Forget huge, expensive rockets. A plan being examined by a US government panel would allow smaller, cheaper rockets to fly to the moon and beyond by stopping off at an "orbiting gas station".

With conventional rockets, many tonnes of fuel are needed on such missions for each tonne of payload. Sending astronauts or the heftiest robotic probes to these distant destinations therefore requires huge launchers.

That may be about to change. The panel convened by order of the White House to assess NASA's plans for the future of human space flight - including the project to send people back to the moon by 2020 - is pondering a radical idea to set up orbiting depots at which relatively small, inexpensive rockets could stop off to pick up fuel. The potential benefits of such a scheme are detailed in a white paper submitted last week by Jonathan Goff, an engineer with Masten Space Systems in Santa Clara, California.

This would allow NASA to mount moon missions without spending billions of dollars developing the gigantic Ares V rocket. Existing, less powerful rockets such as Boeing's Delta IV or Lockheed Martin's Atlas V would suffice, he says.

Prior to each moon mission, fuel would be ferried to the orbiting depot by these or even smaller rockets operated by private companies. Competition for this work would drive down costs and spur development of more efficient launch vehicles, Goff argues. "Until we lower the cost of transportation to space, we're never going to see serious off-world exploration," he says.

On 30 July, the panel's subcommittee on exploration beyond low-Earth orbit came out strongly in favour of creating fuel depots in space as a way to facilitate exploration beyond low-Earth orbit. At a public meeting of the panel in Cocoa Beach, Florida, the subcommittee proposed that depots be part of every space exploration scenario that the full committee puts forward in its final report. Private companies would compete for the job of ferrying fuel to the orbiting depot

It remains to be seen whether the panel will back the idea in its final report, to be published at the end of August. "This panel is probably the best chance depots are going to have in the next 10 years to get actual NASA support and funding," Goff says.

Bernard Kutter of United Launch Alliance is working on a mission concept called Cryote, which if funded by NASA would demonstrate the technology in space. He told New Scientist that panel members have been asking ULA "numerous questions" about the potential of fuel depots and the maturity of the required technology.

Within NASA, some engineers have argued for investing in space-based demonstrations of technologies needed for fuel depots. These include sunshades that would keep stores of liquid oxygen and liquid hydrogen rocket fuel cool enough not to boil away.

Others point to downsides of the plan. Rocket malfunctions are not uncommon, and the more launches are needed for each moon mission, the more likely it is that something will go wrong, a former senior NASA official told New Scientist.