Solar Sailing and Physics

Roland Piquepaille writes "In this article, the New Scientist writes that the next generation of spacecraft might be propelled with the help of the sun. "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." 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." And this is where it's becoming interesting. Gold's paper, "The solar sail and the mirror," states that "either Carnot's accepted rule is in error, or the solar sail proposal will not work at all." So, as this illustration from New Scientist shows, the real question is: "Can it really sail away?" We'll know it in September when the first tests are done. In the mean time, read this summary for more details and read the original stories for far more information."

Comments

Unfortunately

[earthforce_1]

This works well for exploring the inner planets, or if you just want to do a flyby of the outer ones. The sun provides negligable energy out past the orbit of Mars. We still need someting like Prometheus in order get around and about in places where the sun doesn't shine brightly.

Re:nitpicking point in the article

[benhaha]

I suspect Feynmann proposed this as an exercise, since the flaw is obvious to anyone with a degree in theoretical physics.

Flaw: Light is red-shifted climbing out of the gravity well. So when it reaches d2 there is not so much energy as when it left D1, so a smaller amount of mass will be produced. When it falls back down, the mass difference is equivalent to the kinetic energy gaind from falling by the equivalence relation E=mc^2.