I don't know who on this list is up to understanding the technical
parts . . . .
The root problem is the same space flight has had all along--the
rocket equation. All sins flow from the fact that at best one part
in 60 of the liftoff mass gets to GEO or lunar orbit with
chemical fuels. Here it is in graphical form.
<http://en.wikipedia.org/wiki/File:Rocket_mass_ratio_versus_delta-v.png>http://en.wikipedia.org/wiki/File:Rocket_mass_ratio_versus_delta-v.png
And here is what you need in delta V.
<http://en.wikipedia.org/wiki/File:Deltavs.svg>http://en.wikipedia.org/wiki/File:Deltavs.svg
People say correctly that fuel is a small part of the cost of space
flight. That's true, but the rocket wrapped around massive amounts of
fuel is not cheap. I have been talking for some time about a way to
get cost down. I call it "pop up and push." (Better name suggestions
welcome.) The idea is to stack a low performance first stage with a
high exhaust velocity laser stage.
Of the 10 km/sec needed to LEO, the rocket stage will provide about 2 km/sec.
So the laser stage has to provide about 12 km/sec of the 14 needed to
get to GEO.
For a mass ratio of 3, this would require an exhaust velocity of 12
km/sec, for a mass ratio of 2 about 17 km/sec. 12-17k/sec is not hard
to get with laser ablation. That's between 1/3 and 1/2 payload. The
laser stage is about 1/6th of the mass ratio 3 chemical stage.
Everybody who has looked at the rocket equation knows that matching
delta V to the mission profile is the way to go. The problem is that
the combination of high thrust and high exhaust velocity takes
ferocious amounts of power to lift anything substantial. Ion engines
have exhaust velocities that range up to 60 km/sec, but thrust in the
milli-gee range--not useful if you have to do a high delta V maneuver in
a hurry.
Ablation lasers have been considered for earth launch because they can
provide high thrust but the lasers are either really huge or lift
small payloads.
Using a chemical stage under a laser stage does not add much to the
cost per kg because the rocket is relatively small, relatively low
performance and thus can be reusable like an aircraft, i.e., fly it
twice a day for 20 years. The performance of the chemical stage is
low enough that a Mach 5 winged vehicle might do the job.
The laser stage does require a substantial amount of power, 4-5 GW (equal
to a ton of TNT per second). But the hang time you get from the
chemical stage allows a low acceleration, just over a g, and the
payload size can be in the 15-25 ton range.
The laser stays on the ground and is bounced from focusing mirrors in
GEO. The laser stage goes round the Hohmann transfer orbit one and a
half times so the laser and mirrors will be in the right place to
circularize its
orbit to GEO. The rockets launch every 15 minutes to keep the laser
busy. This provides a flow of materials to GEO of 60-100 tons per
hour, just what is needed for serious power sat construction.
That's enough materials over a few decades to replace all fossil fuels
with low cost space based solar power, even liquid fuels can be made
from CO2 pulled out of the air and hydrogen from water for a dollar a
gallon.
The short version is here:
<http://www.operatingthetan.com/SpaceBasedSolarPower/SpaceAccess.ppt>www.operatingthetan.com/SpaceBasedSolarPower/SpaceAccess.ppt
The only one besides the delta v and mass ratio slides above needed to
understand this proposal is the "Optimum flight angle" slide.
Dr Jordin Kare (most of the detail in this is from his work) thinks a
1/1000th scale (5 MW) test laser could be built for a reasonable sum.
Not only would it prove out ablation laser propulsion above the
atmosphere, but it would be able to de-orbit 500 tons of space junk a
year.
The amount of money being talked about in carbon cap and trade is so
high that this project could be funded to profitability on perhaps
1/3rd of it.
There are a lot of people getting interested in this concept. I
could use advice as to where to take it next.
Keith
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