It is a fact of human nature that our imagination often outruns the reality that is. For decades, science fiction writers and futurists alike have written about brick moons and manned projectiles shot out of gigantic cannons and torus-shaped space colonies and vast starships with exotic propulsion sources, but the reality of our species’ technological handicap at the dawn of the second decade of the 21st century makes it unlikely that we will see fully-fledged cities on Mars and human expeditions beyond the Solar System in our lifetimes. Only last week, the White House laughed off a tongue-in-cheek petition to build a real-life Star Wars-type “Death Star” as unrealistic, impractical, and pointless. Yet the humor which the Death Star petition has garnered actually underlines a stark point: that little political support exists for turning us from a spacevisiting civilization into a true spacefaring civilization. “We are still stuck in the 1960s in many ways,” laments the website BuildTheEnterprise.org, “when it comes to putting human beings into space.”
As you read these words, and as I write them, six men from three discrete nations circle the globe aboard the International Space Station. Its size and several aspects of its technology far outmatch any space station which has preceded it, but at a fundamental level it is illustrative of our failure to do much to escape the gravitational clutches of low-Earth orbit in more than four decades. Someday, though, our descendents will set sail for far-off destinations. They will walk again upon the dusty lunar regolith, they will explore the blood-red plains of Mars, they will venture further afield to the outer planets, and, at some stage, they will depart the Solar System forever to establish themselves as children of the cosmos. “Generational” starships, whose occupants are born, live their lives, and die in weightlessness, heading to some unknown and unfathomable destination, have been discussed for years; at some stage, there is little doubt that they will become reality.
The technologies needed to accomplish such incredible feats are many times more advanced than anything we presently possess, but it is good for the human spirit to ponder the possibilities of the future. According to BuildTheEnterprise.org, the appearance of the fictional U.S.S. Enterprise could be recreated as a real craft, with 1 G artificial gravity and the capacity to house upwards of a thousand people. Potential missions—unsurprisingly—would be decidedly more modest than star-hopping and velocities markedly less than “warp speed,” but could enable expeditions to the Moon in as little as three days, voyages to Mars in as little as three months, and possibly visits to the outer planets. It would be nothing less than “a sustainable roving village out in the heavens.”
Yet out in the heavens presents the first key obstacle, for the voyagers aboard such craft will be left acutely vulnerable to the devastating effects of solar and cosmic radiation. Although the Apollo lunar explorers ventured briefly beyond Earth’s protective magnetic field, they did so only for a matter of days, and it would appear suffered few lasting effects. For the remainder of the Space Age, every astronaut and cosmonaut has flown into low-Earth orbit, well within our planet’s magnetic envelope, and thus shielded from the brunt of the fierce, million-mile-per-hour solar wind. Yet even low-Earth orbit carries its own risks and we have seen in numerous occasions the impact of coronal mass ejections and solar flares upon the crew of the International Space Station. When the first explorers travel to near-Earth asteroids, or back to the Moon for long durations, or onward to Mars, they will spend far lengthier spells away from Earth’s veil of magnetic safety … and the implications, though predicted to be dire, are still imperfectly understood.
Certainly, they will have to contend with the risk of direct DNA damage, radiation-induced cancers, and degenerative tissue disorders. In 2001, the Mars Radiation Environment Experiment (MARIE) flew aboard NASA’s Mars Odyssey mission and its preliminary data suggested that inadequately shielded human explorers within the interplanetary environment for around 12-18 months—roughly the timescale for a minimum-length Mars voyage—would receive a radiation dosage of 400-900 milliSieverts per year, as opposed to an average 2.4 mSv on Earth’s surface. Solar flares are of particular concern. In 1859, the so-called “Carrington Event” saw a massive flare erupt from the Sun, travel to Earth in less than 17 hours (as opposed to the normal three or four days), and effect massive geomagnetic storms. Auroral displays were seen over the Caribbean and even over the Rocky Mountains, whose gold miners began preparing breakfast in the middle of the night, since the unearthly glow convinced them that it must be morning.
Yet, frighteningly, if a human crew had been in the Earth-Mars gulf at the time, they could have expected death in a matter of hours. On 20 January 2005, Sunspot 720 released four powerful solar flares, which reached our neighborhood within a matter of minutes. As well as carrying the potential to interfere with radio communications and short-circuit satellites and computers, such events are capable of penetrating a space suit and killing its occupant. “An astronaut on the Moon,” said solar physicist Robert Lin of the University of California at Berkeley, “caught outdoors on January 20th, would have had almost no time to dash for shelter.” Any vehicle travelling beyond the Home Planet would require a multiple-walled hull, perhaps fashioned from hydrogen-based plastics or even utilizing the spacecraft’s own liquid hydrogen propellant dewars as an insulator and a resistor of micrometeoroid penetration. A dedicated “storm shelter,” into which the crew could retreat in the event of coronal mass ejections or flare events, would be essential.
Artificial gravity has long been recognized as an important facet in enabling humans to function away from Earth in a comfortable environment. The absence of gravity has been shown over the past half-century to cause debilitating space adaptation syndrome (“space sickness”), as well as triggering decreases in bone density and calcium loss. During the final mission of Space Shuttle Columbia in early 2003, a series of Canadian experiments investigated the “thinning” and weakening of rats’ hind limbs in microgravity. Since rats’ bones tend to react much more quickly than human ones, a 16-day mission for them represented the cumulative effect of several months in space for us.
Several techniques have been theoretically pioneered for creating a workable form of artificial gravity. On NASA’s Gemini XI mission in September 1966, astronauts Pete Conrad and Dick Gordon achieved a measure of artificial gravity when they established a tethered connection between their own craft and rotated it around the Agena XI target. The intent of such an exercise was to learn how to keep two vehicles in formation, without fuel inputs or control action, and although not wholly successful the astronauts did test a tiny amount of artificial gravity. Neither man physiologically felt the effect of gravity, but at one stage they were able to place a camera against Gemini XI’s instrument panel, let go … and it drifted, in a straight line, to the back of the cabin, parallel to the direction of the tether.
Centrifugal force has long been the mainstay of science fiction writers and futurists as a leading method for generating artificial gravity. Several of the earliest “true” space station designs, from the 1950s and 1960s, envisaged “rotating” complexes, possibly with a habitat joined by a tether to some form of counterweight. Other concepts include continuous acceleration in a straight line, thereby forcing internal objects—such as the crew—in the opposite direction, or the installation of ultra-high-density masses capable of generating their own magnetic fields (such as a captured asteroid, perhaps), or the use of powerful magnets. At present, such technologies remain broadly at the theoretical level and practical methods remain some distance into the future.
Of course, the most visibly dramatic features of deep-space machines or starships are the propulsion sources which they will employ. It has long been recognized that the immense distances between the stars—and, for that matter, between the planets, too—render technologies beyond ordinary chemical methods enormously useful. Although ion propulsion has been demonstrated operationally, far from Earth, by missions such as Deep Space 1 and Dawn, advances of several degrees of magnitude will still be required to achieve the kind of velocities necessary for interstellar travel. Solar sail technology is a possibility, and concepts such as the Variable Specific Impulse Space Magnetoplasma Rocket (VASIMR) have risen from the drawing board and may eventually end up as test hardware on the International Space Station as early as 2015, whist others, such as real faster-than-light warp drives, are further into the future.
VASIMR, developed since 1977 by plasma physicist and former astronaut Franklin Chang-Diaz, utilizes radio waves to ionize and heat propellant, thereby generating plasma which is accelerated using magnetic fields to produce thrust. Although its low thrust-to-weight ratio is insufficient to launch payloads directly from Earth, it may see cost-effective applications in the delivery of cargo to lunar bases, the orbital repositioning of satellites, the compensation of atmospheric drag suffered by the ISS … and fast deep-space missions. In fact, NASA Administrator Charlie Bolden—who flew twice into space with Chang-Diaz—has described VASIMR as a breakthrough technology which may see a 2.5-year mission to Mars cut by more than four-fifths. Several successful laboratory tests of subscale versions of the engine led to an official contract between Chang-Diaz’s company, Ad Astra, and NASA in December 2008 to fly VASIMR to the space station. This flight is tentatively scheduled for 2015, possibly aboard Orbital Sciences’ Antares rocket.
Other concepts for reaching deep space and beyond with humans have come and gone over the years. Among the earliest was Project Orion, initiated in 1958, which would have been propelled by a series of exploding atomic bombs behind the spacecraft. This “nuclear pulse propulsion” technique was deemed so violent that it could only be performed externally to the spacecraft and the exhaust velocity was predicted to be in the range of 12-19 miles per second. Supporters of Orion-type missions stressed its usefulness for staging voyages to the planets, but the 1963 Partial Test Ban Treaty lost political support and sounded its death knell, in view of concerns about radiation fallout from its power source. Still others rose and fell over the years, including the British Interplanetary Society’s Project Daedalus and the U.S. Navy’s Project Longshot. Most recently, in January 2012, the 100-Year Starship was proposed as a project to examine the requirements and groundwork needed to achieve such a mission. Its vision is that such a mission will set sail within the next century.
There are some scientists who doubt that interstellar missions are practically possible, so vast are the distances involved, the flight durations needed, and the sheer quantities of propellants and energy demanded … even to the closest star, Alpha Centauri. Brice Cassenti of the Department of Engineering and Science at Rensselaer Polytechnic Institute was quoted by Universe Today in August 2008 as stating that “at least 100 times the total energy output of the entire world [in a given year] would be required for the voyage.” Others perceive launching a mission which cannot be completed within 50 years as pure folly, for the logical reason that our civilization is on an increasing curve of propulsion system velocity and resources should instead be diverted into building a better means of propulsion. In other words, a “slow” spacecraft, launched at a given time, would be quickly overtaken by a “faster” spacecraft built many years later using more mature technology.
However, such notions have been rejected by Andrew Kennedy in his paper on the dangers of the so-called “Wait Calculation,” published in the Journal of the British Interplanetary Society in 2006. Kennedy argued that from any point on a deep-space journey there is a “minimum” to the total time to the destination, even with continuing growth in the velocity of subsequent travel technologies, and that voyagers can still have a realistic chance to reach their target and not be overtaken by a later, more advanced civilization. Significantly, Kennedy judged the world’s annual economic growth rate of approximately 1.4 percent and a corresponding growth in the velocity of travel and used this data to predict that a vehicle launched today would take many hundreds of years—he cited 1,100—to reach Barnard’s Star, a mere six light-years from Earth.
Interplanetary travel is possible and has been accomplished dozens of times by our species over the past five decades. Interstellar travel, at some stage in the continuing curve of our evolution, will also come, as should the markedly more difficult intergalactic travel—crossing the vast gulf of gas and dust and emptiness between galaxies—but it will come at a point far beyond our own existence or those of many generations of our children and grandchildren. Voyager 1 has spent over 35 years in space and has traversed more than 123 astronomical units, or 11.4 billion miles, across the Sun’s realm. Presently moving at over 38,000 miles per hour, it has covered less than one-sixth-hundredth of a light-year and its progress is a paltry one-eighteen-thousandth of the speed of light. Journeying to Alpha Centauri at this slowpoke pace would take tens of thousands of years. Of course, more modern technologies than the Voyagers could expect to reduce this to a handful of millennia, but therein lies another inescapable reality.
To reach the nearest stars with humans will require us to leave our home world forever and become a truly spacefaring civilization for the first time. The occupants of such immense vessels will be aboard “Generation Starships,” so called because generations will come and go in the quest to reach their destination. Children will be born and will grow to adulthood and mature into old age and die in the absence of Planet Earth, surrounded for the most part by the blackness of deep space, and a terrestrial surface beneath their feet will be unknown to them. Some argue that human nature would make it difficult for such a concept to be realized, with massive sociological and biological issues waiting to be addressed. Religion alone has proven such a divisive factor for thousands of years that it is hard to suppose that it will disappear on such a ship. One thing that will disappear, and disappear quickly, will be the Earth itself. The world which the crew of the first starship once called “home” will fade into a distant memory.
They will no longer be children of Earth, but children of the stars.