Engineering Oldies letter

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

Just after the last official newsletter was send, I mailed these message to
LIT. Because of this some messages seem to be very old, but their content
still applies, so I send them here:

To      : All
>From    : Timothy
Subject : Overheating

I have serious doubts if we can cool the engine of the Asimov or the
beaming-apparatus in solar orbit.

If only a small fraction of the needed power is transferred to heat, things
will melt or be blown away very fast.

Since the power needed will be very big (1E18 Watt) only small portions
(1E12=0.001%) that are not efficiently used can give real trouble. I don't
think efficiecies of more than 99 percent are feasable. So, does any of you
have a solution to this overheating problem?

My guess is that cooling water would not work. And if the engine is on the
Asimov the trouble would even be bigger, since space isn't much of a cooling
fluid.


To   : Kevin
>From : Timothy
Re   : Flat floors, curved walls

>Yes they do flex, or else I missed something major.  consider the hab 
>train while the ship is under acceleration let us designate the floor/ceiling 
<Some text left out>
>familiar trip, you notice that it is the distance between cabs at the top 
>of the cars that is shorter, and the distance near the floor that is longer.

So far OK.

>unless you want people to suit up every time they pass between cars, you 
>are going to have to have a flexible conduit for them to walk through.  

Nope, the junctions would indeed be curved but would be stationary. The
shorter part would always be at the inside of the ring. Now only the tubes
would need to turn. The connection between the junction and the tube would
just be some turnable connection like a wheel that can rotate around an axis.


To   : Kevin Houston
>From : Timothy van der Linden
Re   : MARS Design.

>I agree that the momentum is large, but there will be many transmitters, 
>so each individual one may not be affected so much.  However, if this 
>turns out not to be the case, the effect can be totally negated by a 
<Some text left out>
>but no trqansmitter should have to do this very often.  Of course you 
>would have to double the amount of transmitters, because half of them 
>would be occulted by the Sun at any one time.

Let us take 100 "cubes" weighing approx. 10 ton each: Total weigh 1E6 kg.
Since the total weight of the cubes is much less than the MARS-design
(M=2.5E9) their end-velocity would be greater than that of the Asimov. So
their total weight should be at least 10 to 100 times bigger than that of
the MARS-design if we don't want the cubes to leave our solar system.

According to my calculations each one of the 100 "cubes" would get an
acceleration of about 8000 m/s^2 if they wanted to power the Asimov.
Since this is quite much the "cube" would be blown out of orbit before it
could make one orbit around the Sun, so you add and subtract method would
not work.

Another problem will be that the collectors on the cubes will be blown away
by the Sun's photons. You may think that photons don't have that much
momentum. But I assure you that the amount of photons that have to be
collected is big enough to do that.

In fact you can compare a cube-collectors with a large mirror reflecting
Sun's photons to the Asimov. This means that the collectors get twice the
momentum of the the Asimov.

My idea would be to build mirrors or solar panels with a maser on the moon
or Mars. The only disadvantage is that the mirrors or panels should be
larger but the advantage is that they would not need to be launched.
To get some feel about the size we are talking about:
The mean power we need would be at least 4E17 Joule/second. That would mean
a collector with the size of 4.4E13 square metres in the same orbit as
Mercury or one that is 20 times bigger on Mars. The problem is that Mars is
not big enough!

Having done thes calculations make me realize that the collectors that are
attached to the cubes may weigh much much more than 6 ton and that making
the collectors would be more difficult than making the Asimov. I hope I've
not confused you by the numbers, but I really think they are right.

(The value of 4E17 is an approximation. I first calculated the total kinetic
energy of the Asimov with speed 0.74c and then devided that by the time it
took to accelerate the Asimov to that speed.)

As far as I can see it, direct solar power would not be feasable.


To   : Kevin
>From : Timothy
Re   : Electrons and shielding.

>We can't carry a UV laser with us, because it would never be the right 
>wavelength (due to doppler shifting) so it would have to be a Sol based 
>system.  but if we are going to use a UV laser (to clear our path) then we 
>might as well use that to power our spacecraft, radically altering our 
>design.  anyone know how to convert uv photons to electicity with the 
>nearly 90% efficeincy of a microwave converter? (me niether :(  

Clearing the way for the Asimov with a Sol based system would mean that all
that is in between would be ionized as well. That would mean a lot of extra
energy. I'm sure that in 2040 we have variable lasers in the UV-range. We
now already have them in the visible range.

>The only other way i know to ionize an atom, is to hit it with a positron.
<Some text left out>
>not go where we wanted.  I suppose we could emit some particle that would 
>be nuetral, but would then decay into positrons, but such a particle 
>would violate charge conservation (any ideas?)

Such a particle would be a free anti-neutron it has a decay time of 10.6
minutes and its reaction products are a positron, an anti-electron and a
anti-neutrino. But unfortunately anti-neutrons would cost too much energy to
make for this purpose.

>given all this, I think a simple erosion plate on the front of the ship 
>might be the best answer.  something about 2000 meters in rad, and about 
>20 meters (just a guess) thick. shaped into a blunt cone (we do want to 
>travel at c for part of this trip).  the incoming H,He,etc would hit 
>this, gouging pits and becomming imbeded.  the overall force of this 
>material striking us would be the same no matter if we push it out of the 
>way with magnetic fields or let it impact a physical barrier.

I guess that is like what I was saying all along.

>Oh man, this gets more expensive (energy wise) by the minute.
>Please, Please, somebody flame me and tell me i forgot something that 
>will let us ionize everything ahead of us and go back to using mag fields 
>for shields.  I can't think of a single thing.  we might have to limit 
>our top speed to some high fraction of c, won't add that much more to the 
>trip.  let's say for arguments sake, that we limit ourselves to .95 C.  

I really think a variable laser onboard the Asimov could do the trick.