Taylor Dinerman calls for space solar power in this week’s The Space Review. He trots out hydrogen as an alternative energy source. No–it’s an alternative energy delivery method. Last time I checked, to get hydrogen, we had to use another fuel source and lose energy to crack the hydrogen. To make space solar power viable, we need an advance that will advantage space solar power to terrestrial solar power. Does this meet the objective:

One technology that might radically reduce the weight requirements for these systems is the technique pioneered at the University of Notre Dame where single-walled carbon nanotubes are added to a film made of titanium-dioxide nanoparticles, doubling the efficiency of converting ultraviolet light into electrons. Any solar cell technology that could reach conversion factors of over 50% or even higher would reduce the size and weight of an SPS and thus make it easier and cheaper to build and launch.

It also makes terrestrial solar power potentially reach conversion factors of over 50% too. To make space solar better than terrestrial solar, we need launch costs to be no more than 3x manufacturing costs per kg if space solar is 4x as efficient. With manufacturing costs $350/kg, we need launch costs $1000/kg to make space solar viable.