Re: starship-design: Re: Decelerating a Starship

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

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.

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.

>>>>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.

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...

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).

>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.
-- 
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
 __|_)o(_|__
/___________\ "Mari-san...  Yokatta...
\=\)-----(/=/  ...Yokatta go-buji de..." - Karigari Hiroshi