Crewed missions to Mars. Space tourism. Lunar bases. Asteroid mining. Half a century on from the Moon landings we at last seem to be moving into a second golden age of space exploration.
The work of the intervening decades should not be overlooked. Robotic missions have revealed the furthest reaches of the Solar System in exquisite detail. The Mir and International Space Stations have undertaken extensive research on the possibility of long-term extraplanetary habitation. The Hubble Telescope has captured crystalline images of the depths of our galaxy, and beyond. And despite its troubles the Space Shuttle programme proved the concept of reusable space transportation.
But few of these achievements have sparked the visceral excitement of the age of Sputnik, Gargarin and Apollo. Confident expectations that the Moon landings were simply the prelude to human exploration of Mars and the outer planets dissolved as the economic crises of the 1970s broke public willingness to pay for it, and the Challenger and Columbia shuttle disasters vividly highlighted the possible human cost.
But now the space race is back on as a new generation of affordable technologies reopens the prospect of ambitious human exploration. And this time the track is much more crowded. NASA is still a major player, as is, to some extent, Roscosmos, Russia’s successor to the legendary Soviet space programme. But today they are joined by the space agencies of China, Japan, India and the European Union, and a wave of commercial enterprises, many funded by Silicon Valley entrepreneurs inspired by childhood memories of the age of Apollo.
It’s becoming ever harder to disentangle the confusion of space initiatives. We’re promised a new era of increasingly affordable space tourism, beginning with commercial flights that will orbit the Earth. We are told that astronauts will soon be back on the Moon not only to explore but to establish long-term lunar settlements. Near Earth asteroids are going to be mined for rare materials. And, of course, we’ll be going to Mars – possibly within the next 15 years.
It’s difficult to know what’s actually likely to happen and what’s being spun for national prestige and commercial gain. The Future of Humanity, the new book by New York physics professor and popular science writer Michio Kaku, includes its share of exotic speculation, exploring technologies that might make possible not just travel to Mars but the eventual colonisation of the Solar System and the galaxy beyond. But as with his previous work exploring limits of scientific enquiry Kaku’s futurism is filtered through an informed scepticism about what is and isn’t likely to be economically or intellectually viable.
It’s that capacity for discernment that makes the book valuable as a guide to what our future will probably look like a hundred years or so from now, a future that, even when parsed of its most exotic speculations, promises radical innovation. The vector of technological development makes it entirely possible that by the end of the century our economic ecosystem will extend beyond the Earth to the Moon, near-Earth asteroids, and, quite probably, Mars.
To Mars?
As with the first age of space exploration Kaku expects NASA, for all of the false starts it has suffered in recent decades, to play a pioneering role, suggesting that the agency has regained its focus by orienting its resources towards a human mission to Mars, restoring the momentum that propelled the Apollo programme.
Last year NASA set out a systematic roadmap for realising the mission sometime in the 2030s. The first step will be to put a space station, the Lunar Orbital Platform-Gateway (LOP-G), in permanent orbit around the Moon. The construction of the station, conceived as a portal that in time will allow access to the whole of the Solar System, is scheduled for completion within the next decade. The LOP-G will serve as the assembly point for a spacecraft, the Deep Space Transport, capable of a return journey to Mars.
After a series of test orbits around the Moon the Transport will head to the Red Planet and on reaching its destination will stay in orbit while a crewed lander is sent to the surface. The team will spend several months there, setting up solar panels to provide energy for a simple base from which they will conduct experiments, including searching for minerals, ice and any evidence of microbial life, before reascending to the Transport and making the return journey.
It’s a carefully conceived strategy designed, as with the Moon landings, to realise science fiction through a series of methodical steps. But NASA’s cautious incrementalism means the agency’s astronauts may not be the first to reach Mars. Elon Musk’s SpaceX is set on a much more direct approach, working towards a super rocket capable of travelling straight to Mars from Earth some time in the next decade. Musk envisages that mission as the precursor to a process of colonisation, speaking of a fleet of rockets, each carrying some 100 colonists, embarking on one-way journeys to Mars. The early settlers would include Musk himself, who has said he rather likes the idea of dying on the Red Planet.
SpaceX’s record gives some of Musk’s scenarios real credibility. In 2012 the Falcon became the first private sector rocket to ferry supplies to the International Space Station. SpaceX has pioneered reusable rockets, consistently landing the Falcon and its boosters back on Earth after delivery of their payloads. Earlier this year the company carried out a successful test mission of the Falcon Heavy, the most powerful rocket yet launched. And with a business empire at the forefront of developments in solar energy, automation and artificial intelligence Musk has the capacity to develop a technological infrastructure capable of supporting a Martian settlement.
Kaku’s analysis suggests it is quite likely that both NASA and SpaceX will reach Mars, but that the challenges of establishing long-term settlements might be too great with today’s technology. Quite simply, Mars is a very long way away. Even at the closet point in their orbits Earth and its neighbouring planet are separated by some 55 million kilometres. With current propulsion technology a one-way voyage will take at least nine months, and a return trip two years. Such a voyage would present severe physical and psychological challenges. During the journey the ship and its crew would be subject to sustained exposure to the harsh environment of space, with its radiation belts and solar winds exposing the travellers to an increased risk of cancer and other diseases. The tiny micrometeors that shoot through the Solar System at speeds of 40,000 miles per hour would, even if no more than a centimetre or two wide, be able to rip through a spacecraft’s hull causing rapid depressurisation (a risk that could be mitigated though not eliminated by organising the ship into modules which could be sealed off for repair if hit).
Then there are the extreme rigours of the Martian environment. Mars is brutally cold, with an average temperature of -55 centigrade. The pioneers’ base and equipment would be periodically overwhelmed (though not destroyed) by ferocious dust devils that can reach the height of Mount Everest. The astonauts would have to carry out their explorations within a weak, low gravity atmosphere offering little protection against radiation.
And yet the Martian environment does offer the essential elements for longer-term settlement. Though far distant from Earth Mars is within the inner Solar System, receiving sufficient sunlight to offer pioneers a reliable source of solar energy. The substantial quantities of ice deposited a few feet below the surface and in the planet’s polar regions promise a plentiful reservoir of water, oxygen and hydrogen that could be harvested for air and fuel. And the abundance of iron oxide on the surface that gives the planet its distinctive colour offers the base material for a ready supply of iron and steel.
Indeed the presence of water may in time make possible the realisation of the old sci-fi dream of terraforming the planet. If its ice caps could be melted water vapour would be released that could, on mixing with the atmosphere’s plentiful carbon dioxide, set in motion a greenhouse effect that may create a suitable climate for the cultivation of certain plants, making possible self-sustaining farms able to support substantial human settlement.
The verdant Moon
So it may be possible to colonise the Mars, one day. But the planet’s remoteness, and the limits of current technologies for interplanetary travel, shift the likelihood of long-term settlement to some indeterminate horizon. There is another celestial body that offers the serious prospect of settlement, now: the Moon.
The prospect of returning to our closest neighbour has been given new impetus in recent years by the revelation that it is not quite the lifeless rock of popular imagination. Like Mars, the Moon has ice. Large quantities of it have been detected in the shadows of mountain ranges and craters in the satellite’s southern hemisphere, deposited hundreds of millions of years ago by comets. Recent research also shows that surprising quantities of oxygen are embedded in the lunar soil.
The promise of indigenous sources of air, water and fuel – and of course, sunlight ready to be harvested by solar farms – allows us to envisage sustainable lunar bases resourced with sufficient oxygen and water for the cultivation of food supplies. And those bases could in time serve economic as well as scientific purposes: it is likely the Moon contains considerable deposits of minerals and rare earths that could be mined.
As with Mars the prospect of settling the Moon has attracted both public and private sector interest. NASA’s LOP-G will be ideally placed to serve not only as a portal to Mars and beyond but as a base for supplying lunar missions and settlement. And China has already developed advanced plans for long-term lunar settlement. This year the China National Space Administration will land the first rover on the far side of the Moon, which in prospecting the Aitken Basin in the south pole region for ice will serve as a scoping mission for a subsequent crewed exploration to the area and the construction of permanent station.
The Moon is also attracting commercial interest. Moon Express, a Silicon Valley venture, is seeking to position itself as a future lunar-mining enterprise, and Blue Origin, an Amazon spin-off, has ambitions to ship supplies to future settlements, extending Amazon’s formidable logistics infrastructure beyond the confines of the Earth.
90 million tonnes of platinum
It seems that as well as allowing us to begin the process of settling the Moon current technology will enable us to prospect other bodies that pass close to the Earth: asteroids. We still really don’t know how many asteroids might be out there: the Asteroid Belt between Mars and Jupiter, believed to be the remnants of planet that failed to form early in the history of the Solar System, may contain hundreds of millions of them. Some 16,000 whose orbits take them relatively close the Earth have so far been identified and it is likely there are many, many more. And it’s certain that many of them have exceptional commercial value, being formed of abundant quantities of iron, nickel, carbon and cobalt, and containing significant deposits of valuable earths and metals such as platinum, palladium, rhodium, ruthenium, tridium and osmium. In July 2015 a 900 metre wide asteroid that came within a million miles of Earth was estimated to contain 90 million tonnes of platinum, giving it a nominal value of around $5.4 trillion.
If an asteroid can be nudged out of its natural orbit and put in stable orbit closer to the Earth or the Moon it could be mined. NASA has a programme, the Robotic Asteroid Prospector, that will analyse the feasibility of resource extraction, but commerical interests are making most of the running, notably Planetary Resources, another Silicon Valley enterprise established in 2012 with the backing of luminaries including Google’s Larry Page and Eric Schmidt and the film director James Cameron. The company, which estimates that the platinum within an asteroid only 30 metres wide could be worth $25 to $30 billion has already identified a dozen near-Earth asteroids as prime candidates for extraction.
And because asteroids, like the Moon and Mars, seem to contain significant amounts of ice, they too could offer supplies of air, water and fuel. It may even be possible one day to establish a mining ecosystem in the Asteroid Belt itself: Ceres, by far the largest asteroid, about a quarter the size of the Moon, might be a suitable base for a permanent station.
The political, as well as technological and financial conditions are falling into place for commercial space exploration. The 1967 Outer Space Treaty banned nations from claiming ownership of celestial bodies. But, written during a different age, when space seemed open only to a handful of nations, it said nothing about the possible exploitation of extra-planetary resources for commercial purposes.
The Treaty is now, it seems, in much need of revision. In 2016 the US government passed the US Space Resource Exploration and Utilization Act, recognising the rights of American firms to seek, obtain and use space resources. And a year later it granted Moon Express the right to send robotic spacecraft to the Moon. It seems inevitable that future international space agreements will contain provisions formalising some right of exploration for commercial entities.
The gas giants beyond
The first half of Kaku’s book is of great value in cutting through the hyperbole and helping us discern the likely outlines of the emerging space economy. We will return to the Moon and establish a permanent base. We’ll start extracting resources from the Moon, and from near Earth asteroids. Astronauts will travel to Mars and establish a simple base station. In time, as space travel becomes more efficient, it will be possible to expand that settlement and begin the process of exploring the planet’s material wealth. Much that seems quite likely within the next century or so. But Kaku is on much more speculative ground in the book’s second half, when he investigates the possibility of integrating the further reaches of the Solar System into that infrastructure.
The prospect is tantalising. The outer planets, Jupiter, Saturn, Uranus and Neptune are beautiful but uninhabitable gas giants. But robotic missions in the past 20 years to the Jovian and Saturnian systems have revealed much more of the extent of the scientific, aesthetic and quite possibly economic interest of their many moons.
Saturn’s Titan, for example, as revealed by the Cassini programme, is an intricate patchwork of ponds, lakes, ice sheets and landmasses, a distant Earth transposed to a remote alien key, flowing with liquid methane rather than water. The satellite seems to offer the constituent elements for some future settlement: its ice could be harvested, and the oxygen extracted combined with methane to create an inexhaustable supply of usable energy. Remarkably, some of the other moons are in fact abundant with water. Jupiter’s Europa and Saturn’s Enceladus have substantial subterranean seas, kept liquid despite the freezing surface temperatures by the gravitational pull of their parent planets generating friction and heat within their cores.
The Juno and Cassini missions indicate that the Jovian and Saturnian systems promise the material base for sustainable human settlements. But like Mars they are so very far away. Getting to Mars is going to be hard, but Jupiter is some 530 million kilometres further away from Earth, and Saturn more than 1,200 million kilometres. Even if Jupiter and Saturn could be reached and basic settlements established, it would be immensely hard to develop a supply chain that would integrate them into a space economy established around the inner Solar System.
Fusion rockets and light sails
It seems that any viable space economy extending to Mars, and certainly the gas giants, depends on the development of more powerful technologies for propelling spacecraft than we have now. Kaku offers a thorough, but ultimately somewhat wistful, survey of the current status of the physics of interplanetary travel.
At least one concept is already proven, the ion engine system that will be used by NASA’s Deep Space Transport. The Transport’s flanks will be equipped with gigantic solar panels that will capture and convert sunlight to electricity, which in turn will strip away the electrons from xenon gas creating ions that in the process of being steadily discharged from the ship’s engines will generate thrust. Unlike chemical engines, which can only fire for a few minutes, ion engines smoothly build up acceleration from a standing start in space. Ion engines promise to power a new generation of spacecraft, offering an efficient and elegant means of interplanetary travel. But it is unclear whether they will ever be fast enough make travel to the further reaches of the Solar System possible in weeks or months rather than years. The Deep Space Transport is projected to take nine months to reach Mars: Jupiter is 10 times further away.
Unfortunately no other viable propulsion technologies have yet been discovered. Kaku explores a series of beautiful, but unproven, concepts for significantly faster means of transport, the most enticing of them, perhaps, the possibility of nuclear fusion propulsion. The Project Daedalus study undertaken in the 1970s showed that a fusion engine of sufficient size – in this case weighing 54,000 tons and 625 feet long – could reach a velocity of about 12% the speed of light, fast enough to reach Mars within a few hours, and the edge of the Solar System in a few days. Unfortunately the concept of nuclear fusion has not yet been demonstrated.
Another idea, sublime in its simplicity but unproven, is that of ramjet fusion, which imagines a spacecraft generating its own fuel from the stuff of space itself. As it travelled a ramjet ship would gather hydrogen gas through a funnel system, which it would process on the fly through a fusion reactor generating sufficient energy to propel it at great speed.
Then there’s the light sail concept, which pictures spacecraft equipped with solar sails being propelled through space by picking up light pressure from starlight or lasers, much like an ocean-going vessel harnesses the wind. The craft would be propelled at up to 20% the speed of light towards its destination by surfing a beam of light generated by a powerful bank of lasers.
It is another beautiful, troubled idea. A light sail craft might reach its destination, and do so at speed, but would simply fly by: unless some method can be discovered that would make it possible to reverse the direction of travel of a craft propelled by laser it would shoot past like a bullet, on into the void. Another issue concerns the massive energy that would be necessary to generate a sufficiently powerful beam to set a light sail on its way, which would need to be equivalent to that produced by 100 nuclear power plants. And then there’s the problem of size: any sail able to capture sufficient light to propel a craft large enough for crewed exploration would have to be truly enormous – thousands of kilometres wide.
For these reasons light sails seem more suitable for uncrewed exploratory missions to the outer reaches of the Solar System and beyond. Indeed, the Breakthrough Starshot initiative, whose backers have included the late Stephen Hawking, has developed advanced, costed proposals for sending a cluster of light sail ‘nanoships’ to nearby star systems. These tiny craft, perhaps just an inch or two in size, would be equipped with all of the cameras, sensors, chemical kits and solar cells necessary to send back images and data about the stars and planets they pass. The project estimates that a solar sail could reach the closest star system to us, the Centauri system, about 4.3 light years away, within 20 years.
Ad Astra?
In the absence of any known technology to make it possible, Kaku’s closing chapters speculating about the possibility of crewed exploration of stars systems beyond our own read like science fiction: hard science fiction, with some basis in theory, but science fiction nonetheless.
It may be possible to move painstakingly from star system to system if we are prepared to embrace the concept of multigenerational travel. Perhaps, as many sci-fi writers have imagined, we might be able to construct a starship able to sustain generations of aspirant pioneers during the hundreds of years it would take, with current propulsion technology, to reach neighbouring systems. It might, as the physicist Freeman Dyson has suggested, be possible to ease the challenge somewhat by using comets as interstellar stepping-stones, just as the ancient Polynesians navigated the Pacific by using islands as interim settlements. Our Solar System is surrounded by a sphere of comets, the Oort Cloud, that extends as far as three light-years from the Sun, more than halfway to the Centauri system. If other systems have their own Oort Clouds perhaps the comets, with the water and ice they provide, might serve as way stations to the stars.
If that sounds rather too fantastic perhaps we could simply remove the most significant impediment to interstellar exploration: the human body. Kaku considers at length the prospect of translating human consciousness to pure information which could be ‘uploaded’ to some form of supercomputer or neural network integrated into a robotic craft, maybe some kind of Breakthrough Starshot-style nanoship. It could even be possible to bypass a spacecraft altogether through the two-stage process of what Kaku calls ‘laser porting’. First, a robotic ship would travel through the abyss to a destination star system. Then a pattern of information constituting a digital consciousness would be integrated into a laser beam directed to the ship. On arrival the information would be downloaded into the ship’s computer, where it could contemplate the scene. The ship might even be equipped with robot avatars the intelligence could enter to attain material form.
In the course of elaborating the increasingly fantastic speculations that close out the book Kaku does touch on existing or near-future technologies we can use to facilitate the development of today’s space economy. Advances in AI, machine learning and robotics, and rapid developments in quantum computing, are opening the way for new generations of intelligent machines that, as they become ever more able to operate without direct human oversight, will be able to smooth the way for settlements on the Moon and beyond, mapping hostile terrains, setting up solar farms, unpacking and constructing base stations and beginning the process of mining for water and minerals. The establishment of pioneer settlements could be partially or even fully automated, ensuring the essential infrastructure for longer-term colonisation is in place before humans even touch down on the surface.
And in the next few decades it may be possible to construct those settlements from a new super-light, super-strong material, graphene, a single layer of tightly meshed carbon atoms 200 times tougher than steel. Graphene promises to be an ideal material for robust, elaborate space architectures, and for another innovation long assumed to belong to the realms of the purest science fiction, space elevators reaching 100 kilometres from the surface of the Earth into space.
The idea has never been quite as esoteric as it sounds. Physics has long established that if a sufficiently tall tower could be kept upright by the centrifugal force of the spinning Earth, just as a spinning ball on a string does not fall to the floor. The sticking point has always been that of conceiving of a material strong enough to withstand the pressure such a massive structure would exert. But graphene can be rolled into carbon nanotubes that would could withstand the pressure, making it possible to conceive of the construction of launching mechanisms that would end the expensive requirement to use chemical rockets to launch craft into space.
Biological engineering is another rapidly developing technology that may play an important role in space exploration over the next few decades. Though it’s unclear whether the human body might ever be able to withstand the rigours of long distance space travel, bioengineering suggests ways in which it could be reconfigured in useful ways for the purposes of settling our Solar System. Our bone structure, for example, could be strengthened and enhanced to withstand long gravity environments, and our respiratory systems to require less oxygen.
Asimov’s ghost
By the end of the book Kaku’s sights are set on a far distant future in which we have developed the capacity to harness the full energy of our Sun for our extraplanetary ambitions. Turning to the system devised by the Soviet futurist Nikolai Kardashev to rank civilisations on the basis of their capacity to harness energy, Kaku positions us as an aspirant Type I culture, closing in on the capacity to harvest the total energy of the sunlight that falls on our planet. Kardashev imagined a Type II civilisation developing the capacity to harness the full energies of their home star system, and finally, a Type III civilisation that had attained such a profound understanding of the laws of physics that it would be able to bend the energies of stars and even black holes to its purposes. The concentration of such fabulous energies might allow it to bend and puncture the fabric of space-time, opening the prospect of faster-than-light travel and even the construction of cosmic worm holes, opening access to parallel universes.
In the end Kaku is a romantic, determined to believe that if science fiction can imagine it then – one day – we will be able to do it. The book is haunted by frequent references to two great classics of sci-fi, Isaac Asimov’s Foundation trilogy and Olaf Stapledon’s Star Maker. Asimov pictures a far-future interstellar empire that has colonised so much of the galaxy it has become careless of its origins, overreaching itself in the manner of the ancient Romans. Stapledon imagines a god-like being, the Star Maker, able to stand outside space-time itself and engineer universes with different physical laws. Kaku imagines our distant ancestors achieving similar access to a ‘multiverse’ from which universes emerge, and moving to a new cosmos before the death of our own:
Maybe someday we can become like the Star Maker and from our vantage point in hyperspace look down and see our universe, coexisting with other universes in the multiverse, each containing billions of galaxies. Analysing the landscape of possible universes, we may choose a new universe that is still young, that can provide a new home. We would choose a universe that has stable matter, like atoms, and is young enough that stars can create new solar systems to spawn new forms of life.
For the most part, however, Kaku’s is a sceptical romanticism, bounded by the scope of present technology and the known laws of physics. It should be noted that this is not a political book. There’s not much here about the environmental challenges that threaten our collective future, nor about the ethics of extending capitalism beyond Earth. But that was never its purpose. The Future of Humanity offers a comprehensive, accessible guide to the foreseeable future of space exploration, helping us to navigate the stranger shores of futurism and discern where we will be a few hundred years from now. Beyond that, we simply don’t know.
Image: Crop from the cover of The Future of Humanity by Michio Kaku, Penguin Books.