Getting to the Worlds Next Door

To get a sense of the gulf of space that lies between us and the near­est star systems, let’s return to the scale model from the start of the chapter. Visualize the Earth as a golf ball, a little less than half a mile from a glowing, 20-foot diameter globe that represents the Sun. Light speed shrinks as distance does in the model, slowing to just under three miles per hour, a steady walking pace. The Moon is a few feet away, a light travel time of just over a second. Mars is 1,100 feet away, a fifteen-minute stroll. The outer gas giant, Nep­tune, is 12 miles away, which is four hours of light travel, or walk­ing in our scale model. We have shrunk space by a factor of 230 million; think of it as a map with a scale of 1:230,000,000. At the moment Voyager 1 is 48 miles away and Voyager 2 is 37 miles from Earth (figure 4.4). Proxima Centauri, the nearest star system, is 2,000 times farther away, just over 100,000 miles in this scale model. In the real universe, if it’s taken the Voyagers thirty-five years to get where they are today, it will take them around 70,000 years to get as far as the nearest star. This daunting isolation makes other worlds seem out of reach. The trajectories of the Voyagers were never intended to aim at a particular star. They will each drift past other stars as the eons pass. In approximately 40,000 years, Voyager 1 will come within 1.5 light-years, or 9 trillion miles, of an anonymous star in the constellation Camelopardalis. Mean­while, Voyager 2 is heading toward Sirius, the brightest star in the sky, and will pass within 25 trillion miles of it in 300,000 years.63 Long before then, in less than 25 years, both spacecraft will lose power for all of their instruments and become silent sentinels glid­ing through the Milky Way.

The stars seem as far away as ever. With the Space Shuttle pro­gram over and the International Space Station expensive and un­popular among most scientists, who don’t see it as a cost-effective or compelling platform for research, NASA is struggling to recap­ture the vision that fueled the Apollo program and the “Golden Age” of planetary exploration epitomized by the Voyager probes. Reaching the stars will take much greater speeds than are cur­rently possible. Traveling at the highway speed limit of 55 mph, Proxima Centauri is a 50-million-year trip. At the speed of the

Apollo spacecraft, it’s a million-year trip. And Voyager traveling at 37,000 mph would take 80,000 years to get there. Sending a probe to a nearby star in a human lifetime runs into the obdurate principles of physics. Reaching a speed a thousand times faster than Voyager requires a million times the energy, since kinetic en­ergy is proportional to velocity squared. The space program so far has been powered exclusively by chemical rockets, which are inef­ficient because they get their energy from chemical bonds. Fusion releases energy from atomic nuclei and is 10 million times more ef­ficient.64 Sending a Shuttle-sized craft to Proxima Centauri in fifty years would take about 1020 Joules, which is the amount of energy consumed in the United States in a year. Unfortunately, that would require 500,000 kg of hydrogen fuel, and fusion technology is no­where near being able to put that capability into a Shuttle-sized package.65 Ideally, there would be no need to carry and accelerate all that fuel, but solar sails don’t work efficiently when far from a star, and there’s not enough interstellar hydrogen to scoop up and use along the way. It sounds like a bridge too far.

At the speed of light, traversing the span of our galaxy would take 100,000 years. Even so, we dream of plying the eternal wastes beyond that. It is a remarkable aspiration for such a fragile spe­cies. Some engineers consider interstellar travel an impossible goal. That may be, but in launching spacecraft in the direction of Earth’s rotation, we use in a very simple way a natural energy resource of our planet. Similarly, Voyager harnessed the rotational energy of the large outer planets to sling itself from one planet to the next. In essence, through the gravity assist deployed in Voyager and other missions, we tap into a resource of the Solar System itself and, however minutely, borrow energy from, and leave our mark on, the rotation of nearby planets. Sagan, who characterized walk­ing and driving on the Moon or using gravity assist as natural steps in human evolution, wrote of Voyager: “They are the ships that first explored what may be homelands of our remote descen­dants. . . . [U]nless we destroy ourselves first we will be invent­ing new technologies as strange to us as Voyager might be to our hunter-gatherer ancestors.”66

Research on propulsion concepts for interstellar travel was un­dertaken at NASA’s Glenn Research Center from 1985 to 1992, and then the seed funding of $1.5 million ran out. One tangible result was a 740-page volume that quickly became the “bible” of propulsion science.67 Project leader Marc Millis offers a caution­ary note to NASA’s Breakthrough Propulsion Physics website:

On a topic this visionary and whose implications are profound, there is a risk of encountering, premature conclusions in the literature, driven by overzealous enthusiasts as well as pedantic pessimists. The most productive path is to seek out and build upon publications that focus on the critical make-break issues and lingering unknowns, both from the innovators’ perspective and their skeptical challengers. Avoid works with broad-sweeping and unsubstantiated claims, either supportive or dismissive.68

Yet the visionaries are alive and well, and planning for a future when we will slip the bonds of the Solar System.69 In a move that mirrors the U. S. government’s encouragement of the private sector to develop new launch capabilities, in 2011 the Defense Advanced Research Projects Agency (DARPA) initiated an annual strategic planning workshop and symposium to bring together a wide range of technologists, engineers, members of space agencies, entrepre­neurs, space advocates, science fiction writers, those working in medicine, education, and the arts, as well as the general public. Organized to foster collaboration among these groups as well as academicians and financiers, the “100 Year Starship” project isn’t immediately planning to design a starship that could travel to the stars, but is hoping to kick-start private-public partnerships that will address the technical problems of interstellar travel in the next one hundred years. Colloquia for the project focus on propulsion at light speed, medicine and space travel, possible destinations, the economic, legal, and philosophical implications, as well as the need to communicate a vision for interstellar travel through narra­tive, or storytelling.70

The 100 Year Starship initiative exemplifies the potential of an idea, suggested in mere fiction, to become reality. Flip cell phones modeled on the Star Trek communicator, desktop computers, downloadable mp3 files, iPods, and iPads were all inspired by the fiction of Star Trek. Chief engineer and mission manager for NASA’s Dawn spacecraft, Marc D. Rayman, attributes his design of ion propulsion for interplanetary spacecraft to a Star Trek epi­sode titled “Spock’s Brain” in which the term was used (figure 4.5). The ion propulsion powering the Dawn mission allows continu­ous firing of its engine so the spacecraft can attain speeds surpass­ing chemical propulsion.71 Similarly, the Qualcomm Tricorder X Prize competition, which was launched in 2012 by the X Prize Foundation for the first team to develop an inexpensive device to readily diagnose illness, is yet another Trek-inspired potential innovation.72

Futurist Ray Kurzweil thinks we are facing a critical stage in human evolution due to exponential advances in information tech­nologies, genetics, nanotechnology, and robotics. Kurzweil and others anticipate that emerging technologies in three-dimensional

printing will radically change the world as we know it. Myriad items can be produced via 3D printers, including parts for flyable aircraft printed out of plastics or complete components for build­ings that could be printed from liquid concrete. Made in Space, a fledgling company inspired by Singularity University, based at the NASA-Ames Research Center in California and co-founded by Kurzweil and Peter Diamandis, has proposed using 3D printers on the International Space Station or for establishing outposts on the Moon or Mars. In 2011, NASA funded research focused on print­able spacecraft, as well as 3D printing technologies to construct planetary surface habitats. When astronauts return to the Moon or someday walk on the surface of Mars, they may carry 3D print­ers with them and computer files for printing the tools and habi­tat components needed to build livable spacehabs using nothing more than lunar regolith or the ruddy dirt of Mars. The process of 3D printing involves a sequential layering of powdered or liq­uid plastics or metals, even potentially human cells. The medical community is interested in using human stem cells to print three­dimensional vertebral discs for repairing spine injury, or a human heart or liver as organ transplants.73

In the next thirty years, Kurzweil predicts, disease will be eradi­cated through this and other medical advances in biochemistry, gene therapy, and bio and nanotechnologies. He may be on target, given the success of researchers at MIT who are in the develop­mental stage of a drug that can destroy human cells infected with viruses while leaving normal cells untouched. So far, trials with mice eradicated H1N1, the most common flu virus in humans, and the drug looks very promising in effectively treating stomach vi­ruses and the common cold.74 Kurzweil anticipates that in the next few decades we will begin to incorporate artificial intelligence the size of a blood cell into the human body to enhance our health as well as our intellectual and computational capacities so that it will be possible to extend our lives for hundreds or thousands of years, possibly even indefinitely.75

That is not an unprecedented idea. Consider Turritopsis Dohr – nii, the immortal jellyfish discovered in 1988 by marine biology student Christian Sommer and now being researched by marine biologist Shin Kubota. Upon reaching maturity, the jellyfish reverts in age to its nascent state and then begins life again. The organ­ism’s natural life cycle doesn’t ever end. Kubota believes that in unlocking the jellyfish’s genome humans too might become im­mortal. In such a scenario, human missions to nearby stars seem nearly feasible.

If we’re not attached to sending humans, with our present need for expensive life support, nanotech might propel us into interstel­lar space even sooner. Exoplanet hunters like Geoff Marcy and Debra Fischer are studying the two brightest stars in the nearby Alpha Centauri system, the nearest solar systems to Earth and comprised of three suns. In October 2012, a graduate student at Geneva Observatory, Xavier Dumusque, detected a planet compa­rable in mass to Earth orbiting the star Alpha Centauri B. Though this exoplanet orbits too close to its star to be habitable, the gen­eral consensus among astronomers is that where there is one planet there are likely to be more. Fischer, though not associated with the discovery, has called the finding “the story of the decade.”76 Prog­ress in the detection of exoplanets has been stunning. Starting with a first detection of a Jupiter-mass object in 1995, Earth-mass exo­planets are now routinely detected both with ground-based and orbiting telescopes.

Unfortunately, studying these planets in detail from afar will be extremely difficult; think of a golf ball seen at a distance of 100,000 miles. Listen to what Marcy hopes will happen next: “NASA will immediately convene a committee of its most thoughtful space propulsion experts, and they’ll attempt to ascertain whether they can get a probe there, something scarcely more than a digital cam­era, at let’s say a tenth the speed of light. They’ll plan the first-ever mission to the stars.”77 If there is an “Earth” next door, Alpha Cen – tauri will become the compelling destination that the Moon was fifty years ago. Assuming the tricky issue of miniaturized propul­sion can be resolved, nanobot probes can be small enough that the energy requirements are tractable. They’ll take pictures of the habitable worlds and we’ll see them back on Earth within a gen­eration. These pint-sized emissaries will be able to carry far more information than the quaint phonograph records of the Voyagers; their digital storage will contain the sum of all human knowledge. With the Voyagers, we took our first tentative baby steps beyond the Solar System. The future beckons.