Link to original Ted Talk if the video above does not play.
Dear Bill,
I am very pleased to learn about your involvement in the energy future of our planet. I agree that clean, affordable and available energy is the overriding issue for the future development and well being of the entire human race.
My wish is that you will take a serious look at space-based solar power. I believe it can be a game-changing base load power source. When funded, developed and deployed at the required scale, space-based solar power addresses your requirements for zero carbon emissions, ease of distribution, relatively small earth footprint and zero waste generated.
Uranium is a finite resource, though longer range than conventional fossil fuels. Space-based solar power can provide energy to the earth until the sun burns out.
The website Citizens for Space Based Solar Power is one of many places to begin a review of the current state and potential for space-based solar power. You could be the voice this technology has been seeking.
Sincerely,
Rob Mahan
Citizens for Space Based Solar Power 
I am a big fan of launch loop but there are many hard problems there. Analysis of variation of maglev makes them look really hard to do.
Laser heated hydrogen will get the ISP you need for LEO on a mass ratio 3 vehicle. Lasers are withing a factor of ten of the size needed. It is expensive and doesn’t make sense for less than a million tons per year to GEO.
But whatever works.
Best wishes,
Keith Henson
hkeithhenson@gmail.com
Keith,
Thank you for adding your voice to my appeal to Bill Gates to take a serious look at space-based solar power. Launch costs and their environmental impact is certainly one of the primary challenges to the successful development and deployment of space-based solar power.
In my opinion, one possible solution to this challenge is the use of a non-rocket launch system (launch loop, maglev rails, etc.) powered by the initial solar power satellites. This provides an upward spiraling scenario for the required scale up of space-based solar power … and the space-based solar power would be its first, best customer.
I would be interested to hear your impressions of this idea.
Regards,
Rob Mahan
Dear Bill.
Rob Mahan has the outline of space based solar power correct.
For the last three years I have been working on the other thing you mentioned, “half the price of coal.” If coal is around 4 cent per kWh, then your target (and mine for the same reason) is 2 cents. That limits the capital to about $1.6 B/GW or $1600/kW. For reasonable cost of materials ($900/kW) and the rectenna ($200/kw) that leaves $500/kW for transport to GEO. The power sats are expected to mass about 5 kg/kW which leaves $100/kg to lift them to GEO.
While this is about a 200 fold reduction from current cost to GEO, it seems to be within what could be done with a Skylon type craft for the first stage and laser propulsion for the second stage. Cost to profitability should be a good deal less than was spent on the space station.
A major risk is someone figuring out an even less expensive way to accomplish low cost high capacity energy.
I am looking at a project under an NDA that might just do that.
Best wishes,
Keith Henson