Soon, a small aircraft laden with sensors and a high-speed datalink could be flying over the mountains of Mars - the first aircraft to fly over the terrain of another world.
By Dr David Whitehouse
BBC News Online science editor
Called Ares (Aerial Regional-scale Environmental Survey of Mars), it could, if all goes well, be flying over the Red Planet's southern uplands in just five years' time.
A pre-programmed scientific flight over Mars
After a successful series of half-scale tests, the US space agency (Nasa) has ordered a full-scale prototype to be built.
Ares is in competition with three other Mars exploration proposals for a Nasa launch in 2007. The final selection of one, or possibly two, missions will be made later this year.
Ares represents a dramatic leap in the exploration of Mars, as it combines many of the best aspects of an orbiter and a lander.
Landers make detailed measurements of a small area, orbiters make cruder measurements over great swathes of terrain. An autonomous flyer bridges the gap between the two.
The current mission profile calls for an 850-kilometre (528 miles) flight over the rugged southern uplands of the Red Planet at an altitude of 1.5 km (0.9 miles), making measurements of geological formations spanning four and a half billion years of Martian history.
Taken to the edge of space and released...
Ares would follow a predetermined trajectory over selected mountains, canyons and plains, sending its data back real-time to the Earth via a mother satellite relay.
In addition to a surface survey, it would also sample the atmosphere and make magnetic measurements with unprecedented accuracy.
Last year, a half-scale model was carried by a high-altitude balloon to an altitude of 31,546 metres (103,500 ft) above the Earth for a drop test.
Once released from the balloon, the scale model automatically unfolded its wings and tail and completed a 90-minute return to the surface with a perfect runway landing.
The new plane, to be built by Aurora Flight Sciences of Virginia, is to be a full-scale version, designed to demonstrate and test actual components and aerodynamics.
...only to land perfectly 90 minutes later
The full-size prototype is scheduled to make its first flight later this year, with a similar deployment test in the upper reaches of the Earth's atmosphere.
"This demonstration is another important step on the road to flying the first airplane in another planetary atmosphere," says Aurora's President John Langford.
Ares is one of four Mars exploration concepts selected for a Phase A study as part of Nasa's Mars Scout programme.
The first Mars Scout mission is planned for launch in 2007 with arrival at Mars in 2008.