The Most Scientific Plausible Method of Interstellar Movemen

[Samuel]

Planets and moons in the way isn't a problem too. Odds are it will never happen, and even if it does, just wait for them to pass. Problem solved.

Most planets and objects in the solar system are on the same plane around the sun. Putting your laser "above" (or below- there isn't really a top and bottom) allows you to avoid them.

[Wyrm]

I might explain here, a lot of "advanced science" in my fictional 'verse comes from finding faults in established systems. Like how you can bypass conservation of energy by forming a very complex energy pattern, which suddenly explodes into a spray of all manner of radiation like a cellular automata seed. And then imprint the pattern into metal to continuously reuse the effect. Essentially, I believe this principle has a right to exist in our universe as well. We just haven't enountered the required patterns yet, because they are too complex to have a significant chance of occuring by accident.

Um... okay. That's basically your right as an author to inflict this on your own fictional universe, but understand that your notions don't necessarily carry any real scientific plausibility. Our best theories on how the universe works says that energy is indeed strictly conserved in all physical processes, and its a principle embedded deep into the very structure of existence and is the very farthest thing from scientific plausibility.

And welcome to this wretched hive of scum and villainy. Just keep your fiction well-divorced from your discussions concerning reality and you'll do fine here.

[RedImperator]

And I hate writing things off as "impossible". If it's believed to be impossible, isn't that a reason to try and do it anyway?

It's impossible for a human being to fly under his own power. By your logic, we should all be standing out in our front yards flapping our arms really hard.

When scientists say FTL is impossible, they mean it--FTL travel literally breaks the universe as we understand it (an understanding that's been tested to many significant digits). Conservation of mass-energy, if anything, is even more ironclad. It's fine to say, "Well, for dramatic reasons, in my story, scientists found a loophole" (though honestly, I'd ditch the idea of a loophole in conservation of mass-energy; perpetual motion machines cause most possible plots to collapse in a heap), but that doesn't apply to the real world.

The main reason I started writing hard science fiction instead of soft was because I discovered that the universe is just as interesting without a bunch of pulp-era tropes as it is with them. In most cases, more interesting.

A hostile AI takeover is one relatively plausible catastrophe where I could getting out of the solar system looking like a good idea.

Then again, a hostile AI could plausibly follow you; simply being in another solar system really isn't that much of a defense against a determined immortal entity with the resources of our solar system at its disposal. It'd probably be easier just to hide out in the Oort Cloud.

I'm pretty sure in the case of a hostile AI with solar-system wide reach, we're totally boned unless there's a friendly AI in a nearby solar system willing to offer asylum.

Yes, so would throwing tin cans out the back, if you had enough time. But in this case, the exhaust velocity and fuel requirements of the NSWR are sufficient to allow you to accelerate up to 3.6%C before the universe experiences heat death.

I wrote a book about people flying around in 90% enriched NSWRs. I picked them for two reasons: first, they had the right combination of thrust and specific impulse for the plot I had in mind to work. Second, they're incredibly complicated and explode if you look at them funny, which made them much more dramatically interesting than a rocket which just stops working if it breaks. Honestly, they're stupidly hard and almost certainly will never work, let alone work within the safety tolerances necessary for any human being in his right mind to ride on one.

[Shinova]

For FTL the alcubierre drive is the only thing that's taken relatively seriously.

[Questor]

For FTL the alcubierre drive is the only thing that's taken relatively seriously.

I ran into that, in Star Carrier. Do you know if the presentation in that novel is accurate, or just pulling a name?

[Guardsman Bass]

For FTL the alcubierre drive is the only thing that's taken relatively seriously.

I don't know if you can really say it's taken "seriously". There's a model for how one might work*, but you get all kinds of weird requirements like a shit-ton of "negative mass-energy" for it to work. Same goes for Wormholes, if I remember right.

*In the sense of how the basic principle of it might go, not in the sense of a model of a drive that we could actually build anytime soon, obviously.

[RedImperator]

"Relatively seriously" means "yeah, this almost certainly doesn't work, but there's a tiny sliver of a chance all your assumptions are right--good luck actually engineering it, if they are" as opposed to "LOL get out of my office".

[Simon_Jester]

Even Alcubierre drive requires very large supplies of matter that weighs less than nothing. So... not actually seriously, except in relative terms.

[eion]

Yes, so would throwing tin cans out the back, if you had enough time. But in this case, the exhaust velocity and fuel requirements of the NSWR are sufficient to allow you to accelerate up to 3.6%C before the universe experiences heat death.

Based on incredibly optimistic, arbitrary assumptions, nothing more. Even so, that number assumes a mass ratio of 10. For every ton of payload, you need 2 tons of highly enriched uranium and 8 tons of bromine and water, given the assumptions on Atomic Rockets (and assuming when he said "by number", he meant moles rather than mass). Sounds cheap!

Who ever said any of this would be cheap? Your mission (which lacks any estimates for power requirements) could require 43-Thousand times more power than is generated by the whole planet, and you'll more than likely have to base you laser in space, so now you have to generate 43-thousand times more power than a whole planet in a vacuum with far more issues of heat dissipation and such. That 43,000 number comes from the Star-Wisp 83,000 ton manned model.

Now fuel availability is BIG problem. You'd probably only use the NSWR in early excursions, and would very likely also use laser sails, fusion drives, and perhaps eventually antimatter drives. It was NEVER my point that NSWR are the ONLY way to get to the stars, though you seem to think so. I merely mentioned them because they are a novel concept that no one else had mentioned.

Now Orion can be even faster, but others have already mentioned some of the problems with carrying several thousand nuclear bombs along with you on a five light year tour.

Several of which probably apply to the NSWR too, such as the natural decay of the highly enriched uranium your assumptions require.

Undoubtedly, but it does sidestep the Nuclear Test Ban Treaty and prevents a rogue captain from selling off his propellant as ready-made bombs.

The key concept behind it is nuclear fission, are we still on the fence about that?

That's not the key concept. It is being able to put it in a salt water solution and maintain the reaction in a stable manner as it flows out. Fission isn't hard, a nuclear salt water reaction is.

So hard in fact that reactors have to be designed to prevent the very reaction required (a prompt-critical reaction) to make them work, SHOCKING! If you can build a bomb, which rely on prompt-critical reactions, you should be able to design a NSWR. It's just that such a drive could never be tested on Earth, unlike your laboratory concept.

As for skeptical, Atomic Rocket just throws that in, without any reference to whom these guys are and what their concerns are.

Atomic Rockets doesn't give any sources whatsoever beyond Zubrin's name. So it isn't a problem when results you like are unsourced, but if they question your love, it is suddenly unbelievable?

Having a copy of his book next to me, I know that the figures are the same in both sources, and knowing that Dr. Zubrin is a noted rocket scientist with multiple degrees in NUCLEAR ENGINEERING(rather than a Fox-Newsesque "Some people") gives me a certain confidence in his expertise and his numbers. I'll be the first to claim no capability in nuclear engineering beyond the "billiards analogy".

You'll notice the listing for the Laser-Moth really doesn't mention any of its drawbacks there.

I'm talking about a photon drive, the laser at home bounces photons off your ship, pushing it forward.

Okay, so: How big's the laser? What's its power output? Exactly how will you generate that power? Where will the laser be? How will that location affect your lasing of the ship? How will you construct the laser station if it is in orbit? How will you get rid of the waste heat if it is in orbit? How big is the sail? How much does it weigh? How will you construct and launch that? What's your mass ratio for sail vs. payload? Do you include an on-board reactor in case of catastrophic power outage or do you rely on generating power off the laser? How do you deal with abrasion of the sail material?

Yes, we both seem to have our favorites. Yours is just as fictional as an NSWR, at least until someone sends a probe to Mars or the moon using a laser sail.

Momentum transfer by laser has been proven in the lab, including reflecting it several times to amplify the effect without cranking up the power. The NSWR has... what?

It's a prompt critical reaction which has been demonstrated (sometimes accidently) numerous times, including:

Los Alamos Scientific Laboratory, 11 February 1945
Los Alamos Scientific Laboratory, December 1949
Los Alamos Scientific Laboratory, 1 February 1951
Los Alamos Scientific Laboratory, 18 April 1952
Argonne National Laboratory, 2 June 1952
Oak Ridge National Laboratory, 26 May 1954
Oak Ridge National Laboratory, 1 February 1956
Los Alamos Scientific Laboratory, 3 July 1956
Los Alamos Scientific Laboratory, 12 February 1957
Mayak Production Association, 2 January 1958
Los Alamos Scientific Laboratory, 30 December 1958
SL-1, 3 January 1961
Idaho Chemical Processing Plant, 25 January 1961
Los Alamos Scientific Laboratory, 11 December 1962
Sarov (Arzamas-16), 11 March 1963
White Sands Missile Range, 28 May 1965
Oak Ridge National Laboratory, 30 January 1968
Chelyabinsk-70, 5 April 1968
Aberdeen Proving Ground, 6 September 1968
Mayak Production Association, 10 December 1968
Kurchatov Institute, 15 February 1971
Idaho Chemical Processing Plant, 17 October 1978
Sarov (Arzamas-16), 17 June 1997
JCO Fuel Fabrication Plant, 30 September 1999

One question, how exactly do you stop your probe if there isn't a laser or a mirror already there?

You bring a mirror with you.

Which I mentioned in the next line that you snipped.

The laser is going to be the easy part (if we're going by current tech); the hard part is going to be getting the kilometers wide sail up there to begin with.

If you haven't solved launching to orbit, you sure as fuck aren't going to other stars any time soon.

Granted.

Power outages aren't a big deal, since you can just fix it and get back to business. Christ, power outages are a much bigger problem when you're on your own. This should be obvious.)

No no, not "whoops the plug fell out" power outages, more like "whoops all civilization just annihilated itself 5 times over in a massive global thermo-nuclear war" power outages. What's worse than being fucked because of a problem 100 feet away? Being fucked because of problem 2.5 light years away, right when you need that power from home to start braking.

What if your NSWR screws up and the salt water goes critical in the tank?

This would only happen if the tank was ruptured somehow. If it happens, you're fucked.

Or what if the nozzle degrades from the passing heat and radioactive materials?

One idea is to run a sheen of pure water over the surface of the nozzle (much as the Orion has a lubricant continuously sprayed on its bumper). The great majority of the radiation will be carried away from the ship VERY VERY quickly along with the massive head of water plasma. Also, you can run a magnetic field around the nozzle and reaction chamber to keep the plasma from contacting the walls, this will keep most of it and its radioactive hanger-on safely away from the nozzle.

The point is, those problems are potentially solvable. No matter how much you try, your idea will always have a 5 light year extension cord. If something happens to home base, your mission is over, and your crew gets to enjoy floating powerlessly in space. Something goes wrong on my water rocket, the crew won't even be around to know it.

Planets and moons in the way isn't a problem too. Odds are it will never happen, and even if it does, just wait for them to pass. Problem solved.

Well if the laser is on Earth or in orbit of Earth it will happen for at least a few days or weeks of the year (the time it takes for the Earth to pass behind the Sun. If you locate your station around say Pluto's orbit to prevent anything big getting in the way, you now have all the fun of building the station out there, plus if you mission is very long you might lose power more often if your station is allowed to get to far away in its orbit. I suppose you could design it as a statite, but then we haven't even built one of those in the inner solar system yet. And how much safety margin will you build into your system to allow for objects interrupting the beam? Too many interruptions of the laser and the ship won't be able to slow down enough.

Course corrections can be done by angling the mirror. All that's left is the beam spreading out, but that's why the sail is so big.

Which will create great forces on your presumably atoms thick sail, how will you prevent it ripping itself apart in the process?

See, you answered the natural concerns a laser-sail raises quite nicely. Destructionator's concept didn't go much beyond "IT'S BETTER WITH LASERS!"

This coming from the guy who didn't go much beyond "IT'S BETTER WITH NUKES".

Yes, but mine has always been "IT'S BETTER WITH NUKES, and here's why." I've given at least some info in every post. For one thing, I linked to a concise description of the overall idea in my first posting. Until this post, your idea was vague, now we're starting to see a few details.

EDIT: Minor correction in Dr. Zubrin's credentials.

[eion]

I do adore a mag-sail; every ship should have one, cuts your fuel bill in half They're not so far out there, what we're lacking is high-temperature superconducting wire. If it exists, the sail can be made, if not, it can't.

I don't see why in principle you couldn't chill the wire. It'd be a lot easier if you didn't have to, but I don't see why needing a cooling system is necessarily a showstopper. Especially since it'd be mostly or entirely operating in a pretty cold environment (interstellar space) anyway.

You can, but then you have to carry something to chill them with, which adds payload. And since the wires for our sail are many kilometers long, we're talking about a lot of coolent. And you have to remember that not only is the mag-sail good for slowing you down, it can also be used to move you effortlessly about the star system, just turn it on to move away from the star, turn it off to coast.

The less you have to cool the wires, the better because that means more payload and propellent, which means you can get there faster and do more when you get there.

[CSJM]

And I hate writing things off as "impossible". If it's believed to be impossible, isn't that a reason to try and do it anyway?

It's impossible for a human being to fly under his own power. By your logic, we should all be standing out in our front yards flapping our arms really hard.

Is it now? Granted, that's not unassisted flight, but still "flight under his own power".

As far as "scientifically plausible" goes, we're quite limited here with regards to interstellar travel. It's either variations of "use a VERY large rocket using such-and-such propulsion", or photon propulsion, either by laser or solar wind. I believe we should first extend the reach of "scientific plausibility" before we seriously venture to the stars. Should improve our chances significantly.

(and did someone just say that space is cold?)

[Samuel]

Okay, so: How big's the laser? What's its power output? Exactly how will you generate that power? Where will the laser be? How will that location affect your lasing of the ship? How will you construct the laser station if it is in orbit? How will you get rid of the waste heat if it is in orbit? How big is the sail? How much does it weigh? How will you construct and launch that? What's your mass ratio for sail vs. payload? Do you include an on-board reactor in case of catastrophic power outage or do you rely on generating power off the laser? How do you deal with abrasion of the sail material?

You construct the laser the same way you construct the ship in space- orbital industries. Unless you plan on building your ship on the ground and sending it up in pieces, that is the way to go. As for generating the power for the laser, there is a nice fusion reactor in the center of our solar system we can exploit.

It's a prompt critical reaction which has been demonstrated (sometimes accidently) numerous times, including:

Don't you want it controlled so it doesn't kill the crew?

No no, not "whoops the plug fell out" power outages, more like "whoops all civilization just annihilated itself 5 times over in a massive global thermo-nuclear war" power outages. What's worse than being fucked because of a problem 100 feet away? Being fucked because of problem 2.5 light years away, right when you need that power from home to start braking.

Unless this is an "insure the survival of humanity" project, that is irrelevant. It would make whatever goal the ship had no longer meaningful.

[Simon_Jester]

The point is, those problems are potentially solvable. No matter how much you try, your idea will always have a 5 light year extension cord. If something happens to home base, your mission is over, and your crew gets to enjoy floating powerlessly in space. Something goes wrong on my water rocket, the crew won't even be around to know it.

That's not a very good argument.

"If the solar sail power supply fails, we might as well all commit suicide, because we're dead anyway."
"If the NSWR fails, we all die."

Those arguments boil down to the same thing- if the engine screws up, you're dead. Thus, the entire question boils down to probability of failure, which isn't something you can address trivially without knowing the details of the NSWR (as in, after they build a prototype) and the solar sail design in question.

Well if the laser is on Earth or in orbit of Earth it will happen for at least a few days or weeks of the year (the time it takes for the Earth to pass behind the Sun. If you locate your station around say Pluto's orbit to prevent anything big getting in the way, you now have all the fun of building the station out there, plus if you mission is very long you might lose power more often if your station is allowed to get to far away in its orbit. I suppose you could design it as a statite, but then we haven't even built one of those in the inner solar system yet. And how much safety margin will you build into your system to allow for objects interrupting the beam? Too many interruptions of the laser and the ship won't be able to slow down enough.

Actually, there's no reason you can't fire the laser beam directly past the sun; the only time during which you can't keep the laser going is when the sun is on the direct line between the earth and the ship. Given the size of the sun and the speed of the Earth in its orbit, that's not going to be true for more than a few minutes a year, if that. For most possible flight paths it never happens.

Other debris interrupting the beam is even less of an issue, and you should know it. Objects in space travel fast enough to cover many times their own diameter in short periods of time; they can't block the beam for long.

[Junghalli]

Your mission (which lacks any estimates for power requirements) could require 43-Thousand times more power than is generated by the whole planet, and you'll more than likely have to base you laser in space, so now you have to generate 43-thousand times more power than a whole planet in a vacuum with far more issues of heat dissipation and such. That 43,000 number comes from the Star-Wisp 83,000 ton manned model.

If you're referring to the Forward lightsail, most of the craft's mass would be in the aluminum sail. The numbers potentially get a lot better with dielectric sails because they can take more energy without melting, allowing your laser beam to be tighter, hence the sail to be smaller and the ship to be less massive. Link.

The less you have to cool the wires, the better because that means more payload and propellent, which means you can get there faster and do more when you get there.

Thing is assuming you mean room temperature superconductor or something along those lines IIRC that is one of the holy grails of electronics research and we can't say for sure that such a thing is even actually possible. I'd rather not bet the success of a promising technology on what may be unobtanium.

As far as "scientifically plausible" goes, we're quite limited here with regards to interstellar travel. It's either variations of "use a VERY large rocket using such-and-such propulsion", or photon propulsion, either by laser or solar wind. I believe we should first extend the reach of "scientific plausibility" before we seriously venture to the stars. Should improve our chances significantly.

We're limited because of limits set by the laws of physics as we understand them. It's possible that our understanding of physics is wrong, but it is not parsimonious to assume so.

I think the real key to being ready to go to the stars will be greatly increasing our industrial capacity and overcoming our limited lifespans. At this point things like the Forward lightsail look daunting to us because we're like ancient Romans gaping in incredulity at the resources you'd need to build an aircraft carrier.

(and did someone just say that space is cold?)

Interstellar space is a low energy environment, to use more correct terminology. The point is an object floating in interstellar space isn't likely to heat up much.

[Arthur_Tuxedo]

Sorry if this is a dumb question, but how the hell are you supposed to aim a laser so accurately that it can hit an object smaller than most asteroids at interstellar distances? Even with future-tech, the difficulty of this task would seem to approach infinity.

[Junghalli]

Sorry if this is a dumb question, but how the hell are you supposed to aim a laser so accurately that it can hit an object smaller than most asteroids at interstellar distances? Even with future-tech, the difficulty of this task would seem to approach infinity.

The Forward lightsail design calls for a focusing mirror 1000 km across to focus the laser to something that's still usably focused at light year distances, but I'm not sure what system they proposed for aiming it.

An easier alternate possibility in this respect is to use a sailbeam. Instead of a laser propelling a big lightsail you use the laser to send out a stream of little tiny lightsails that can be accelerated much faster that are later ionized and hit a magsail on the ship, transferring their momentum to it. The ship would have to use some other means of stopping at the destination system though, either a rocket or a magsail brake (the latter would still allow it to get away with carrying little or no actual fuel for the entire trip).

[Wyrm]

As far as "scientifically plausible" goes, we're quite limited here with regards to interstellar travel. It's either variations of "use a VERY large rocket using such-and-such propulsion", or photon propulsion, either by laser or solar wind. I believe we should first extend the reach of "scientific plausibility" before we seriously venture to the stars. Should improve our chances significantly.

Dude, the current physical laws can plausibly allow one to colonize the entire galaxy in about ten million years, given only what is scientifically plausible today. The principles you propose to bend or break are so well-founded that by the time you find your beloved loophole, we could have colonized the galaxy already... if you find it at all.

Because as far as we know, the universe has no Rule of Cool, and does not run on Hot Blood. Sorry.

[eion]

Who ever said any of this would be cheap? Your mission (which lacks any estimates for power requirements)

Without knowing the mission, you can't estimate mass, and thus can't get power. If it is a probe, like Voyager, it could be just a few tons. In this case, output power on the order of 10^9 W (single-digit gigawatts; less than one large power plant's output) could give it a nice, constant acceleration (~0.1 m/s^2 - no rush to accelerate), letting it complete a mission to a nearby star in some twenty years. We've run probes in the solar system for periods longer than that.

Note that Voyager 2 is a real life example of an interstellar probe, launched in the 1970's, with chemical rockets, and still returning data today, though it won't actually be visiting another star during its operational lifetime. A similar probe, accelerated to a small percent of the speed of light by means of laser reflection, could make it to another star in the time it has taken Voyager 2 to leave the solar system and plausibly radio back data about that star as it flys by. If you're willing to do a 50 year mission, your probe could stop there for the scenic route.

Well no, if Voyager 2 isn't able to collect or return any data when it passes within 4 light years of Sirius in about 300,000 years it isn't really a probe at that point, it's a time capsule.

So far, Voyager 2 has surpassed all its design expectations, but it's only been going for 32 years, and after 2025 (48 years after launch) there will not be enough power to operate any of the on-board instruments. I'm not sure any RTG or even a nuclear reactor could supply sufficient power for operations over a 50 year lifetime. You would need a fusion reactor probably. And we haven't even discussed the issues with returning data to earth.

If you're talking about Noah's Ark, well, the power requirements will naturally skyrocket, but it could still be solved with a solar satellite swarm. The sun puts out a lot of power that could be captured.

So one 100,000 ton launch for an NSWR versus 100 or a thousand 100,000 ton launches for the solar swarm, laser platform, Fresnel lens, and the ship itself. As a onetime go, the NSWR has the benefit, but as a sustained means of travel or exploration some manner of laser-sail might pay off.

could require 43-Thousand times more power than is generated by the whole planet, and you'll more than likely have to base you laser in space, so now you have to generate 43-thousand times more power than a whole planet in a vacuum with far more issues of heat dissipation and such.

There's lots of energy to be gotten in space. We don't even use a significant fraction of what the sun sends right to Earth!

Yes, but the infrastructure required to harness that may push back interstellar exploration by decades or centuries. Building up that capacity is worthwhile, but need not invalidate efforts to explore the stars by other means.

It was NEVER my point that NSWR are the ONLY way to get to the stars, though you seem to think so.

The thread is asking the most plausible method.

Which can mean either likely or worth of praise. the OP does not ask what method we will use for sustained travel, or for the initial exploration of other stars. If it is the former, laser & solar sails will almost certainly play a part, but the intial infrastructure required for such a system will certainly mean that a more self-contained system will be employed for the first steps outside the heliopause. That most likely means nuclear, whether fission or fusion is a good question.

So hard in fact that reactors have to be designed to prevent the very reaction required (a prompt-critical reaction) to make them work, SHOCKING! If you can build a bomb, which rely on prompt-critical reactions, you should be able to design a NSWR.

We can build fusion bombs* today, but fusion rockets are way off, if they can be made at all. My biggest problem with the NSWR is heat management and keeping the solution from spontaneously detonating in the tanks. Those aren't big issues with bombs (well, spontaneous detonation would be, but you know what I mean), but matter a lot for a rocket.

We can build fusion reactors right now, just not self-sustaining reactions. If you can build a fusion reactor, all you need to do is stick a tailpipe in it and you have a fusion rocket. As to your concerns over the NSWR, heat management is achieved primarily by letting the exhaust carry away the heat. Further if the nozzle does heat up significantly, you might wrap the nozzle in a coolant-circulating jacket you can operate a heat exchanger and power your ship and cool the nozzle simultaneously. As each fuel tube contains a subcritical mass, and the interstitial space is full of neutron absorbing material such as boron means that unless those tubes and the insulating material are breached there can be no runaway reaction.

Having a copy of his book next to me, I know that the figures are the same in both sources, and knowing that Dr. Zubrin is a noted rocket scientist with multiple degrees in NUCLEAR ENGINEERING(rather than a Fox-Newsesque "Some people") gives me a certain confidence in his expertise and his numbers.

People with fancy credentials are wrong all the time. Is his work peer reviewed?

The original article was published in the Journal of the British Interplanetary Society, a highly respected organization that has forwarded such plausible concepts as Project Daedalus. They are known for forward-thinking, but not pie-in-the-sky, concepts. I am unaware of the journal's peer-reviewed status. Here is the original article in full, it is the first listing. Having never seen the original article in full before, I am posting it and will read it afterwards.

What's its power output? Exactly how will you generate that power? Where will the laser be? How will that location affect your lasing of the ship? How will you construct the laser station if it is in orbit? How will you get rid of the waste heat if it is in orbit? How big is the sail? How much does it weigh? How will you construct and launch that? What's your mass ratio for sail vs. payload? Do you include an on-board reactor in case of catastrophic power outage or do you rely on generating power off the laser? How do you deal with abrasion of the sail material?

I'm not a rocket scientist nor mission engineer. The question at hand is one of plausibility, not detailed plans for NASA.

Well my concept has such detailed information available. You should either provide your own specifications or find a concept with such details so we might better compare the merits of each.

It's a prompt critical reaction which has been demonstrated (sometimes accidently) numerous times, including:

Not one of those used a salt water solution, and they weren't exactly well engineered solutions (being a list of accidents means this is to be expected):

That which can be done by accident can certainly be done by design, and far safer.

No no, not "whoops the plug fell out" power outages, more like "whoops all civilization just annihilated itself 5 times over in a massive global thermo-nuclear war" power outages. What's worse than being fucked because of a problem 100 feet away? Being fucked because of problem 2.5 light years away, right when you need that power from home to start braking.

The nuclear accident 100 feet away kills people right now. In interruption in the laser still leaves a lot of time to find a solution (fixing the laser, turning on the backup, whatever). Now, if the home system is completely annihilated, you're probably fucked, but that's a retarded situation to worry about.

Besides, you're not necessarily screwed - you might be able to improvise something, or just take a slower trip. The odds are against it, but it isn't "RADIATION'D YOU'RE ALL DEADER THAN THE INCOMPARABLE LEGION OF LIGHT".

Improvise something? On a ship one one-thousandth (or one one-millionth) of the size of your home transmitter, with potentially no-onboard power generation, no backup drive system, no life-support if it's powered by the laser, etc. And the problem isn't getting there slower (though if you life support is only useable for 50 years, and it takes you 51 years to get there, well time to draw lots I guess), it's not being able to slow down.

This would only happen if the tank was ruptured somehow. If it happens, you're fucked.

You just posted a giant list of times when what you say is the core principle of the system failed accidentally and killed people, but now you don't seem concerned.

All those instances involved a closed vessel. If the end is open to space, and you have a continuous wave reaction as designed, all that energy will take the path of least resistance, out into space, and send you the other way very quickly. And since each of the individual tanks is sub-critical, no reaction can take place in them, so they are safe so long as the massive boron shielding (not to mention whatever Whipple shields and other armor you naturally surround the fuel tanks with) remains intact you are perfectly safe from a runaway reaction. And if something is powerful enough to penetrate the reactor housing it is more than likely it will have destroyed the rest of the ship anyway, so no, I'm not especially worried about that.

The point is, those problems are potentially solvable. No matter how much you try, your idea will always have a 5 light year extension cord.

You say this like its a bad thing, with no actual reasoning. We all live with a 93 million mile "extension cord" right now, but it has never failed.

Here's just one example of why it’s a bad thing: The SS Photon misaligns itself just slightly, pushing it out of the local correction margin and the sightline of the laser. Without a backup drive system (this was left out to save weight) it cannot realign itself to the laser, and since a signal to realign the laser takes 2.5 years to reach the operators at their current distance, and then a further 2.5 years for that redirected laser-beam to reach their new position, they miss their braking window and speed past their target system with no hope of slowing down.

Communication delays matter.

If something happens to home base, your mission is over, and your crew gets to enjoy floating powerlessly in space. Something goes wrong on my water rocket, the crew won't even be around to know it.

Rofl, yay, you die quickly.

I'll take a quick death over sitting there unable to do anything while the air runs out. Besides, the resources available to a NSWR in terms of independent power, independents drive system, and other resources carry-able by a self-propelled craft means they may well be able to fix small problems that could doom a laser-sail.

Well if the laser is on Earth or in orbit of Earth it will happen for at least a few days or weeks of the year (the time it takes for the Earth to pass behind the Sun.

Space is 3d dude, the odds of a direct line being formed is quite rare. (Though, my preference would probably be to put the laser in a solar orbit, since there's less movement there.)

Most things are in the ecliptic, dude. Your target stars probably aren't (a few are, including some near and interesting ones), but any laser platform, unless a magic statite, will have to pass through the ecliptic at least twice every orbital period, and the likelihood is several objects will pass between the laser and your ship. It's all a balancing game, you can design a schedule that accounts for any intersections, but at what point does it become too costly. There's also the issue of shooting a multi-terawatt death beam through the solar system, which if miss-timed could be quite disastrous.

Too many interruptions of the laser and the ship won't be able to slow down enough.

The odds of this are near zero, and easily controlled anyway. Just start firing the laser a wee bit early, and if everything goes well, shut it down a wee bit early.

So what if you think things are okay at home, but 5 light-years away they know that they need another day of laser to slow down enough. That delay kills you every time. You need to have a go/no-go call 5 years out; I don't know of any probe or system that has the capability. I suppose they can just leave the laser on, and you can rotate the ship, but then those powerful forces come back into play and done wrong your laser ship will tumble end over end until your atoms thick sail rips itself apart.

I'm not even sure if a NSWR can be shut down prematurely; quite a few rockets can't be (not reliably anyway).

Um, close the valves, and it shuts off just fine. You can even design a SCRAM procedure in if you’re paranoid that dumps a massive neutron-poison into the stream that cuts off the reaction until a backup shutter-valve can close if you so desire. The plumbing on this thing is so incredibly simple compared to a traditional chemical rocket or a fusion rocket.

Which will create great forces on your presumably atoms thick sail, how will you prevent it ripping itself apart in the process?

Be gentle with it, you have lots of time.

The problem is that even small errors will compound over time perhaps uncontrolable if there isn't a backup drive.

[Junghalli]

Improvise something? On a ship one one-thousandth (or one one-millionth) of the size of your home transmitter, with potentially no-onboard power generation, no backup drive system, no life-support if it's powered by the laser, etc. And the problem isn't getting there slower (though if you life support is only useable for 50 years, and it takes you 51 years to get there, well time to draw lots I guess), it's not being able to slow down.

If they're going anywhere but one of the nearer stars I really doubt this ship would have a mortal human crew with limited provisions. If you can undertake a voyage of decades or centuries waiting a couple of extra centuries for a faster rescue ship to catch up to you while you drift helplessly at .5 c could plausibly be a viable option.

Aside: I calculate a one-way NSWR mission to Alpha Centauri with a mass ratio comparable to the Apollo mission (22) and a magsail for braking would take over 80 years to get there. If this is to be a human-crewed mission, you will probably want some kind of suspended animation for that too.

[eion]

Well no, if Voyager 2 isn't able to collect or return any data when it passes within 4 light years of Sirius in about 300,000 years it isn't really a probe at that point, it's a time capsule.

NASA's designation for Voyager 2 is interstellar, which fits, since it is now studing the space between stars.

NASA also calls the Space Shuttle a reusable launch vehicle, which is laughable on many levels. And they call it an interstellar probe now, when it is 0.00145 ly away from Earth and still able to power some of its sensors. When it passes by Sirius in 300,000 years that definition will no longer be accurate, nor will it be accurate a decade or two from now when it loses all useful power and enters its terminal mission phase, also known as coast until some alien discovers it and its handy map back to Earth with all the pretty noises.

I'm not sure any RTG or even a nuclear reactor could supply sufficient power for operations over a 50 year lifetime.

48, when rounded to the one significant figure I always use is.... 50. Hence, it is close enough for me.

Okay, let me explain it to you this way:

Voyager's RTG, when launched, produced 470 W of power. 38 years later, it now produces about 50% of that. In 1998 (21 years after launch) they shut down the scan platform (optical cameras, spectrometers, cosmic ray and particle detectors, basically all the way-cool sciency stuff except the magnetometer), in 2015 (38 years after launch) they expect to stop gyroscopic operations, which will essentially shut down the magnetometer because they can no longer subtract the craft's own magnetic field from their observations.

So, you want to send a scientific probe on a 50 year journey to another star when it will likely lose all scientific capability 2/3rds of the way there.

You need to find a power system that will give you peak power when you arrive at your target star system. Laser transmitted power might provide that, as could a fusion power plant.

But, something you'll note: my laser assumption here is faster than the NSWR numbers. It achieves closer to 20% the speed of light, assuming the one way trip past Alpha Centauri. That one gigawatt laser gives it a slow, but steady acceleration the whole time.

So, if powering the probe for 50 years is not possible, how do you intend to power your ship for the 120 years it will take to get there?

Well once the burn is over you could switch to a fusion power plant, but likely if it is a probe the whole thing would shut down until time for magsail braking. Then it would power up its fusion power plant and begin charging the sail.

You would need a fusion reactor probably.

What the makes you think a fusion reactor is any better at this than anything else? (This is a peeve of mine; I find fusion grossly overrated.)

Because unlike fission its fuel doesn't degrade over time. You can shut down a fusion reactor and come back 50 years later and it'll start up as long as there is gas in the tank. And what exactly do you find "overrated" about fusion, and what is the weight of your findings?

And we haven't even discussed the issues with returning data to earth.

That's relatively trivial, especially if you assume the laser propulsion works. Use the same thing in reverse.

Except many of the concepts requiring enormous Fresnel lenses to focus the laser to keep it dissipating in the light-years long journey. Of course any interstellar probe has the same problems.

So one 100,000 ton launch for an NSWR

Remember, that's a 10,000 ton payload, at best, not including the launch from Earth. My probe is assuming 10 tons of spacecraft for the 1 GW of power.

A 1 GW power plant can be had in 1,000 tons. (Assuming 1 kW / kg, which is a reasonable near future specific power for solar panels. It is feasible to get several times better, but I'm conservative)

I don't know what the mass of the laser would be. Let's say the whole unit is 5,000 tons, multiplying it to include inefficiencies too.

Your payload is 1000x bigger than mine, so let's get 1000x the mass of my assumption. We're now talking 1 million tons total - 50x bigger than your launch. So your 100x is more realistic than 1000.

But, this is also reusable infrastructure. We could start with a small probe and work our way up. These satellites could potentially be used to power stuff at home too.

But it comes down to cost. I would love to have your infrastructure or power satellites and laser statite platforms, but getting funding for one launch is far easier than getting funding for 100 launches. "We shall go to the stars, after we launch this enormous power plant" It may well be more scientifically sensible, but it may be politically impossible.

As for sending other probes with it, you'd need to build multiple lasers as each one will be in use for 50 years plus, so unless you're alright only sending out one probe to one star every 50 years, or reaiming the laser and powering the ships in rotation (thereby slowing them all down) you'll only be getting one or two trips out of each laser per human lifetime.

Which can mean either likely or worth of praise. the OP does not ask what method we will use for sustained travel, or for the initial exploration of other stars. If it is the former, laser & solar sails will almost certainly play a part, but the initial infrastructure required for such a system will certainly mean that a more self-contained system will be employed for the first steps outside the heliopause. That most likely means nuclear, whether fission or fusion is a good question.

The technology for lasers is being developed for other means too. Besides, a 10 ton robotic probe is more expendable than a huge ass nuclear ark.

Inter-planetary death beams?

We can build fusion reactors right now, just not self-sustaining reactions. If you can build a fusion reactor, all you need to do is stick a tailpipe in it and you have a fusion rocket.

A big problem with fusion is confinement. If you put a tailpipe on it, you no longer have that.

Keep knocking fusion all you want, but a mere 0.00285 grams of 3He-D fuel can produce a gigawatt of power per second. Solar my ass.

And in order to have a rocket you need to throw something out the back, but you can tune the magnetic field to keep most of the higher energy (read hot) fuel plasma inside and exhaust only the "mundane" hydrogen propellant you heat with the exotic tritium/deuterium fuel.

As to your concerns over the NSWR, heat management is achieved primarily by letting the exhaust carry away the heat.

The problem is the exhaust is really fucking hot. Even moving quickly, they'll be heat transfer.

So you build the nozzle out of something robust and non-transmutable (the article mentions graphite or silicon carbide), and run a magnetic field to keep it off the sides, use the water curtain as described in the article, or just cool the damn thing and power your ship off of it.

The original article was published in the Journal of the British Interplanetary Society, a highly respected organization that has forwarded such plausible concepts as Project Daedalus. They are known for forward-thinking, but not pie-in-the-sky, concepts. I am unaware of the journal's peer-reviewed status. Here is the original article in full, it is the first listing. Having never seen the original article in full before, I am posting it and will read it afterwards.

All in all though, it seems lacking in details to me; a lot of handwaving assumptions are in the paper. But, again, I'm not qualified so the peer review is required to judge it.

nor am I, but at least I have a benchmark I can point towards, you're drawing on the backs of napkins as far as I know.

Well my concept has such detailed information available.

Where?

The article mentions a few important details all in once place, while you've been dispensing details at a drip as you are proded. If you're basing your arguments of an established concept such as the Star-wisp it'd be worthwile to just link to the source information.

Improvise something? On a ship one one-thousandth (or one one-millionth) of the size of your home transmitter, with potentially no-onboard power generation, no backup drive system, no life-support if it's powered by the laser, etc.

The point is merely that a 0.001% chance of living is better than a 0% chance. If this kind of thing is considered a problem, they could carry backup drives and local life support too.

All greatly reducing the weight savings of outsourcing your propulsion to home.

And we're assuming the NSWR only option is to blow up, they may well be able to jeniston the drive and continue on at a slower pace or scram the drive in some recoverable way.

And the problem isn't getting there slower (though if you life support is only useable for 50 years, and it takes you 51 years to get there, well time to draw lots I guess), it's not being able to slow down.

Our chief engineer is attempting to fashion a makeshift magsail. We have high hopes.

okay, that was cute. But unless your ship just happens to use superconducting wire for Christmas lights you might not have the local resources to MacGyver such a magsail, but if magsails are possible, EVERY ship will likely use them as they save you so much in propellant.

All those instances involved a closed vessel. If the end is open to space, and you have a continuous wave reaction as designed, all that energy will take the path of least resistance, out into space, and send you the other way very quickly.

The open to space thing might be an engineering dealbreaker.

What the fuck are you talking about? A rocket without a nozzle isn't a rocket, it's a bomb!

Here's just one example of why it’s a bad thing: The SS Photon misaligns itself just slightly, pushing it out of the local correction margin and the sightline of the laser.

That would suck, but the same thing applies to any rocket. What if you were a fraction of a radian off when doing your burn? What if the exhaust didn't go exactly backward? That would add up over time too, but once you've done your burn, you're out of gas. You can't hope for ground control to help you at all.

Yes, but I don't have to wait 5 years to correct.

(a few are, including some near and interesting ones), but any laser platform, unless a magic statite, will have to pass through the ecliptic at least twice every orbital period

Its beam won't.

True. You'd probably want to station multiple laser platforms in a polar-solar orbit, or better yet use statites hovering over the poles of an inner body like mercury (if they are solar powered as you desire they should be as close in as possible to utilize the solar power best)

, and the likelihood is several objects will pass between the laser and your ship.

No, that's not likely at all. Space is big and empty; it isn't like Hoth.

Gee, being all of 5 I didn't know that. see "objects" meaning anything, Planets, dust, iceteroids, the Sun, TNOs, and if you laser hits them it will stop powering the ship. The odds are VERY VERY low, but every intersection slows down the journey a bit more.

There's also the issue of shooting a multi-terawatt death beam through the solar system, which if miss-timed could be quite disastrous.

Meh, the sun does it and nobody seems to mind. Note the picture though, it isn't a problem. (And btw, the probe scenario only calls for single gigawatt.)

Yes, because a coherent beams of energy and non-coherent beams of the same overall energy have the same effect on objects. But, the likelihood is low, but I'd be really careful moving in to dock at Laser Propulsion Station No. 4.

I suppose they can just leave the laser on, and you can rotate the ship, but then those powerful forces come back into play and done wrong your laser ship will tumble end over end until your atoms thick sail rips itself apart.

Photon rockets aren't powerful forces. The probe scenario would be a force on the order of a 1000 newtons, spread over several square kilometers. It is a gentle, yet steady push for the long haul.

A thousand newtons on an atoms thick surface can do some serious damage, even if spread over several square kilometers if not balanced properly, and you still haven't even hinted at how you'd deal with abrasion of the sail by stray particles as you zoom along at appreciable values of C.

The problem is that even small errors will compound over time perhaps uncontrolable if there isn't a backup drive.

Then put a backup drive on, problem solved.

And what multi-ton (sans propellent) backup drive will you add to you featherweight vessel? You don't seem to like anything for interstellar voyages but sails.

[Sea Skimmer]

As for sending other probes with it, you'd need to build multiple lasers as each one will be in use for 50 years plus, so unless you're alright only sending out one probe to one star every 50 years, or reaiming the laser and powering the ships in rotation (thereby slowing them all down) you'll only be getting one or two trips out of each laser per human lifetime.

You hardly need to change anything so drastically merely to power the on board systems, RTGs would work fine, you just need a larger mass of them, and perhaps using a sterling engine which could roughly quadruple the power to weight ratio over thermocouple designs. It does not matter what peak design power is, just that remaining power is sufficient. Weight can solve such an issue, it would just mean the booster rocket has to be bigger and more expensive, but by the time we are done engineering a probe that can last 50+ years, operate 100% autonomously and have enough transmit power to send back data from another star I really don't think cost could be an issue. Either we pour billions into it, or its just not happening.

[Wyrm]

Because unlike fission its fuel doesn't degrade over time. You can shut down a fusion reactor and come back 50 years later and it'll start up as long as there is gas in the tank.

Actually, yeah, it does. At least if your process involves tritium (the low-hanging fruit of fusion processes), which has a half-life of about 12 years. After fifty years (4.16 half-lives), you have only 5% of your tritium remaining. Even if you generate your tritium on-site from lithium, you still need a seed to get it started. That fuel will also be filled with 3He impurity, which will interfere with the fusion process.

Also, just about every practical process involves some neutron radiation (because that's how you extract power from the damn thing), which will cause your fusion vessel to embrittle just as surely as a fission plant would.

We can build fusion reactors right now, just not self-sustaining reactions. If you can build a fusion reactor, all you need to do is stick a tailpipe in it and you have a fusion rocket.

A big problem with fusion is confinement. If you put a tailpipe on it, you no longer have that.

Keep knocking fusion all you want, but a mere 0.00285 grams of 3He-D fuel can produce a gigawatt of power per second. Solar my ass.

You won't be using 3He-D, because it's too hard to get the energy out of the 4He + p products. DT produces neutrons which will go right through your magnetic confinment and be absorbed by a blanket, heating it, which is what you will use to run your power plant. See above for the long-term problems with that.

[adam_grif]

Wtf is with this "true AI" bullshit? All AI is "True AI". The AI we have now just happens to be primitive and nowhere near human-level.

As far as "most plausible method of interstellar movement"... that's tricky.

I'm partial to the idea of building a large "railroad" of satellites in orbit around Sol, configured in such a way that they constantly boost the interstellar craft in the desired direction by ablating a special plate at the back to provide thrust. It gets out of range of one, and into range of another, building up speed constantly.

It doesn't actually accelerate at all under its own power, excepting for course-correction burns later in the journey. Then, it slows down with as many "free" sources of drag as possible, before firing its drive up to slow the rest of the way down when it nears its destination, decades (or hundreds of years) later.

Return trip is not likely early on. The goal would be to set up infrastructure in the target system. Advances in AI and material science would be required, with the holy grail being an interstellar ship that could arrive in the target system and start construccting the infrastructure, self-replicating as necessary.

But that is NOT a near-future sort of feat. Although if it can be done, it's obviously preferred since it's not feasible to cart all of the supplies necessary for a colony from Earth.

[Channel72]

Wtf is with this "true AI" bullshit? All AI is "True AI". The AI we have now just happens to be primitive and nowhere near human-level.

They probably mean "strong AI"; that is, an AI capable of solving "AI complete" problems. This implies an AI that is on par with human intelligence, meaning that it is capable of things like natural language processing, common-sense knowledge, and intuitive reasoning, as opposed to the mostly-algorithmic AIs that exist today.

[eion]

Because unlike fission its fuel doesn't degrade over time. You can shut down a fusion reactor and come back 50 years later and it'll start up as long as there is gas in the tank.

Actually, yeah, it does. At least if your process involves tritium (the low-hanging fruit of fusion processes), which has a half-life of about 12 years. After fifty years (4.16 half-lives), you have only 5% of your tritium remaining. Even if you generate your tritium on-site from lithium, you still need a seed to get it started. That fuel will also be filled with 3He impurity, which will interfere with the fusion process.

Have I mentioned tritium once? It might well be seen as "low hanging fruit", but you've mentioned just a few of the problems with it. Helium-3/Deuterium is the smart, long-term choice.

Also, just about every practical process involves some neutron radiation (because that's how you extract power from the damn thing), which will cause your fusion vessel to embrittle just as surely as a fission plant would.

I've argued in favor of D-He3 fusion before, and I'm not really in the mood to repeat those arguments. The major benefit it brings to interstellar propulsion is the fact that it produces virtually no neutrons, and therefore no significant neutron radiation and the resulting reactor embrittlement. And since you can just extract the energy directly by magnetohydrodynamic means your reactor efficiency is more than double what a steam-turbine system can offer. The biggest problem facing D-He3 is fuel availability, which means we'll have to go to the Moon and outer planets to get our Helium-3. The increased ignition temperature is a solvable engineering problem, once you fine tune D-T reactor design you can scale that up or increase your confinement efficiency over time to achieved D-He3 ignition. Since you aren't replacing the entire reactor assembly every decade or so you can afford to design a "tighter" confinement system.

But it's already been made clear that we can just double or triple the size of the RTG to power a small probe, though what kind of data return we'll get from 500 or even a 1,000 watt RTG at 5 light years I don't know. At some point it just makes more sense to put a reactor on the thing.

A big problem with fusion is confinement. If you put a tailpipe on it, you no longer have that.

Keep knocking fusion all you want, but a mere 0.00285 grams of 3He-D fuel can produce a gigawatt of power per second. Solar my ass.

You won't be using 3He-D, because it's too hard to get the energy out of the 4He + p products. DT produces neutrons which will go right through your magnetic confinement and be absorbed by a blanket, heating it, which is what you will use to run your power plant. See above for the long-term problems with that.

Yawn, I hate repeats.

You can either dump a portion the heated He4 and proton into the exhaust along with mundane hydrogen, or heat slush hydrogen propellant as it passes through a tube in the center of the reactor as seen here in the fine work of several people at the Glenn Research Center (As far as I can see, no leaky reactor here), or use the fusion reactor to power an ion or other electric drive. D-T is too dirty to be useful to any sustained traveller, as you've needlessly pointed out, so we'll have to eventually do the grunt work to get He3 and up-engineer reactors. D-T fusion is a stepping stone, nothing more.