WHEN it comes to living in the reduced gravity of space, Mary Poppins could
teach us a thing or two, according to two researchers in the US. They reckon
that 鈥渦mbrella power鈥� will be one of the most efficient and controllable ways of
moving about in microgravity.
Philip Watts of Applied Fluids Engineering in Long Beach, California, was
considering the best way of getting people around a large space station under
their own steam. Pushing yourself off from a surface in the direction you want
to go is fine, he says, except that, once airborne, you have no control over
speed or direction. 鈥淢oving at speeds of around 40 kilometres an hour, it could
be downright dangerous,鈥� he explains.
Assuming normal Earth air pressure, Watts and his colleague David Carrier, a
comparative physiologist at the University of Utah in Salt Lake City, simulated
various propulsion systems used by creatures on Earth to see how they would fare
in microgravity conditions.
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To test a simple drag-based system like that used by winged seeds, the pair
flapped an open umbrella up and down while standing on a set of weighing scales,
and calculated the forces that were produced. Taking into account the effects of
gravity and their own mass, they then calculated the forces that would be
produced by the same motion in microgravity. Umbrellas proved effective for
propulsion, the researchers reported at a meeting of the Society for Integrative
and Comparative Biology held in Chicago last week. This is because the air
resistance differs significantly depending on whether the umbrella is moving up
or down, resulting in a significant net force in one direction.
Donning wings or bat-like suits with webbed arms to simulate flying were less
successful. In the absence of gravity, the net effect of upward and downward
wing motion was negligible. And jet-based systems, as used by jellyfish, would
be difficult to use in space without spinning out of control.
One of the biggest problems is that humans鈥� relative lack of upper body
strength appears to rule out arm-powered systems. 鈥淲e wouldn鈥檛 be able to
sustain the motion for very long,鈥� says Carrier. 鈥淲e are just too big to
蹿濒测.鈥�
So Carrier and Watts favour leg-powered propulsion. Future astronauts might
鈥渏og鈥� around the space station, powered by umbrella-shaped devices strapped to
each foot. Another of their ideas is a vehicle something like a reclining
bicycle, with directional propellers that can be turned by pedalling.
As well as providing a way of getting about, astronauts would get much-needed
exercise. 鈥淢usculoskeletal and cardiovascular atrophy in microgravity represents
one of the greatest obstacles to extended space travel,鈥� says Watts.
