[ExI] Solving big problems

[Keith Henson]

People on this list know I have worked for years to get the cost of
electricity from power satellites down to where it could displace
fossil fuels.

The peak investment to get started has fallen over the years.  The
original estimate was ~$300 B.  It fell to $140 B in 2012 and to $60 B
last year.  In the last week, it fell to ~$30 B.  That does not
include the Skylon development.  The UK and ESA are doing Skylon for
independent reasons.

The current schedule for Skylon is for it to fly in 2021.  At
reasonable flight rates (for power satellites) the cost falls around
$100/kg.  That's to LEO.  There is at least a 2.5 multiplier for
chemical rockets to get cargo to GEO.  Unfortunately, we can't build
power satellites in LEO and use electric thrusters to fly them to GEO.
 It takes 6 months and the cross section for running into space junk
reduces the chances to near zero that one will arrive at GEO intact.

Sunlight does not have enough energy per square meter for a rapid
transit.  Raising the output of the sun ten fold wouldn't be a good
idea even if we had an idea of how to do it.  (Talk about global
warming!)

But we can beam microwaves from ground to space at an intensity of ~10
kW/m^2.  It would take a 1 km rectenna on a rather large vehicle,
around 21,500 tons, for a 15,000 ton payload.  The rectenna and
thrusters would mass around 2000 tons, the reaction mass around 4500
tons.  We stack 1001 Skylon payloads 91 to a layer and 11 layers high.
 This presents a small enough cross section that space junk is not
likely to destroy it.

Humans can ride this vehicle.  There is plenty of shielding even
though it spends a month in the Van Alan belt.

The scale is not large, only ~20 GW/year.  That doesn't come close to
enough to get humanity off fossil fuels.  But the business makes a
_lot_ of money and can grow over a decade to a couple of TW/year.
That would end the use of fossil fuels and solve the climate concerns
to whatever extent the build up of CO2 is affecting it.

Keith