As Nasa prepared to launch its debut mission in a programme aimed at returning astronauts to the moon, a Presidential panel began looking at alternative ways to get there and whether the US should even go.

The Lunar Reconnaissance Orbiter is designed to map the lunar surface so Nasa can find safe and scientifically interesting landing spots for future human missions.

The US is shifting the focus of its human space programme from research and technology development in low-earth orbit with the space shuttle and International Space Station to an exploration initiative. That would culminate in the return of US astronauts to the moon in 2020 - a half-century after the pioneering Apollo lunar landings of 1969 to 1972.

Nasa plans to retire the shuttle fleet in 2010 after eight more missions to complete space station construction. It would then shift funding to ramp up development of a pair of expendable rockets, known as Ares, and a beefed-up Apollo-style capsule called Orion that can ferry crews to the moon and other destinations.

Orion's debut flight to the space station is targeted for 2015 - five years after the shuttle stops flying.

With costs estimated at more than €71.7 billion for a lunar excursion and concerns about the five-year gap, President Barack Obama has ordered a top-level review of the US human space programme.

Hearings in Washington opened on Wednesday with commercial companies, Nasa and other space advocates laying out options for flying astronauts to the space station and getting to the moon.

Panel members will also consider whether the moon should even be a destination. The panel, headed by retired Lockheed Martin chief executive officer Norm Augustine, is expected to issue a report in August.

At the meeting, United Launch Alliance, a Boeing and Lockheed Martin joint venture that markets the unmanned Atlas and Delta rockets, pitched an upgraded version of its rockets to replace Nasa's planned Ares booster, an option a Nasa-backed study found to be less expensive.