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Re: Re: starship-design: Interstellar Probes

In a message dated 8/11/98 11:37:56 AM, stk@sunherald.infi.net wrote:

>Gene Marlin wrote:
>> Using current and near-term technology, how fast could we get a 2
>> kilogram probe to nearby stars such as Tau Ceti, Epsilon Eridani,
>> Proxima Centauri, and 61 Cygni?
>Depends on what kind of propulsion you use. To get it there fast is
>virtually impossible with current technology. 
>To give you an example of how bad it really is, this is how much it
>would take to send a school bus sized payload past Alpha Centauri in 900
>Propellant:       Specific Imp.:            Fuel mass:
>Chemical           500                      10^137kg (not enough mass in
>Nuclear fission    5000                     10^17kg (a billion
>Nuclear fusion     10000                    10^11kg (a thousand
>Antimatter         50000                    10^5kg (ten railway tankers)
>If you want to get there faster that 900 years, it gets worse. If you
>want to actually stop at the destination, it gets even worse. That's why
>I don't believe we will make it with any of these propulsion systems. It
>would be better for a 2 kg probe, but not good.
>Kyle R. Mcallister

Actually the numbers for a couple hundred thousand ton ship with a max speed
of .4 light (with a external Boost to speed) was 25 million tons, not billions
of tons.  Thou carrying the accel and decel fuel internally would add several