Re: starship-design: Re: Decelerating a Starship

[KellySt@aol.com]

In a message dated 8/8/97 8:41:56 AM, kuo@bit.csc.lsu.edu (Isaac Kuo) wrote:

>KellySt@aol.com wrote:
>>In a message dated 8/7/97 5:22:11 AM, kuo@bit.csc.lsu.edu (Isaac Kuo)
wrote:
>
>>>I guess we're not seeing eye to eye.  As I see it, the purpose
>>>of the acceleration and deceleration tracks is to provide
>>>thrust in a way similar to the RAIR concept.  The serious problem
>>>with the RAIR concept is that interstellar hydrogen just isn't
>>>dense enough.  The fuel pellets are supposed to remedy this
>>>(so ignore all that interstellar hydrogen).
>
>>>These pellets are _supposed_ to get scooped up at very high speeds.
>>>In fact, the ramjet depends upon the high speed "impact" with the
>>>magnetic fields (and possibly on board lithium stores) in order to
>>>ignite the pellets without ever braking them to the ship's speed.
>
>>That wasn't part of the idea for this.  Especially if you are doing 30%-40%
>>of lightspeed.  You'ld shread the frount of the ship.
>
>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.)
>
>2.  The starship is a ramjet design, with a powerful magnetic ramscoop
>    in the front, a hollow cylinder hull for the main body, and a
>    magnetic rocket nozzle in the rear.
>
>3.  Fuel pellets are scooped up by the magnetic ramscoop and fused.
>    When they first encounter the magnetic field of the first coils
>    (which may extend far forward of the ship), inducted electric
>    currents instantly plasmatize them.  Then the pinching effect
>    of the converging magnetic field lines compress these pellets
>    as they are funnelled through the hollow central core of the
>    ship.  This compression further heats the pellet and provides
>    the inertial confinement for fusion.  At high speeds, it may
>    even initiate fusion, but at lower speeds impacting with lithium
>    or boron from on board stores may be needed.
>
>4.  The fusion reaction ideally takes place beyond the main body of
>    the ship within the magnetic rocket nozzle in the rear.  This
>    nozzle directs the products backwards with a somewhat higher
>    velocity than they entered with, thus producing thrust.

This is a complicated system using technology (the magnetic scoops, mag
thruster external to the ship, interstellar fuel targeting, etc..) we can't
figure out how to design, or feel is unlikely to work.  So we went for the
lighter and more compact laser fuel launcher system.

For example.  If you hit the fuel at high speed, the magnetic scoops probably
couldn't efect it fast enough to scoop it in and fuse it.  (It would blow
past before the mag fields could ionize it, and be past the ship before it
fuses.)  The scoop systems are very large and heavy and require huge amounts
of power to work.  Then they cause a lot of drag the motor needs to overcome.


>As you can see, the pellets don't hit the front of the ship, and
>the ship actually _depends_ upon them entering at a high enough
>velocity.
>
>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.

The decel run would last for months.  <more below>


>>>>>If you can tackle the problem of the acceleration track, the
>>>>>deceleration track shouldn't be a problem.
>
>>>This presumes the ability to "shoot" fuel pellets or packets at
>>>relativistic speeds in a very short time frame (about half the
>>>total time of the acceleration run).  This requires a _lot_ of
>>>power--maybe even more power than using a laser sail to propel the
>>>target ship (which is less efficient, but can be spread out over
>>>practically the entire time of the acceleration run).
>
>>Thats possible.  Actually its likely to be more since the fuel launchers
>>probably would be as efficent as a microwave beam source.
>
>The fuel launchers would be as efficient?  I can't imagine how, assuming
>you want muzzle velocities greater than 1,000km/s.

Sorry.  I ment to say they probably wouldn't be as efficent.


>If you want a muzzle velocity of 10,000km/s or more, I doubt you can
>make an electromagnetic accelerator long enough to not melt and vaporize
>your pellets before they even reach the muzzle.  In order for the pellet
>to not absorb some percentage of the energy being used to accelerate
>it, it would have to be superconducting--but that puts a limit on how
>strong the magnetic fields can be!  Since the length needed is
>proportional to the square of the muzzle velocity...

Yeah, had to give up on electromagnetioc fuel launchers.  The luancher would
need to be to huge.  So I  went to the multi stage laser launcher system
described.  That would also lean toward fewer big launches, rather then lots
of little fuel pellets.


>That leaves accelerating pellets by laser sail or RPB magsail.  Of
>the two, RPB magsail is more efficient (and has the added bonus of
>eliminating the problem of heating up the sail), but it's still
>not very efficient (compared to an EM mass driver).

If your going to launch the fuel with a sail, you might as well add it to the
ship like in my Fuel/Sail system.  Other wise your launching multiple vessels
for no advantage, and extra complexity.


>>However this is talking about the accel track.  In the decel track its
>>irrelavent since you can't catch fuel runing faster then you.
>
>You turn the ship around 180 degrees.  I thought that was obvious,
>but I guess it requires pointing out.

You expect to be ramed from behind by fuel doing from zero up to .4 c
relative velocity?  This isn't the way 'scooping' is normally described.
 Thou it would get around the problem described.  On the other hand since the
fuel would all hit it going .4c (or whatever the cruse speed is) absolute.
 It seems to offer no advantages.  Assuming you fired the fuel accurately
enough to hit the ship (assuming it never had to move, and the fuel stream
never hit anything on route), why not pick it up on route and store it
onboard?  This would be simpler and less chalenging then scooping.  Also a
LOT safering during the decel.  The high sped impacts would prevent scooping,
and probably trash the ship.

This would leed to another configuration by the way.  If fuel is fired at the
ship as it leaves Sol, and the ship catches it magnetically.  Then the ship
could be 'boosted' by the  act of catching the fuel.  Effectivly it is using
a odd magnetic partical sail to accelerate.  It then holds the fuel for
deceleration.

Kelly