Digest Number 509

--- In ssi_list@... Ian Woollard wrote: victoriatangoman wrote: I see what you mean about laser beaming. Yes, it definitely makes mroe sense. I'm with you except . . . do you think that Dubya would be happy with a multi-gigawatt concentrated laser in orbit. Wouldn't that be considered a WMD because of its energy density? Depends on how it is constructed. If it is kept down to 1kw/m^2 then its no death ray. Provided the lenses are small enough, it's physically impossible to get the light too concentrated. OK, I'm missing something here. If we keep the energy density to 1,000 watts/m^2 compared to the 1,360 watts/m^2 of sunlight, comparing efficiencies of 70% and 20%, respectively, then the laser would be 157% more efficient than solar PV. So here's what I don't get: you still need PVs on the lunar surface to convert the laser light, albeit at a higher efficiency but now you need a large laser, power source and radiator in orbit, or at L1. Is this less expensive or complex? I don't know. No. It's just an array of LEDs or laser diodes. They're really cheap; under a dollar a watt; and really low mass.

Oh yeah and you need a lens infront; think telescope mirror.
Also, a laser that can focus a beam for 30,000 miles is considered dangerous, isn't it? No. Whether a beam of light is dangerous or not depends on the power density.
Also, the laser will be producing a prodigious amount of energy but focusing it across a large area to achieve a weak energy density, but how difficult would it be to change the optics and increase the energy density on short notice? Pretty difficult; large mirrors are expensive and difficult to make. It's like making a telescope twice the diameter, the costs mount rapidly. Upping the energy requires installing bigger solar panels, which would be very obvious, and you'd still have to install more LEDs or laser diodes, and reallign everything; it's slow difficult work.
If your answer to the above points is that they are indeed valid concerns about weaponization, then is there really a need to keep the energy density down to 1,000 m^2? If the concerns are satified, then why not pump it up to 10-20,000 watts/m^2? Well, the PVs start to fry at some point, and keeping the power down prevents it from becoming a death ray accidentally or on purpose (20 kw/m^2 is probably a death ray). The whole point is to build something that isn't a death ray, not build something that is.