The Economist has an article about how the age of space exploration is over. They are a little late on this announcement, as the peak distance that any human has traveled from Earth was reached about 40 years ago. The first age of space exploration has been over for a while.

But does that mean that our adventures in the Final Frontier are over forever? I’m not so sure. After all, think about maritime exploration. For thousands of years after the first canoe was launched, the high seas remained basically empty of human ships. Once we got the technology to conquer the seas, however, we quickly did so.

What technology would be needed to conquer space? It’s clear that what we use now is too expensive for large-scale use. To reduce launch costs from Earth, we need either mass drivers, laser propulsion, or something of similar energy savings (a “space elevator“, sadly, will probably never exist).

But we need more than that, because even with cheaper launch systems, manned space exploration is extremely expensive, especially given the radiation shielding and other add-ons that we’ll need for interplanetary travel. What we need is a bigger, better energy source. With the Earth energy-constrained as it is, there are no fossil fuels to spare for Mars missions, and we’ll be lucky if we get renewables to the point where they save us from backsliding to the iron age. That means that we need nuclear fusion.

But in addition to the means, we need a reason to go. What is in space that we can use? Well, if fusion becomes a power source, we might want to mine tritium from other planets. And with fusion, terraforming of Mars might one day be possible (fusion is really that good as an energy source!).

As for interstellar travel, that is really and truly off the table without technological breakthroughs so advanced that we currently can barely imagine what they are.

So basically, no fusion, no space adventures. But if we do invent fusion, then the whole equation changes, not just for space travel, but for every conceivable human activity. Hence, we should focus our engineering efforts not on manned space travel, but on fusion power. And if we ever succeed, then the Second Age of space exploration may begin, and the Economist’s article may come to look as silly as those medieval assertions that the Atlantic could never be crossed.

Originally published by Noah Smith at his Noahpinion blog.