# starship-design: Fuel costs

```Hi all,
I was runing through some numbers, and it looks like if you have matter
conversion the "fuel mass" needed to get to half of lightspeed is .42 (42%)
of the the ships unfueled mass.  (That doesn't include the deceleration
fuel!).

Then I started to run some cost numbers.  A kilogram of mass converts to 25
E9 kilowatt hours worth of power.

e=mc^2
e (in joules) = M(in kilos) C^2  = 9e16 joules per kg.

1 joule = 10^-6 Mw-sec = 3,600,000 kilowatt hours

Electricity costs about 4-10 cents per kilowatt hour.  If you could convert
the energy directly into antimatter.  Antimater would (at \$0.05 a KwHour)
cost \$1.25 E9 per kilogram.  Thats one and a quarter billion dollars a
kilo!  Given that an Explorer class ship has a mass of 500,000 tons.  That
comes to a fuel mass of 210,000 tons.  Half of which is anti-matter.  Thats
105,000,000 kg of anti-matter for a cost of roughly \$130 E15  or about 130
thousand trillion dollars, or a bit under 100,000 times the federal budget.
8(

For comparison a Li-6 fueled fusion craft would take 4,570 times its dry
weight in fuel to get to half light speed.  For an Explorer class thats
2.23 E9 tons of lithium-6.  (Which is about 8% of the mass of a given mass
of mined Lithium.  Maybe we can seel back the other isotopes of lithium
after we remove the isotope we want?)  At current comercial rates ( priced
at about \$300/lb.  Or \$660/Kg) for Lithium (ignoring procesing fees) that
tonage would cost about \$1,470 Trillion dollars, or 1 thousand times the
federal budget.  Nearly a hundred fold improvement.  8(

To get to 1/3rd C thou an Explorer Class only needs 25,000,000 tons or
about 16.5 trillion dollars worth.  A meer dozen federal budget years!
~~~~8(

Then again, we should be able to get a substantial bulk discount.

Kelly

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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
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