[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: For Consideration

To Brian:

>>Ionize interstellar gas, you are talking about it as if you could see it,
>>the best guesses are that the there is too few interstellar dust. Only a
>>ramscoop with a 1000 km radius may be enough to make some significant use 
>>of it.
>>I still have a hard time imagining how a magsail could work efficient,
>>magnetic fields have the peculiarity to be not very bundled.
>When you say "bundled" do you mean that the adjacent fields have a
>tendency to repel because of pole orientation and field lines?

No, the field doesn't repell itself. With not very bundled I mean that if
you create a magnetic field here on Earth, it will "dissolve" very fast.
Thus unlike a beam of light it won't be noticed after traveling some
distance. Of course if you would use charged particles, the field would stay
bundled around them. But then I wonder why not use the particles themselves.

Or maybe I'm confused about what you meant by magsail, do you mean a scoop?
If so, why is it called a sail and not a scoop?

>Or just design a multi-layer sail that takes the bundling problem into 
>account (isn't that what you already  implied was needed?)

I'm not completely sure how you plan to make the scoop, but I myself haven't
the faintest clue how to build one that could be  of any use to us.

>As for the interstellar gas.  Could we get even .01c down using a
>100km wide sail as a paracute if it were deployed throughout the
>cruising phase?  I'm assumed that we don't try to ionize anything on
>our own but use what little ionized material there is of what little
>material there is in the first place.  Even .01c would help if it
>didn't cost us too much power to keep the magnetic sail powered.
>Suggestion would be to use superconductive loops.

I think that if you restrict yourself to already ionized particles, the
amount of mass you can scoop will decrease seriously.

>>We use engine thrust and centrifugal forces for gravity, there are no other
>>known possibilities.
>I understood this.  I meant that we would need to account for
>vector accelerations in floor design, such as tilting the floor in
>some way to compensate for the centrifugal forces and the
>deceleration forces which would probably occur at right angles to
>each other.  Did any of that make sense?

I think the group discussed that some time ago. Indeed the tilt-angle and
the rotating-speed of the habitat-ring can be adjusted so that the linear
acceleration and centrifugal acceleration together give exactly 1 g at the
bottom of the floor (assuming that the linear acceleration does not exceed 1
g). There may be small problems with respect to the 6 tubes (see Kelly's
MARS) inside the torus. Because not all points of a tube are as far from the
center of rotation, "gravity" will vary slightly along one tube. (In the
middle of the tube gravity is lowest)

>You say we can't get our many tons of fuel to .3c?  I think I must have 
>confused you somewhere (if I'm the one who is confused then we'll find out 
>real soon and I sincerely hope that you'll tell me).  So, allow me to 
>rephrase my starship idea (you'll find I have to do that often to get my 
>ideas collected and across clearly).
>This ship design which we're discussing here is an ion or pulsed fusion 
>rocket which is launched using external fuel/power/whatever source from the 
>Sol system during the launch phase.

As long as the fuel is prelaunced there is no problem, but you were
suggesting to use the fuel as shielding. If you planned using that fuel for
deceleration, it could not work because there isn't an engine that can stop it.

>I do not believe that the drive will be either durable enough or fuel 
>efficient enough to run most of the way to Tau Ceti.  The acceleration phase 
>can only last only as long as we can externally fuel/power the ship (say 
>half a year at 10 m/s^2).

OK, If you assume a maximum velocity of 0.33c than you won't need such a
long acceleration, but be warned, 0.33c will take at least 35 years to get
you to TC.
And I'm quite certain that certain members will not agree with such a slow

>I admit that I really don't have a clue to how much fuel we'll have to 
>carry/pre-launch because I don't know the equations that will figure out a 
>launching ship weight given how powerful the engine is, how fast we want the 
>ship to go, and how much the hull and fuel weighs.  If you know this Tim, 
>I'm willing to learn.  Going on the knowledge that a fusion pulsed rocket 
>(Daedalus class) is, in theory, capable of achieving a cruise velocity of 
>.15c  with a ship weight of a few thousand tons and a fuel weight close to 
>50,000 tons, I figure that we could scale it up for a manned mission. 
> Again, only real stumbling block I see here is finding millions of tons of 
>3He in the solar system.

m=5E7 kg  v=.15c --> E = 0.5*m*v^2 = 5E22 Joule (= approx. 1.7E8 kg of
fusion fuel that is needed to externally launch it.)

>Of course, using Kevin Houston's maser idea would be divine and with it we 
>could accelerate/declerate the whole way.  But I just don't see how he is 
>going to keep a maser beam on a starship that is 11.8 ly away.  Or is it 
>11.9 or even 12.2 ly.  I can't find a single pair of sources that agree on 
>how far away Tau Ceti is!

I think 11.53 ly.

>Therefore, I'm not willing to risk a crew, ship, 
>and mission on the chance that a maser beam, originating from Sol and using 
>NO deep, deep space correction antennas along the way to Tau Ceti, will 
>actually be able to stay within even an A.U. of the starship.  As I said to 
>Kevin in the original Core Dump, if he can get his power plug to reach to 
>Tau Ceti with the accuracy needed, then we are going.  Otherwise, while he 
>is working on that, I want to check out this option.   Okay, now I'm really 
>getting repetitive (I hope you're still reading Tim).

I've some one working to find the accuracy of modern telescopes, I hope to
hear from him soon.

>I proposed that to keep fuel ratio down we launch some of it in the form of 
>tanker drones to the target star at incrimental speeds of say .01c faster 
>than the previous tanker (.01c is arbitrary.  If we have enough launching 
>devices, we could cut this even more).  The slowest tanker will be a whopper 
>because it will have to carry enough fuel mass to slow the starship as much 
>as .15c.  Any slower and it will be a century before it reaches its 
>rendevous position near Tau Ceti.  Since the trip at .33c will already take 
>35 to 40 years, we can launch 60 or so years after Tanker 1.  That is almost 
>half a century to improve the original starship design but probably not 
>enough to build a much faster one.

>By the way.  Personally, I don't think that we will be able to try this 
>manned interstellar mission idea before 2100 or later.  Also, because I 
>don't see maser power reaching across the light-years to fire up the ships 
>engines for a return trip, and because the crew would have to weigh the ship 
>down with incredibly huge quantities of scarce fusion fuel/reaction mass, I 
>don't envision a return trip. Given that the speed limit I am hoping for is 
>.33c, half the original crew would be dead before they got back.  The 
>mission we are considering here, then is one of exploration and 
>colonization: something humans should be good at by 2100 or 2200.

Hmm, although your ideas may be more realistic than ours (the rest of the
group) we had decided(?) that waiting 100 years or more wasn't realistic
because we could only guess what techniques would be available.
Also such a long mission would NEED to be selfsufficient, and a return
mission would be impossible. About selfsufficiency, join the discussion...

Brian wrote:
>>For the cruising phase of the flight, we can afford to make a habitat that
>>is spacous and comfortable.  As soon as we want to slow down, however, 
>>we'll have to stuff the crew into a collection of cramped, space economized,
>>modularized, trailer car-like habitats that fit into the cargo bay of the
>>space shuttles that we'll use to explore planet surfaces.
>>I'll rephrase the preceding.

 <Some text left out>

>>You had asked:
>>After having thrown away the biggest part of your ship, how are you going 
>We are not.  See above.

OK, I see your point and indeed as you say it, it would make sence, but as I
said before, the ideas of the group are somewhat different, so we have to
figure out what we will do. (Is everybody listening?)

>Since you made this comment I tried to brainstorm a few ideas.  I was not 
>happy with what I came up with but here they are.
>1. Fold and recapture the arrays at recycling stations in orbit of Mercury 
>and Venus perhaps.
>Problems that I see here are with:
>     a. the stations.  They will need positional stablizers, big catching 
>nets or magnetic breaks if we could fit the solar arrays into magnitizable 
>capsules, and high automation (course we assume that already.  The way I've 
>been making the automated future out to be I sometimes wonder what the 
>uneducated masses will be doing for a living.  Hopeful computers won't be 
>thinking for themselves yet or otherwise they'd realize their superior 
>abilities and TERMINATE us).  There would be some counter force against the 
>incoming array capsules in the form of the relaunching capsules.
>     b. the array.  They must fold themselves, not rip in the prossess, not 
>get stuck like the hubble telescope's panel did.  I'm running out of time 
>and ideas.

All this seems really complicated (and unreliable). And where did you plan
to get the energy from to relaunch the arrays? (You'd be better of using
that energy directly for the Asimov)