How big is the Earth? Any encyclopedia will give you an answer: Its equatorial diameter is 7,926 miles. Ah, but then there is the atmosphere. Should that count? Perhaps the planet's true diameter is actually nearer 8,060 miles, including all its air. But even that may no longer be an adequate measure. For the Earth now reaches farther still.
The vacuum surrounding it buzzes with artificial satellites, forming a sort of technosphere beyond the atmosphere. Most of these satellites circle only a few hundred miles above the planet's solid surface. Many, though, form a ring like Saturn's at a distance of 22,300 miles, the place at which an object takes 24 hours to orbit the Earth and thus hovers continuously over the same point of the planet.
Viewed this way, the Earth is quite a lot larger than the traditional textbook answer. And viewed this way, the Space Age has been a roaring success. Telecommunications, weather forecasting, agriculture, forestry and even the search for minerals have all been revolutionized. So has warfare. No power can any longer mobilize its armed forces in secret. The exact location of every building on the planet can be known.
Yet none of this was the Space Age as envisaged by the enthusiastic "space cadets" who got the whole thing going. Though engineers like Wernher von Braun, who built the rockets for both Germany's Second World War V2 project and America's Cold War Apollo project, sold their souls to the military establishment in order to pursue their dreams of space travel by the only means then available, most of them had their eyes on a higher prize. "First Men to a Geostationary Orbit" does not have quite the same ring as First Men to the Moon, a book von Braun wrote in 1958. The vision being sold in the 1950s and 1960s, when the early space rockets were flying, was of adventure and exploration.
The facts of the American space project and its Soviet counterpart elided seamlessly into the fantasy of Star Trek and 2001: A Space Odyssey. Other planets may or may not have been inhabited by aliens, but they, and even other stars, were there for the taking. That the taking would begin in the lifetimes of people then alive was widely assumed to be true.
No longer. It is quite conceivable that 22,000 miles will prove the limit of human ambition. It is equally conceivable that the fantasy-made-reality of human space flight will return to fantasy. It is likely that the Space Age is over.
Today's space cadets will, no doubt, oppose that claim vigorously. They will, in particular, point to the private ventures of people like Elon Musk in America and Richard Branson in Britain, who hope to make human space flight commercially viable. That market seems small and vulnerable. One part, space tourism, is a luxury service that is, in any case, unlikely to go beyond low-Earth orbit at best (the cost of getting even as far as the moon would reduce the number of potential clients to a handful). The other source of revenue is ferrying astronauts to the benighted International Space Station, surely the biggest waste of money, at $100 billion and counting, that has ever been built in the name of science.
The reason for that second objective is also the reason for thinking 2011 might, in the history books of the future, be seen as the year when the space cadets' dream finally died. It marks the end of America's space shuttle program, whose last mission launched Friday. The shuttle was supposed to be a reusable truck that would make the business of putting people into orbit quotidian. Instead, it has been nothing but trouble. Twice, it has killed its crew. If it had been seen as the experimental vehicle it actually is, that would not have been a particular cause for concern; test pilots are killed all the time. But the pretence was maintained that the shuttle was a workaday craft. The technical term used by NASA, "space transportation system," says it all.
But the shuttle is now over. The International Space Station is due to be de-orbited, in the inelegant jargon of the field, in 2020. Once that happens, the game will be up. There is no appetite to return to the moon, let alone push on to Mars, the El Dorado of space exploration. The technology could be there, but the passion has gone.
The future, then, looks bounded by that new outer limit of planet Earth, the geostationary orbit. Within it, the buzz of activity will continue to grow and fill the vacuum. This part of space will be tamed by humanity, as the species has tamed so many wildernesses in the past. Outside it, though, the vacuum will remain empty.