SONIC booms from a propeller-driven aircraft could reverberate across the
bleak surface of the Red Planet in 2003. If the plane鈥檚 propeller does break the
Martian sound barrier it will not be deliberate, but rather part and parcel of
the many technological challenges NASA faces in trying to fly a robotic
aeroplane in the planet鈥檚 thin atmosphere.
Though the craft鈥檚 precise design and mission have yet to be decided, NASA
announced last week that it has set aside $50 million to celebrate the
centenary of the first powered flight on Earth. Likely to be named the Kitty
Hawk, after the North Carolina site of the Wright brothers鈥� brief powered
flight, the craft will fly at a height of about 300 metres and might have a
propeller powered by hydrazine fuel or electric power. A rocket thruster is
another option.
鈥淭here are three concepts [being] considered by the space science
enterprise,鈥� says Henry McDonald, the director of NASA鈥檚 Ames Research Center in
Moffett Field, California. 鈥淲e鈥檙e looking at a couple of metres wing span, with
something like an hour to four hours鈥� flight time, carrying about 15 pounds鈥�
Earth weight of instrumentation.鈥�
Advertisement
Armed with cameras and perhaps a radar, the aeroplane could take
higher-resolution pictures of the Martian surface than a satellite and wouldn鈥檛
be restricted to a small area like a lander. One of the most exciting missions
would be to fly into the Valles Marineris, an enormous canyon, and take pictures
of the cliffs, giving planetary geologists images of rock strata. 鈥淵ou鈥檙e able
to look sideways at the cliff faces,鈥� says McDonald. 鈥淭hat鈥檚 something only an
aircraft could do.鈥�
However, designing a plane that can handle the Martian atmosphere is no easy
task. 鈥淚t鈥檚 different aerodynamically in that rarefied gas鈥攊t鈥檚 similar to
flying at 100 000 feet [on Earth],鈥� says Anthony Colozza, from NASA鈥檚 Lewis
Research Center in Cleveland, Ohio. 鈥淏ut on the other hand, gravity on Mars is
much less, so you don鈥檛 need to generate as much lift.鈥�
Nonetheless, this means that the aircraft must have relatively large wings
and large propellers to stay aloft, which might be a problem. 鈥淭he speed of
sound on Mars is less than on Earth,鈥� says Colozza. And in Mars鈥� thin air, a
propeller would have to spin so fast that its tips might break the speed of
sound, greatly reducing the aircraft鈥檚 efficiency, he adds.
Without a runway, starting the flight will not be easy, either. The aircraft,
which will piggyback upon another Mars mission, will probably deploy with the
aid of a parachute and take flight in midair, before it hits the ground.
Alternatively, it might be fired into the air by a mortar.
There are also more prosaic problems, such as creating an autopilot for the
craft, and how to beam the enormous volume of high-resolution data back to
Earth. But nobody thinks the problems are insurmountable. 鈥淚 believe technology
has evolved to the point where it鈥檚 very feasible,鈥� says McDonald. 鈥淚 think it
will provide a significant science return.鈥�
