Paul Krugman, in a rare burst of sanity, has joined Gregg Easterbrook in calling for the end of the manned space program. On the other side, innumerable commentators, such as Glenn Reynolds, Charles Krauthammer, E. J. Dionne, and a parade of NASA veterans such as Jay Buckey and Buzz Aldrin, have endorsed the continuation of manned space missions, using woolly justifications like "the spirit of adventure", "mankind's destiny", and so on.

Now, I don't necessarily agree with these space travel enthusiasts, but let us suppose for a moment that I supported their goals, at least in the long run. It doesn't necessarily follow that I'd consider the best way to advance their cause right now to be continued launching of manned missions at all costs. After all, any such efforts today would involve only known, well-understood technology, and are more likely to lose public support, by failing spectacularly, than to garner votes by serving as a platform for performing the standard, tired "stupid weightless astronaut tricks" in front of a TV camera.

Real progress towards space travel would require first solving some of the daunting problems that make long-term human habitation of space so difficult. Here, for example, off the top of my head, are three avenues of scientific research, enormous progress in each of which is absolutely essential for any large-scale manned space travel to be possible. Moreover, they can all be pursued today without the cost and risk of actual manned space missions, and they also possess enormous potential for beneficial technological spin-offs quite apart from their space travel applications.

(Mostly) self-sustaining environments. The failure of the Biosphere II project demonstrates that even under the most ideal circumstances, and even given huge resources, creating an environment capable of sustaining humans with no input of resources from outside (apart from energy) is exceedingly difficult. Even inventing better technologies for partially recycling life-essential materials would not only make space travel more plausible, but may also be profitably applicable to other settings where resupply is difficult and costly, such as submarines, desert or (ant)arctic stations, and drilling platforms at sea.

Energy-harvesting. Solar energy conversion is obviously already an established research field, as is geothermal energy. In space, still other forms of energy, such as "solar wind", may conceivably be exploitable, not only by future manned missions, but by unmanned spaceships and satellites as well.

Large-scale upgradeable systems. Today's aircraft industry builds extremely complex, highly reliable systems that must be maintained over many years. Their solution is to spend enormous effort creating and thoroughly testing a single modular design, keeping it unchanged over the lifetime of the system by replacing worn parts with identical substitutes. The downside of this solution is that it does not accommodate upgrades, such as technological improvements, very well at all. Spacecraft involved in long missions may not have the luxury of airline-style maintenance practices, and need to be designed with many more contingencies in mind than the average aircraft faces. Under those circumstances, a more variable, upgradeable design may be necessary--without losing any reliability.

I predict that if these (and a few other) fundamental research problems are successfully addressed, then the advances in "core" space travel technology--rockets, orbital vehicles, and so on--needed to make space stations, moon bases and even mars missions possible will be a relatively simple afterthought.