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Re: starship-design: The Size of the Problem

At 3:07 PM 8/4/96, DotarSojat@aol.com wrote:
>TO:      The Starship Design Group
>FROM:    Rex Finke
>SUBJECT: The Size of the Problem
>A challenge has been identified to convey to the SD group the
>size of the problem of providing the energy required for inter-
>stellar flight.
>Let us consider an example mission to deliver 100 tonnes to a
>distance of 8 light-years at a continuous acceleration/
>deceleration of 1 g, a mission for which we have some numbers.
>Calculations below indicate that this mission, if powered by
>antimatter, requires a mass of antimatter that represents an
>investment in energy equivalent to at least 105,500 years of
>the rate of production of electric energy in the entire US in
>My 1994 Grolier Encyclopedia says, under "power, generation and
>transmission of,"
>"In 1987, production of electric energy by utilities in the United
>States totaled 2,570 billion kilowatt-hours."


>         =  51.47 kg am

>the minimum energy requirement to create the antimatter to deliver
>1 kg to a distance of 8 lt-yr at 1-g continuous acceleration/
>deceleration becomes
>         54.3 kg am / 51.47 kg am/USE = 1.055 USE   .

>Similar considerations could be applied to relate to the USE the
>fusion-powered-rocket energy requirement, the sail/beam energy
>requirement, etc.  All will certainly be about as much beyond
>current power-generation capabilities as antimatter creation is.
>Human interstellar flight in a human lifetime is even further
>beyond current physics/economics than I had imagined.  Orders of
>magnitude reduction in payload and increase in transit time are
>required to reduce the energy problem to a "manageable" size, to
>only a few USEs, say.
>What to do about the energy problem for human starflight?
>A few plausible ways around the problem (requiring extensions of
>physics, however) come to mind:
>     1. Find some process to make antimatter which does not
>        require creation energy, such as changing matter to anti-
>        matter through some kind of quantum manipulation (trans-
>        mutation).  On 3/27/96 at 9:06 p EST, Lee Parker quoted
>        Kelly Starks (private email of 3/22 at 8:40 a EST), para-
>        phrased, "So physicists are talking about the possibility
>        of rotating the quantum particles to convert a particle
>        of matter to antimatter."
>     2. Discover some ultra-cheap source of energy (cold fusion?).
>     3. Tunnel through space ("warp drive"?).
>The group might think of others.

A few come to mind.  ;)

1) Don't use anti-matter.
2) Don't try for a constant 1 g acceleration for the full durration of the
3) Scale up your power systems.

Space travel always involves rediculas amounts of power.  Actually most
forms of travel do.  The Saturn-V's supposedly put out more power than the
whole eastern seaboard.  To quote myself in the numbers I worked up for the
500,000 ton dry weight Explorer class:

"Assuming we're go to accelerate to 1/3rd of light speed (100 million
meters per second, a.k.a. 1. E8 m/s). At 1 Ship_g (10m/s^2) our ship will
take. E7 seconds to get to speed. That's 115.7 days or about 16.5 weeks.
All that time its out accelerating a Corvette (The Explorer class starship
has a 0-60mph time of 2.7 seconds.). All that time the home fuel launchers
are sending us care packets of fuel. How much fuel?

To accelerate a 25,000,000 ton loaded ship at 10m/s, with a fusion engine
with a specific impulse of 2,500,000 we will need to 'burn' about 10 TONS!
of fusion fuel per second! You'll need 100,000,000 tons (that's a hundred
million tons!) of fuel to accelerate it up to 1/3rd light speed."

Fortunatly Lithium is extramly plentifull on Earth (i.e. cheap) So the fuel
should only cost us a couple dozen billion dollars.  Building a fusion
reactor that can process fuel in those quantities is scaling problem (an
extream scaling problem) but not unprecidented considering the scale of the
ships were talking about.  If we have the infastructure to build the ship,
and the space platforms to construct it at, we can build the power systems.
If we assume we don't have extensive space platforms and infastructure.
We should assume we wouldn't be launching maned or unmaned interstellar

I realize we're talking about unprecidented power levels, but theirs no
fundamental reason we can't generate those amounts of power.  We just never
had a reason to before.  (After all, how much has the U.S. energy levels
gone up in the last half century?  How much growth could we expect in the
next half century?)

Frankly, the cost is a more serious concern.  That of course is complicated
to figure out.  But critical to a project like this.

Who in 1910 U.S.A. would have beleaved we'ld dump the equivalent to a
couple hundred billion $ into the Apollo program, just to plant a flag and
show up the Russians?  Assuming we can work out a technically practical
system, and figure out the types of advancements we'ld need to implement
it, we could then try to figure out cost assumption.

Would we do it this way?
No.  As you later imply their are big holes in physics current
understanding of things.  Since were talking about a half century from now.
We can assume tremendous advances in physics and science.  (Nuclear power
for example was only developed in about the last 50 years.)  By the time
were talking about, the technology were discusing would seem as ludicrus as
a supersonic aircraft designed with wood and fabric, and a piston propeler
engine.  On the other hand coming up with a possible system using the tech
we're using could stimulate others to seriously consider the topic, and
come up with better ideas.

By the way.  What could you do with a 100 ton interstellar space probe?
Assuming it could generate enough power to transmit back what it saw.  It
sounds like little more then a camera platform.  That hardly seems worth
the bother of sending.  I.E. you could get that degree of info from here
via big scopes.  I'm assuming your not considering majic tech like Nano?
)If you were willing to consider that, the power levels wouldn't have
concerned you.


Kelly Starks                    Phone: (219) 429-7066    Fax: (219) 429-6859
Sr. Systems Engineer                                     Mail Stop: 10-39
Hughes defense Communications
1010 Production Road, Fort Wayne, IN 46808-4106
Email:  kgstar@most.fw.hac.com