Re: Engineering Newsletter

[T.L.G.vanderLinden@student.utwente.nl (Timothy van der Linden)]

Timothy re: Kelly
Subject   : Plasma mirror

>Yes, the beam from earth can be maintained by a massive infrastructure of
>people carefully tuning it to keep it in the track to T.C.  They also can
>make up for accuracy problems by making a bigger beam.  Transmitting a
>hundred or a thousand times as much power as needed to compensate for all the
>waste that misses the ship.  Thats not very efficient (but thats not a
>problem), and will cost a lot more (which might be a problem); but it could
>still work.  (Actually you would need to do that anyway in order to give the
>ship some room to maneuver around in the beam.)  
>
>The retro-sail on the other hand is a weak flimsy structure of huge
>dimensions, which has to keep a pinpoint aim of nearly all its reflected
>energy at a distance of light years.  A neat trick given its basically a huge
>unsupported sheet of foil being blown along by the beam.  Oh, and it would
>have to keep a pinpoint aim on a moving object up to two light years away.
> So it would be 2 years out of date in its understanding of where the ship
>was, and was going.  

OK, I see the difference.
But what I want to make clear is that it does not have to know where the
ship is. (see next comment)

>And no you can't just not turn.  First, given the load on it from the beam,
>its certain it will being twisted by beam asysmetries.  Secound the ship
>can't be in direct line between the mirror and the beam, so their will be a
>changing angular offset.

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.

>Also the more power you need to drive it and the ship up to speed, and more
>power needs for its maneuvering systems to turn it to keep aimed at the ship.
> Besides you couldn't possibly add enough mass to a structure hundreds to
>thousands of kilometers across to keep it optically flat!

Both are true, but since you are talking about losses of 99% or 99.9% (due
to beam that is bigger than the mirror) I guess that energy to maneuver is
just a minor extra.
Also the heavier the mirror, the less it is turned by the beam, so it takes
less to turn it back. (So the total energy stays about the same)

>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)

>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!

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

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.

>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)

My calculations tell me that to reach 0.9c one needs approximately:
 1 spoon of spacevessel
 1 spoon of anti-matter
 4 spoons of normal matter

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

Timothy re: Kelly
Subject   : nanoAI

>I have no idea how you plan to convert energy directly to anti-matter.
> Certainly thats not how we make it now.  Even if we could generate the anti
>matter, how would you store and move amounts on that scale safely?  And of
>course how do you refuel for the return trip?

Today we use the brute force method of collision. The particles that are
created during that collision are not used and the energy of them is thrown
away after detecting them. (nothing gets much overheated since we are
talking about only a few particles)
The biggest losses are due to the cooling of the (super-conducting) magnets.
If such a collider is build in space or if room-temp. supercoliders are
discovered these big losses may come down.
Also the collision should be made more efficient in the way that some
particles like neutrons and protons are created more often than other
particles. I think this could be done by using the exact right collision
energies.

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.

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.

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.

>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.

>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.
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.

>Hum... I just ran some numbers through the LIT Delta V program using the
>specific impulse of Bussards Fusion engines.  I got about the same numbers at
>.3c but I though I got slightly better numbers at .2c.  But I don't have the
>numbers with me.   Then again, I'm not even sure the LIT program nows to add
>the need to accelerate the fuel mass with the ship (I certainly hope it does,
>I'll have to test it.)

I've made a derivation and a Pascal program that can do such calculations.
It's on the WWW at URL:

http://www.cpedu.rug.nl/~N0642983/calc.txt

>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.

>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 until we change the physics we have to work with (or learn a much better
>way to manufacture and store anti-matter) we are limited to slower, shorter
>range fights.  But flights that would be technically (and financially) far
>less chalenging.  Does anyone disagree?

Indeed, even with anti-matter there will be a limit, it will be something
like 100 ly. But what a world would we create: It isn't possible to ask
something and receive an answer within a lifetime.
Even 4 ly is a big barrier. What happens if one creates a world that far
away from Earth. It is in fact a isolated world. There won't be interactive
communication. All information streams will be one way (from boths sides).

Timothy