The US space programme is trapped in a war between financial constraints and costly inertia. For decades, the political talk was that manned space flight would continue as it always had, or become even bolder and more inspiring. Last week's final flight of the space shuttle Discovery, piggy-backing on a jumbo jet on its way to a museum, showed the reality — the glory days of NASA, for now at least, are behind it.

Next month, the agency is scheduled to take a small but significant step towards a different future. Supplies for NASA's one remaining flagship piece of manned hardware, the International Space Station, will be packed into a capsule built and sent into orbit by a private firm — SpaceX of Hawthorne, California.

Success is far from assured — a scheduled 30 April launch had been delayed as Nature went to press, and the testing schedule of the Falcon 9 launch rocket has been accelerated to accommodate the unmanned supply flight. But if the Dragon capsule does succeed in its mission to dock with the space station and then return to Earth, NASA will be optimistic that the craft could soon carry more than supplies. With the retirement of the shuttle, the agency lost its independent link to its space station, and must now rely on the Russian Soyuz system to launch new crews and bring its astronauts home again. A contract with SpaceX to send people into space in Dragon would restore some national pride, as well as reducing crucial dependence on the production and continued success of a foreign rocket. A Soyuz failure that saw the loss of astronauts would effectively close down the space station.

The impending launch of Dragon has brought conflicting reactions. Enthusiasts see a new frontier opening up for commercial operators at all levels, from suborbital research flights to full-on private hotels in space. In a World View article on page 417, Alan Stern, an unashamed enthusiast, explains how far private firms are determined to boldly go.

The great unknown remains the demand from scientists and wealthy individuals willing to pay to access space.

Then there are the curmudgeons, those who claim that the new model is a classic case of the emperor's new clothes. NASA has always relied on private companies to build its rockets and capsules, they point out, and is handing a huge subsidy to SpaceX. So this heralded new dawn is merely a reworded contract here and a shift in financial emphasis there. The dragon, they say, has no teeth.

The truth, as so often, is likely to fall somewhere in between. Although aerospace firms such as Lockheed and Boeing have always helped NASA to carry the stars and stripes aloft, they did so on a cost-plus basis, with the agency meeting all costs, however large the eventual bill, and then adding on a substantial and guaranteed profit. If Dragon shows that the private sector can do more on its own terms — from design to sourcing component parts — then the costs will come down. Scientists should welcome the move. The further NASA can get from the cost-plus contracts of the past, and the nearer to buying room on a rocket as a commodity — similar to seats on a commercial airliner — the better. NASA could then spend more of its money on the things to be launched, people and probes, rather than on rocket launches that remain as expensive as they have always been.

And as the News story on page 426 shows, the planned launch of Dragon — and its ability to bring back scientific samples under controlled conditions — is already raising hopes in the space-science community that the space station could finally begin to fulfil its potential for research.

There is strong precedent for the way the US government is trying to nurture the commercial space-flight business. In the early days of aeroplane flight, government officials handed out guaranteed contracts to aviation pioneers for carrying airmail. And in the 1970s, by both funding the developers of microchips and promising to buy the results, the US Department of Defense kick-started the computer industry.

The market for the services provided by SpaceX and its ilk is, of course, smaller. The space station is scheduled to operate — and so will need to be supplied — until only 2020. Contracts to launch satellites are lucrative, but the great unknown on the balance sheet remains the demand from scientists and from wealthy individuals willing to pay big money for tourist flights to space.

A successful SpaceX operation next month will not resolve such questions, but it would make more people ask them more seriously. And that can only be a good thing.