Re: Engineering Newsletter

[KellySt@aol.com]

>From    : Timothy
Subject : Prelaunching

>>> This method of prelaunching fuel packets will cost the 
>>> same amount of energy that is needed if you take those 
>>> same packets with you from the start.
>
>True, but since the ship doesn't have to supply the energy, it saves an
>incredable amount of fuel.

TV > The ship does not have to supply the energy! It will leave
TV >  fully fueled. It is still accelerated by some kind of 
TV > photon beam.

No, Kevins starship design is propelled by a photon (maser) beam.  My
origional Explorer design is propelled by fusion powered mass drivers.  I
call it an externally feed system since the fuel is thrown out ahead of the
ship by a launcher in Sol.  (See my Explorer  starship design page on the LIT
site.)  Thats probably the central thing confusing you.  Unless your
confusing the Explorer ship with the plasma mirror design I came up with more
recently.

>To put it bluntly no fusion powered ship could
>carry enough fuel, to accelerate itself and its fuel up to high reletivistic
>speeds.  Estimates are that a ship would need a 1,000,000 to 1 fuel to ship
>mass ratio to get up to 10% of light speed.  But if the ship doesn't have to
>carry its fuel, a 200 to 1 ratio could get you most of the way to light
speed
>(or was that 1/3rd light speed.  Been a while since GES ran the numbers off
>for me.)


TV > Huh, if it doesn't carry its fuel, how do you calculate a ratio?

Figure out how much fuel it would take to run the reactors & engines enough
to accelerate the ship (but not its fuel) up to speed.


TV > !! Please be specific if you mean FUEL or REACTION MASS !!

I was being specific.  I ment fuel.  (Thou I suppose you could save some
bucks by adding in extra reaction mass to the launched shipments.)

>>> The problem is that there are no accurate numbers of 
>>> the density of interstellar debris. So any number is almost 
>>> a guess.
>
>Thats been a constand problem for us.  How do you design a ship to travel
>through something you know next to nothing about?


TV > It would be best if we could find a solution without using the
interstellar
TV > particles, but at the same time we should keep in mind 
TV > that we have to protect us against it. This may sound a 
TV > bit contradictory but a general solution would be best. 

How about working out a high and low range based on the most and least mass
expected out there? 

===========================================================================

ReplyTo : Kelly
>From    : Timothy
Subject : Plasma mirror

>>> Replenishing the "mirror" will probably take lots of ions 
>>> or in other words mass that has to be taken with us. 
>
>Agreed, but I don't have a handel on the amount of mass.

TV > Why doesn't it have to do with the amount of mass? 

Don't understand you question.  I was assuming it would depend on the mass,
but I didn't know how much mass that would be.

TV > Ions are particles too.  They may have small masses, 
TV > but if you have enough of them you could build a
TV > complete dragon-fly sail.

I don't know which system would be lighter, but of course we couldn't build
the dragon-fly system, so thats kind of a mute point.

>>> Also using such a light (non heavy) sail will mean that 
>>> the "mirror" is accelerated a lot and lot of energy is lost
>>> due to the Doppler effect.
>
>Given that the mirror is the surface of a plasma, and said plasma is being
>continuously being replenished.  I'm not sure the reflective "surface" is
>actually moving?  Althou obviously the particals in the plasma are moving
>(and accelerating) rapidly.  Are the micro waves reflecting off the
>particals?  Or off the area where the plasma is ionized enough to reflect
>them? 


TV > Probably all the way in between. But that is not important
TV >  here, because a reflection means transfer of momentum, 
TV > and with it energy. Since the plasma will be accelerated 
TV > a lot, it will retrieve a lot of energy.

Do you mean absorb a lot of energy?  That is a problem with a drop mirrow or
plasma mirror idea.  But as long as you can do it and get thrust to
decelerate the ship (the big problem in al this), it might work well enough
to get us somewhere.  (Assuming the whole thing doesn't melt the ship!)

>>> Also I have doubts how well the "mirror" reflects, ionized 
>>> particles attract or repell each other so, it won't take long
>>>  befor the "mirror" has destroyed itself.
>
>The ions in a plasma of the same material wil repell each other.  You might
>be able to do some magnetic tricks to hold it, but it probably wouldn't be
>worth the trouble.
>
>[ Hum --- I wounder if you could wiggle the exausting plasma to for a laser
>to get back some of the energy? ]


TV > Don't talk about plasma as if it where some easy to 
TV > control stuff. The movement of the plasma itself would
TV >  create magnetic fields. It's like boiling water but much
TV >  worse.

I didn't say it was going to be easy. (Thou compared with the sail, the power
generator, and transmitters; It will be a snap!)   I just said it might be
worth doing.  I mean the plasma will have a LOT of energy in it.  It might be
worth tapping some off.

>As to reflectivity.  That would depend on the nature of the plasma and a lot
>of other variables.  This is probably not a question we could easily figure
>out for ourselves.

>>> Shock wave? I don't understand, please explain again.
>
>You have a mass of plasma being hit with E18 of energy.  It will be HOT, and
>highly ionized.  It will be explosivly expanding.  The light pressure of the
>beam (or the feed mass) will probably keep it from flowing straight up the
>beam.  But it will be moving rapidly to the sides and forward or the ship.
> We should be able to tap this for thrust.


TV > My guess is that this shock wave will move mostly 
TV > forward instead of backward.

If by forward, you mean toward Tau C.  I agree.  But like you said, plasmas
get messy.  One this hot will be blasting outward violently!  We might be
able to use the lateral plasma stream to push the ship beamwards.  (Every
little bit helps.)


TV > You seem to want to do the same thing Kevin did: Make a 
TV > easy thing complicated and so loose complete control
TV >  over what you are doing.  Whatever method you can think
TV >  of, it will take just as much energy that the
TV > dragon-fly-sail will use.

On the contrary.  I'm trying to take a very complicated system and make it
simpler.  Notice I don't have the massive microwave to electric power
converters of Kevin's origional drive system.  Nor do I have the ultra exotic
A.I. controled active structure of Forwards drop reflector sail.  Forwards
design would have had to steer itself, while steering the reflected beam back
to the main ship, while tracking the main ship over interstellar distences.
 This is not easy, and it is REALLY pushing the envelope of probable 2050
technologies!

On the other hand my plasma mirror idea would all take place in the area of
the ship, and be directly controlable by the ship.  Assuming it wasn't mass
or energy prohibative, it would clearly be the prefered system.  (Assuming it
would work of course.)

Kelly