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Re: starship-design: Ramjet workings?

In a message dated 9/2/97 2:52:44 AM, TLG.van.der.Linden@tip.nl (Timothy van
der Linden) wrote:

>In a letter to Isaac you wrote:
>>>Also since the ship would be decelerating in the deceleration track.  At
>>>point it will be going at minimal speed, geting impacted at fuel still
>>>at high relatavistic speed.
>The fact that your fuel is moving fast relative to your engine isn't a big
>problem, as long as you add momentum to the pellet-stream that goes through
>the ramjet.
>I think one of the problems in you letters with Isaac is that you assume
>that the pellet has to be stopped first before it can be fused. And that
>thus most kinetic energy of the incoming particles is lost. (If this is not
>the problem, then likely you can neglect the rest of my explanation.) 

I don't assume it must be stoped but I assume:

The fuel will be accelerated inward in order to get it into the ships axis
 quickly, and this will need to be a major delta-v due to the high relative

That this delta -v will heat the fuel and put a major structural and power
load on the fields.

That particals don't instently fuse when they ram one another.

That given the time delays I'ld expect in fusion, and the high relative
speed, I'ld worry the fusion won't release usefull energy until its past the

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.

>The particles will enter the mouth of the ramjet, which is a giant magnetic
>funnel that gets smaller the further it goes towards the heart of the
>ramjet. This funnel pushes the particles towards the central axis of the
>ramjet. Since they don't like to be in a more convined space, they'll to try
>to slow down (kinetic energy is transferred to "heat" energy).  While
>slowing down they'll also accelerate the ramjet backwards. (This is the
>wrong direction for a ramjet!)
>However they have too much kinetic energy to stop and turn around, so they
>will fly through the smallest part of the magnetic funnel of the ramjet.


>If the particles wouldn't fuse, they would expand again in the output nozzle
>(which also is a magnetic funnel, but now expanding in the direction of the
>particles movement). The outward expansion of the particle will push against
>the widening magnetic funnel and accelerate the ramjet forward so that its
>final velocity is the same as before the pellet entered it. (Pushing against
>a widening magnetic funnel, is like pushing against a slanting plane: the
>direction of your push is partly converted into forward motion and partly to
>sideward motion.)

I'ld agree with this if it wasn't for the high relative speed.  Since the
plasma can only expand outward at a certain maximum speed due to internal
presure.  If the relative angle formed by the lateral velocity of the plasma
relative to the 'rearward' velocity of the plasma stream, is shallower then
the slat angle of the magnetic exaust nozzel, you won't get any "push against
the widening magnetic funnel".  

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.

>If the particles would fuse they'd become hotter. That means that they do
>like it even less to be so close together (mass is transferred to "heat"
>Now that they want to expand even more, they'll push harder against the
>magnetic funnel of the output nozzle and thus the ramjet will gain more
>speed than it lost while the pellet entered it.
>(Also the exhaust velocity will be bigger than you'd expect from a fusion
>reaction where the particles had no preferred movement just before they

The forward thrust is based on several factors that may or may not add up to
more forward thrust then rearward drag from the scoop.

Not sure what you mean about "(Also the exhaust velocity will be bigger than
you'd expect from a fusion reaction where the particles had no preferred
movement just before they fused.)".

>So in the end, even though the particles came in with relativistic
>velocities, they will come out with an even higher velocity.

Maybe.  Depends if the deceleration during the scooping process is less then
the addition from the fuel burn and exaust process.

>(Note: several concepts have been simplified a bit, but I believe the
>general idea is correct.)
>P.S. Isaac, if you feel I made a large error, don't hesitate to tell me.