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starship-design: Re: starships

In a message dated 1/8/99 9:51:03 AM, jdavis@crcom.net writes:

>KellySt@aol.com wrote:
>> In a message dated 1/5/99 10:02:26 AM, jdavis@crcom.net writes:
>> >Your explorer class starship is a nuclear electric propulsion
>> >interstellar ramjet, and so are many of my own designs.
>> >The idea of placing fuel in the starships path artificially
>> >,however is impractical. A nuclear electric ramjet must use
>> >ion or plasma type engines to propell it. A nuclear fission
>> >electric power source is sufficient to energize such a vessel.
>> >Nuclear fusion , and antimatter power sources are desirable,
>> >but they are not required . The strength of the interstellar
>> >magnetic field is 1 * 10 to the - 6 power gauss. The strength
>> >of the interstellar electric field is 1.6 * 10 to the -19 power
>> >electron volts. The ion collection radius of a ramscoop is
>> >the distance at which the ramscoop field is stronger then the
>> >interstellar field. The strength of the ramscoop field declines
>> >proportional to the inverse square of the distance from its sources.
>> >This means that an electrostatic field achieves the greatest ion
>> >collection radius in interstellar space. If we use a 1000 volt
>> >electrostatic ramscoop field the ion collection radius will be
>> > equal to 1.6 * 10 11 th power meters. 1.6 * 10 (19) + 1 * 10 to
>> >the 3rd power volts is 1.6 * 10 to the 22nd power. The square
>> >root of 1. * 10 to the 22 power is 10 to the 11 power by the
>> >inverse square law. 10 to the 11 power meters is equal to
>> >100,000,000 kilometers. This 1000 volt bussard ion collector
>> >will then have an ion collection radius of 60,000,000 miles.
>> > This is why the electrostatic bussard ion collector is the
>> >solution to the problem of ramscoop design. Any comments?
>> >Timothy J. Mayes
>> Sorry its not a nuclear electric propulsion interstellar ramjet, its
>a fusion
>> direct plasma drive.  We gave up on ramjets when we realized there was
>> little known mass in this area of interstellar space, the scoops would
>be hard
>> pressed to scoop up as much mass as the scoop gear would weigh.  (I wen't
>> that somewhere in the site but can't find it at the moment.
>> Sorry for the delay geting back to you.  Been crazy around here lately.
>> Kelly
>The density of hydrogen in space is 1 atom per cubic centimeter.
>Ion and plasma engines require only grams, not kilograms of
>reaction mass per second to function. I believe it is feasible to 
>collect grams of reaction mass per second with the ramscoop field.
>1 gram of mass accelerated to 5% of the speed of light can generate
>about 100,000 pounds of thrust. 5% of light is about 45,000,000
>feet per second. The thrust of a rocket is equal to the exchaust
>velocity times the amount of  mass ejected per second. 
>On direct thrust fusion drives, I would recomend Nuclear pulse 
>propulsion .  This can be either a Deadulas, or an Orion class
>nuclear pulse rocket. It has been possible to build an Orion class
>nuclear pulse rocket since the 1960s. Deadulas class nuclear pulse
>rockets use 1mg, to 1gm size fusion fuel pellets, which are heated
>and compressed by either particle beams, or laser beams to induce
>nuclear fusion in them. Lithium 6 hydride is the best fuel for them.
>This is also the fuel used in most H-bombs. Orion class Fusion nuclear
>pulse Rockets are propelled by the detonation of H-Bombs behind an
>inertial plate. A little more engineering work is required to create
>a Deadulas class fusion drive. Orion is feasible already however.
>Nuclear fusion only converts about 1% of the mass of its fuel into
>energy. This is why the maximium exchaust velocity that can be
> generated by a fusion drive is about 11% of the speed of light.
>A single stage fusion drive rocket with a reasonable, and realistic
>mass ratio can achieve at most only 15% or 16% of lightspeed.
>For this reason a fusion drive interstellar rocket is going to be
> non relatavistic. 
>Timothy J. Mayes

The problem isn't reaction mass but fuel.  Accelerating a material 5% os light
speed (a 15,000,000 meter per secound delta-V requires a lot of power.  We
need the hugh fusion fuel amounts to generate the power.  Since fusion
reactions that exaust all their energy as charged particals kinetic energy
effectivly convert 100% of the fuel energy to thrust.  A direct fusion plasma
drive gets about all the thrust out of the fuel thats possible.

The Explorere and fuel sail designs use a modified single fusion stage.
Eiather be launching fuel to the explorer externally (effectivly the launcher
system acts as a plus stage), or using a microwave sail to boost the Fuel/Sail
craft up to speed on the trip out, or decel it on the way back.  This still
does require HUGE fuel mass ratios on the ships (10's og millions of tons of
fuel on a craft weighing 100's of thousands of tons), but it does allow
reasonable speeds up to 30% - 40% of light speed.