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

Re: New idea Laser launcher/scoop systems

At 3:08 PM 3/6/96, Kelly Starks x7066 MS 10-39 wrote:
>At 11:40 AM 3/6/96, Steve VanDevender wrote:
>>Kelly Starks writes:
>> > Hi,
>> > A couple days back, Tim ran threw the numbers to show what acceleration a
>> > 'fuel packet' would need to get it up to 1/3rd light speed.  Assuming a 100
>> > meter long launcher, the numbers came out at E14 m/s^2  I.E. 10 trillions
>> > G's.  I was obviously upset to hear this.  However that information and a
>> > flip comment I made about the size of a fuel packet ("it could be as big as
>> > a freight car if you wanted") combined.
>>Actually, now that I think about it there is a dangerous likely flaw in
>>this fuel launcher idea.
>>Remember a while back when I ran the numbers on fuel-to-payload ratios
>>for different fuel types?  Remember that hydrogen came out at _minimum_
>>to need 1,000,000 units of hydrogen to one unit of payload to reach even
>>low relativistic speeds.
>>So, suppose we do prelaunch fuel along the ship's track, on the
>>assumption the ship will catch up to the fuel and can then pick it up
>>and use it to decelerate.  For each chunk of fuel, how much ship mass
>>can that chunk effectively decelerate?  Not bloody much if the ship is
>>travelling at relativistic speeds.  The fuel packet may not be able to
>>decelerate its own canister down from 1/3 c, let alone any useful
>>fraction of the ship.  At 1/3 c, you'd have to put more energy into
>>accelerating the fuel than you could get out of the fuel.
>>If we could launch chunks of antimatter, it would be no problem.  But
>>the fundamental problem is that hydrogen fusion is nowhere near
>>efficient enough to reach high relativistic speeds; even with 1000:1
>>fuel-to-payload ratios you can't get near 1/10 c.
>I ran some numbers for fuel to ship mass ratios to get to (or down from)
>various speeds, depending on the spec impulse.  (I think that was one of
>the docs I sent around for review.  1/10th was fairly easy, 3/10 ths became
>obsurd without well over 2,000,000 spec imp fuel.  Higher then .3c and you
>get a geometric escalation of fuel to weight ratios.  (Which is why I never
>consider them for internally fueled operations.)
>The fuel launched by the launcher, will take more energy to launch then it
>will return, but it will return it on the ship.  Look at it this way, the
>microwave beam systems will probably need to beam hundreds of times (maybe
>thousands of times) the power that the the ship will catch.  Other wise
>there's to much risk the sail will drift part way out of the beam, or into
>a weak area of the beam.
>We are not going to be able to do this without a fantastic amount of power.
>Which means a huge support infastructure.
>Lifes tough with those kind of speeds.

Opps forgot to add the mass ration numbers.  :(

Specific impulse
 (exaust velocity)
                Speed 50,000,000 m/s (1/6 light
                                              Speed 100,000,000 m/s (1/3 light
   2,500,000 sec
                7 to 1 mass ratio.
                                              55 to 1 mass ratio.
   2,000,000 sec
                12 to 1 mass ratio.
                                              148 to 1 mass ratio.
   1,500,000 sec
                27 to 1 mass ratio.
                                              785 to 1 mass ratio.

Notice the mass ratios vary rapidly with changes in spec impulse and total
delta-V.  Anyway if we can get 2,500,000 spec impulse, stoping the ship
from .3 c is possible given some real good equipment!  But notice how much
more fuel this takes then externally feed mode!



Kelly Starks                       Internet: kgstar@most.fw.hac.com
Sr. Systems Engineer
Magnavox Electronic Systems Company
(Magnavox URL: http://www.fw.hac.com/external.html)