Re: starship-design: Pellet track

[KellySt@aol.com]

In a message dated 8/14/97 2:19:57 AM, kuo@bit.csc.lsu.edu (Isaac Kuo) wrote:

>KellySt@aol.com wrote:
>>In a message dated 8/8/97 9:49:36 PM, kuo@bit.csc.lsu.edu (Isaac Kuo)
wrote:
>>>Timothy van der Linden wrote:
>
>>>>If the pellets are slow moving, then what is the use of pellets?
>>>>Catching pellets like this, will not give a significant energy advantage
>>>>over taking the pellets with you (=attached to the starship) from the
>>start.
>
>>>The advantages are:
>
>>>1. You only have to accelerate the unfueled ship.
>
>>Well not really.  The ship slams into the unaccelerated fuel and has to
>>accelerate it up to most of the ships velicity in order to scoop it into
the
>>engines.  Otherwise it would blast through the scop mechanism and past the
>>ship before the scoop could shift it inward.
>
>First off, I'm going to view this in terms of the inertial frame of
>the ship.  Thus, the ship has no kinetic energy but the incoming
>pellets have a lot of kinetic energy.
>
>When the fuel first hits the magnetic field, induced electric fields
>would heat it up and turn it into plasma.  For the most part, this
>energy is lost forever (because the effective expansion ratio of
>the magnetic rocket nozzle won't cool the exhaust down to such a low
>tempurature).
>
>However, once broken down into charged particles, the plasma can
>be directed with the magnetic fields in an energy conservative
>way.  The electrons in a TV travel at around .75 c, and yet
>TV tubes don't have to be many times longer than they are wide.
>You could do the same thing with protons with magnetic fields
>only a 1000 times stronger than a TV CRT's.

Note the mass of the TV tubes deflector magnets in comparison to the mass of
the beam they are deflecting.  Now scale such a system up to handel tons of
fuel over tens if not hundreds of miles.

Oh, you forgot the lateral thrust needed to bend the fuel stream, has to be
countered by a similar force on the ship.  Assuming a balenced and centered
partical streeam (unlikely) that would translate into structural loads on the
ship and scoop mechanisms.


>So the individual particles will continue to travel at the same
>speed that they entered the magnetic fields at (despite having
>their path radically bent).  The challenge is to direct all these
>particles rearward with the magnetic rocket nozzle.  Here's
>really where the losses can really creep in if the nozzle isn't
>designed just right.  All the kinetic energy of each particle
>is still there (magnetic fields are conservative), but the nozzle
>has to direct the particles in the rearward direction.
>
>>>2. You don't have to bend over backwards trying to ignite fusion (since
>>>   you're using the pellet's kinetic energy).  It's actually _easier_
>>>   to implement a fusion ramjet than it is to implement a onboard
>>>   fusion drive.
>
>>Ah, but that would ignite the fuel during the point of Max acceleration in
>>the system.  Which would be when it hits the scoop, not when its in the
>>engine?  The fuel would produce nothing but drag.
>
>No it wouldn't.  Acceleration isn't the same thing as compression.
>A magnetic field affects charged particles by making them tend to
>follow the field lines (actually, they make a helical path around
>a field line).  Thus, compression is caused where field lines
>get closer together.  A ramscoop design uses several coils to
>generate a magnetic field with field lines converging toward
>the center.  This has the inevitable effect of compressing whatever
>it scoops up in the center.

Since the plasma starts out as frozen particals (high density).  The flash
heating as the pellets slam into the scoop fields would cause uneven inertial
confinement fusion in the particals as they hit the collector fields.  Asside
from scattering the unburned fuel.  It would also rattle te hell out of the
scoop system, and starve the engines.


>>I also doubt magnetic confinement fusion will ever be practical.  Certainly
>>the systems the U.S. gov. research group are coming up with suggest that.
>> Thats why I'm using the voltage compression system described by Bussard
(and
>>decribed in the web site).  You however ARE assuming we can megnetically
>>control ultra hot plasmas.  Thats how your scoop/drive system works.
>
>I assume we can magnetically control ultra hot plasmas because we _can_
>and _do_ control ultra hot plasmas.  Demonstrating fusion in a magnetic
>confinement research reactor like Tokomak is routine.  Demonstrating
>_sustained_ fusion isn't (obviously).  That's why I'm so much more
>optomistic about pulsed fusion.
>
>Anyway, magnetic confinement is a very mature technology, thanks to
>millions upon millions of dollars worth of research over the last
>several decades.  At least we're already familiar with it and its
>technical pitfalls.

Actually stable magnetic confinement of dense high energy plasma streams is
the critical failure in our magnetic fusion research.  Since its the brick
wall we can't get past now, why are you so confident that its the easiest
tech for a future rocket system?

Kelly