[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: starship-design: Re: Decelerating a Starship

I just joined this list, and maybe this e-mail will even work...

KellySt@aol.com wrote:
>In a message dated 8/5/97 1:31:54 AM, you wrote:

>>KellySt@aol.com wrote:
>>>In a message dated 8/4/97 12:49:39 PM, you wrote:

>>>>>Now for the bad news - you have to slow down. We can't pre-load
>>>>>a deceleration course track into the target star with fuel across
>>>>>interstellar distances. ...

>>>>This simply is not true!  It is indeed possible to pre-load a
>>>>deceleration course track.  The trick is that this deceleration
>>>>course track is travelling at relativistic velocities, catching
>>>>up with the starship.

>>>>The basic idea is to launch a bunch of fuel packets after the
>>>>starship has launched at relativistic speeds.  IMO, the best
>>>>launch method would be RPB propulsion.  These packets travel
>>>>faster than the starship to catch up with it when it reaches
>>>>the destination system.
>>... I was imaginining larger packets, ala those described
>>in your "externally fueled fusion drive" web page.  These wouldn't
>>be affected by interstellar magnetic fields much and would include
>>a pellet launcher (and possibly also a dedicated rocket) to roughly
>>maintain course.

>>The pellet launcher would allow its load of fuel to be scattered
>>evenly along a long "track" for the ramjet to use.  Not much of
>>a targetting system is needed assuming these packets are remotely
>>controlled by the starship.

>Ok, similar problem thou.  The onboard propulsions going to need to be as
>extensive as the ships, and going at about the same speed as the ship.  So
>you might as well dock with the ship and save the hassel.

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.

>>>Secound.  To avoid the deta-v gain from scooping up fuel thats going faster
>>>then you (your are trying to slow down) the fuel has to be at a relativly
>>>slow velocity.  (Ideally slightly slower than you at all points of the

>>This is nonsense.  The problem is similar to that posed by the
>>acceleration track--at first, the relative velocity of the incoming
>>packets/pellets is low, but it increases as the starship accelerates
>>until at the end of the run, the relative velocity is approximately
>>the terminal velocity.

>>If you can tackle the problem of the acceleration track, the
>>deceleration track shouldn't be a problem.

>>In the acceleration track, delta-v gain is avoided by using a magnetic
>>scoop ramjet.  The same ramjet could be used for the deceleration

>No thats not how the accel track works.  The fuel is launched to intercept
>the ship at a given time, going at about the ships speed (or a little less).
> Over solar system distences you can do that, but over interstellar you'ld

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).

Because of this, I assumed the acceleration tracks discussed wrt
RAIR and externally fueled fusion rocket were relatively slow,
set up over several years before the acceleration run.

>Besides if the fuel was going as fast as the ship.  When the ship
>slowed down it would blow past it.  If it was going slow enough to scoop up,
>it would have needed to be launched decades to centuries ahead of time.
> Other wise the ship would have outrun it years before.  

I thought the RAIR was _supposed_ to scoop up "fuel" blowing past
it at the same relativistic speeds as its cruise speed.
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
/___________\ "Mari-san...  Yokatta...
\=\)-----(/=/  ...Yokatta go-buji de..." - Karigari Hiroshi