[ExI] Millions of tons to space

[Keith Henson]

On Fri, Apr 1, 2011 at 5:00 AM,  Stefano Vaj <stefano.vaj at gmail.com> wrote:

> My Gedankenexperiment - which I admittedly like, but am ready to drop
> against the harsh truths of arithmetics - was:
>
> - You bring "n" tons of energy-generating solar-power stuff of the
> gravitational well by making use of large-scale Project-Orion nuclear
> propulsors (why a continuous flow of materials would be so different from a
> small number of very large launches?);
>
> - That "n" is calculated in a measure sufficient to send energy back to
> Earth which be enough to maintain and expand your installed space-based
> solar power facilities (e.g., by making use of lasers or by cheaply
> synthetising chemical fuels such hydrogen or hydrocarbons) without the need
> to continue resorting to nuclear propulsion.

If you are ever going to do laser propulsion, you don't need Orian
type propulsion at all.  The energy needed to power the lasers is
relatively modest and can be pulled from the existing grid, at least
in places such as Three Gorges or Sylmar.  The problem is the cost of
the lasers--$60 B or so at $10 per watt.

> - You end up with a permanent flow of energy in exchange for a
> pre-determined, "once for ever", increase in environmental radioactivity.

A million tons per year makes 200 GW/year.  We need on the order of 20
TW over the next few decades, so the production rate will probably go
to 2 TW per year.  Especially if the power sats are made of the
obvious material (Invar) then I suspect that mining asteroids for
nickle will start by ten years after the first power sat is turned on.

The combination of burning hydrogen with air to get above 20 km and up
to about 2 km/sec combined with the "long boost" of about 15 minutes
is the key to getting the laser power so low.  Previous work on
straight boost gives a laser requirement of a GW per ton.  This
approach puts 50 tons of vehicle and 50 tons of payload in LEO with 6
GW of laser power (up to 12 GW off the grid).  The cost is a flotilla
of redirection mirrors in GEO that lets the beam sweep along the
equator for good fraction of the circumference of the earth.
Relatively low acceleration takes a long distance to get up to orbital
speed.

Is it worth doing?

It all depends on how long humans stay in charge.  If I was sure the
singularity would get here before the energy crisis starves a
substantial fraction of the population, I would not bother.  Surely
thinking power that extreme can solve such simple problems as energy.

Keith