chemical rockets and cost was Apologizing . . .

>,,,or a mass driver, or space elevator or laser
>launcher,,,all of these are potential solutions
>but none of them are being built. So, for now,
>we're stuck with chemical rockets,,,(come on Bussard. Make it work,,,)

Dear Madam,

If the goal is a continued and growing human
presence in space, going back to the moon for flags and footprints won't do it.

There _are_ reasons for a massive presence in
space. All of the major problems, global warming
(or at least CO2 buildup), energy-including
liquid transport fuels, water, food and poverty
can all be helped if not completely solved with
vast amounts of inexpensive space based solar power (SBSP).

How vast?

In round numbers humans need, 25 TW of SBSP over
the next 25 years starting as soon as possible.

How inexpensive?

Two cents per kWh will under price electricity
from coal or nuclear. One cent per kWh will
displace oil with cleaner, carbon neutral
synthetics for about a dollar a gallon. To meet
these goals, the power satellites can't cost more
than $800 million to $1.6 B per GW ($800-1600/kW).

Toward the end of 25 years of construction, the
flow of materials into power satellite
construction (at two TW/year) will be close to
1000 tons per hour (at 5kg/kW). It seems likely
that most of that will be from extraterrestrial sources.

An initial flow of parts from earth of 100 t/hr
and a cost of $100/kg or less is a near term
design target (build up to this rate in less than
ten years). This side of nanotechnology it's
probably impossible to do with chemical rockets.

To appreciate why you need to understand the
rocket equation and "mass ratio." For business
people it is like compound interest at a high
interest rate--ruinous if you need multiples of
the exhaust velocity. A mass ratio 3 vehicle
(100 tons of structure and payload, 200 tons of
fuel) will reach its exhaust velocity. To get to
LEO is about 2.5 times chemical rocket exhaust
velocity and takes a mass ratio of 12. For an
empty mass of 100 tones, the liftoff mass is 1200
tons. This is why rockets are staged.

Laser propulsion is one way to get around the low
exhaust velocity problem. We have understood
laser propulsion for a long time. It is not
efficient at low velocity and requires huge lasers for small payloads.

The combination of a mass ratio 3 chemical first
stage (providing 4 km/sec) and a mass ratio 2
ablation laser upper stage (providing 10km/sec
from an 15km/sec exhaust velocity) looks like it
will get the transport cost to GEO into the sub
$100/kg range. For the same laser, this method
provides payloads of 4-6 times that of laser propulsion from the ground.

Dr. Peter Schubert has done parametric analysis
to minimize cost. Below about $450/kg, direct
from earth construction of power sats cost
less. Above that number, supplying materials from the moon is less expensive.

Even if we start by hauling the power satellite
parts up from earth, in a few years it will makes
sense to construct them for lunar or asteroid
materialsespecially if a lot of the mass of a
power satellite is Invar (35% nickel) or lunar dust used for heat transfer.

In the next decade, it looks like reducing the
cost to GEO using a chemical/laser two stage or
some other method will get space industry
started. (Probably not by the US/NASA though.)

Space habitats happen naturally in the context of
large SBSP production. A crew of 1000 at GEO
building and unjamming automation cost almost
nothing in the context of profits of $500 million
a day. With a materials pipeline of 100 t/hr, supplies are insignificant.

Mining camps at asteroids and/or on the moon make
sense with an established market.

I went into more detail recently. Google Henson
oil drum. A first pass proforma statement
indicated a peak investment of a bit under $60 B.

Keith Henson