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Re: starship-design: Ramjet workings?

In a message dated 9/16/97 3:33:11 AM, TLG.van.der.Linden@tip.nl (Timothy van
der Linden) wrote:

>Hi Kelly,
>>>Whether one can catch the fuel will of course greatly depend on the
>>>of the pellet-track and the strength of the magnetic fields.
>>>Isaac mentions using "fuel-drones" to enhance the accuracy, my guess is
>>>one indeed can use these to deliver pellets with an accuracy of meters.
>>Given that these drones would need to do that at up to 2.5 light months of
>>distence, after floating in space for a decade, I'ld be far less confident
>I can't answer this, maybe Isaac can convince you (and me) better.
>>>This [delayed fusion] indeed might be a problem, though I think that in
>>>theory the particles could be decelerated to fuse while still within the
>>>magnetic field.
>>True, but that that involves a lot of delta-V on the ship in the wrong
>>direction.  Given the deceleration of the fuel stream could need to be
>>greater then the acceleration possible by fusing the fuel.  Ram scoops
>>well be incapable of boosting themselves against their fuel stream.
>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.

>>>>Also due to the high relative speed and the comparativly meager exaust
>>>>velocity, I'm not clear how you can gat any thrust out of the system.
>>>What other reasons than those you mention above would give a meager
>>The maximum velocity of the fision products are limited by the physics of
>>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
>>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

>>>>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,
>>>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
>>>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
>>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.

>I'm not so sure if we can compress the plasma much faster than it can
>expand. In the case that the plasma can expand faster than we can compress
>it, the intake has to be than the maximal size of the exhaust nozzle.
>However this is becoming so practical that 'I' don't have the answers,
>you've to ask Isaac.

Also this topics going on long enough to be geting tedious.  ;)