Re: starship-design: Ramjet workings?

[TLG.van.der.Linden@tip.nl (Timothy van der Linden)]

Kelly,

>>I think this is why Isaac almost turned purple on you ;)
>>If I understand corrrectly: When the particles decelerate into the magnetic
>>funnel, their kinetic energy will be turned into potential energy (ie. they
>>will be pushed into a small area). As soon as the magnetic funnel widens
>>again the process will be an exact reverse, the particles potential energy
>>will be turned back into kinetic energy again (while accelerating the scoop
>>in the right direction). The only losses I can imagine are those of
>>increased radiation during the time that the particles were close together
>>and thus were being hotter.
>
>Thats pretty iffy.  That assumes a lot of very heavy power transfer through
>the field systems and some suspiciously clean magnetic control.  Fusion would
>be a trivial trick in comparison.

I've no anwer to such engineering limits. If I had, I would have submitted a
design myself long ago.
(In a previous reply to Isaac, I too questioned him about the maximum
strength of the superconducting magnets.)

>>>The maximum velocity of the fision products are limited by the physics of the
>>>fusion reaction.  That speed is, as I remember, about an order of magnitude
>>>less then the maximum relative velocity of the fuel stream to the ship.  At
>>>best the fusion motor could only add a trivial amount of speed to the
>>>exaust stream.  If the fuel stream had to be decelerated to much, the
>>>exaust speed could well be less then the initial fuel stream speed.
>>
>>As above, the particles will regain their initial velocity because the same
>>process that slows them down, will also speed them up.
>>If somewhere in the middle you add some energy, you may speed them up to
>>just a bit more than their initial velocity.
>
>I find it hard to visualize how the fields will be able to do this so
>automatically.

Well this is not so much an "automation" its more or less a property. It is
simply the fact that compressed particles will expand as soon as they can.
So when the funnel widens, the particles cloud will expand (turning it
potential energy into kinetic energy).

>>>>>I think the relative velocities would give a 1 to 8 to 1 to 15 angle.
>>>>>Pretty hard to use in a magnetiv rocket nozzel.
>>>>
>>>>The intake velocity and exhaust velocity are probably rather similar,
>>>>since the fusion reaction will likely add only a little bit of velocity.
>>>>So both intake and exhaust nozzle have a similar geometry. The angle
>>>>depends on how far the magnetic field can extend. A longer exhaust
>>>>nozzle means more time for the plasma to expand and thus a smaller
>>>>angle can be used.
>>>
>>>Not really.  The intake has to be very wide to scoop up the dispersed
>>>stream.  So it needs to be wide, and presumably short to limit the power
>>>and structural loads.
>>
>>I think I misunderstood your angle notations. You may want to explain them.
>
>Just noting that since the maximum lateral speed of the expanding exaust is
>the fusion product exaust stream speed.  Since its at best about 1/10th the
>maximum fuel stream speed.  The the tangent of the nozels expansion angle
>would need to be 1/10 or less.  Pretty narow.

Yes this seems to be right. 
I don't understand though why such angles would be hard to generate with a
magnetic field.
Inside a coil having a direct current (DC) the magnetic field is along the
axis of the coil and thus the angle is zero.
I don't think the magnetic field far outside the coil (not even a
superconducting one) will be strong enough for our purposes. In other words
the funnel is completely within the material parts of the engine.

Timothy