Re: Re: starship-design: Pellet tracke

[kuo@bit.csc.lsu.edu (Isaac Kuo)]

KellySt@aol.com wrote:
>In a message dated 8/29/97 5:08:31 AM, kuo@bit.csc.lsu.edu (Isaac Kuo) wrote:
>>KellySt@aol.com wrote:
>>>In a message dated 8/22/97 1:51:40 PM, you wrote:

>>>>I feel like I'm talking in circles, constantly having to repeat the same
>>>>things to the same responces.  We already went over this at the start of
>>>>this pellet track discussion.
[snip]
>>I find this particular point annoying, because right from my very
>>first e-mail, I explicitely described the concept of the
>>deceleration track moving at relativistic speeds catching up with
>>the starship, and from you very first responce you mentionned
>>the problem of these things slamming into the ship, destroying it.

>In the above statement I was refuring to said: "they arrive near the target
>system with an error of10km or less."  Normally people distinguish between
>ariving at a place, with flying through it.  I.E. when you say you arrive at
>a gas station.  People assume you stoped their, as apposed to saying you
>passed a gas station.

This is a bad assumption to make, especially in this situation.

What if I had said, "they fly through the target system with
an error of 10km or less"?  And then talked about how they
shot pellets into a pellet track?  I suppose you'd pose the question
of how this pellet track is supposed to help decelerate the starship
if the pellet shooters have already flown past the target system.

Could you try and pay attention and stick to what I actually write,
rather than set up the same straw men over and over again based
on your inappropriate assumptions?

>As to the secound part you refure to the ship as a ramscoop.  Ramscoops, or
>any kind of scoop, scoops up material as it over takes it.  Like the intake
>scoops for a jet engine.  In your case the ship would be catching the fuel as
>it hits it from behind.  But using the scoop term confused it.

Umm...what would you call a "scoop" which scoops up material which
is being shot into it?  I've repeated many times about the ship
turning around 180 degrees to scoop up pellets as they "catch up"
with the ship.  How many times do I have to repeat it?

>Also since the ship would be decelerating in the deceleration track.  At some
>point it will be going at minimal speed, geting impacted at fuel still going
>at high relatavistic speed.

And how many times do I have to repeat _this_, and how it is,
as far as the starship is concerned, _identical_ to the situation
with the acceleration track?

Let me try and repeat this again, in simple terms:

1. The acceleration track is essentially moving at speed 0.
   The starship starts off at around speed 0, so initially
   it is scooping up pellets at a low relative speed.  As
   it accelerates along the acceleration track, its speed
   goes up while the speed of the pellets in the track stays
   at 0.  The relative speed of the pellets steadily goes
   up until it reaches .5c, the cruise velocity of the starship.

2. The deceleration track is essentially moving at speed .5c.
   The starship starts off at around speed .5c, so initially
   it is scooping up pellets at a low relative speed.  As
   it accelerates along the deceleration track, its speed
   goes down while the speed of the pellets in the track
   stays at .5c.  The relative speed of the pellets
   steadily goes up until it reaches .5c.

>Also of course, catching a heavy fuel stream (10's to 100's of tons per
>hour?) going at up to .5c relative to the ship.  Will be very chalenging to
>the rear catcher structure and fields.  If any blows through without being
>completly caught.  It would rip the ship to shreads.

Are you doing this on purpose, just to annoy me?  I'm beginning to think
you understand perfectly what I'm trying to say, but for some perverse
reason you're pretending to misunderstand just to be difficult.

Later on in my post, I repeat many many many times that the ship
turns around 180 degrees.  If you forget or pretend to forget
this simple little statement once more, I'll simply ignore your
e-mail messages forever.

>>Get this straight.  The fuel packet drones have their course
>>corrections during their acceleration run, and this is sufficient
>>to acheive an accuracy of 10km or better (I analyzed this before
>>assuming the target system of Bernard's Star about 6 LY away).  I
>>did not explicitly explain that the packet drones don't make
>>course corrections during the cruising run, because:

>>1. It wasn't necessary.  Course corrections during the acceleration
>>   run (accomplished by using the accelerating RPB and varying the
>>   magnetic field of the magsail) were enough to acheive the desired
>>   accuracy of 10km.  (The pellets which are shot have to be able to
>>   hit an area the size of the starship's ramscoop at 10km.)

>>2. I would have had to explain about the extra overhead involved
>>   in built in thrusters not being worth it.

>>3. I would have had to explain about the fact that although the
>>   pellet shooter itself could be used as a rocket thruster, it
>>   has a pathetically low Isp (1km muzzle velocity is merely 100sec
>>   Isp).

>>The fuel pellets aren't fired until a short time before reaching
>>the deceleration track's position.  Why?  To make those
>>interstellar effects irrelevant.

>You agree that interstellar effects could cause the fuel stream to drift of
>course, but assume they would have no effect on the fuel tankers?  My
>mistake.  I assumed you'ld realize eiather would be subject to interstellar
>forces that would probably disrup their course.

Both are subject to interstellar forces, but the massier fuel packet
drones will be influenced much less.  The biggest problem is magnetic
fields, since they extend so far into interstellar space.  Any fuel
pellets will inevitably have a small non-neutral charge, which would
result in magnetic fields affecting their course slightly.  For
relatively heavy fuel packet drones, this effect could easily be
insignificant.

>>>Then the pellats will have to be fired at the rear of the ship.  For
>>>collection in rear scoops.  An done befor the ship is passed by the
>tankers.

>If you turn the ship around.  Then the frount effectivly becomes the rear.

If you really understand what I'm saying, why talk about "rear scoops"
at all?

There's only one ramscoop--it's the same one used during the
acceleration run.

>>I'm aware of this.  Which is why I explicitly explained that the
>>magnetic nozzle is what provides the forward thrust.  In order
>>to calculate which effect is greater, you need only consider
>>what effect they have on the momentum of the pellet--the ship
>>will necessarily experience an opposite momentum change.

>Good we agree.

>>>If the fuel is successfully funneled into the engine.

>>We understand how to manipulate plasma with magnetic fields
>>well enough to do this.

>Tons of it impacting at up to .5c?  All being scooped up with an extreamly
>large, light structure extending over miles, which is trying to catch this
>fuel stream magnetically almost instently.  This implies extreamly high g
>loads on the fuel stream, and similar structural and thrust loads on the
>ship.

It's not impacting all at once (I posted before a reasonable mass
rate) for a 1km long ship (not even 1 mile long) weighing 1000
tons (not exactly lightweight).

Yes, it's beyond anything we're doing today, but that's because
we don't have any way to create a very heavy stream at .5c.
That doesn't mean the powerful magnetic fields in today's
research fusion reactors couldn't handle them.

>>Anyway, I did already explain how the fusion cross section
>>increases linearly with the rate of compression, and how
>>the rate of compression in this design is proportional to
>>the speed of the incoming pellets.  The time allowed to
>>fuse with sufficient yield is, of course, also proportional
>>to the speed of the incoming pellets.  If this thing works
>>at any speed, it will work at high speed.

>As I remember nuclear interactions take a finite amout of time.  Even
>assuming the fuel instently started to fuse, it would still take a finite
>amount of time for the fusion reaction to happen.  After that the fusion
>reaction would trigger the resulting particals (we've been assuming
>anti-nutronic fuels that release all fusion energy as fission products).
> These particals travel at far less then .5c (off hand I think about 1/10th
>that) so the resulting expansion would be a rearward 10 to 1 cone.  Unless
>you can interatct with this to provide forward thrust (and I'm not sure how)
>and can do it rapidly, you don't get thrust. 

The interaction is provided by the magnetic nozzle, which takes the
off center paths of the particles and bends them so that they leave
the starship straight rearward (in the starship's frame of reference).

>How?  The mag field cant accelerate the fusion particals rearward.

Yes they can.  In the starship's frame of reference (where the
magnetic field is fixed), the magnetic field is conservative--meaning
that it can bend the direction of a particle's motion, but can't
add or remove from it speed.

However, that does mean it can bend the motion of a particle moving
at an angle other than directly rearward to a straight rearward path.
That _is_ accelerating it rearward (as well as sideways).

>You seem to assume that the magnatized fuel stream wil follow the magnetic
>lines of firce into the engine system without being subjected to the velocity
>changes nessisary to alter its direction.   I.E. violating conservation of
>momentum. 

There will be _velocity_ changes, but not speed changes.  Actually,
the apparent speed of a particle macroscopically will look as if
it has been slowed down a little, whereas in reality it's taking
a helical path around a magnetic field line at its original speed.

>>Yes, but the power is entirely from the speed of the incoming
>>pellets.  The magnetic scoop, being superconducting, does not require
>>energy to maintain its magnetic field.  The pellets, OTOH, see a
>>different thing.  They see a changing magnetic field (because to
>>them, the magnetic field is moving at high speed toward them).
>>As they pass through the "bottleneck", it looks to them like the
>>magnetic field lines got compressed.

>No, it still takes power for the magnetic field to shove the fuel stream
>inward toward the center of the reaction zone.  That power needs to be
>suplied by ships systems, and needs to be restrained by the ships engines and
>scoop structures.

No it doesn't.  The magnetic field is being generated by
superconductors, which don't require any input of energy
to maintain their (fixed) magnetic field.  The pellets
see a changing magnetic field because they are moving
w.r.t. it.  Where is the energy coming from, then, if
it's not coming from the ship?  It's coming from the kinetic
energy of the pellets (in the frame of reference of the starship).
-- 
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
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