Saturday, April 14, 2007

The Ultimate Power Ball

I originally made this post on It is a complex concept, so please bear with me.

I heard a news story around 15 years ago (probably on NPR) about two retired NASA scientists who had an idea for electrical power generation. The idea involved creating a huge gyroscope, mounted on the earth so that its plane of rotation bisects the circle formed by the Earth's equator. A huge gear is mounted on the same plane as the equator, inscribing the axis on which the gyroscope rotates. A generator is attached to this gear, and the entire enclosure is put inside a vacuum. The diameter of the gyroscope was described as having to be quite large, > 100 meters. The theory was that as the gyroscope was spun up, the rotation of the earth would force the structure to rotate, spinning the gear and generating electrical power. This would trivially slow the earth, and would convert the earth's kinetic energy to electrical power. I have been unable to find any reference to this, but it seems like it would work as long as friction could be lowered sufficiently. Over a two year period, I received two responses, reposted below.

Answer 1: "I am an aerospace engineer with a Ph.D. in astronomy. I can't tell you what ever happened to this interesting idea, because I have never heard about it in the course of a 16 year career in astronomy and aerospace; but I can at least attest that it is theoretically sound, even if not technologically practical. Moreover, it appears to be an inexhaustible clean energy source! A quick back of the envelope calculation (hope I didn't make a mistake) suggests that the stored rotational energy of the earth is of the order of 10 to the 10th power Gigawatt-millenia. (I chose these units, because they are easily compared to historical time and human power use rates)."
-Answer provided by Walter F. Kailey, Ph.D.

Answer 2: "I agree. The forces driving the generator are not applied against the direction of rotation of the gyroscope so it would not slow down even while the generator siphoned off energy from the rotation of the earth. Only bearing friction would slow it down. The more important question is: would it be practical? To a ground-based observer the gyroscope would appear to rotate one revolution per 24 hours, so if the generator had to rotate at, say about 100 revolutions per minute (a low but not unreasonable speed), the gear-up ratio would need to be 1 : (100 x 60 x 24) or 1 : 144,000. High gear-up ratios tend to be inefficient (high friction losses) so finding a generator that produces enough power at a slow speed i.e. lower gear-up ratio would be important. For Example: If a single-step reduction were used and the driven gear were 30 cm diameter, at 1 : 144,000 the driving gear would need to be 4.32 km diameter - rather large!"
-Answer provided by Keith Labrecque

Of course many people find the idea of slowing down the Earth to provide power somewhat horrifying. I think it is appropriate. Like Sting said, "When the world is running downYou make the best of what's still around".

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