Charles Darwin could not have known he might one day improve cell phone communications and help win wars. But a new computer-based "genetic algorithm" based on Darwin's ideas about how the fit survive may do just that.
The algorithm, created by researchers at Purdue University, created ideal satellite orbits with the help of hours and hours of computer processing time. The orbits were designed to help overcome a basic conundrum in satellite communications:
The highest flying satellites, at some 22,000 miles, can see half the Earth and, while orbiting at the same speed as Earth, be in constant touch with a ground station. But it is very expensive to put them there. Lower, cheaper-to-attain orbits -- as low as 80 to 300 miles -- result in satellites that are blocked by the Earth's curvature from communicating with a given ground station for much of their 90-minute orbit around the planet.
Even constellations of four low-orbiting satellites, with offset orbits designed to work in concert, have limitations. Inevitable blackout periods are undesirable for military operations or even many commercial applications, like cell phones and pagers.
So the Purdue researchers led by William Crossley, an associate professor at the university's department of Aeronautics and Astronautics, set a computer about to dreaming up numerous possible configurations for groups of four satellites. As in Darwinian evolution, bad orbits were tossed out. Good ones were allowed to ferment, to see if they could be improved.
The genetic algorithm selected the best-performing constellations by interchanging variables such as how far apart the satellites are from each other, the heading of the satellites as they cross the equator, and how high they are above the Earth's surface.
As with evolution, genetic algorithms are known for producing unexpected results.
Normally, in constellations containing small numbers of satellites, the spacecraft are spaced at equal distances from each other as they track across the globe's equator. But in the best-performing configurations discovered by the genetic algorithm, the satellites were not spaced at equal distances.
"For example, the constellations might have two satellites spaced very far apart, and the third one will be very close to the second one," said Crossley, who developed the algorithm with former graduate student Edwin Williams.
Blackout time was reduced by 90 minutes, though not eliminated.
"For small numbers of satellites, at low altitude, we find constellations that outperform significantly the ones that you would find using the traditional approach," Crossley said.
The new orbital approach has been used to design a constellation of satellites for a possible defense mission, the researchers say, and collaborators at the Aerospace Corporation in El Segundo, Calif., are using the approach to investigate other possible constellation designs.
Crossley's team says low-altitude satellite constellations are expected to bring a boon to mobile computing by making it more possible for people to use wireless communication devices.
A research paper about the findings is in the July-September issue of the Journal of Astronautical Sciences, published by the American Astronautical Society.
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