"Christopher M. Jones" wrote in message ...
Terrell Miller wrote:
"Alex Terrell" wrote in message
om...
Besides, once the first operational SSPS is built, it won't be long
before they can supply all of Earth's energy needs.

sorry, that's completely wrong.

do the math: a single SPS, even based on the latest ultralightweight
designs, would require thousands of launches to get everything uphill and
assembled (weight isn't the only consideration, there's the simply matter of
*volume*). That's just for a single SPS, which would generate less than 1%
of the domestic power comsumption in the US, at roughly twice the cost per
kWH as a conventional terrestrial plant.

Current energy usage world-wide runs at around 400 EtaJoules
per year, or an average of roughly 13 teraWatts continuously.
Even at 100% conversion efficiency of the ~1400 W/m^2 of
insolation at Earth this corresponds to over 9,000 km^2 of
area in solar power systems. This is a lower bound, a more
realistic estimate would be at least a factor of 4 larger
due to inefficiencies in each step of the process. Even
very low estimates of the mass of SPS systems and of the
launch costs yield values of tens of thousands of tonnes of
material put into orbit at a cost of hundreds of billions
of dollars.

Key phrase: "Put into orbit"

Significant SPS will not happen if we need to put mass into orbit
(from Earth surface).

If however we use NEO (or lunar) resource, there is no reason why the
mass increase should not be exponential.

500,000km2 a few decades after launch is quite feasible. The total
mass is half that of a single O'Niell cylinder.