On Tue, Oct 12, 2010 at 11:00 AM, "Dan Minette" <danmine...@att.net> wrote: > To: "'Killer Bs \(David Brin et al\) Discussion'" > > Just a quick point. > >>Run 80,000 hours in ten years the return is $800 per kW >>per penny payment for a kWh. For power satellites, assuming 5kg/kW, >>$100 per kg lifted to GEO and about 1/3 of the cost going to >>transport, you get the required $1600/kW for 2 cents per kWh. > > Well, that seems really low, so I looked up present costs. At > > http://crowlspace.com/?page_id=50 > > there is a talk promoting space based solar. It was honest enough to admit: > > The launch cost from Earth to low earth orbit is the greatest impediment to > this project. It is currently about $5,000 per pound to low earth orbit, and > it has been about that cost for a long time. Geosynchronous orbit would > raise the cost to 10,000/pound. > > Given the fact that, as mentioned in the talk, lift costs have been fairly > constant, where does the factor of 200 improvement come from? How do you > know it will happen when it hasn't?
We probably will never know if this StratoSolar method works. But it's based on the rocket equation. If you want to get into LEO with a reasonable payload, say 1/6th with a rugged, reusable vehicle also 1/6th of take off, then the average exhaust velocity needs to be about the same as the 9 km/sec you need to get to orbit. You just can't do that with *any* chemical fuel. You can do it with laser heated hydrogen. The project would require $60 B of lasers. If you want the long and slightly out of date paper I wrote for the beamed energy propulsion conference, ask. David Hobby <hob...@newpaltz.edu> wrote: >> I see bigger problems with losses in the light pipe. >> The plan seems to be to have a flexible tube lined >> with reflective material to guide the solar radiation >> down to steam turbines or whatever on the ground. >> Most of the light would have to reflect off the sides >> many times, losing at least a few percent of its >> intensity at each reflection. So nothing makes it >> to the ground, and the light pipe melts. There may >> be solutions to this too, but they're going to be >> tricky. > > How many reflections are you assuming light will make > as it goes down the pipe, and how glancing are they? It depends on the acceptance angle and the diameter of the light pipe. This stuff: http://www.revelationlighting.co.uk/OLF%20Spec.pdf has a .99 reflectivity for angles less than 27 deg, and almost all the loss comes from the points not being sharp. At .999, which the optical guys say is not hard, and a 30 meter diameter light pipe, the loss is about 7%. One option is to fill the pipe with argon which reduces the Rayleigh scattering. There is 4 GW coming down the pipe. At 7% loss, 280 MW. The area of a 30 meter x 20 km pipe is 2 million square meters so the loss would be 140 W per square meter. In open air it is only going to get slightly warm. Keith _______________________________________________ http://box535.bluehost.com/mailman/listinfo/brin-l_mccmedia.com
