An interesting response

[hkhenson]

At 12:00 PM 4/11/2008, Dan M wrote:

(Keith wrote)
> >Takes 10 200 ton payload
> > rockets each flying once a day to do it and with a blank check
> > perhaps under 5 years to work up to this production rate and 6-7
> > years from start to get to a $50 billion a year revenue stream
> > increasing at $25 billion a year.
>
>OK, let's do the math on that.  At the present time, the cost of lift to
>geosynchronous orbit is $20,000 per kg or $20M per metric ton. Ten 200 ton
>payloads would be about 40 billion per day or 14.6 trillion per year.
>That's roughly the GDP of the US.

And the analogy would be how impossible it is to build a dam sending 
all the contents in Fed Ex envelopes.

>The trick is, as it always has been, to lower launch costs.  Unfortunately,
>even in inflation adjusted dollars, launch costs haven't dropped much over
>the past 40 years.

I agree with you.  The question is why?  It's not the cost of 
energy.  A nearly hundred percent efficient space elevator lifts 
about 2400 mt a day to GEO on an input of about a GW.  That's 2.4 
million kg/24 million kWh.  At ten cents a kWh that's a dollar a 
kg.  At the target sales price of a penny a kWh it's ten cents a kg.

Of course you have the cost of the elevator and cleaning up the space 
junk as capital costs.  It can't be done at all now because we don't 
have the cable, but just for analysis put a $1000 billion price tag 
on it.  Since it is going to be used at least ten years, write it off 
at $100 billion a year.  2.4 million kg x 365 is close enough to a 
billion kg.  So the capital cost would be around $100 a kg.

Done with rockets of this sort 
http://www.ilr.tu-berlin.de/koelle/Neptun/NEP2015.pdf the energy 
input is about 15 times that high, or from $15 /kg down to $1.50 as 
you get less and less expensive energy.

The rockets are only assumed to make 200 trips before being 
junked.  At 200 tons payload, they deliver 40,000 mt or 40 million kg.

The mass of one of them is about 3 times a 747.  If they cost a 
billion dollars each (produced at 20 a year), $1000 million/ 40 
million is $25 a kg.  I.e., there is no reason for large volume space 
travel to cost more than $100 a kg even with rockets.

What we need is a transcontinental railroad.  What we have in NASA is 
the Pony Express.

Incidentally, the energy returned from a kg of power sat is 4000 
kWh.  At a penny a kwh that's $40 a year, at ten cents, $400.

>The income stream (which you estimate at 25 billion/year)

Actually it was rising at $25 billion a year from selling power.  If 
you sold the satellites for ten years power production the income 
stream would be $250 billion a year.

>would also have to
>support ground receivers,

Rectennas are (from a cost standpoint) installed chicken wire over 
farmland and inverters (the diodes are almost free).  Collecting 1/4 
kW from 400 square meters would give you a hundred kW.  At pc power 
supply prices, the inverters are $60 a kW.  Counting the chicken 
wire, poles, diodes and power collecting grid, a 5 GW rectenna would 
cost $500 million or less and deliver $400 million to $2 billion a 
year at the bus bars.  It would take  decades to saturate the market, 
which for oil alone is about $3 trillion a year.

>safety mechanisms,

Can you be specific about what you mean here?

>transmission lines, etc.

At least for a while you could site the rectennas near existing 
transmission lines.

>Plus,
>it costs money to build the actual arrays.

That's true, but with just mild concentration you can get at least 10 
times more power out of a solar cell in space.

>If you can find a way to drop
>launch costs a factor of 100 to 500, then space based solar becomes a
>player.  There is nothing like that on the horizon.

There doesn't seem to be any reason a really huge throughput 
transport system should not be able to give you that much 
reduction.  However, I don't thing NASA is the right organization to do it.

Keith

Keith