In 2007, China demonstrated a new anti-satellite missile by blowing one of its own defunct weather satellites to smithereens: a cloud of shards that still orbits the Earth. The message was not lost on the US, and just before Christmas last year Donald Trump launched his “Space Force”. The heavens are being remilitarised in a new superpower space race; China is planning manned Moon missions, and Elon Musk wants to build a city on Mars. But what exactly is space good for, apart from being the ultimate sniper’s nest for violence directed back at Earth’s surface? In particular, why would anyone want to live there? Science writer Christopher Wanjek’s book is a nerdily engaging (and often funny) attempt to answer that question, though he begins by challenging many of the reasons that people give for colonising space. It’s not a necessary defence against imminent extinction, he argues: pandemic disease or nuclear war might kill a lot of us, but a few would survive to carry on. Wanjek seems to underrate the danger of asteroid impact: a big enough space rock could sterilise the face of the whole planet. There is one threat, though, that everyone agrees could be curtains, which is a gamma-ray burst from an imploding star near enough to ours. When that arrives without warning (as it is bound to do at some point) and destroys the atmosphere, it might be handy to have a spare planet to live on. Colonising space is not a necessary defence against extinction, Wanjek argues: after a pandemic a few survivors would carry on Colonising Mars, in reality, is going to be quite tricky, which Wanjek proceeds to demonstrate by taking us through the trials experienced by humans living in the most extreme conditions on Earth. There are the scientists who overwinter in Antarctica, which gets nearly as cold as Mars but still has the home comforts of full Earth gravity plus breathable air, and the crews of nuclear submarines, who live – as astronauts travelling to Mars will have to do – in a completely sealed system for months on end. And that’s before we get to the extra dangers of space travel. “It’s illegal for the United States to send a human to Mars,” Wanjek notes, because the expected radiation dose on the journey far exceeds the maximum allowed for any federal worker. Earth rising over the moon’s horizon. Photograph: Nasa What’s more, zero gravity (or, properly, microgravity, because there is always gravity from somewhere) causes bone loss and eyesight deterioration as well as cognitive impairment. This we know from the experience of astronauts who have spent time aboard the International Space Station: coming back down to Earth, they can’t walk for the first day. Mars’s gravity is 0.38G or 38% that of Earth’s, which will feel hellishly heavy after six or nine months of gravity-free travelling for the first Martian astronauts. We don’t know, meanwhile, whether 0.38G is enough gravity for foetuses to gestate and become healthy babies. If it isn’t, there will never be a self-sustaining settlement on Mars. There's much delight here for the technology and science fiction enthusiast, as Wanjek goes into rich detail on rocketry But let’s suppose that gravity is not a dealbreaker. (It is baffling that Nasa is not investigating means of providing artificial gravity during a long interplanetary voyage.) Perhaps we’d like to live in a village of little domes on Mars, or the moon, or one of the moons of Saturn. Of course you’d never be able to go outside without donning a bulky spacesuit. As Wanjek observes drily, being a pioneer in space is going to be very like living in a shopping mall. But space does have its seductions. For one thing, it has limitless free energy in the form of sunlight. There is also an enormous amount of water ice and so-called “rare earth” minerals out there, which it might one day become economical to mine. Technology and science fiction enthusiasts will find much here to delight them, as Wanjek goes into rich detail on rocketry and propulsion methods, including skyhooks and railguns to fling things into orbit, or maglev trains running around manmade orbital rings. He recommends growing sweet potatoes and dandelions hydroponically to feed Mars colonists, and further into the future hollowing out comets to turn them into well-shielded interstellar spaceships. He is a sensible sceptic, yet also convinced that, in the long run, our destiny is among the stars. Some green thinkers have long despised space exploration as a money-wasting distraction from improving life on our home planet, but Wanjek is having none of this. A lot of what we know about how human activity is heating the climate, for example, is owed to space-based observations. And let’s suppose the lure of the final frontier inspires us to create the technology to “terraform” entire celestial bodies, to give them a habitable atmosphere. Well then, Wanjek remarks: “If we have the technology to terraform Mars or the moon, we’d have the technology to terraform Earth back into Earth.” Which might, as the climate changes, become our only option. • Spacefarers by Christopher Wanjek is published by Harvard (RRP £23.95). To order a copy go to Free UK p&p on all online orders over £15.