Workable Fusion Starship Proposed 260
Adam Korbitz writes "A former colleague of Edward Teller — father of the hydrogen bomb — has published a new paper proposing a design for what could be the first practical fusion-powered spacecraft (PDF). As described at Centauri Dreams, the design has certain similarities to MagOrion, a 1990s-era proposal for a nuclear-powered spaceship with a magnetic sail and propelled by small-yield fission devices. The proposal's author also has links to the British Interplanetary Society's Project Daedalus, a 1970s proposal for an unmanned fusion-powered interstellar probe designed to reach 12% of the speed of light on its way to Barnard's Star."
Oxymoron? (Score:2, Insightful)
Workable Fusion Starship Proposed
If it's only a proposal, how do we know whether it is "workable" or not?
Re:Oxymoron? (Score:5, Informative)
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Workable = WORKing + DeniABLE
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Re:Ramscoop design? (Score:5, Informative)
Re:Ramscoop design? (Score:4, Funny)
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Really? Could a magnetic scoop then be used for braking on a ship that used a different type of propulsion? Because more than half your propellant on an interstellar journey is required due to the need for braking when you get to your destination.
Re:Ramscoop design? (Score:5, Interesting)
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You don't have a keel in space. (http://en.wikipedia.org/wiki/Keel) The best approximation on earth would be a hot air balloon. In space you can't go faster than the solar wind without adding extra energy. You might be able to get a little by tacking between to planets but going to have some hard limits and it's not going to work with a magnetic solar sail.
Re:Ramscoop design? (Score:4, Informative)
Nope: http://www.iceboat.org/seasons/08-09/index1-29-09-1.jpg [iceboat.org]
"Modern iceboats designs are generally supported by three
skate blades called "runners" supporting a triangular or cross-shaped frame with the steering runner in front." http://en.wikipedia.org/wiki/Ice_boat#Modern_designs [wikipedia.org]
Ice boats don't use a keel, but their blades do the same thing. Blades such as ice skates provide plenty of resistance in one direction much like a keel does on the bottom of a boat.
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Only 0.12c? Man, those things depreciate so fast.
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I have designed a spaceship that uses a scoop to collect amazon affiliate codes.
It will be able to reach Barnards star in a matter of hours.
from the article.. (Score:5, Funny)
a deuterium fusion bomb propulsion system is proposed where a thermonuclear detonation wave is ignited in a small cylindrical assembly of deuterium with a gigavolt-multimegampere proton beam,
that has to be right up there with back to the future. I mean, it has a frickin' gigavolt-multimegampere proton beam
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Doc Brown says:
"JIGAvolt it's JIGAvolt!"
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Gigawatt is correctly pronounced jiggawatt. And it's 10^9 watts, not 2^20.
Damn kids.
Re:from the article.. (Score:5, Informative)
Gigawatt is incorrectly pronounced jiggawatt.
Fixed that pronunciation fubar for you.
In English, giga is pronounced with a hard-g (as in "giggling girls give gifts"). Check the Oxford English dictionary, or any other English dictionary if you don't believe me. There was an attempt by the US NBS to redefine it to use a soft-g (as in "giant giraffe giblet gin"). http://en.wikipedia.org/wiki/Giga#Pronunciation [wikipedia.org] Thankfully, this hijacking attempt to a new and wrong pronunciation has been quite unsuccessful - I have worked with a great many American scientists and engineers over decades, and every one of them uses the correct hard-g pronunciation (so do the newsreaders on US TV, even). I work in R&D at a fairly large US-centric multinational, and I have yet to hear anyone pronounce giga as "jigga", not even MBA-handicapped marketing types. And it's really hard to imagine an executive saying "jiggabuck" instead of gigabuck - the audience would crack up completely...
If you want to pronounce giga with a soft-g, then please use French...
And it's 10^9 watts, not 2^20.
Indeed it is. Giga means 10^9 numerically, by definition. Alas, we are still fighting against recent attempts to hijack it to a new and wrong numerical definition.
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But English is hard to pronounce with an English accent.
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My car has multiple photon beams, powered by an engine generating up to 100000 volts many thousands of times per second. It's not as impressive as it sounds, though --- my torch has a photon beam too.
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Protons and photons are different tho. I doubt your torch has a proton beam.
To save time & skip the pdf (Score:5, Informative)
See here:
http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) [wikipedia.org]
and here:
http://nextbigfuture.com/2008/12/micro-fusion-for-space-propulsion-and.html [nextbigfuture.com]
Re:To save time & skip the pdf (Score:4, Funny)
Great idea but pie in the sky... (Score:5, Interesting)
Moon colony, orbiting L5 colony, whatever it is it must be permanent and able to manufacture using locally sourced materials because building something like this from within the gravity well doesn't make economic sense.
Re:Great idea but pie in the sky... (Score:5, Funny)
Re:Great idea but pie in the sky... (Score:4, Funny)
Only in James Bond films.
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Moon colony, orbiting L5 colony, whatever it is it must be permanent and able to manufacture using locally sourced materials because building something like this from within the gravity well doesn't make economic sense.
Under what set of conditions does it make any sense to launch a manufacturing plant into space, then send up raw materials? I assume that's what you mean by "locally sourced" because there isn't any 'local' material at the L5 point.
How would that ever be cheaper than launching pre-built sections and assembling them in orbit?
Re:Great idea but pie in the sky... (Score:5, Insightful)
Moon colony, orbiting L5 colony, whatever it is it must be permanent and able to manufacture using locally sourced materials because building something like this from within the gravity well doesn't make economic sense.
Under what set of conditions does it make any sense to launch a manufacturing plant into space, then send up raw materials? I assume that's what you mean by "locally sourced" because there isn't any 'local' material at the L5 point.
How would that ever be cheaper than launching pre-built sections and assembling them in orbit?
No what I meant by locally sourced materials was either moon mined materials or asteroid mined materials. Probably the latter as I believe things like iron are a little weak [neiu.edu] on the moon.
There's no way shipping ANYTHING up from the gravity well would allow us to build a ship of this nature within any reasonable time frame with the exception of using absolutely huge space elevators.
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There's no way shipping ANYTHING up from the gravity well would allow us to build a ship of this nature within any reasonable time frame with the exception of using absolutely huge space elevators.
*THE* gravity well?
The moon has one too. Asteroids have a different but similar problem in being so far away and having such different orbital mechanics.
What exactly are you proposing?
Re:Great idea but pie in the sky... (Score:5, Interesting)
There's no way shipping ANYTHING up from the gravity well would allow us to build a ship of this nature within any reasonable time frame with the exception of using absolutely huge space elevators.
*THE* gravity well?
The moon has one too. Asteroids have a different but similar problem in being so far away and having such different orbital mechanics.
What exactly are you proposing?
For practical engineering purposes the gravity well of the moon is weak enough to not be a problem for the transportation of materials off it's surface.
Asteroids do have gravity obviously but almost nothing due to their size. Thus materials transported from them are again easy to move into open space.
What I'm proposing is this:
1) Establish a colony on the moon or at L5.
2) Use moon materials to build the manufacturing framework.
3) Construct mining ships for asteroid field work.
4) Mine asteroids and use the materials to construct the large-scale interplanetary transport.
Now while this is a workable plan it is _also_ pie-in-the-sky as we can't even get our collective butts to agree on how to get a primary established off planet.
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For practical engineering purposes the gravity well of the moon is weak enough to not be a problem for the transportation of materials off it's surface.
You mean, it's less than earth and that makes it less of a problem, but it's still a gravity well, and your wishing it away won't make it so.
Asteroids do have gravity obviously but almost nothing due to their size.
I asked about asteroids having different orbits and being a long ways away. It's not just the orbital planes being different, but there are speed differences.
A lot of energy to expend in both places.
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But neither problem is insurmountable as an engineering challenge.
My point is that either one would have to happen to create a practical material source in space _before_ a serious interplanetary ship would be feasible.
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With the two and a couple of pop bottles you could get escape velocity
Maybe if you had a couple of pop bottles and a way to mine Mentos on the moon.
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Maybe if you had a couple of pop bottles and a way to mine Mentos on the moon.
Moon ... Mine ... Mento .... mmm good!
Not so much (Score:2)
The delta v between your typical Amor class earth crossing asteroid and the Earth-Moon system is on the order of a few meters per second. In other words if you could stand on it and chuck a rock, you could hit the Earth.
Existing propulsion technology could easily move one of these rocks around. It would be expensive and take time, but it could probably be done without requiring the invention of any fundamentally new technology.
A 100 meter diameter rock like Apophis would mass on the order of a gigaton or so
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You use catapults! From the moon, the catapults lift the materials into high lunar orbit. From the asteroids, the catapults act as a rocket.
Actually, while the "Mass driver" would work, I think that a rocket would be better. Most asteroids have a lot of methane or other low vaporizing material on them (or in them). Use that with a solar mirror to heat them into a rocket exhaust. Or possibly convert them into fuel for an ion rocket. It'd be slow, but fast compared to something that only ran for a shot
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Your inability to comprehense the feasibility of this design does not make it "pie in the sky".
My whole life, I ran into people claiming that this and that is so far away and today still impossible, because they did not remotely know what was already done and possible.
Project Orion (same thing, but with fission bombs only) was already completely possible in the 60s!. Fusion bombs have since been perfected. They are not much harder anyway. So this is no far thought. It's the logical next step. At least if we
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Your inability to comprehense the feasibility of this design does not make it "pie in the sky".
I comprehend the idea just fine. But looking at our track record of growth I maintain that we won't get to this project without a close permanent manufacturing facility in space or space elevators.
My whole life, I ran into people claiming that this and that is so far away and today still impossible, because they did not remotely know what was already done and possible.
Project Orion (same thing, but with fission bombs only) was already completely possible in the 60s!. Fusion bombs have since been perfected. They are not much harder anyway. So this is no far thought. It's the logical next step. At least if we want to see interstellar travel in our lifetime.
And there's nothing in the world that I would like to see more.
I too would love to see that in my lifetime but hoping and wishing won't build a starship and nobody I know of is going to commute both themselves and materials from the surface of the earth to high orbit or open space to construct a ship of this nature for the 5 - 10 years minimum it would take our slow asses to
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Sure. Right. Get a bunch of yahoos up in space where they can't go to the nearest Starbux for an arguably decent cup of coffee. Not.
People want to go home for the weekends. They want to have sex with their partners. They want to go to the park and have a beer. None of that will be in space, or on the moon.
None of that is available on an oil platform either and yet there are plenty of people prepared to put up with that for a large wedge of cash.
My memories of Edward Teller (Score:5, Interesting)
Edward Teller hired my Dad into the Physics department at UC Berkeley and I remember him as a gentleman - he was occasionally at our house. Once my parents had a costume party and Teller was provided with a bird costume - he did not want to wear the mask so he had these big white wings on. The SF Chronicle columnist Herb Caen ran a story the next day saying that Teller was dressed as the angel of peace. Until Teller died a few years ago, my Dad would occasionally travel to Berkeley to visit with him.
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Edward was a remarkable man. Fortunately, not too long before his death, he published his memoirs, which give great insight into his thoughts and outlooks. He was far from perfect, but no real man is.
Re:My memories of Edward Teller (Score:4, Informative)
The SF Chronicle columnist Herb Caen ran a story the next day saying that Teller was dressed as the angel of peace.
An interesting story about a man who was awarded the first Ig-nobel prize for peace: [improbable.com]
Re:My memories of Edward Teller (Score:5, Informative)
But the root of the problem between Teller and Oppenheimer was that Oppenheimer opposed the hydrogen bomb (fission/fusion) and Teller was all for it. That made Oppenheimer an enemy to Teller.
Teller, instead of leaving it as a difference of opinion as to whether such a powerful weapon was needed, went on the attack and set out to discredit Oppenheimer.
In the cold war it was pretty easy to make Oppenheimer seem subversive. The time was paranoid and anyone with a different opinion was suspect. Others set out to paint anyone as communist who they didn't agree with. Teller used it to his advantage to silence and discredit a rival.
Who knows if Teller or Oppenheimer was right. No fission/fusion device has ever been used in war. The only devices that have been used were the ones that Teller and Oppenheimer and many others invented.
However, a good person, a patriot, and someone who in spite of his own misgivings about the kind of weapon he helped develop, did it anyway and in so doing probably saved hundreds of thousands of American lives, had his own life destroyed because Edward Teller was on a personal quest for his own glory, his own stature, and his own place in history.
Edward Teller was an asshole. He took it personal that Oppenheimer opposed developing the hydrogen bomb and set out to destroy Oppenheimer for it.
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Here's an odd bit of confluence... My uncle was Harold Green (he died recently) - an attorney who worked for the US Government and who was responsible for figuring out how to "get" Oppenheimer when the government went after him. He mentioned feeling conflicted over his part in that - proud for coming up with a legal novelty, but ashamed for helping to ruin a great man.
It was a very odd experience for me reading a biography of Oppenheimer and seeing my uncle in it, reading about what he did.
Then a miracle occurs... (Score:3, Informative)
One of my grad school profs worked on a project like this. The concept involved a ship farting (for lack of a more appropriate term) out a series of small fusion bombs. When they went off the heat would cause the shielding at the rear of the ship to sublimate, and this ablation process would drive the ship. As I recall there were only two teensy problems with this: 1) even with the best shielding material available today, the intense heat from the detonation would still cause the maximum heat in the shield to occur at a depth greater than the surface (i.e. the shield would come off in great blobs instead of the slow steady ablation required for thrust) and 2) the amount of anti-matter required for the devices was only about a million times the total amount ever produced on Earth.
But apart from that it worked like a champ.
A great way to make contact with aliens . . . (Score:4, Funny)
. . . speeding through their neighborhood whilst "farting out a series of small fusion bombs."
They will come looking for us.
"Hey, Earthling, is this your flatulent spacecraft that fouled our air? We'd just like to return it to you, by chucking it at one of your major cities."
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Good question. Almost as good as what was a guy that sits on a space propulsion committee doing teaching Gaussian quadrature to a bunch of slacker engineers?
I may have combined a couple of his papers on that one, I'll have to look when I get home. It may have been one using fusion and one using anti-matter. I loved hearing his stories about some of the papers he had to review as part of the committee, some were downright interesting, but most seemed to involve some sort of device that pissed-off the 2nd law
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We don't need more speed (Score:3, Insightful)
All the interesting places are either within reach now or too far to go there at ANY speed. What we really need is to find a way to autonomously survive in space for a long time.
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Sure, it would be nice to send a probe there, because it is another star, but interesting is more like, Eridani, which is about 10ly away, but has a planet.
I'm not saying that Alpha Centauri isn't interesting, I'm just saying you're missing the point of the OP. The idea is that even if we were to be able to travel at the speed of light, we aren't going to be able to travel more than 70ly away. While there is plenty of stuff in a 70ly rad
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You might want to check your understanding of time dilation. If they could go at the speed of light, they'd get to their destination instantaneously, from their own perspective.
We on Earth would still have to wait 4.2 years for them to arrive, and another 4.2 years to hear anything back.
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The point of that part of my comment was really just the idea that being that far away would be difficult for humans, not to suggest the precise amount of time it would take for observers on Earth to realize relativistic astronauts had gone mad.
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No, you're still not getting it. If they went at the speed of light, they wouldn't have any time to go crazy. The trip would be instantaneous for them...an eyeblink.
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I'm pretty sure they would send out status reports every day or so, regardless of whether anyone asking them.
I have no idea what you are proposing, and either way, it doesn't really change the gist of what I was saying.
Geometers (Score:2)
That should have read... (Score:5, Insightful)
... Edward Teller, the self-described father of the hydrogen bomb.
Other people who worked on the project tend to disagree with that title.
I does not matter (Score:2, Interesting)
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I'd characterize Teller's role in the H-bomb as similar to Oppenheimer's role for the A-bomb. As Oppenheimer is routinely called the "father" of the A-bomb, it seems reasonable to use the same language. Obviously, both projects were the result of a substantial number of people working a lot of hours.
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My mother had the same problem whenever my father would describe himself as such. How could he be the father when she worked on the project, too?
Kinda optimistic (Score:3, Informative)
Hmmm, if we can't build lasers and power supplies like that on Earth, even given tens of years and billions of $, how soon will these be doable in outer space, with 100% reliability.
The old project Orion looked into atomic kabang propulsion. There were a few major showstoppers-- two dud impulses in a row and the pusher plate goes flying off into space. No way on Earth to test it. Which is kinda important for a device that has to be 100% reliable with no misfires.
Also the idea of discharging all those Joules in 10 nanoseconds is mighty ambitious-- just the inductance of the objects limits the rate of current rise to a whole lot more than that.
Re:Kinda optimistic (Score:5, Funny)
Yeah, and what's worse, they can't even get acronyms right:
practical fusion-powered spacecraft (PDF).
That should be abbreviated as PFS or PFPS, not PDF.
Where is the ZPM? (Score:2)
Where is the ZPM?
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Actually in the Stargate universe currently (end of Season 5) the humans of Earth have multiple ZPMs. Spoilers ahead if you haven't seen the last episode of Season 5 yet.
.
.
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Two were taken back to the Milky Way after the Replicators occupying Atlantis back in Season 3 were destroyed. One of those was put aboard the Odyssey to help give them a chance against the Ori. It's never again mentioned but it's likely still there. In addition I find it interesting that at the time of the last Atlantis episode the
it may be the lead in for stargate universe (Score:2)
it may be the lead in for stargate universe.
Oh, but it gets better (Score:4, Insightful)
If you read the proposal, you'll note that the proposed method of working in space seems to be that the rocket engine actually fires in two directions - first, it fires a very high energy plasma beam AT THE SPACESHIP, which, in the vacuum of space, turns the whole assembly into a Gigavolt capacitor. THEN the spaceship fires a GV proton beam back at the rocket. This proton beam then ignites a classic fission explosion (using Deuterium-Tritium), but "very small", and this DT explosion ignites a second, much more explosive Deuterium-only fusion explosion AWAY FROM THE SPACECRAFT. Repeat one million times per second, or as needed.
What could possibly go wrong?
If that's not exciting enough, the whole plasma/proton beam doesn't work on earth, so, hey, we use a disposable argon laser, which can generate a lot of power, but (sadly), is really inefficient. But wait, we can fix that! All you have to do is set off a small hexogene explosion around your rod of solid argon, and the laser will suddenly work at 80% efficiency. Oh, repeat that every microsecond or so.
Honestly though, if you can get past the insane energies involved, he's come up with a rather brilliant way to use readily available fuel (Deuterium, as opposed to Deuterium Tritium, which is hard to come by), and using a whole chain of events, make the process really efficient (i.e. you need a lot less mass to make all this work). And, since your main burn is fusion (which consumes the fission by-products), not a lot of radiation to speak of (oh, well, there are some pesky neutrons, but who doesn't like neutrons?)
Re:Oh, but it gets better (Score:5, Insightful)
Did you know your car runs on explosions [wikipedia.org]? What could possibly go wrong? :P
Or do you ride a bike to work?
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Woah (Score:2)
That is fast, but since Barnard's Star is 6 light years away, assuming a constant acceleration and deceleration it would still take 100 years to arrive.
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According to google, it will take 50 years [google.com] to get there, unless you're talking about a round trip. Personally, I'd just be happy with a space probe. The six years it would take to receive information from the post, and for it to receive commands, would be a pain in the ass though.
Amazing (Score:2, Offtopic)
Building a starship is the least of our concerns. It baffles me that we are discussing building a fusion spaceship when it seems that very little is being done to get fusion working for making our energy here on earth. Our priorities are all mixed up. While we are spending billions on wars to give money to banks so they can use it to by their yachts, we desperately need to be spending that money on fusion and clean, environmentally friendly energy sources NOW. We cant afford to wait any more on this.
It amaz
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If fusion is feasible for a spaceship, why the hell are we not building fusion plants right now or at least spending billions on development of this.
I think the short answer to that is that fusion power is probably not feasible for a spaceship. It's just easy for somebody to pretend it's feasible while they're writing a pie-in-the-sky paper about interstellar spaceships.
If we can develop fusion, global warming is solved and we dont have to worry about it anymore. Then why are we not doing it. Why is it sometimes I get the feeling that while everyone moans about global warming, no one wants to take the initiative and actually fix the problem?
I agree that switching all our energy production to fusion would help with pollution and CO2 production, but there's at least a few climate scientists that think that we've already dumped so much stuff into our atmosphere that we'll still have something to worry about even if CO2 produc
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I do quite a bit. I ride the bus a lot, even though this is a great inconvenience. I would be happy to ride it if it were made convenient enough to do it. But the republican government here seems to like the idea of flooded coastal cities so they do not want to do anything to make public transit better. I use a clothesline (which is, astonishingly banned in places, which should be illegal!). I turn off lights. I dont run the AC unless its absolute unbearable without it. I recycle everything they will let me
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Glad to hear it, even though it does make me a real asshole for putting you on the spot. :) If everybody making noise about global warming did that much, we'd probably be a lot better off.
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If we can develop fusion, global warming is solved and we dont have to worry about it anymore. Then why are we not doing it
We are doing it.
Fusion in a "make H fuse into He" sense is fairly easy. Build a bomb, set it off, and presto - fusion.
Fusion as in a "make atoms fuse in a controlled setting" is harder, but still done on a fairly regular basis.
Fusion as in "create a fusion reaction that produces more energy that you spend creating the reaction" is fucking hard. Which is why we do #2 at all, and why you don't have unmetered power.
(Oh, and if all you care about is global warming, nuclear fission's perfectly suitable. Hell,
All other considerations aside, why Barnards Star? (Score:2)
Alpha Centauri A and B are more likely to harbor an earth like planet... not to mention are almost 2 LY closer.
If you want some red dwarf action, swing by Proxima on the way.
CGS WTF? (Score:2)
Whatever may be the reason, on most of the paper, his calculations and figures are in the obsolete CGS system (Centimeter, Grams, Seconds). Forces are in dynes, pressures in g/cm^2, etc.
And then you see later in the paper Amperes and Watts (which are SI units).
CGS and SI (or MKS) don't mix.
Fusion is EASY/Maybe they should have built Orion (Score:3)
Yet these equivalent fusion-based proposals seem to be only plausible with some assumptions of technological advancement, rather than with assumptions that people wouldn't mind the irreparable damage to the earths biosphere.
I think the approach is all wrong by many proposals so far. Thing is, we can create and contain fusion right now, and you can do it your backyard (no kidding - see lower). I think a plausible fusion drive would be something like a Bussard electrostatic confinement based drive. Essentially you are accelerating ions to high enough velocity for fusion, but allowing some to escape by a neutral charged nozzle.
We don't have fusion reactors right now that break even in any practical generative fashion, however that is absolutely not necessary. Give up the need to generate power from fusion, for example use an existing fission pile to power the thing, and you start to get results. The high-velocity fusion products become a nice boost to your specific impulse, along with your exhaust velocity much higher than any Ion or VASMIR thruster for any high-energy fuel leaking out the rear.
Ditch the perfectionist science and apply practical engineering and tune the thing for efficiency. Go to the stars.
Interestingly, electrostatic inertial confinement in a hard vacuum doesn't even need reactor walls .
What makes this even more exciting is that hobbyists build electrostatic confinement devices, and even get fusion reactions. Oh, OpenSource too.
http://www.fusor.net/ [fusor.net]
http://en.wikipedia.org/wiki/Inertial_electrostatic_confinement [wikipedia.org]
Now figure out how to make a drive out of a Fusor, strap some solar cells on it, and convince a private space launch company to put in orbit.
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no not at all u have it completely wrong
as u approach the speed of light
time at that velocity "slows" down
so if something is 6 light years away .5 light speed
and u are going
then it takes 12 years
so on earth 12 years would pass for it to arrive
however if u were on the ship it would take less then 12 years to arrive
in the extreme case if it was 6 light years away
and u were going light speed then on earth it would take 6 years for the ship to arrive
but if u were on the ship it might take seconds or no time at
Re:Relativity and time dilation make my head hurt (Score:5, Insightful)
Please read up on Relativity sometime. There are a number of decent resources on the subject.
As is, you've just lowered the IQ of everyone who read this post....
Specifically...
The time dilation effect on an object is irrelevant to an observer at its point or origin. It WILL reach its destination, unless it's aimed wrong, or hits something really hard.
No, there is no such speed as you propose in your second conjecture.
Time dilation is a wonderful thing. It helps to shorten trips from the point of view of the traveller. But it doesn't change the trip at all from the point of view of an observer back at the start point.
Unless, of course, you're carrying one end of a wormhole with you on the voyage. Still doesn't change the voyage from the point of view of the observer back home, but can have some interesting effects later (if, that is, you consider time travel interesting, of course).
Re:Relativity and time dilation make my head hurt (Score:5, Informative)
From your post, you don't make it 100% clear, but I suspect your understanding of time dilation might not be 100% accurate.
Say the distance from Earth to another star is 1 light-year, and we manage to accelerate a probe to an average speed of 0.1*c (1/10th the speed of light). For the sake of our thought experiment, let's assume the probe comes back, too, for a total trip distance of 2 light-years.
On earth, 20 years will have passed--it's a simple, easy "distance = rate * time" kind of thing. No time dilation to consider.
If you placed a clock on the spaceship, though, you'd see some time dilation effects on the moving clock. It would have experienced less than 20 years' worth of time passing. So if your Earth-bound clock and your space clock were perfect, and you synced them up before the trip started, they would be out of sync when the ship got back.
Remember, in your own reference frame, you don't experience any time dilation. The fact that the ship is travelling fast doesn't make clocks on Earth run slower.
If this isn't clear, go read the Wikipedia article on time dilation, and read the part where it talks about muons decaying as they travel from the upper atmosphere to the surface of the Earth. That's the easiest example to understand, I think, as long as you get how radioactive decay operates.
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I think the point the GP was trying to make is a valid one - if we made a probe that travelled to a certain star at 0.9c, there's no point doubling its fuel tanks so it can go at 0.95c. From our P.O.V, the probe would take 19 years instead of 20 - clearly not worth it. If it was a manned spaceship, the time dilation would reduce the supply requirements sufficient that it might be worth it.
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Patrick, did you read the second paragraph in the GGP? If not, go back and look at this quote:
"First, as an object approaches C the time dilation effect becomes such that from a frame of reference of the origin, the object never in fact can reach its destination. Would it not become in essence stuck in time?"
This is nonsensical in special relativity. In the frame of reference at the spacecraft's origin (Earth), the spacecraft will certainly reach its destination eventually as long as it has a positive vel
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the GGGP is getting a little confused. From a stationary observer's P.O.V, time slows down for someone else going faster and/or falling into a black hole, and if that traveller were ever to reach C (or the event horizon) time would stop. From the traveller's P.O.V, they cover a light year in much less than a year, and the length contraction turns the universe into a paper-thin disk of dust that they promptly slam into and explode. I always found that amusing.
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As the probe speeds up, the time the observer on earth sees it take remains equal to the distance it must travel divided by its velocity (in Earth's frame). Time dilation affects the probe because what the probe sees is a relativistic shortening of the distance it must travel, thus giving a reduced total time of
Re:Relativity and time dilation make my head hurt (Score:4, Informative)
But it seems to me that going faster and faster you reach a point where although it might only take the probe x number of years to reach the star, on Earth it takes significantly more time. Therefore in the case of an unmanned probe, since it's time passage on earth that matters, at a certain point it's not desired to have the probe go any faster.
Actually, it's the other way round; from the point of view of someone on Earth, clocks on a rapidly moving spacecraft appear to go more slowly.
The actual time dilation factor, known as the Lorentz factor, is a simple 1/sqrt(1 - v^2), so for your vehicle going at .12c the difference in speed in clocks is 1.007 --- as you say, negligible. An observer on Earth sees a second metronome on the vehicle tick every 1.007 seconds.
This usually works out to your advantage. Passengers on a fast-moving ship will have less time to get bored, and there'll be less wear and tear on the structure. A sufficiently fast moving ship can cross the galaxy in subjective days (see A World Out Of Time by Larry Niven), although you're still going to get to your destination at least 100,000 years later. (You'd need a Lorentz factor of about 5000000 for that, which means you'd need to be travelling at 0.99999999999998c.) OTOH you run into severe navigational problems: such as the inability to dodge oncoming obstructions. Because, of course, the faster you go, the less warning you have of them...
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Not to mention the acceleration getting to that speed would either take a very long time or turn the passengers into soup.
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The actual time dilation factor, known as the Lorentz factor, is a simple 1/sqrt(1 - v^2)
By your formula if v==1 you have an infinite factor....
I think the actual formula for the factor is 1/sqrt(1-(v**2/c**2)) where v is velocity and c is the speed of light, both measured in the same units. It's also the same for the relativistic mass of an object: Mv = M0/sqrt(1-(v**2/c**2)) where Mv is mass at velocity v and M0 is rest mass; meaning your mass goes to infinity as your velocity approaches c. Another w
Re:Human starship has already landed on Mars? (Score:5, Informative)
Dude...you've got what appears to be about a 50px kinda round thing in a crater, and your first assumption is a man-made biosphere? Well, I've got about a hundred pictures of alien spacecraft for you to look at then....
Seriously though, different planets have vastly different conditions, so it's no surprise you don't see things like this on Earth. I'd say it's essentially a sand dune. There's a _lot_ of similar formations on Mars. In fact, there's a few more on the string of pictures that original is from:
http://ida.wr.usgs.gov/html/m15012/m1501228.html [usgs.gov]
There's one in the first image, there's some somewhat similar phenomenon in the second and third, there appears to be one in the fourth, two in the fifth, and part of one in the sixth.
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It's a pristine impact crater.
Look around it there are at least 30 others in progressively more eroded states ALL AROUND IT. IN THE SAME PHOTO.
Impact crater with bump in the middle... impact crater with bump in the middle... impact crater with bump in the midle. that one is just much less windswept and eroded.
Use your eyes not your crazy brain. No on second thought... use your crazy brain. It fails the brain test too.
Don't you think NASA would photoshop out a secret NASA project. Or at least not send t
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As far as the Nuclear drive, my brother ( who is a Nuclear Engineer ) and I have discussed it for over 30 years and though it might work, it could also end up buried somewhere with a message "Do not open until Ch
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It seems likely that this sort of ship would be built in space, so any such accident would be taking place many hundreds or thousands of miles away from the earth's surface.
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> The peper makes no suggestions on how a ship will generate and store the necessary
> gigajoules of energy to maintain a sustained reaction.
Yes it does.
> We may need a separate nuclear reactor to providing the ignition energy.
Read the papaer again.