The next big hurdle wouldn’t be the question of how to divert the asteroid, though. Say, for example, Mainzer’s NEOCam is in orbit and her team spots an object bigger than 1 km that has a 1-in-50 probability of smashing into the Earth. “Should we spend money on that now?” Ailor asked. “Given the fact that it takes you years to build a new payload and fly a mission out to do something, you may have to start spending money before you’re certain it’s going to hit. And that’s the challenge for decision-makers.” The problem is that every PHO is a probability … until it isn’t. And the time to act decisively to push an incoming object out of the way is almost inevitably going to be long before we can establish that a collision is a certainty. Meanwhile, as the object hurtles closer to us in space, the less likely it is that we’ll be able to gently nudge it into a new orbit, out of our way.
So who would have to step up and push the world to launch anti-PHO spacecraft? The U.N. Committee on the Peaceful Uses of Outer Space has a group called Action Team-14 that deals with NEOs, and would likely be the first agency to coordinate Earth’s defense in this situation. Provided they can get buy-in from countries and corporations with the means to build spacecraft for the mission—and that’s a big if—the group would have to decide exactly what method of PHO deterrence would work best. Ailor’s company, the Aerospace Corporation, did a study in 2004 on what would be required to take a 200-meter object from a 1-in-100 probability of hitting Earth to 1 in 1,000,000. “You have to launch quite a few spacecraft,” Ailor said. “There’s a misconception that you would send up just one vehicle.” Redundancy would be crucial, in case one of the crafts fails—and besides, some techniques for moving the object require multiple spacecraft to work. Also, despite what we saw in the asteroid-nuking flick Armageddon, the vehicle would be a remote-controlled robotic craft. “If a human can get there, it’s way too close,” Ailor asserted.
If we have enough time, we’d want to try what Ailor called slow-push techniques. One would involve using a swarm of small spacecraft equipped with lasers designed to boil material off the surface of the object. As the PHO spat pieces of itself into space, enough thrust would be generated to gently move it out of its deadly path toward Earth. Another possibility would be to create a “gravity tractor” with one or more spacecraft. Parking bulky objects like other asteroids or big spacecraft near the distant object might generate enough gravitational pull to move it just enough. Many years later, this small perturbation would elegantly divert its course into a completely harmless orbit. Both of these techniques are untested. But as more spacecraft venture to NEOs and the asteroid belt over the next decade, we’re likely to see experiments to test whether these techniques could, in fact, jar a large object out of its current orbit.
In this image by Ron Miller, we see a probe pushing an NEO out of Earth’s path. (illustration credit ill.18)
What if the asteroid were heading toward us today, and we hadn’t had a chance to test the slow-push systems? “We don’t have anything off the shelf other than a kinetic impactor,” Ailor said casually, as if he were talking about computer parts. A kinetic impactor is “basically hitting it with a rock,” he explained. We’ve already tried this method on a comet with NASA’s Deep Impact mission, when a probe hit the Tempel 1 comet with a giant copper slug, dislodging huge amounts of dust and ice. Tempel 1’s orbit was perturbed slightly. So we know for certain that if we hit an incoming object with slugs or rocks, we have a good chance of redirecting it. “If you have one that gets too close or is bigger, you might have to use a nuke to move it,” Ailor conceded. That’s a last resort, and also untested.
The problem is that even our “off the shelf” kinetic-impactor solution would be tough. “You’d have to pull a craft together, grab the right kind of payload to do what you wanted, and find a launch pad,” Ailor said, seeming to be mentally ticking off a list he’d pondered many times. On top of that, there would be the issue of how to inform the public without causing either mass panic or denial. It’s easy to imagine people voting against an expensive anti-PHO program if there were only a 1-in-500 chance of mass extinction. Still, it’s possible we might band together as a civilization to deal with this existential threat, and fail anyway. As Ailor put it, “Of course, you might miss.”
In the Event of Fallen Civilization, Please Open This File
If we’re facing an impact that’s a 10 on the Torino scale—that is, from an asteroid comparable to the one that hit at the K-T—we are certainly facing a mass extinction. The world would be wrapped in fires, and cities would be shaken by quakes, broiled by volcanic eruptions, and flooded by tsunami waters. Over the long term, the climate would be transformed by aerosols thrown into the stratosphere. How would we survive?
Initially, our survival would depend on retreating to the kinds of underground cities we discussed in chapter 17. The immediate aftereffects of the hit would be similar to a massive nuclear war, minus the radioactive fallout. Underground, we would be relatively safe from the worst of the firestorms and other disasters. Aboveground, temperatures and fires would die down relatively quickly. Within weeks, we’d be able to poke our heads back up and see the roiling clouds of dust that had replaced our sky. And that’s when our real troubles would begin. We’d likely suffer through something like a nuclear winter. Alan Robock, the atmospheric scientist who warned against solar-management geoengineering with particles in the stratosphere, was among the first scientists to suggest that supermassive explosions would result in planetary cooling. And the cold would likely intensify for several years. In an early paper about nuclear winter, Robock outlines a scenario that sounds like a mild icehouse. The first year after the explosion—in this case, an asteroid strike—we’d see a global buildup of ice and snow and lowering of temperatures by about two degrees. But as the cold deepened, the planet’s snowy surface would reflect even more light—creating a runaway effect that would cool us down possibly as much as 15 or 16 degrees in the following several years.
Without sunlight, agriculture would grind to a halt and wild plants would die back. Herbivores would die, and then the carnivores who fed on them would die out, too. Creatures who dwelled near the surface of the water would suffer in the immediate effects of the hit. Then, over time, runoff from the decimated land would fill the oceans with carbon and create deadly pockets of anoxic waters. Humans would have to rely on greenhouses for food, as well as whatever we could cultivate with little sunlight. Mushrooms, fungus, and insects would play a much bigger role in our diets than they do today.
There is also the distinct possibility that enough people would be killed in the strike that it would be impossible to maintain our civilization at its current level of development and energy needs. Megacities and high-tech societies require many people with specialized knowledge to make them function, and if only a few million people are left alive on the planet, it’s unlikely that we’ll have the right combination of skills to resurrect New York or Tokyo. What would we do if we had to rebuild human civilization from scratch? This is the kind of question that dogs apocalyptic science fiction, but preoccupies people in the real world, too. Alex Weir, a software developer based in Zimbabwe, is part of a small group that maintains the CD3WD database, a relatively small set of computer files that contain as much human knowledge as possible about what amounts to a pre-technological civilization. There are sections devoted to basic medicine, agriculture, town building, and power generation. At 13 gigabytes, it’s easily stored on a few DVDs, or (ideally) printed out as a thick sheaf of papers and stored in a three-ring binder. The idea is to keep the CD3WD database in your survival kit, a backup copy of everything history has taught us about creating an early industrial society. It is one of the simplest and most profound examples of how survival requires us to remember what has come before. If people need guidance with rebuilding the world after the icehouse is over, CD3WD and similar projects can help us restart civilization as quickly as possible.
It is inevitable that the Earth will be on
a collision course with a PHO at some point. Obviously, our first duty is to keep mapping the skies, tracking NEOs, and perfecting our asteroid-nudging technologies. But we also need to accept that the Earth isn’t the safest place for us if we want to survive for another million years. We need to scatter to other planets and moons, building structures in space so that even if Earth is wiped out, humanity will survive. That’s why one of the keys to long-term existence involves creating devices that will help us escape the planet. One such device is the subject of the next chapter.
21. TAKE A RIDE ON THE SPACE ELEVATOR
EVENTUALLY WE’LL HAVE to move beyond patrolling our planetary backyard and start laying the foundations for a true interplanetary civilization. Asteroid defense and geoengineering will only take us so far. We need to scatter to outposts and cities on new worlds so that we’re not entirely dependent on Earth for our survival—especially when life here is so precarious. Just one impact of 10 on the Torino scale could destroy every human habitat here on our home planet. As horrific as that sounds, we can survive it as a species if we have thriving cities on Mars, in space habitats, and elsewhere when the Big One hits. Just as Jewish communities managed to ensure their legacy by fleeing to new homes when they were in danger, so, too, can all of humanity.
The problem is that we can’t just put our belongings into a cart and hightail it out of Rome, like my ancestors did when things got ugly in the first century CE. Currently, we don’t have a way for people to escape the gravity well of planet Earth on a regular basis. The only way to get to space right now is in a rocket, which takes an enormous amount of energy and money—especially if you want to send anything bigger than a mobile phone into orbit. Rockets are useless for the kind of off-world commuter solution we’ll need if we’re going to become an interplanetary civilization, let alone an interstellar one. That’s why an international team of scientists and investors is working on building a 100-kilometer-high space elevator that would use very little energy to pull travelers out of the gravity well and up to a spaceship dock. It sounds completely preposterous. How would such an elevator work?
That was the subject of a three-day conference I attended at Microsoft’s Redmond campus in the late summer of 2011, where scientists and enthusiasts gathered in a tree-shaded cluster of buildings to talk about plans to undertake one of humanity’s greatest engineering projects. Some say the project could get started within a decade, and NASA has offered prizes of up to $2 million to people who can come up with materials to make it happen.
The physicist and inventor Bryan Laubscher kicked off the conference by giving us a broad overview of the project, and where we are with current science. The working design that the group hopes to realize comes from a concept invented by a scientist named Bradley Edwards, who wrote a book about the feasibility of space elevators in the 1990s called The Space Elevator. His design calls for three basic components: A robotic “climber” or elevator car; a ground-based laser-beam power source for the climber; and an elevator cable, the “ribbon,” made of ultra-light, ultra-strong carbon nanotubes. Edwards’s design was inspired, in part, by Arthur C. Clarke’s description of a space elevator in his novel The Fountains of Paradise. When you’re trying to take engineering in a radical new direction that’s never been tried before, sometimes science fiction is your only guide.
What Is a Space Elevator?
A space elevator is a fairly simple concept, first conceived in the late nineteenth century by the Russian scientist Konstantin Tsiolkovsky. At that time, Tsiolkovsky imagined the elevator would look much like the Eiffel Tower, but stretching over 35,000 kilometers into space. At its top would be a “celestial castle” serving as a counterweight.
A century after Tsiolkovsky’s work, Bradley speculated that a space elevator would be made of an ultra-strong metal ribbon that stretched from a mobile base in the ocean at the equator to an “anchor” in geostationary orbit thousands of kilometers above the Earth. Robotic climbers would rush up the ribbons, pulling cars full of their cargo, human or otherwise. Like Tsiolkovsky’s celestial castle, the elevator’s anchor would be a counterweight and space station where people would stay as they waited for the next ship out. To show me what this contraption would look like from space, an enthusiast at the Space Elevator Conference attached a large Styrofoam ball to a smaller one with a string. Then he stuck the larger ball on a pencil. When I rolled the pencil between my hands, the “Earth” spun and the “counterweight” rotated around it, pulling the string taut between both balls. Essentially, the rotation of the Earth would keep the counterweight spinning outward, straining against the elevator’s tether, maintaining the whole structure’s shape.
Once this incredible structure was in place, the elevator would pull cargo out of our gravity well, rather than pushing it using combustion. This setup would save energy and be more sustainable than using rocket fuel. Getting rid of our dependence on rocket fuel will reduce carbon emissions from rocket flights, which today bring everything from satellites to astronauts into orbit. We’ll also see a reduction in water pollution from perchlorates, a substance used in making solid rocket fuel, and which the Environmental Protection Agency in the United States has identified as a dangerous toxin in our water supplies.
A space elevator would be a permanent road into space, making it possible for people to make one or more trips per day into orbit. Passengers could bring materials up with them so that we could start building ships and habitats in space. Once we started mining and manufacturing in space, elevators would be used to bring payloads back down, too. Most important, a working space elevator is many thousands of times cheaper than the one-time-use Soyuz rockets that bring supplies to the International Space Station, only to destroy themselves in Earth’s atmosphere. NASA reports that each Space Shuttle launch cost about $450 million. Much of that money was spent on storing enough fuel to complete the round-trip back to Earth. But groups working on space-elevator plans believe their system could reduce the cost of transporting a pound of cargo into space from today’s $10,000 price tag to as little as $100 per pound.
In this illustration by Pat Rawlings for NASA, you can see the climber in the foreground and the tether stretching back down toward distant Earth. (illustration credit ill.19)
Getting Ready to Build
The elevator would be attached to the Earth at the equator, where geostationary orbit happens, probably on a floating platform off the coast of Ecuador in international waters. This is a likely building site because it is currently an area of ocean that experiences very little rough weather, and therefore the elevator could climb out of our atmosphere with as little turbulence as possible. According to Edwards’s plan, the elevator ribbon would stretch 100,000 kilometers out into space (about a quarter of the distance to the Moon), held taut by a counterweight that could be anything from a captured asteroid to a space station. A ride up would take several days, and along the ribbon would be way stations where people could get off and transfer to orbiting space stations or to vessels that would carry them to the Moon and beyond.
The elevator car itself is the easiest thing for us to build today. It would be an enormous container, with atmospheric controls for human cargo, connected to large robotic arms that would pull the car up the ribbon hand over hand. We already have robotic arms that can scale ropes and lift incredibly heavy objects. This aspect of the space elevator is so widely understood that the Space Elevator Conference sponsored a “kids’ day” that included LEGO space-elevator-climber races. Robots designed by teens and kids competed to see which could climb “ribbons” attached to the ceiling and place a “satellite” at the top.
Of course it will take some effort to get from LEGO climbers to lifters big enough to haul components of a space hotel up through thousands of kilometers of atmosphere and space. But this is within the capabilities of our current industrial technology. So we’ve got our elevator car. But how will it be powered?
One of the many arguments in favor of the elevator co
ncept is that it will be environmentally sustainable. The dominant theory among would-be space-elevator engineers at this point is that we’ll install lasers on the space-elevator platform, aimed at a dish on the elevator that will capture the beam and convert it to power. This technology is also within our reach. In 2009, NASA awarded $900,000 to LaserMotive for its successful demonstration of this so-called “wireless power transmission” for space elevators. In 2012, NASA offered a similar prize for a power-beaming lunar rover. The biggest problem with the power-beaming idea currently is that we are still looking at fairly low-power lasers, and as the space elevator ascended higher into the atmosphere the beam from such a laser would scatter and be blocked by clouds. It’s possible that only 30 percent of the beam would reach the dish once the elevator was in space.
Still, we have seen successful demonstrations of power beaming, and companies are working on refining the technology. We don’t quite have our perfect power beam yet, but it’s on the way.
The Missing Piece: An Elevator Cable
At the Space Elevator Conference, participants devoted an entire day to technical discussions about how we’d build the most important part of the space elevator: its cable, often called the ribbon. Again, most theories about the ribbon come from Edwards’s plans for NASA in the 1990s. At that time, scientists were just beginning to experiment with new materials manufactured at the nanoscale, and one of the most promising of these materials was the carbon nanotube. Carbon nanotubes are tiny tubes made of carbon atoms that “grow” spontaneously under the right conditions in specialized chambers full of gas and chemical primers. These tubes, which look a lot like fluffy black cotton, can be woven together into ropes and textiles. One reason scientists believe this experimental material might make a good elevator cable is that carbon nanotubes are theoretically very strong, and can also sustain quite a bit of damage before ripping apart. Unfortunately, we haven’t yet reached the point where we can convert these nanoscopic tubes into a strong material.
Scatter, Adapt, and Remember: How Humans Will Survive a Mass Extinction Page 24