstand the scrutiny of the ages to come? Who is saving the database, the less obvious documentation of successes and failures? Who is conducting the oral history of the pioneers? Are there interviewers able to handle the science, the technology, and the industrial and administrative components of modern space achievements?
There are a few who can, historians of science and technology. On the members of that fairly young profession we shall have to rely for the preservation of the record, and for the assessment and authentication of what has been happening during this early, heroic period. We are lucky that such people, in the United States, in the U.K, and in Europe, dedicate their lives to such scholarship. But altogether, the number of these professionals are few, and their support and the infrastructure of their professional societies are now under severe constraints. Let us not be chided by future historians, for neglecting our opportunities of preserving the full record, as we ourselves might blame Nicholas Cusa's contemporaries for not having preserved more of his pioneering thoughts.
The cheapest and simplest way to do anything interesting in space beyond low-Earth orbit is to visit a nearby asteroid. Oliver Morton suggested this idea in his contribution below, and mentioned our B612 Foundation's goal of changing the orbit of an asteroid. Indeed, it would be natural to combine asteroid deflection practice with actual human exploration of an asteroid. That way, the astronauts putting themselves at risk would know that at the same time they would have the potential of saving millions of lives on Earth.
Astronauts can play a useful role by setting up a mass driver that can throw rocks off the surface in order to move the asteroid in the opposite direction. In the long run, that may well be the most efficient way to ride asteroids. In the near future, plasma engines can be used to push an asteroid tugboat style in case of an unmanned mission. While fuel efficient and simple, plasma engines do consume lots of energy. In contrast, a mass driver presents a very low energy alternative, but the logistics for picking up the 'fuel' (rocks) are daunting. For a robotic mission to set up and anchor a mass driver, select and pick up the rocks and position them for launch presents challenges well beyond what has been demonstrated so far.
While we hear a lot about Mars as the next target beyond the Moon for human exploration, it is not often realized that it is energetically cheaper to visit an asteroid, even compared to visiting the Moon. Getting out of the gravitational grip of the Earth carries about the same cost as going to the Moon, while landing on an asteroid and taking off costs almost nothing: the escape speed of a 100 meter diameter asteroid is only a few cm/sec, and that of a 10 km diameter asteroid a few meters/sec. The challenge would be for an astronaut to stay put on the surface and not 'launch' herself inadvertently.
Getting to an asteroid will take only a few months, rather than years, if we pick one on an orbit close to that of the Earth. If we land on an asteroid just before it passes us, and then get off again soon afterwards in order to return, it would be as simple as switching between two moving walkways that have almost exactly the same speed.
Finally, missions to an asteroid would present far better prospects for the commercialization of space than missions to the Moon or Mars. Anything we find, from precious metals to possibly water (on inactive comets, say, that may pose as asteroids), can be easily brought back to Earth orbit, to provide raw material for the space station or for other space flights. It is energetically far more favorable to bring matter from an asteroid down to the space station than to send it up from the surface of the Earth. While it is too early to know what exactly we will find there, we may hope that an extraterrestrial 'gold rush' may help push the frontiers of exploration to include asteroids.