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Re: starship-design: Pellet track

In a message dated 8/8/97 9:49:36 PM, kuo@bit.csc.lsu.edu (Isaac Kuo) wrote:

>Timothy van der Linden wrote:
>>You wrote to Kelly:
>>>Well, then I guess my idea is more original than I thought.  So here is
>>>my concept for the acceleration track:
>>>1.  An relatively slow moving acceleration track is set up so that
>>>    somehow a track of small fission/fusion pellets are spaced along
>>>    a line.  (I imagine a string of pellet shooting fuelpacket ships,
>>>    to minimize the time/distance between firing the pellets and
>>>    their target pickup points.)
>>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
>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.

>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.

>3. The fuel requirements for a given cruise velocity go up roughly
>   linearly, as opposed to exponentially for a fusion drive.  I am
>   not even convinced that we will even develop sustained fusion
>   reactions in the next millenia, given the technical problems
>   with the high magnetic fields and pressures needed (magnetic
>   fields are "leaky" and plasma just loves squeezing out and
>   amplifying those "leaks").  Needless to say, I'm skeptical about
>   the potential to develop fusion drives, and looking at the designs
>   envisionned for normal fusion drive starships, I'm _very_ skeptical
>   that we can hope to acheive any large fraction of the theoretical
>   maximum Isp.

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.
 Considering the kinetic energy of the fuel to scoop impacts.  Holding a
stable fusion plasma would seem to  be trivial in comparison.

>4. The effort involved may be spread over a long period of time.
>   For the acceleration track, this might not be much of an issue,
>   because all the time spent setting up the acceleration track
>   is simply delaying the completion of the mission that much
>   longer.  For the deceleration track, this is a critical bonus
>   because you can manufacture and send fuel packet drones over
>   a period of years while the starship is progressing toward
>   the target system.
>And no, you do not "catch" the pellets in the sense that you brake them
>up to the ship's speed.  The plasma remains of the pellets blow through
>the hollow central core at high speed.  It's a ramjet.

So the fuel impact would be boosting you forward at the full fource of the
fuel stream.  The motor then has to counter thrust enough to compensate and
still slow down?  Remember the scoop can't turn and channel .4c fuel into the
ships motors.  (Ramjets are not considered very doable anymore.)

>>>The idea for the deceleration track?
>>>Same idea, but with the ship turned around 180 degrees.  Yes, this
>>>implies having some shielding in the back of the ship, but the
>>>deceleration run shouldn't last too long.
>>Still you have to launch the pellets many many years in advance.
>No, I assume that all resources prior to launch were devoted to
>the acceleration track and the starship itself.
>The deceleration track, which takes longer to set up and requires
>much more power, is launched _after_ the starship, at velocities
>somewhat higher than the starship's cruise speed to catch up with
>Assuming a mission to Bernard's Star at .5c, these deceleration
>track packets drones could be launched over a period of 3 years,
>at a maximum velocity of .67c (for the ones launched at the end),
>and all arrive at around the same time.  Before arriving at the
>intercept points, each drone would fire its load of fuel pellets
>to arrive in a steady line to meet up with the starship.
>Now, this still requires a pretty heavy set up of RPB emitters
>to accelerate the packet drones up to relativistic speeds,
>but presumably these same RPB emitters could have been the ones
>used to accelerate the starship up to the minimum speed needed
>to operate the ramscoop (for the acceleration track).
>The difficulty of launching the packets gets progressively more
>difficult as time goes on, because they have to get faster and
>faster to catch up with the starship in time.  However, this
>is perfectly in line with the idea of manufacturing more and
>more (and hopefully better) RPB emitters as the mission continues.

What is a RPB emitter?  All I can think of is relatavistic partical beam
emitters, but that doesn't seem to make sence in this context.