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Re: starship-design: How to build a station.

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In a message dated 4/20/00 9:50:04 PM, bfranchuk@jetnet.ab.ca writes:

>KellySt@aol.com wrote:
>>
>> In a message dated 4/20/00 2:45:48 AM, bfranchuk@jetnet.ab.ca writes:
>> >With a 40:1 mass/payload ratio 5 tons is a 200 ton space/craft,
>> >a bit large for a first time design. How about 2.5 tons... 100 ton
>> >space-craft.
>>
>> Why do you assume a 40 to 1 ratio?
>
>  There is about a 20:1 mass ratio from the rocket equation
>for a ISP of 350. ( lox/ kerosene or lox/ch4 ). If you assume
>the mass of the craft empty is the same of the payload, that
>becomes a 40:1 ratio.

That doesn't sound right, I remember a paper about LoX/Kero SSTO I I was
pretty sure it didn't need that kind of mass ratio?  Wait a minute I worked
that out for a chapter draft,  I got 17.3 to 1 for a Kero/LOx SSTO  And with
a airbreather combined cycle it came out to 5.8 to 1.  I was assuming 1/4th
of dry weight  was cargo.  Cost of fuel per pound of cargo was \$7.3 and \$2.7.

Anyway since we were refuring to combined cycle birds I couldn't figure out
40 to 1.

>> Solar in general is expensive.  The panels however are simpler and more
>> relyable.
>
>They have been claiming cheap solar panels, as long as the have
>been claiming cheap access into space.

The term cheap takes on stange meanings in the space busness.  ;)

>> A LOX/Kero rocket based SSTO would use 14:1 fuel/craft ratio.  The air
>> breather could cut that to 7-1 maybe less.  Given Kerosine is far more
>dence,
>> it needs a far smaller and lighter tank.
>
> I just think in the near future +25 years the price of oil/gas will
>skyrocket and CH4 will be cheaper than synthetic Kerosene.

Projects ae with current projected reserves, we can meet all growing oil
needs for 200-300 years.  Prices have been going down (eratically) for a
century, and is likely to keep doing so for another century or so.  If need
be, there is LOTS of oil drifting around near earth space.  So if you can cut
the launch costs of empty frighters enough, you can sell oil from space down
here.  Global warming folks will scream though.  ;)

>
>> Kelly

Kelly
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