Clarke wrote this book in the last good year of believing. 1968: Apollo 8 hadn't yet orbited the Moon, but the trajectory was locked in, and a man of Clarke's temperament could reasonably extrapolate from that trajectory a future of permanent lunar bases, crewed missions to Mars by the 1980s, and cities — he actually says cities — on Mercury and Pluto. The Promise of Space is not prophecy. It is engineering optimism committed to paper at the exact moment when engineering optimism had the most evidence behind it and the least experience of what comes after. What comes after, it turns out, is budgets.

The book's prescience is real but narrow. Clarke understood that communications satellites would reshape civilization, which is unsurprising given that he essentially invented the concept two decades earlier. He grasped that space technology would become commercially indispensable before it became exploratorily routine. He acknowledged the political motivations tangled into the space race with more candor than many of his contemporaries, noting that national prestige was the engine and science was, at best, the payload. This observation has aged into something like a law of nature. What he could not see — what almost no one in his cohort could see — was that the political will would evaporate so completely after Apollo, that decades would pass in a kind of institutional paralysis, and that when ambition finally returned to spaceflight it would arrive wearing corporate logos. SpaceX, Blue Origin, the entire privatization of launch infrastructure: Clarke's framework has no room for this. He imagined governments growing bolder. Instead, governments grew tired, and billionaires grew restless.

The blind spots are era-typical but worth naming. There is no climate crisis in Clarke's future. Earth is a launch pad, not a patient. There is no developing world with its own space agencies; India's Chandrayaan missions, the UAE's Hope orbiter — these would have been unintelligible to the geopolitical map Clarke was reading. Women and non-Western scientists are functionally absent from his narrative, not out of malice but out of the profound unselfconsciousness of a British man writing in 1968 about what "mankind" would achieve. The word sits there on every other page, doing its quiet work of circumscription. And Pluto, of course, is no longer a planet. Clarke wanted to build cities on it. We sent a probe past it in 2015 and took photographs. The photographs were worth it. The cities were not coming.