Re: Engineering Newsletter

[KellySt@aol.com]

> > Timothy re: Kelly
> Subject   : Plasma mirror

> What I meant with no turning, was that it just had to reflect the beam
> STRAIGHT back. To do that is has a very precise orientation: the incoming
> beam. The mirror does not have to track a moving object, that is the task
of
> the Earth beaming station. If Earth beams it to the Asimov, then it also
> aims to the mirror. because the Asimov and the retro-mirror are always
lined up.

That wouldn't work, but eiather way.  Straight back is still a direction to
aim at, and it couldn't do it.

--- snip ---

> >The beam must be much bigger then the sail, and wasting energy isn't a
> >critical problem.  The purpose of the beam is to drive the ship.  As long
as
> >enough of the beam gets to the ship to do that, the system can work.
 (I.E.
> >the it can get the ship where it wants to go.)  Efficiency is a cost
concern,
> >but would not effect the success of the project.  After all you don't have
to
> >move the transmitters.  The ships engines however have to be pretty
efficient
> >in order to get the job done (and not melt the ship in the process).
 We're
> >nowhere near being able to design a starship that can "affordably" get
back
> >and forth to Tau Ceti.
> 
> Efficiency is not only a cost concern, if we had 100 to 1000 times more
> energy available, then certain things would be a lot easier.
> 
> >I expect it will need to maneuver around any interstellar rocks or other
such
> >junk. (Hitting a 4 kilometer comet at relativistic speeds is hard on the
> >hull!!)  One advantage of the beamed concept is that the unreflected
energy
> >acts as a radar searchlight to show whats ahead of the ship.
> 
> I think that the beam from Earth has completely ionized and blown away
these
> rocks before the Asimov gets into sight. Also there won't be that many big
> rocks in interstellar space. (If they were, they would certainly make a
good
> braking force)

We have no real idea whats in interstellar space, but is fair to expect a few
comets, asteroids ect; and I don't think we can plan on everything in our way
getting neatly blown out of the way.


> >The plasma reflector will be right next to the ship (surrounded by it
> >actually).  So couldn't possibly miss the ship, and doesn't need to keep a
> >tightly aimed beam.  The retro-mirror on the other hand will be up to 2
light
> >years from the ship, and need to reflect a perfectly beam that converges
> >inward toward a smaller drive mirror on the ship.  The later is a much
harder
> >problem.
> 
> Both the retro-mirror and the mirror on the Asimov are about the same size!

NO!  A retro reflecter mirror wil not work unless the retro-mirror is much
bigger.
-If its the same size and the retro mirror is straight in frount of the ship.
 It will be in the shaddow of the ships drag mirror.  So it won't 'see' any
of the beam to reflect.
- Even if its not in the line of sight.  Being the same size as the drag
mirror on the ship.  It can't reflect anymore energy back to the drag mirror,
than the mirror gets directly from earth.  So It wouldn't be able to
decelerate the ship.

So it will have to be larger and focus the beam backward to a smaller beam.

> 
> You say the plasma surrounds the ship, I thought they were at the TC side
of
> the ship. Does design looks like this:
> 
>             )
> -------------)
>            //)
>          (--------| Plasma
>          (--------| Plasma
>            \\)
> ------------)
>            )
> 
> ( are the small mirror at the Earth side of the Asimov
> ) are the big mirror at TC side of the Asimov
> -- / \ Light rays

Pretty much it.  Imagine the ship as a hollow pipe with a plasma in the
inside of the pipe and in frount of it.  (The ship surrounds the plasma, not
the other way round.)  The microwaves are reflected back and inward by the
forward main ring sial, toward the rear ring sail (drag sail) which reflects
it forward inside the open area of the ship toward the plasma.  It heats and
is reflected off the plasma backward.

> As soon as the photons hit the plasma how are they reflected?
> 
> >Do you mean you don't want to use a beam system thats that inefficient?
> >Efficiency in catching the beam is a luxury we can worry about later.
> 
> Indeed, that's what I'm saying. If a system is only 10% or even 0.1%
> efficient, then for example a fusion system that uses a 1:1000 ship:fuel
> ratio as well.

As well what?  Efficency is not nessisary for a system to be usable, but a
ship that needs to carry a thousand times its weight in fuel simply can't be
built.

> >Right
> >now we're just trying to devise a system that could possibly get us there
at
> >all!  The choice isn't going wastefully vs going efficiency, but going
> >wastefully or not going at all!
> 
> I do not agree, as I said before, the anti-matter engine WILL work. Only
you
> do think that it is very difficult to make anti-matter if you have the
> energy available. I, on the other hand don't see a reason why this should
be
> so extremely difficult in 50 years.
> (And if efficiency isn't that important this will certainly be an option)

You've never suggested how you think such amounts of anti-matter could be
made.  Or how we could build such engines.  Or store such amounts of
antimater.  2050 is to close for us to overcome all those problems on that
scale.


> Another possibility could be to create an energy field (eg. a box with a
lot
> of photons) Then more (virtual) particles will form that may be extracted.
> This method is never used because it is not so easy to create such high
> energy fields, but I think it should work.

Why?  We've never tried any of it.

> How to store the anti-matter? Just like normal matter, create anti-atoms
and
> anti-solids. Finally charge it and suspend it in electro/magnetic bottles.
> OK, it sounds easy, but it seems to be possible.

In theory, but its a big jump from theoretically possible to usable.

> How to refuel? First of all, I'm not so certain that it will return. You
> would be 65 when you're back on Earth while all you worked and lived for is
> on TC. Just to come back and play the hero doesn't seem that much fun.
> But if you really want, than you have to build a refueling station at TC.
> Too difficult? All methods need to build some kind of beaming or fuel
> station at TC and all are probably difficult to realize.

We went around on that question a lot a few months ago.  Yes you have to
bring the crews back.  No one would fund a suicide run without a desparte
need, and we don't have one.
 
> >Your probably right about the E18+ power being a 'show stopper' thou. I
can't
> >think of any reasonable scenario that would have us able to put that kind
of
> >power on line, in space, in about 50 years.
> 
> I think that we have to assume that this minimum is possible, otherwise no
> system is possible unless we "invent" anti-gravity, or if we use a ship
that
> has much less mass (which is almost impossible).
> So it would be better if one the rules of the SD "discussion" was that a
> minimum (unknown?) power source of 1E18 watt is available in 2040.

Or limit the discussion to systems and power levels that seem likely.

> >Your definitely more optimistic about nano and A.I. than I.  We after all
can
> >and do reflect radio and microwave off ionized gas all the time.  We have
no
> >Nano systems, and are making painfully slow progress in A.I.  (A.I. first
> >learned to read aloud over ten years ago.)  So I do think they are
unlikely
> >to be mature enough in 50 years to help us much.
> 
> We indeed do reflect radio-waves, but we do that always at a
> non-perpendicular angle. I'm not sure but, I think it works worse for right
> angles.
> 
> >Actually, even if they did work, they wouldn't solve any critical problems
> >for us.  Just improve effecency and affordability.
> 
> Increasing efficiency or affordability make any design more probable and
> feasable. If for example the space shuttle had AI and nanotech. it would
> probably much more saver, reliable and cheaper.

True, but since we havn't figured out a near lightspeed ship thats more than
marginaly plausible, trying to cut costs on it doesn't mater.  All that would
do would be to make a nonfunctional system cheaper.

> If one makes such a big ship, a lot of things may go wrong and endanger the
> trip. The more complex the ship, the more probable that the trip isn't
> completed. NanoAI will decrease that probability significantly.

But of course, Nano are about the most complex and unrepairable systems we've
even theorized making.


> >Like I said above, I ran some numbers off using the delta-v program on the
> >LIT site, and got a 60 to 1 fuel to ship mass ration for a .2c  Delta v,
> >using the Bussard fusion drive motors.  Thats not an impossible number
(bad,
> >but not impossible).  So I think such a ship could be built by 2050.  So
we
> >could get to the nearer stars.  At .2c we could get to the 4.5 to 5ish ly
> >stars in 22-25 years.  Which should be quick enough to be do able (thou
its
> >pushing it!), thou the crew will probably die durring the 25 year return
> >flight.
> 
> My ratios where for acceleration AND deceleration together.
> 
> Nearer goals would indeed make a better chance of succeeding, also it would
> be a cheaper way to "test" interstellar space-trips.
> The disadvantage is of course that the number of stars is much smaller and
> so are the chances of finding lifeforms or habitable planets.

I'm suspicious of your fuel numbers.  They seem too favorable.

The odds of finding lifeforms and planets are how to judge.  Certainly we're
only taking about a handful of stars within search range.  But it seems
likely all of them could have planets, and we have no idea how picky life is
about where it can form.  In Sol, earths a yes, Mars is a maybe (please send
unbroken lab gear) Venus I'd bet strongly against.  As for the rest and their
moons... ??

One thing we can be sure of, none of the planets out there will be habitable.
 Earth wouldn't be habitable to us if we hadn't evolved here.

In any event a handfull of starsystems should keep us busy for a couple
decades.  Obviously past 2100 all the systems were discussing will seem
archaic, and our physics quite naive.

> >Remember, the limitation on accelerating in a pre-launched fuel stream.
 Is
> >how far out you can get before the fuel gets so spread out that you can't
> >scoop up enough fuel to run the engines.  I.E. how accuratly can you
launcher
> >put the fuel?  A striped down ship could not only accelerate faster,
getting
> >to higher speeds within a given distence from the fuel launcher.  It could
> >also get by on less fuel, allowing it to still keep up thrust farther out
> >from the fuel launcher then its heavyer brother.  If the folks back home
> >really like you.  They will have upgraded their fuel launcher in your
> >absence.  Allowing you to get a usable fuel density at far farther out
from
> >Sol.  
> 
> I've done some calculations, these show there is not that much profit (in
> energy) when one compares prelaunching with take-all-with-you (from now on
> TAWY).

So?  It would make a critical difference in the fuel mass ratio of the ship.

Kelly