## A proposed solution to the problem of space flight

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• 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
Message 1 of 4 , Mar 31, 2009
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

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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• ... You missed your posting time by 3 hours, 53 minutes. _______________________________________________
Message 2 of 4 , Apr 1, 2009
On Tue, Mar 31, 2009 at 8:07 PM, hkhenson <hkhenson@...> wrote:

> The laser stage does require a substantial amount of power, 4-5 GW (equal
> to a ton of TNT per second).

You missed your posting time by 3 hours, 53 minutes.

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• ... I think I am. Or I was. Probably now I switched from being one of the good guys (working in the space industry) to become one evil minion (working in
Message 3 of 4 , Apr 1, 2009
Keith wrote:
>
> I don't know who on this list is up to understanding the technical
> parts . . . .
>
I think I am. Or I was. Probably now I switched from being
one of the "good guys" (working in the space industry) to
become one "evil minion" (working in the oil industry) :-)

> 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.
>
If you want to play with the rocket equation, just use
this javascript:

http://www.geocities.com/albmont/relroket.htm

It's a relativistic rocket equation, but it works (obviously)
for v << c.

The whole problem is that you need energy/power/speed/name-it
to get the rocket away from Earth's athmosphere. Right now,
the only way to do it is by chemical rockets.

Now comes the second problem. Suppose you get to LEO. Theoretically,
it's possible to use "more efficient" ways to transfer to GEO. One way
is to continously thrust with a high-specific-impulse engine. But this
would make the transfer take eons - and now economy plays a very
important part in the equation: you don't want to _wait_! Time is money.

So, the pretty little mathematical and physics of transfer bows
to the implacable and ruthless laws of economics, and we use
chemical rockets.

Darth Alberto Monteiro

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• ... There are other ways that would almost certainly work. Laser ablation, which takes a GW/ton of payload, and various methods that accelerate a vehicle to
Message 4 of 4 , Apr 1, 2009
At 11:00 AM 4/1/2009, John Williams wrote:

>Keith wrote:
> >
> > I don't know who on this list is up to understanding the technical
> > parts . . . .
> >
>I think I am. Or I was. Probably now I switched from being
>one of the "good guys" (working in the space industry) to
>become one "evil minion" (working in the oil industry) :-)
>
> > 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.
> >
>If you want to play with the rocket equation, just use
>this javascript:
>
>http://www.geocities.com/albmont/relroket.htm
>
>It's a relativistic rocket equation, but it works (obviously)
>for v << c.
>
>The whole problem is that you need energy/power/speed/name-it
>to get the rocket away from Earth's athmosphere. Right now,
>the only way to do it is by chemical rockets.

There are other ways that would almost certainly work. Laser
ablation, which takes a GW/ton of payload, and various methods that
accelerate a vehicle to escape plus enough to get through the
atmosphere. But your point is correct in that rockets or something
closely related seem to be the current and possibly the best way to
get above the atmosphere.

Though in the long run (and assuming we can get the cable) you can't
beat a moving cable space elevator for efficiency. 15 cents of
electric power per kg to GEO.

>Now comes the second problem. Suppose you get to LEO.

Ah, but you didn't read the specifications. The first stage in this
design does not go to LEO, and the second (laser) stage doesn't
either. It heads directly to GEO on one continuous burn. Amazing
what you can do with 12-17 km/sec exhaust velocity and over a g of
thrust. The energy in the laser beam is equal to a ton of TNT per second.

>Theoretically,
>it's possible to use "more efficient" ways to transfer to GEO. One way
>is to continously thrust with a high-specific-impulse engine. But this
>would make the transfer take eons - and now economy plays a very
>important part in the equation:

It's not as bad as you think. Ion engines will take a power sat
constructed in LEO to GEO in a few months. Unfortunately by the time
it got there it would be full of holes and in dire need of
repair. They are big enough to intercept a *lot* of space junk.

> you don't want to _wait_! Time is money.

If you put another batch of lasers on the ground or build a set at
GEO, then lift off to GEO is 5 hours. Initially, with only one set
of bounce mirrors, we let the laser stage go around the Hohmann
transfer orbit one and a half times. This puts the laser and bounce
mirrors in the right place to circularize the laser stage to GEO.

The time is money is certainly true. The "design to cost" criteria
is to have parts delivered to GEO be incorporated into a finished
satellite in a week or less. Starting at GW of power sat every day
or two, ramping up over time to 2 GW/day or more. The intent is to
displace fossil fuel entirely by mid century.

>So, the pretty little mathematical and physics of transfer bows
>to the implacable and ruthless laws of economics, and we use
>chemical rockets.

They are ok for the first step, but using high exhaust velocity laser
propulsion for the second stage reduces the lift off mass by a factor
of 5 and the cost by a factor of 6. It's the difference between 5
cent per kWH which won't really compete with nuclear and 1 cent,
which takes over even the oil market.

Keith

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