"The next generation of spacecraft propulsion systems could be dead in the water before they are even launched. A physicist is claiming that solar sailing - the idea of using sunlight to blow spacecraft across the solar system - is at odds with the laws of thermal physics.
Both NASA and the European Space Agency are developing solar sails and, although never tested, the concept is quite simple. A solar sail is essentially a giant mirror that reflects photons of sunlight back in the direction they came from.
Although photons do not have mass, they are considered to have momentum, so according to the law of conservation of momentum, the photon loses some of its energy to the sail as it bounces off, giving the sail a shove in the opposite direction.
But Thomas Gold from Cornell University in New York says the proponents of solar sailing have forgotten about thermodynamics, the branch of physics governing heat transfer. "
-- William T Goodall Mail : [EMAIL PROTECTED] Web : http://www.wtgab.demon.co.uk Blog : http://radio.weblogs.com/0111221/
One of the main causes of the fall of the Roman Empire was that, lacking zero, they had no way to indicate successful termination of their C programs. -- Robert Firth
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