Back to the old drawing board
In what could be a blow to a commonplace method of space travel in recent decades’ sf, a scientist is arguing that solar sails can’t work :
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. […] Thomas Gold from Cornell University in New York says the proponents of solar sailing have forgotten about thermodynamics.
I’ve always suspected that more of their popularity in sf owed to the romantic appeal of invoking images of sailing ships than to their practicality. But given that they’re being developed in the real world, maybe that was unfair.
I think the appeal of solar sails came more from the coolness-factor of relativity: "Hey, if light has momentum, let's make it do some work!" Other than one story by Arthur Clarke that cast solar sailing vessels in a sort of America's Cup in space, I can't recall any major science fiction author making much of a connection between solar sails and ocean-going vessels. They were too busy concentrating on the engineering.
That said, I'm quite surprised that all of those SF authors, with their training in physics and engineering, missed such a major flaw in the science. But I'm willing to be convinced, as soon as I can find a link to the article that actually works.
Posted by Jimcat on July 8 2003 13:25
oops. is fixed now.
Posted by Zed on July 8 2003 13:32
Interesting. So really, the jury is still out on this one. Dr. Gold says that the solar sail proponents don't understand the physics at work, and the solar sail people reply that Dr. Gold doesn't understand. I'm not sure whom to believe myself, but I lean towards those who say that the solar sail will work in some form.
To me, saying that a photon bouncing off a perfect mirror will not impart any momentum to the mirror is like saying that a perfectly elastic collision won't obey Newton's First Law. There is no such thing as a perfect mirror in the real world, any more than there is such a thing as a perfectly elastic collision. The photons would have to impart at least some energy to anything they hit. The big question is, will they actually push the mirror, or just heat it up?
I'm all for some practical experiments to resolve this one. If it works in any useful form, no one will be able to deny it. If the effect is too feeble to do any good, we'll leave it to the die-hard physicists to argue it out. (And to think I wanted to be one of those die-hard physicists at one point in my life. Look at all the fun I'm missing...)
Posted by Jimcat on July 9 2003 14:16