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jayscheuerle
Post Laureate
Reged: 01/16/06
Posts: 4076
Loc: S. Philadelphia, PA
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Quote:
Quote:
Frankly, I'm still waiting for my flying car... - j
http://www.terrafugia.com/
Well that's depressing...
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Fight indignorance!
The Green Goblin - 12" of dobsonian excellence!
The PortaBowl-a $100 4.5" f/8 ball-scope YOU can build!
Eero2-a 6" f/5 ball-scope you probably can't. 
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ColoHank
professor emeritus
Reged: 06/07/07
Posts: 516
Loc: western Colorado
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Our physiological limitations are the greatest stumbling block to human inter-stellar travel. So let's leave human travelers and their appetites and frailties (including lack of longevity) out of the equation, and instead send a fleet of probes that employ those propulsion technologies deemed most likely to succeed. The greatest challenge then will be to ensure that someone on Earth will still be around umpty years/decades/centuries/millennia from now with the interest, commitment and wherewithall to monitor the probes' transmissions when they finally approach their destinations. What we're most likely to learn from these little experiments is that travel to even the nearest extra-solar planetary system will take so long that succeeding generations of mankind will have forgotten about the launches or long-before judged the endeavor inconsequential by the time the missions are presumed to end.
For now, I'm going to worry more about whether I-70 will be open so the kids and their families can drive over the Rockies from Denver for Thanksgiving. At only 265 miles, the trip isn't measured in light years, but it can be extremely problematic at this time of year -- even with proven propulsion and navigation systems.
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Questar 3.5 standard - pyrex and BB coatings
Powerguide II
8mm, 12mm, 16mm, 24mm and 32mm Brandons
modified Bogen 3030 w/ homebuilt wedge
Homebuilt Galileo scope and very large and ugly homemade tripod
other odds and ends, including iPod Touch with StarMap Pro (what a marvelous combo)...
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"Nothing exists but atoms and empty space. Everything else is opinion."
Titus Lucretius Carus 99-55 B.C.
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Jarad
Post Laureate
Reged: 04/28/03
Posts: 4330
Loc: Atlanta, GA
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I am a proponent of solar sailing as the architecture of choice for nearby interstellar travel. I have not seen the numbers in Decades but as I recall it basically takes a 1 kilometer class rock from the asteroid belt and retrofits it as a colony ship. Lots of room for a crew of 1000 with large parks and other amenities.
There was a book that used this concept to visit a nearby star. I think it was called "The Sparrow". Good book - light on science, heavy on philosophy, but interesting.
Quote:
Disclaimers:
Please operate your Enterprise D safely! Remember that many of its features are complete fantasy and do not actually work.
If you choose to build a kilometer class colony ship please remember to stay in the shadow of the rock. Never look directly forward. Also be careful with that momentum exchange with the sun as a careless traveler may place the ship into a situation where the gravity of the sun greatly exceeds the thrust available from the solar sail.
I hate it when my solar sailboat falls into the sun. Especially when I left my sunblock SPF50,000,000 at home...
Jarad
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tatarjj
Pooh-Bah
Reged: 04/20/04
Posts: 1134
Loc: Austin, TX
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Well, considering that we have the technology NOW to send probes to other stars (but not the money to do so), I would say that calling interstellar travel impossible shows ignorance to the current state of technology, and likely future advances. With advances in nuclear fusion, space access, materials, biology, computers, radiation hardening, agriculture- we WILL have the technology to send humans on a long duration voyage in a hundred years or so. We DO NOT have to violate light speed to do this! Personally, I believe that FTL travel is PROBABLY impossible, but there is no way to tell until we discover more about physics.
Lemme go through some points in more detail.
One thing that makes it very narrow-minded to say that we will never travel to stars is the assumption that stars will always be far away. In the short term, yes, but stars will get alot closer to us than a measely 4 light years over the next couple million years. Will we survive that long? Who knows, but still... there will come a point when a star is pretty nearby.
Another thing that makes it narrow-minded to say humans will never spread to other stars is the assumption that future humans will live with today's biological limitations. We will not. Genetics, medicine, biological technologies are all advancing quite nicely, with no end in sight. In the future, it is almost certain that we will be able to do at least one of the following things:
-Stop aging
-Go into suspended animation or some other low metabolism mode
-Grow humans automatically from DNA on reaching a distant star after a thousand year voyage
Another point that persons who claim interstellar travel to be impossible fail to consider is the progress of computer technology. While silicon-based computer technology is finally reaching some limits, quantum computing looks quite possible. Quantum computers will be many orders of magnitude better than silicon computers. After the advent of quantum computers (assuming they will be perfected, and will be as powerful as predicted) it is my professional opinion that true artificial intelligence will become possible.
So what does true artificial intelligence have to do with interstellar travel? Quite alot, actually. The possibilities are endless. For example, humans may not be smart enough to figure out how to travel between stars, but our computers might be. Artificial intelligence machines could tend the human infants grown on-site from DNA after a 10,000 year voyage.
Nuclear energy advances- We are already able to harness the power of fusion in an uncontained environment (a "fusion" bomb, though that's a misnomer as most energy in a fusion bomb comes from fission, but I digress). A fusion rocket engine need not be contained either. Also note that with today's nuclear technology, we can get to the stars already with an unmanned probe.
Space access- an interstellar craft would many WAY bigger than anything that we can currently launch. It would have to be built in space. We are already getting good experience building stuff in space. Future advances in space access, such as a space elevator (which requires possibly carbon nanotube materials technology) would greatly help.
So lets talk about some ways of getting to the stars. Right now, two viable methods exist:
Light sail
Nuclear propulsion
Light sails would probably be a bit slower, but they are possible. You would need a light source much brighter than the sun to power it- a nuclear-powered very high energy laser on the moon would do the trick. Unfortunately, it might be a one-way trip, as stopping would be quite difficult.
Nuclear propulsion- nuclear bombs were already proposed to power a spacecraft, and it looks like they would work. Other methods have been proposed, like an "antimatter catalyzed nuclear fusion" or some such, which basically uses SMALL amounts of antimatter to help nuclear fusion along. Antimatter is getting more accessable as time goes on, so this doesn't seem all that impossible. You wouldn't need much, as the antimatter is NOT used to propel the craft, just to help the fusion reactions take place.
Finally, there is the space-ark concept- a slow-moving space craft that is very large and has a self-sustaining ecosystem and human population. We live on one of these already. The question is, how small can we make an artifical space ark. Can we make it small enough to be practical?
Anyway, just my thoughts on the subject. Right now, money and motivation are keeping us from lauching stuff into interstellar space. For good reason too- at this point, the huge amount of money that would be required to make an interstellar probe would be far better spent on science that needs to be done, and on issues here on earth.
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John T.
Austin, TX
25" f/4.2 Dob
18" Obsession #701
4" Stellar Vue Achromat
8X56 Binos
Edited by tatarjj (11/02/09 05:20 PM)
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moynihan
Carpal Tunnel
Reged: 07/22/03
Posts: 1606
Loc: Wisconsin
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Interesting thread.
I myself do not know if traveling past, or faster than, the speed of life is "impossible", in the absolute, dictionary sense of the word. At our current level of knowledge it does seem to be the case. So for operant reasons I accept it as a biogeophysical limit.
Of course, there are currently speculative ideas on not going faster than the speed of light, but rather getting around it, so to speak (worm holes, etc.).
But, two things;
1. If we cannot obtain a velocity in excess of that of light, interstellar travel/exploration/settlement is not ruled out. It would just take a really long time. It would then be a political/social question, not really a technology one.
2. Working partially in the area of (suject verboten in forum, therefore not stated) I have to consider biogeophysical constrants that are "real", in that for given a goal, they bound the potential solution space. So yes, I can think of something being literally impossible. But the goals are rarely impossible,though some ways of acheiving them are.
A mundane, non-work example; i accept that absent augmenting my morphology (an ultralite)i cannot fly under my own power on this planet.
As the sci-fi writer Phillip K. Dick said, "Reality is what is left, when you stop believing."
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"Gosh, you've... really got some nice toys here"
Dual mount/ambient temperature Hominid Widefield Photon Collectors®
Pleistocene™ ˝ watt Wetware Integration Unit.
entia non sunt multiplicanda praeter necessitatem
Edited by moynihan (11/02/09 05:33 PM)
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astrotrf
professor emeritus
Reged: 09/30/07
Posts: 709
Loc: Rodeo, NM
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tatarjj wrote:
Quote:
... (a "fusion" bomb, though that's a misnomer as most energy in a fusion bomb comes from fission, but I digress).
Can you provide a reference for this?
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Terry (astrotrf)
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kcbridgeman
member
Reged: 03/26/09
Posts: 80
Loc: Kansas City, MO
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Quote:
tatarjj wrote:
Quote:
... (a "fusion" bomb, though that's a misnomer as most energy in a fusion bomb comes from fission, but I digress).
Can you provide a reference for this?
Is this maybe a reference to the fact that it takes a fission bomb inside of of a fusion bomb to produce the x-rays that are needed to create the high temperatures and pressure needed to initiate fusion? The fusion of the lithium deuteride then induces fission of the urianium-238. This fission causes the bomb to explode, so I guess the process could be considered mainly fission, but I would consider it a moot point.
How fusion bomb works.
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Orion XT10/Telrad/Stellarvue F50M RACI
Numerous Eyepieces
Starry Night Pro Plus 6/Pocket PC w/Pocket Stars
Who are we? What are we? We find that we inhabit an insignificant planet of a hum-drum star lost in a galaxy tucked away in some forgotten corner of a universe in which there are far more galaxies than people. ~ Carl Sagan
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astrotrf
professor emeritus
Reged: 09/30/07
Posts: 709
Loc: Rodeo, NM
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Thanks, kcbridgeman, for the reference. The claim was that most of the *energy* in a fusion bomb actually comes from fission -- and that's the reference I'd like to see.
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Terry (astrotrf)
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Glaucus
member
Reged: 07/12/09
Posts: 45
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If you want humans to colonize other planets why sent the bags of water?
You would only sent a few nanobots. They then would build stuff that would build stuff that would build the factory that turns DNA into human. You can sent information through photons. So you wouldn't even sent a chip containing the data you need.
Even if you don't have nanotechnology you can just sent DNA. Yeah, it has some challenges. But I bet the space ship carrying just human DNA will overtake the ship carrying frozen bodies. The question is if the late arrivals will be unfrozen.
And unless it takes billions of years, travel time isn't really important. Only issue is the star of your destination blowing up. If you are sending stuff to other galaxies and it takes a billion years then that's not a problem either. Once you arrive you can pick a good destination system. And if that what you are sending is below a gram it doesn't take much energy to get reasonably close to light speed. Basically 100% of your mass will be fuel. And no issue of accelerations either. And when a civilization has nano technology I bet they can just build a cannon and shoot the 1 gram probe to a good fraction of light speed. So no need to carry fuel.
Edited by Glaucus (11/04/09 08:35 PM)
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kcbridgeman
member
Reged: 03/26/09
Posts: 80
Loc: Kansas City, MO
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Orion XT10/Telrad/Stellarvue F50M RACI
Numerous Eyepieces
Starry Night Pro Plus 6/Pocket PC w/Pocket Stars
Who are we? What are we? We find that we inhabit an insignificant planet of a hum-drum star lost in a galaxy tucked away in some forgotten corner of a universe in which there are far more galaxies than people. ~ Carl Sagan
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groz
Pooh-Bah
Reged: 03/14/07
Posts: 1079
Loc: Duncan, BC
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Quote:
Future advances in space access, such as a space elevator (which requires possibly carbon nanotube materials technology) would greatly help.
Space elevator is a great concept for a science fiction book, and in the fiction book, where you can ignore some realities, it works well. But, if you have actually studied the concept, you would understand why it's self defeating.
First, we need the actual cable. That cable has to be built from impossiblium. Yes, I know, the hypsters talk a lot about carbon tubes, but, they dont quite understand the actual engineering problems. The tubes may well be able to be refined to the point they can withstand the tensile forces of the cable weight, but, then they wont be able to withstand the compression forces of the crawler thingies gripping them. To deal with that, we need re-inforcement, and that re-inforcement adds more mass to the cable, which increases the tensile forces. This becomes a circular problem, which wont solve. Now, once you do think you have it solved, consider now the real compression forces that have to be withstood. Surface area of a few thousand miles long, by some measureable diameter, with all these heavy crawler thingies hanging off it. It's to big a cumbersome to maneuver out of the way when there's an incoming particle arriving at 20,000 mph + in velocity, so, it's going to have to withstand the impact, without breaking, and dropping the little crawlie thingies trying to climb up to orbit. Hmm, the strenght of materials problem just got even tougher, and, we haven't yet visited the stability problems of this long slender cable touching the ground on one end, a couple miles up it's being exposed to wind velocities regularily in the 200mph range, and, it's got to stay still so the crawlie things dont fall off.
Now, lets look at the crawlie things, they sort of suffer the same problem as the enterprise D references much earlier in this thread, gotta power them. BUT, there is a distinct advantage, since they are more or less localized, we can beam power up from the base in some fashion. That doesn't require use of an element that falls between impossiblium and nogotany in the periodic table, that's just an engineering problem, that can be solved with todays technology and a few truckloads of money tossed in for good measure. So, assuming we toss the truckloads of money at the power problem for the crawlie things, and solve that one, then we are still stuck trying to figure out just what they will crawl up, or are we???
If we have the ability to beam the energy into the climbers that is required for them to do the climb, and we dont have anything for them to climb, that's an EASY problem to deal with. We rip off the stupid gripper gadgets, replace with wings, and voila, we have self contained little climbers that can fly circles above the energy source, and climb right on up there without the silly cable.
As a whole, the space elevator concept requires two problems to be solved, one of them very hard, and the second comparatively easy. But, the solution to the easy one, negates the need for the solution to the hard one. So, the space elevator will never happen, there's no point to it. Figure out how to provide an unlimited energy source to the lifting vehicle in a way that it's not 95% of the starting mass, and, you no longer need the silly cable for it to climb.
And, as another thought, since we have now figured out how to send unlimited quantities of energy to a vehicle in transit, then it's time to go back and re-visit that Enterprise D concept. It doesn't need 80x vehicle mass in fuel anymore, we will just send it the energy it needs on a similar beam, problem solved...
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tatarjj
Pooh-Bah
Reged: 04/20/04
Posts: 1134
Loc: Austin, TX
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Quote:
Quote:
tatarjj wrote:
Quote:
... (a "fusion" bomb, though that's a misnomer as most energy in a fusion bomb comes from fission, but I digress).
Can you provide a reference for this?
Is this maybe a reference to the fact that it takes a fission bomb inside of of a fusion bomb to produce the x-rays that are needed to create the high temperatures and pressure needed to initiate fusion? The fusion of the lithium deuteride then induces fission of the urianium-238. This fission causes the bomb to explode, so I guess the process could be considered mainly fission, but I would consider it a moot point.
How fusion bomb works.
It is not a moot point, as a "fusion" bomb gets most of its energy yield from fission. What the fusion process does is produce ALOT of high speed neutrons. These neutrons are so plentiful that they ensure that a much higher quanity of the fissile material in the "fusion" bomb actually undergoes nuclear FISSION. The U-238, normally inert, unders alot of fission as well. Remember, FISSION is caused by a neutron hitting the nucleus of an unstable atom. More neutrons = more fission, and fusion produces ALOT of neutrons. So basically, what happens is this:
1) Explode first stage of the weapon, fission bomb
2) Fission bomb causes fusion of deuterium and tritium
3) High speed neutrons cause highly efficient fission of fissile material, including normally non-fissile material (U-238)
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John T.
Austin, TX
25" f/4.2 Dob
18" Obsession #701
4" Stellar Vue Achromat
8X56 Binos
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tatarjj
Pooh-Bah
Reged: 04/20/04
Posts: 1134
Loc: Austin, TX
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Look, I didn't bring up the space elevator as a central point to my arguement, it was just PART of it. I think it is POSSIBLE we may some day get it. I am DOUBTFUL it will ever be built, but I'm not about to sign off on it as being impossible as you are. If they can prove that it is a physical impossibility that any material can be strong enough to work as a space elevator cable due to some fundamental limit in the laws of physics, only THEN will I say it's impossible.
You mentioned something that reminded me of those laser-powered rockets they were looking at... what's the status of those?
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John T.
Austin, TX
25" f/4.2 Dob
18" Obsession #701
4" Stellar Vue Achromat
8X56 Binos
Edited by tatarjj (11/05/09 03:04 AM)
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tatarjj
Pooh-Bah
Reged: 04/20/04
Posts: 1134
Loc: Austin, TX
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Quote:
Thanks, kcbridgeman, for the reference. The claim was that most of the *energy* in a fusion bomb actually comes from fission -- and that's the reference I'd like to see.
Here's one, pay attention to page 5.
http://www.progressive.org/images/pdf/1179.pdf
Note that if half of the energy came from U-238 alone, that isn't even counting the first fission stage of the weapon, and then, any remaining fissile material in that first stage that gets split by neutrons from the fusion process.
Also wikipedia, while definately not the most reliable source, has information on this too:
http://en.wikipedia.org/wiki/Thermonuclear_weapon
Maybe if you follow wikipedia links to their sources, you can verify for yourself. Tell me what you find, I'd like to hear it. There's not much information about this topic out there you know...
While none of these sources are perfectly reliable, you have to understand that's all the general public has to go on. The government sure isn't going to tell us.
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John T.
Austin, TX
25" f/4.2 Dob
18" Obsession #701
4" Stellar Vue Achromat
8X56 Binos
Edited by tatarjj (11/05/09 03:32 AM)
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astrotrf
professor emeritus
Reged: 09/30/07
Posts: 709
Loc: Rodeo, NM
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Thanks, tatarjj, for the references -- interesting reading, for sure.
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Terry (astrotrf)
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Shadowalker
Unpretentious Rocket Scientist
Reged: 11/23/04
Posts: 3560
Loc: Poplarville, MS, USA
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Quote:
Space elevator is a great concept for a science fiction book....
Several good ones have been written. In Ben Bova's book (Mercury, iirc), one was constructed. Which fell down - sabotage (again, iirc). Caused a man-made disaster the entire circumference of the earth along the equator.
Anyway, that's not the point. As an under graduate a student selected as a seminar topic the physics of Ringworld. Some of you may remember Larry Niven's Ringworld, where a ring the diameter of earth's orbit is constructed around a star as a habital land mass, providing orders of magnitude more surface area than a planet.
Anyway, my classmate analyzed the forces such a structure would have to endure. Answer? not able to be built with any known material. And that didn't even address the stability issues - of which there would be plenty for a 50,000mile high tower.
Of course this was in the 70s, before the current plentiful supply of Impossibilium.
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Tom Nicolaides
http://www.first-light.org
My evil self is at that door, and I have no power to stop it
-- Dr. Edward Morbius
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Shadowalker
Unpretentious Rocket Scientist
Reged: 11/23/04
Posts: 3560
Loc: Poplarville, MS, USA
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Here's one i don't think is impossible, but has been devilishly difficult to obtain. That's Single Stage to Orbit.
All rockets launching payloads are either staged or have strap-on boosters that fall away during ascent. The reason is chemical propulsion hasn't enough energy to lift the necessary mass of a single stage vehicle.
For years we've been investigating ways to do it - many of which required large amounts of impossibilium, the salient properties being light weight and high strength.
Some of you might remember the X-33 program. It was to be a 1/3 scale of a reusable single stage to orbit space plane. To reduce weight a carbon fiber fuel tank was designed and tested. I worked that test program. We filled it with liquid hydrogen and pressure cycled it. Short answer: it leaked. A lot. Project mangement decided to go to an aluminum tank. Not long after that the program was canceled.
To reduce weight on the Shuttle, ways to reduce the weight of the external tank were looked at. How do we do it, they asked? Well, lithium's a light metal, they answered. Let's mix it with Aluminum and see what happens. So they did. Hence the invention of Mystery Metal - the Aluminum-Lithium light weight external tank. A variation of Impossibilium, this one turned out to be Possibilium.
I have a picture somewhere of that X33 tank on the test stand somewhere. I'll dig it out.
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Tom Nicolaides
http://www.first-light.org
My evil self is at that door, and I have no power to stop it
-- Dr. Edward Morbius
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Rick Woods
Postmaster
Reged: 01/27/05
Posts: 5684
Loc: Inner Solar System
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Quote:
Several good ones have been written. In Ben Bova's book (Mercury, iirc), one was constructed. Which fell down - sabotage (again, iirc). Caused a man-made disaster the entire circumference of the earth along the equator.
That's just what happened in K. Robinson's "Mars" trilogy. Makes you wonder how good an idea it even is to begin with.
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- Rick
14" LX200GPS
Dyslexics Untie!
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Michael A. Earl
vendor- Canadian Satellite Tracking and Orbit Research
Reged: 11/17/08
Posts: 1122
Loc: Brockville, Ontario, Canada
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Quote:
You would only sent a few nanobots. They then would build stuff that would build stuff that would build the factory that turns DNA into human. You can sent information through photons.
Is this the definition of a perpetual motion machine? 
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dreamregent
sage
Reged: 04/06/09
Posts: 457
Loc: Clearwater, FL
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Quote:
space elevator
There's a new article about this subject and NASA's little contest this week in the Mojave Desert on CNN.com. Actually, I think the most interesting part of the article is the last paragraph. It's a quote from Arthur C. Clarke.
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"Every revolutionary idea seems to evoke three stages of reaction," Clarke once said. "They may be summed up by the phrases: One, it's completely impossible. Two, it's possible, but it's not worth doing. Three, I said it was a good idea all along."
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I've read the first two arguments a number of times on this very forum...almost word for word. I'm sure that one day I'll be reading the third phrase as well. You can read the full article HERE.
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Building a f5.24 10" Dob
in an octagonal wood tube
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