Re: Engineering Newsletter

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

>Oh, any idea why the LIT site droped off the SUNSITE server again?

Yes, they had a major harddisk failure.

Timothy re: Kelly
Subject   : Plasma mirror

>> Is it really that hard to keep the mirror straight? And still, if the beam
>> deviates, the Asimov can still follow it (too a certain amount) by
>> redirecting its own mirror.
>
>Its kind of like balencing a meter square sheet of aluminum foil on the blast
>from a fire extiquisher, and expect it to never wrinkle or twist.

You should compare each of the 2 parts of the retro-mirror with a bridge
over a valley. The mirror itself would be the road, behind the mirror there
would be strenghtening structure, that would be curved just like the bridge.
The mirror would stay reasonable flat just like the road that connects both
sides of the valley.

>The ring sail is anchored to the ship.  Sort of like a parachute. I.E. a
>parachute attached to a weight forms a nice shape.  Cut the corts and it
>turns into a lose sheet flutering and twisting down.

This assumes the wind is constant and comes always from the same side
without small deviations. As soon as the wind comes a bit from aside, the
parachute will turn a bit so that its movement is parallel with the incoming
wind.

>>If there are indeed so many rocks that we have to worry, then we certainly
>>should make use of them. How big do you think the chances are that any of
>>these lumps comes even near the Asimov?
>
>How could you make use of them?  Your runing past them at a relativistic
>speed.

Lower an anchor... :)  But seriously, we have a minimum of 1E19 Watt
available, with that power you could move a mountain (literal). Then why do
we need so much power, we are only 2E9 kg? We move at 1E8 m/s relative to
that energy, that's why.

>Sorry thought that idea was droped.  With this you have two mirrors flaping
>in the breze trying to aim at something.  Your odds of aiming accuratly have
>droped accordingly.  Also you still have to focus back toward a smaller sail
>on the ship.

I don't see why these mirrors are flapping, see also the above.

>>If it reflects straight back, then it enters the plasma pipe, that must mean
>>trouble. Please tell me what happens after the (first) reflection on the
>>plasma.
>
>Ideally, the beam reflects straight back toward a flat drag sail behind the
>ship (and straglers bounce of the inside of the ship tpward the drag sail).
> The beam is then directed forward toward the plasma again, and bounces back
>again.  The plasma gets an extra boost forward.  Then the ship gets an extra
>push backward.  (repeat until beam is lost, absorbed, or canceled out by out
>of phase other parts of beam.)

I assume that the plasma is replenished all the time. So at the same time
that the plasma is replenished inside the plasma-pipe, there are also coming
reflected photons from the TC side. Doesn't that create a problem?

>Because you can't build a craft thats engines and structure are so light,
>strong, and powerfull; that they could carry a weight a thousand times
>greater than their own and accelerate it at about 1 G.  As a mater of fact
>I'm concerned that a fusion driven ship capable of carrying 40 or 60 times
>its weight is overly optimistic.  (But I haven't gotten aroiund to looking up
>the numbers in the Bussard papers.)

I don't see why you can build a craft of 1E8 kg that can propell itself but
not a craft of 1E11 kg. Just scale up the engines. If that isn't possible,
the initial acceleration should be less, after a while the ship gets lighter
and the acceleration can be increased.

>Also of course if the energy to accelerate the fuel doesn't need to be
>carried in the ship, the ship can get by on less fuel.

Yes, but that would involve a beaming technique.

>Fusion could be developed in a decade or so if their was any push for it.
> Possibly power for intersystem space craft might entice someone to invest in
>the R&D money for it.  Though your right.  Their are no current plans to do
>so.  Nor for that matter to build enough of a space infastructure to support
>a project like this.

How much push did you have in mind? There is already much research going on.
Already a few seconds of "controlled" fusion are possible. Development isn't
possible yet, because not enough is known about the plasma flows that are used.

>But, if we had usable space launchers.  There is a big
>pent up demand for public and comercial access to space.  When that demand
>starts, building up to the space infastructure we'ld need.  Think of how fast
>aviation and its infastructure developed between 1915 and 1965.

You yourself told me that you can't compare past developments so easely with
future developments. But I don't want to hold this against you, I also see
that space will become a bigger and bigger part of the economy. I know that
certain commercial firms (General Motors) are developing small easy to
produce and relative cheap launchers.

>Actually NASA played around with the idea on a satellite. A couple public
>groups were trying tyo build and launch a solar sailer in the '80's, but they
>never finished them.

Wasn't there an experiment with a solarsail last month?

>>What I mean is that probably none of the existing and almost-ready-to-use
>>techniques could bring us to TC.
>
>To T.C.?  Definatly.  Thats why we spent so much time on the maser mirrors
>and such.

The mirrors might be feasable but how about the maser itself? Making a beam
of 1 or 1000 kilometres in radius... that would mean a massive area filled
with maser cannons. So actually the beam would consist of many small beams
evenly distributed. Say we take a 100x100 km area, that is 1E10 square
metres. We need a power of about 1E18 Watt per square kilometre, so if we
install one maser per square metre, each maser (there would be 1E10 of them)
should need a power of 1E12 Watt. So that means every maser needs its own
fusion power plant, meaning 1E10 power plants. These power plants would need
a total of about 5000 kg of fuel per second.

This story is almost the same for Alpha Centauri as for Tau Ceti the biggest
difference is the total time these masers have to be turned on. Or if you
lower the acceleration you may devide all numbers by 10 or 100.

I hope this makes clear why existing or almost-ready-to-use techniques are
not usable.

>If your planing to send yourself to somewhere you can't really live at, and
>can't come back from, its suicide.  If you propose sending others there its
>murder; and no western government or major group would be allowed to launch
>such a mission.

It's just how you want to see it. Confing the crew to 15 years living in a
spaceship is bad enough. Giving them another 15 years may be even worse.
Probably most people would fail the psychological test only for this reason.
Imagine 15 years in the same environment, always busy with the same kind of
job, then finally you find a 10 whole planets to build new things. Would
they really like to go back? Would it really be such a crime to let those
people stay there and try to make a living? Even if it are all rotten
planets (which is doubtful) it probably would be better to be there than to
be in that stinking old spaceship for another 15 years

If we aren't planning on staying there, why go there? If it's just to
investigate it may be better to send unmanned probes. (That would be a task
for AI)

>>Lower power levels mean not going to TC! Lower levels mean a much longer
>>trip, and we agreed that wasn't our goal.
>
>Agreed.

So TC is out?

>>It makes a lot of difference if one needs 1000 Watt or 1000*1000 Watt. For
>>the first a simple petrol-generator will do, but for de latter you need
>>almost a complete power-plant.
>
>If you can build one petrol (gasoline) generator, at worst you can build a
>thousand others and string them together for a special project.  Maybe well
>start mass producing O'Neil type solar power sattelites.

String them together, there you said it. Doing that is not as easy as you
make it sound. You have to fuel them all, a mayor cloud of smoke would hang
around them, no to mention the noise they would make.
Other power supplies may not smoke or make noise but tying them together
tends to make problems expand non-linear. For example, wires get thicker but
their surface does increase at a slower rate, so the heat that is created by
resistance has more difficulties to escape.

>>Maybe unrepairable, but there will be many of them, so one or two less
>>doesn't matter. The strength of nano is not only their tinyness, but also
>>their vastness (for small price? and weight). The goal will be that they
>>become selfreproducive in a (hopefully) controlled way.
>
>Hopefully.  Otherwise we launched a gray goo plague to T.C. ;-)
>
>Eiather way its pretty iffy tech, and doesn't solve the fundemental problems.

Safety is a fundamental problem.

>Agreed.  Their is a reasonable chance of finding worlds with ecologies as
>complex as Earth and with life forms similar to ours in size, complexity,
>etc...  And if you could survive a couple secounds on them outside of a
>biosuit I'ld be stunned!  The history of explorers here on this world, and
>our present problems with plagues like Ebola, AIDs, Etc, don't speak well for
>the odds of a carless interstellar explorer.  Your microbes, and the planets
>microbes would rapibly try to digest the alien life forms it sees.

I heard that our genes would probably be so different from independant
developped species that they would mean no harm at all. But if they weren't
we certainly would be able to immunize ourselves. The humane genome project
would be completed by then and we would be able to detect and probably cure
every virus-disease (including AIDS). 
The reason for the history of Earth-based explorers is that their genes are
so identical to those of the species in the newly dicovered areas.

>True, though I think big platforms harvesting near earth asteroids and comet
>cores would go first.  Moon and Mars lack a human healty gravity, and its
>much easier to ship the mined cargo from near earth objects around and much
>richer pickings!!  (One estimate places the value of the oil on one average
>near earth comet core at several hundred billion dollars US!)  Which is one
>of the reasons I expect space development to progress much faster than
>expected.  Free-for-the-taker valuble materials tend to encourage that.  ;-)

Comets are probably not very handy, there are few of them and they have a
peculiar orbit. Asteroids would be easier but probably less rich of organic
material. Do you know why comets have that much oil? Oil means organic
leftovers. And if there is that much of it, that means there is a big chance
of life out in the galaxy.

As indeed many suggested once you start living on Mars or Moon, you can't go
back to Earth easely. Maybe we should look for a low gravity object (a
moon), work on the ground and sleep in orbiting space stations with
artificial Earth-gravity. Or we should build massive spinning buildings that
create 1g.

Timothy


P.S. Why does your mailer add 2 >'s and a space for replied pieces of text?
It looks a bit messy...