# [ExI] Fwd: Material from the talk at NASA Ames

hkhenson hkhenson at rogers.com
Mon Mar 30 17:24:03 UTC 2009

```This went to another list, but I thought it might be of interest to some here.

Keith

>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
>
>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 long form of the slides for the talk are here:
><http://www.nss.org/settlement/ssp/library/CO2andSpaceResources.ppt>http://www.nss.org/settlement/ssp/library/CO2andSpaceResources.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 gettomg interested in this concept.  I
>could use advice as to where to take it next.
>
>Keith

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