There was a little bit of a buzz in the blogosphere a few days ago about Gizmodo's report that the Japanese plan to bombard the planet with frickin' laser beams from outer space. No word on whether or not they would be attached to the heads of sharks.
I thought it was a little strange, myself. While lasers have been proposed for space solar power, most of the concepts over the past four decades (ed-- wow, it's really been four decades since Peter Glaser came up with the idea? Yup) have been to transmit the power with microwave beams. Lasers (probably free-electron lasers with tuned frequencies) have the advantage of higher power density (and thus less need for large ground receivers). But they don't penetrate the atmosphere and clouds as well, and they are less efficient for power conversion. Also, they raise exactly the fear described in the Gizmodo piece--that higher power density is a double-edged sword. Microwaves are preferred because the energy conversion efficiency is very high, and the beam density is less than that of sunlight (it's better than sunlight despite this, because the beam is available 24/7 and the conversion efficiency is much better, at least with current solar cell technology). It's much more difficult to weaponize, by the nature of the technology.
Anyhoo, I'm assuming that what was actually being referred to was this:
On February 20, JAXA will take a step closer to the goal when they begin testing a microwave power transmission system designed to beam the power from the satellites to Earth. In a series of experiments to be conducted at the Taiki Multi-Purpose Aerospace Park in Hokkaido, the researchers will use a 2.4-meter-diameter transmission antenna to send a microwave beam over 50 meters to a rectenna (rectifying antenna) that converts the microwave energy into electricity and powers a household heater. The researchers expect these initial tests to provide valuable engineering data that will pave the way for JAXA to build larger, more powerful systems.
Microwaves, not lasers, as Gizmodo mistakenly claimed. The article does mention lasers as a potential means of getting the power down, but that's not what next Wednesday's test is about.
There were some reports recently of the US Army doing feasibility studies on this; even if it isn't cost effective as such, building an antenna at your big base in e.g., Iraq could be a lot cheaper than trying to ship fuel in.
Diode pumped fiber lasers may eventually be efficient enough for laser transmission to make sense. I don't think they (or photovoltaic receivers optimized for a single frequency) are there yet, though.
The payoff could be considerable, though, since it would enable space solar power to be piloted at a much smaller scale than microwave-based schemes. The laser technology would also possibly be useful in launchers and transmission of power to assets in cislunar space.
>>most of the concepts over the past four decades (ed-- wow, it's really been four decades since Peter Glaser came up with the idea?
Rand,
Although the site you link to credits Glaser with having, "invented the idea" of solar power satellites in the late 1960s, Isaac Asimov, in the robot story "Reason", first published in 1941 and later collected in "I Robot", described satellites near the orbit of Mercury collecting solar energy, converting it into collumnated beams, and beaming it to Earth and Mars. I don't know if the idea was original to Asimov or if he took it from somebody else. Either way, although Glaser certainly did the first technical work on the subject, the idea goes back a good deal earlier.