Future Index

Beamed Power, and William Sidis
October 18, 2003

Steve Coy's Contribution Regarding Beamed Power
Steve Coy has contributed this note to the discussion of powering a "lifter" to geosynchronous orbit. As the president of MZA Associates, Steve is an expert in the field of modern optics. 
    He makes one very important point in his letter below:  that less and less power will be required as the "lifter" climbs the "beanstalk". At a distance of one Earth radius above the ground, the "lifter" will only need one-fourth of the power it would require at the Earth's surface, since the gravitational attraction will be only one-fourth what it is at ground level... that is, one-fourth gee. At two Earth radii, it will require only one-ninth the power it will need at the beginning of its climb.

Hola Roberto,

Have you looked at using laser or microwave power-beaming for space elevator lifters? Either way, we should be able to achieve close to diffraction limited spot size at the lifter receiver antenna, in which case an antenna of diameter 2*lambda*z/D should suffice to capture 90+% of the power. (Here, lambda = wavelength, in meters, and D = diameter of the antenna, also in meters.) Suppose we use a laser operating at a near-infrared wavelength of 1.0 micron (10-6 meters or 10,000 Angstroms); to capture 90+% of the energy broadcast from the ground when the receiver is at geosynchronous altitude, we need to satisfy the following:

D_rcvr * D_transmitter >= 2 X 10-6  * 3.6 X 107  = 72 (m2

If both the transmitting aperture and the receiver antenna are chosen to be the same size, they'd need to be 8.5m in diameter - that implies a pretty big telescope on the ground, but smaller than some already existing, and a lot smaller than some proposed. At the receiver, all we need is a 2-d array of photoelectric cells, which can be pretty light. We can make either the telescope or the receiver antenna smaller if we make the other bigger. Also, it's not really necessary to capture such a large fraction of the energy all the way out to synchronous, because the power required drops off with altitude due to decreasing gravity. 

PS: to achieve close to diffraction-limited performance at optical wavelengths, we'd need to use "adaptive optics", to compensate for the optical effects of atmospheric turbulence, but this is a relatively easy case for it, because we can set up a cooperative "beacon". I'm less familiar with microwave power-beaming systems; obviously the transmitter would need to be a lot bigger, in inverse proportion to the wavelength, but I believe its perfectly feasible to construct very large microwave phased arrays, they have much higher operating efficiency, you don't need adaptive optics, and clouds are less of a problem.

Hasta la email,


Leon Hansen's Insightful Remarks Concerning William Sidis.
"I just browsed through your article on human intelligence, i.e. the sections featuring William Sidis. If you had read the Sarah Sidis' "Sidis Story" carefully, you would remember her commenting that she was astounded he learned Latin at 2 since in her opinion he began to talk late. I understand your point about the New York Times and am fully aware of the fact that, in terms of language, others should greater precocity than young Sidis. However, he was not subject to any pressure until his adolescence when he entered Harvard at 11. He passed the Harvard Med School and M.I.T. examinations at 8 but was only admitted due to his father's influence. His father, Boris Sidis, was a genius as well, who knew 27 languages and wrote excellent works on social psychology. Despite the possibility of a genetic inheritance, I believe that his educational methods were primarily responsible for his son's brilliance. Sadly, even today his method remains not understood. It is common knowledge that people learn best at an early age. He reasoned that instead of teaching them silly nursery rhymes you could attempt to interest them in more intellectual matters. Their own curiosity will then drive them. Since now and then people share a general dislike for learning, because it means forcefully stuffing their heads with knowledge to them, Sidis' method remains controversial. It wasn't until M.I.T. professor Comstock predicted young Sidis to be the greatest mathematician of the century and a combination of envy and his supposed failure to live up to that claim that the failure myth came about. I do not doubt that he lived as an eccentric throughout his later years, but he nonetheless produced fabulous works on history and contemporary politics. There is evidence of other genius's early education influencing their intelligence, i.e. Hypathia and Pascal. However, there is evidence against this found in geniuses such as Newton. Attempts of influencing intelligence through early education have not been exclusively unsuccessful and I believe that if Boris Sidis' method were properly understood this would further hold true."

Thanks, Leon.  I appreciate your arguments. I don't disagree with you.. 

Below are a couple of "commentaries" that have appeared on this website in the past. 
 Is IQ Trainable?
The Prodigy
Bringing up the retarded