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If they were able to store a lot of energy and then release it at once, we should never know the world which we know.

All human history is a history of energy concentration.
Muscle → mechanical → chemical → nuclear → moar nuclear → antimatter.

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13 hours ago, 0111narwhalz said:

I want low-tech options to store large amounts of energy in a way which can be released rapidly and recharged.

By low-tech, I mean: No electrics, no composite flywheels, and absolutely no atomics or—kraken forbid—antimatter. Relatively modern metallurgy, without the exotic stuff like amorphous metals, not much in the way of polymers or composites. Detailed understanding of oxidation, though I would prefer a non-chemical solution.

By large amounts, I mean: Somewhere on the order of megajoules per kilogram, and megajoules per liter.

By rapid release, I mean: Somewhere on the order of megawatts to gigawatts, or less than a tenth of a second, whichever is a smaller amount of power.

By recharged, I mean: Reliant upon an easily-reversible process. Only certain chemical processes are applicable, and I'd prefer to find a more interesting solution than a hydrogen fuel cell. Something like a flywheel qualifies.

Outside the scope of the question are: Actual retrieval/regeneration of the energy; what will be done with the energy; acquisition of the energy in the first place.

Yeah, like @StrandedonEarth i think using a gravitational potential is the best low tech option. But equally alike i don't know if your conditions could be met on earth. Otoh, liquid mercury on the sunlit side of one of those superearths ...

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On 10/9/2018 at 4:22 PM, Gargamel said:

Subs are made to hide.   They are, for all practical purposes, invisible.     Deploying such a system would require knowledge of the subs location.

Not at all, that's the whole point. Yes, I do need very precise locations of the jammers relative to each other. That would require additional hardware on the relevant ships. I'd go with VHF/UHF interferometers for that. They have wavelength comparable to acoustic, which ought to make positioning juuust right. Variations in water density will "move" false targets around, but it's the same effect that it has on sub's acoustics. That is, if you have density changes in the water, the target can always appear at the slightly wrong bearing than it really is due to refraction. That effect will be unchanged.

With all of that in mind, I don't need to know where the sub is. The acoustic wave produced by the jammers is almost exactly identical to the wave produced by a single emitter if it was at false source' location. That's how holography works. Again, I can write out the exact numerical decomposition of the target waveform into waveforms that have to be produced by individual jammers. This is just mathematics.

This means that regardless of where the sub is located, the sound will appear to come from a location selected by the system. One that does not correspond to location of any ship in the group. Now, the grid is discrete, and there are only so many ships you can have the jammers running on. That does create limitations. There can be additional "shadows" showing up in random spots, appearing as additional sources of interference. These are almost guaranteed not to correspond to locations of real ships either, but they are hard to minimize without having a periodic grid of ships. Second problem is that viewed from different angles, the false source location might be slightly different. If you had an entire grid of subs in communication, they would be able to use this to filter out the false locations and resolve true sources of jamming. But that's fundamentally impossible for the subs without revealing their location. As I've mentioned before, if you had that sort of linking capability, just feed locations of ships to subs from the satellite.

This method explicitly produces a false target for the sub regardless of where the sub is located and is mathematically impossible to resolve to true sources of jamming for a single sub.

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2 minutes ago, K^2 said:

With all of that in mind, I don't need to know where the sub is. The acoustic wave produced by the jammers is almost exactly identical to the wave produced by a single emitter if it was at false source' location.

Wait..... so you're not jamming, you're creating a decoy.   Single emitter decoys are a lot more effective.  

Will the 'sonar holograph' also mask the resonant noises of the ships?   The rotational sounds of the screws, the engine rumble, a crewman randomly dropping a wrench?  Even with visual holograms, I can still see some light being emitted from each source.   All it seems we will be doing is creating an extra target, requiring insanely precise positioning of the ships, while making each ship slightly louder, but obscured.

12 minutes ago, K^2 said:

But that's fundamentally impossible for the subs without revealing their location. As I've mentioned before, if you had that sort of linking capability, just feed locations of ships to subs from the satellite.

This is already do able.  First off, subs use a long towed antenna, usually 500m-1km in length, and it floats behind the sub as it is underway.  Even at depth, the sub can receive ELF transmissions from a base site.  The data transfer rate is insanely slow, like a bit or 2 per second, but is able to deliver detailed messages.   Getting the location of a convoy or surface group, detected by satellite or other means, via ELF is common for sub warfare.  And since we're talking a wolfpack scenario here, the pack would be placed strategically placed along a patrol line or zone.  Only a small percentage of them would be in danger of detection if they popped up to talk to the satellites.  Those subs would know not to do so, while the others could relay info back and forth, and the resulting picture could be transmitted over ELF to all the subs. 

Now, if this is a jamming scenario, not only would it jam the subs sonar systems, but any system trying to hunt them.  The subs would be able to narrow down generally where a group would be, and could get close enough for scoped shot, like they have been doing for 100 years.   Any ASW systems deployed would also fall under the guise of the jammers, and be unable to see a sub coming.    It would seem a large scale jammer like this would only increase the threat to the group, not mitigate it. 

While I'll concede that your theoretical system may actually create a false signal, there really isn't a practical application for it. 

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2 hours ago, Gargamel said:

Wait..... so you're not jamming, you're creating a decoy.

Both. You want to jam passive and active sonar that may be employed by the sub or incoming torpedoes. The problem with jammers is that even if they can mask everything else, the source of jamming signal is too strong to hide in its own noise. You can always target source of such strong interference. The goal, therefore, is to present strong source points that don't correspond to physical locations of the ships. You get your all-masking noise, and anyone trying to target the source of the noise will hit nothing but empty space. (A dense grid can produce uniform, omnidirectional noise with nothing to target, but then your ocean surface is basically blanketed with ships, so that makes it kind of pointless. XD With discrete points, you have to have "hotspots" of noise, but they don't have to match locations of ships.)

You might also be able to use it for your own detection. The pattern of the jamming noise is known to the source. You can actually use it as active sonar - in theory. I'd have to run numbers to see what the signal-to-noise is going to be like, and whether you can actually use it to look for subs while you're blinding them. Again, the advantage here is that you have a fleet that uses surface communication to network their jammers and sonars. But yeah, your ability to look for enemy subs is going to be greatly reduced at a minimum, and leaving you blind at the worst. Whether the advantages are worth it might depend on the situation. Can I guarantee detection within periscope range? *shrug* I'll have to run the numbers. That's definitely a good point.

2 hours ago, Gargamel said:

This is already do able.  First off, subs use a long towed antenna, usually 500m-1km in length, and it floats behind the sub as it is underway.  Even at depth, the sub can receive ELF transmissions from a base site.  The data transfer rate is insanely slow, like a bit or 2 per second, but is able to deliver detailed messages.

ELF won't be enough to break the above jamming strategy. You do actually need fairly high bitrate. The towable antenna would work, but it gives away subs. Not exact location, but presence for sure. I can see a group switching tactics the moment they spot multiple subs using surface communications.

But yeah, if the sub is receiving anything from the surface, your game of hiding ships is basically up anyways. During cold war, when satellites had limited coverage, it was a different game. Today, any military that can hope to take on a supercarrier is going to know where every single one is at any given minute with sub-meter precision, and ELF has enough data rate to convey that for sure. Even though the sub can't get a GPS reading while submerged, the modern INS is precise enough to keep it within the sort of drift that will still let it put torpedoes within magnetic sensor range of a carrier without needing to see it. So unless you can prevent the sub from receiving data, decoys, jammers, and anything else you might try to throw off the sub is useless. If you allow it within torpedo range, you'll get hit. And here we'd have to talk about ECM and counter-ECM available, and I'd have to admit that I have no clue who has the edge. So...

2 hours ago, Gargamel said:

While I'll concede that your theoretical system may actually create a false signal, there really isn't a practical application for it.

That definitely is a possibility. Jammers and decoys are still used. So it seems like there'd be some room for it. But they might be fallbacks for situations where everything else breaks down.

With kinetic kill ICBMs, we might end up with no need for ship-hunting subs at all in the future. Any tactic, no matter how clever, can be superseded by another that just works better and is cheaper to implement.

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Nope.

Reflection, refraction alter the speed depending on frequency and material properties. Some wavelengths can pass, others not (atmosphere), in glass for example, red comes out first, blue last (telescope, refractive index ;-)), ... etc.

Edited by Green Baron
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19 hours ago, K^2 said:

ELF won't be enough to break the above jamming strategy. You do actually need fairly high bitrate. The towable antenna would work, but it gives away subs. Not exact location, but presence for sure. I can see a group switching tactics the moment they spot multiple subs using surface communications.

What are you smoking?   The towable antenna is submerged.   It's only called a floating antenna because it doesn't sink.  The forward motion of the sub is what drags the antenna behind it, keeping it way below the sruface.   It is for receiving only, it does not transmit.   The transmitting stations are located thousands of miles away, and are known locations to most militaries in the world.  

24.06N32.42W   That's not many bits at all.  In fact, people have been sending this info for centuries using flags and lanterns

I'd respectfully request you do a bit more research into a topic you clearly know nothing about, before throwing nonsensical info trying to be passed off as fact.  

 

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Something came into my mind recently and I cannot find an answer so far:

Why are planetary rings (like the Saturn rings) shaped like a disc? Why is there no (clear visible) difference of inclination between different (inner/outer) rings or a 'cloud' instead of rings?
The only explanation I can find for myself is: The rings are created by the same source of material (like a moon/huge astroid crossing the Roche limit) but I wonder if there is actually a real explanation or at least a theory about it?

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3 hours ago, Gargamel said:

What are you smoking?   The towable antenna is submerged.   It's only called a floating antenna because it doesn't sink.  The forward motion of the sub is what drags the antenna behind it, keeping it way below the sruface.   It is for receiving only, it does not transmit.   The transmitting stations are located thousands of miles away, and are known locations to most militaries in the world.  

24.06N32.42W   That's not many bits at all.  In fact, people have been sending this info for centuries using flags and lanterns.

You are conflating several things again. Lets split them up neatly into two scenarios.

First, sub can receive messages from outside world. These can include locations of ships in enemy fleet. If fleet ECM aren't sufficient to prevent these, that's it, that's the end of discussion. The sub flat out doesn't need to use its sonar to look for surface targets and can engage them completely blind using satellite data.

Now, lets suppose that you are cut off from communications from the surface for whatever reason, and you have to rely on sonars of the subs to hunt the surface ships. Jamming strategy is in place. Can communication between subs be used to cut through jamming? In theory yes, but anything you can use sub-to-sub is too short ranged and low rate. You can use the towable antenna to get a much stronger, higher rate signal across, that should be sufficient to link several subs together. But that signal is omnidirectional. The moment you start using towable antenna to send the signal, it will light up every console of the enemy fleet with unidentified contacts. That is how towable antenna gives you away.

1 hour ago, 4x4cheesecake said:

Something came into my mind recently and I cannot find an answer so far:

Why are planetary rings (like the Saturn rings) shaped like a disc? Why is there no (clear visible) difference of inclination between different (inner/outer) rings or a 'cloud' instead of rings?
The only explanation I can find for myself is: The rings are created by the same source of material (like a moon/huge astroid crossing the Roche limit) but I wonder if there is actually a real explanation or at least a theory about it?

This isn't a strict requirements. However, most of the moons of a gas giant are going to form from the protoplanetary disk. Because of that, they share an inclination. The rings are formed either from leftovers of the same protoplanetary disk, or due to destruction of the moons. Moons can be destroyed either through collision or by entering planet's Roche limit. In either case, most of the debris ends up in the same plane as the protoplanetary disk used to be in.

Of course, moons can, and often enough do, end up orbiting in completely different plains. This can be due to captures or various gravitational interactions. In either case, if one of these moons becomes destroyed, it can form a ring matching inclination of its original orbit. This would then allow for multiple ring systems with different inclinations orbiting the same planet. I'm not aware of any examples, but there is no reason why it can't happen.

Edited by K^2
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27 minutes ago, K^2 said:

This isn't a strict requirements. However, most of the moons of a gas giant are going to form from the protoplanetary disk. Because of that, they share an inclination. The rings are formed either from leftovers of the same protoplanetary disk, or due to destruction of the moons. Moons can be destroyed either through collision or by entering planet's Roche limit. In either case, most of the debris ends up in the same plane as the protoplanetary disk used to be in.

Of course, moons can, and often enough do, end up orbiting in completely different plains. This can be due to captures or various gravitational interactions. In either case, if one of these moons becomes destroyed, it can form a ring matching inclination of its original orbit. This would then allow for multiple ring systems with different inclinations orbiting the same planet. I'm not aware of any examples, but there is no reason why it can't happen.

So it's just a coincidence that we don't have planets with multiple rings in different inclinations in our solar system but it's possible...well, thank you for the explanation :) 

Now I have to find out if I can build such a multiple ring system in ksp with a little help of kopernicus^^

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2 hours ago, K^2 said:

The moment you start using towable antenna to send the signal, it will light up every console of the enemy fleet with unidentified contacts. That is how towable antenna gives you away.

/facepalm    It is for receiving only....

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2 hours ago, 4x4cheesecake said:

So it's just a coincidence that we don't have planets with multiple rings in different inclinations in our solar system but it's possible...well, thank you for the explanation :) 

Now I have to find out if I can build such a multiple ring system in ksp with a little help of kopernicus^^

Ring systems are not very stable over geological timelines. Having shepard moons who stop the ring from spreading out help a lot, if ring is formed at an odd inclination its very unlikely that it has shepard moons. 
You would also not want intercepting rings, that would be pretty unstable :)

 

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10 minutes ago, magnemoe said:

Ring systems are not very stable over geological timelines. Having shepard moons who stop the ring from spreading out help a lot, if ring is formed at an odd inclination its very unlikely that it has shepard moons. 
You would also not want intercepting rings, that would be pretty unstable :)

 

Yeah, I've read about this kind of moons and Saturn got a few of them but where is the connection between rings and a shepherd moon in an odd inclination? Just because it is unlikely to have such a moon in a similar odd inclination?
I also thought about intercepting rings and of course, in the first moment I thought that it will be pretty unstable but on the other hand: how dense are these rings? Just because they are intercepting visually, does it automatically mean that they will intercept physically as well? During a lifespan of millions of years, I would expect some collisions but is it enough to destableize these rings? Or are the gravitational effects between intercepting rings strong enough to destableize the system?
Some time ago (probably I cannot remember properly), I saw video of (I guess) Neil deGrasse Tyson, spreaking about collisions of galaxies and, IIRC the result would be pretty unspectacular since a galaxy isn't dense and most stars and planets will not collide with anything and 'just' the gravitational forces will affect the orbits of stars and planets.
Maybe, comparing planetary rings and galaxies is not the smartest thing to do but it came into my mind when I thought about it^^

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You don't need a sheperd moon or the ring origin to make the ring to match the equatorial plane.
As well as coincidences (tens rings from tens crashed moons coincidentally in the same plane, lol?).

The planet rotates. None of the planet and the ring is perfectly round. A ring is an unstable dynamical system of particles.
So, a tidal wave from the planet will pull the particles in equatorial direction, disturbing the ring. The greater its inclination - the greater is disturbation.
So, the ring in whole is being constatly disturbed into equatorial direction.

When a particle crosses the ring plane, it from time tot time collides with other particles. The more its velocity vector differs from the ring plane, the more often this happens.
So, the transversal speed of the particles stay more or less the same, while their (much lesser) perpendicular velocities get closer and closer to zero.
So, the ring forces the particles to follow its plane.

At last the ring gets into the planet equatorial orbit, gets perfectly round, so tidal waves no more disturb it, it happily follows the planet rotation.
Perpendicular velocities of the particles get close to zero, so the ring gets perfectly plain and thin.

This should happen at any planet in the Universe, so no tilted ring systems except the very young, from the just crashed moons.

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@kerbiloid Thanks for your explanation :)

edit: I came across two interesting papers and want to share them if anyone else is interested in more stuff about rings ;)

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1743921314008321
http://webpages.uidaho.edu/mhedman/papers_published/UNESCO_dynamics.pdf

Edited by 4x4cheesecake
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What is the fastest velocity humanity could achieve for a spacecraft with 2018 technology?

Excluding all 'speculative' technology, i.e., limiting to technology based strictly on accrued physics, what is the maximum velocity we could currently achieve? I have specified "manned" specifically to exclude miniaturized technologies like Breakthrough Starshot, which obviously can go faster but with enormous constraints on payload.

What method(s) of propulsion could be used?

Given this is a spacecraft, I suppose the velocity would be relative to either Earth or the Sun.

Based on what I presently understand, 0.1 c (around 29.9 million km/s) using nuclear pulse propulsion seems to be the fastest with technology that is possible in principle; though whether the technology could actually be made to work is impossible to say without trying.

My main reason for asking is: some years ago I had reviewed the topic and reached the conclusion that the fastest actually feasible was with external nuclear pulse propulsion and that this technology might be able to achieve speeds in the 0.2 c ballpark. I recall a web site or series of websites I found with rather detailed and seemingly rigorous fairly recent (late 1990s or early 2000s) analysis and synthesis which built off of the Project Daedalus and Project Orion stuff, but included some additional corrections based on more modern bomb and materials technology. I want to say this was a University of Pennsylvania research groups page, but it seems to have evaporated now.

My recollection is that, improvements in materials and bombs since the 1950s, and 1970s analyses are what accounted for the doubling in achievable velocity, but it may be that my memory is faulty and I'm just confusing make-believe stuff (like fusion containment, or antimatter powered) with straight up bomb-surfing "can do it if you got the money and willing to ignore the treaties" technology.

Appreciate any help on clarifying this. I'm at the point in writing up my timeline where I need to know, and while the difference between 0.2 and 0.1 is arguably 'not that great' my goal is to keep things as close to diamond-hard hard science fiction as possible for as much of the imagining as possible . . .

Oh, and btw, money is no object; nor are flimsy things like "treaties," human-rights, or "risks" :sticktongue:

All I need to know is: what is the LEAST fanciful 'fastest speed we can do with present physics technology,' and given no constraints in terms of money or ethics.

Edited by Diche Bach
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20 hours ago, Gargamel said:

/facepalm    It is for receiving only....

Receiving what? We've already talked about it. If you have any source of information besides the subs in the area, you aren't even going to use your sonar to hunt surface targets. You have more reliable information, be it from surface ships' radars, aircraft, or satellite. Sonar is useless, and discussing jamming is pointless.

If all you have to receive additional data from are other subs, I don't care if you want to insist that you can only receive on towed antenna, or suggest jury rigging the transmitters to send through it. The bottom line is that if you want to have subs share sonar data, you will give their presence away, regardless of which antenna you want to receive with and/or transmit with.

Please, keep track of your own argument. If you want to drag radio into discussion, remember why you're doing it.

22 hours ago, 4x4cheesecake said:

So it's just a coincidence that we don't have planets with multiple rings in different inclinations in our solar system but it's possible...well, thank you for the explanation :) 

Keeping in mind that majority of large moons are going to be in equatorial plane, making such rings far more likely. But yes, we could have ended up with a planet with inclined rings, and we didn't get any. As rare as they might be, some systems out there definitely have them.

Also, I'd like to point out that the ring instability argument is absolute hogwash. Rings are very nearly circular, because anything in elliptical orbits will collide with each other. And the only effect on a circular orbit of the tidal forces from the planet is precession, which will be roughly uniform for the entire ring due to self-interaction of the objects comprising the ring (drag). So if you have multiple rings at different radii and inclinations, their relative orientation will change over time, but there is no force bringing rings to alignment with equator. Anyone who studied classical perturbation theory should know that. So again, there is absolutely nothing in orbital mechanics that would prevent stable inclined rings from remaining for a very long time once they are created. Even though initial formation of such rings is far less likely than these in equatorial plane.

The second paper you've linked [this one] covers all of that. Specifically, the only non-periodic effect on inclination is dampening with respect to the plane of prevalent motion. (eq 13) In other words, inclination of particles tends to zero with respect to plane of the ring, not equator. Meaning the rings flatten, but remain otherwise stable in terms of inclination. The orientation of that plane drifts due to planet not being spherical. (eq 19, 20) This tells you that over time, the rings will precess around the planet. Note the R/a term, which tells you that different rings will precess at different rates. However, the damping forces discussed above, will keep each ring group intact. So even if you had just one plane in which rings were originally created, if they were spread over large enough distance, eventually they'll break down into multiple rings at different orientations, but common inclination angle. Could be quite an interesting sight.

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Looks like this is more complexe than I thought :D

22 minutes ago, K^2 said:

In other words, inclination of particles tends to zero with respect to plane of the ring, not equator.

Well, I'm not experienced with these equations and even when I look up the symbols, I still don't know what they will tell me (for example: what's the meaning of the 'planetary oblateness parameter' named 'J2'). So please correct me if I'm wrong somewhere:

Eq. 13 shows the change of the orbital inclination (of the ring particles) over time while eq.14 shows, that the longitude of ascending node will not change over time.
Well, my understanding of the 'orbital inclination' is in respect to the equator and the inclination can be changed without chaning the long. of ascending node, so do you mind to explain it a bit more precise why eq.13 needs to be in respect to the plane of the ring and not in respect to the equator?

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40 minutes ago, K^2 said:

Receiving what?

Everything.   The towed antenna does not transmit, it will only receive data.   This is not my limitation, this is how they work.  They are used for transmitting data to subs that are submerged.   There are large transmitting stations located onshore that can transmit ELF signals that can basically span the globe.  The data trickles into the subs, and they act on it.   It is usually used for tasking orders from command. 

Which is exactly what I am talking about.   You have described a wolf pack style of attack on a surface group.   There are secure means of communication that a sub can use to communicate in both directions.   But yes, subs close enough to the group will be detected, but they would be smart enough to not do so.    But your hypothetical jamming system would be louder than a group travelling without it.   It might create false targets, but at the ranges a wolfpack would detect it, would be far outside the range they would be able to discern individual targets, they would only see a single, weird, source.   Through communication relayed back to command by the subs not in EMF detection range of the group, a coordinated attack would be planned. 

And, as stated before, if your jamming system cannot completely mask the existence of every other vessel in the group, but only create a false target, it would have no real affect on the attacking subs. 

So while, as I said, your system might be hypothetically possible, it has no practical application, and is therefore pretty much useless and ineffective. 

 

See what you started @ARS?? :D

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2 hours ago, Diche Bach said:

What is the fastest velocity humanity could achieve for a spacecraft with 2018 technology?

 

Ignoring money and ethics (Although, I don't really see it as unethical to use Nuclear in space considering there's no life)?

You're right about Orion giving you around ~10% light speed, but I don't ever remember seeing 20% (Except now that I remember, I do remember some Ben-10 episode talking about Orion getting that high, but I wouldn't call that a reliable source :D). 20% may be possible for something akin to Daedalus, but not Orion. And Daedalus definitely isn't possible with current technology. If we were really serious, I suppose we could start the research for that, but it'd probably take decades.
The caveat for Orion is that you're only going to see about ~5% light speed if you want to slow down. So that's 90 years to the nearest star. Not horrible, but not really fast either.

With current technology, anything we build will be limited by nuclear fission. If we had fusion, our options would be pretty large, but alas.
In this list, you can see a lot of options. I believe you want your specific impulse in the (high) hundreds of thousands of seconds - or higher - to be viable for an interstellar drive http://www.projectrho.com/public_html/rocket/enginelist.php#werkaffre

If you want to coast to the nearest star using current technology to around ~5-10% light speed, a combination of laser sails and nuclear pulse propulsion, or (maybe?) nuclear salt water would be your best bet.

And here we begin with starshot. Ignoring the fact I don't know if its possible to have a postage stamp sized spacecraft that can last decades; the basic idea of using a massive laser array to push a solar sail is a good one, and has been around for decades (Scroll down http://www.projectrho.com/public_html/rocket/slowerlight.php). You could get pretty impressive velocities too, at least 0.1-0.2c (or ~40-20 years to the nearest star. Now we're talking). But the catch is that there's no laser on the other end, so you'd be limited by your maximum velocity to something manageable (<.1c) by your drive (AKA, Orion), until you can build a laser array on the other end to catch your ship. You could also slow down using the solar wind of the target star, but I don't think it'd slow you down a whole lot to be done alone.

Going back to a fusion drive in general (http://www.projectrho.com/public_html/rocket/realdesignsfusion.php), you might be able to get away with it if it's powered by a new generation nuclear fission reactor. However, I don't know how inefficient/ineffective that would be. Or if a design could match or exceed 5% the speed of light. Someone more knowledgeable will have to answer that.

Finally, using current technology to build a starship would be hard, and if crewed, dangerous. I'd bet that if we started on one today, it would be delayed by things we hadn't considered, and require technology later down the line. But I would also say we have most of the base technology already. So we're in an ok position to begin. I'd try to account for the wait calculation though :)

Edited by Spaceception
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1 hour ago, Gargamel said:

There are large transmitting stations located onshore that can transmit ELF signals that can basically span the globe.

Again, I don't honestly care about the specifics. If you can communicate to the sub from pretty much anything above surface, our entire discussion of sonar is irrelevant. We either assume there's a reason why such communication is impossible (ECM, destruction of other assets, etc.) or we don't bother with jamming, decoys, or any other means of throwing torpedoes off course. A sub that can receive a signal from anywhere else will know exact relative location of all relevant targets in the modern world, and the torpedoes can engage on inertial alone until they are in magnetic range. There is no way to fight that with any form of countermeasures available to the fleet short of taking out the sub before it's in range.

Which is why these are two separate discussions. If you insist that communication will always be possible, then countermeasures are useless, and sub will only use its sonar to look for other subs. If your position is that this is the only way it can be, then our discussion of jamming or anything else the fleet might do is meaningless.

In order to talk about jamming strategies, we have to be talking in context of the sub relying on them, which precludes communication with outside sources. Again, if you think that's unrealistic, that's fine. But it's a separate discussion.

1 hour ago, 4x4cheesecake said:

Well, I'm not experienced with these equations and even when I look up the symbols, I still don't know what they will tell me (for example: what's the meaning of the 'planetary oblateness parameter' named 'J2').

Typically, when you have a body that's mostly spherical, but not quite, the sensible thing is to decompose the bits that aren't into spherical harmonics. J2 is one of the relevant terms. You can see a bit more discussion about it in this Wikipedia article, for example. Indeed, most of the numerical models used have been developed for Earth's satellites and ICBMs, so that's the context in which I've learned classical perturbation theory as well. But all of the physics is essentially the same when applied to objects comprising the rings.

1 hour ago, 4x4cheesecake said:

Eq. 13 shows the change of the orbital inclination (of the ring particles) over time while eq.14 shows, that the longitude of ascending node will not change over time.
Well, my understanding of the 'orbital inclination' is in respect to the equator and the inclination can be changed without chaning the long. of ascending node, so do you mind to explain it a bit more precise why eq.13 needs to be in respect to the plane of the ring and not in respect to the equator?

It's because of their choice of the coordinate system. You can see that they have a special term for drag in the Z direction. The reason for this is quite obvious if you picture this from perspective of an object passing through the rings. The amount of drag will be almost zero for an object passing through along the motion of the objects within. But any object moving perpendicular to the rings will experience significantly more drag.

All orbital elements are taken with respect to some datum. The choice is somewhat arbitrary, but the moment you break the symmetry, some choices end up much more convenient than others. When dealing with a ring system, taking plane of the ring as part of your datum just makes sense.

Unfortunately, that particular paper doesn't really make a distinction, because they essentially restrict the discussion to equatorial rings. The math, however, is exactly the same. So long as you chose Z axis, such that drag in that direction is significantly higher, the inclination will tend to zero in that particular frame of reference. In other words, inclination tends to zero with respect to plane motion in which provides least resistance. Id est, the plane of prevalent motion in that particular band.

If you're still uncertain, the crucial bit here is that drag has nothing to do with orientation of the planet. We're talking about drag with respect to environment of the ring, which is governed by initial orbital plane of the debris. You can tilt planet's axis relative to that any which way, and it doesn't change the math. The only place where planet's orientation starts to play a role is in precession as per eqs 19, 20.

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20 minutes ago, K^2 said:

then countermeasures are useless

There a many things that can hide a ship or group.  Long lasting weather for one.   It is possible, and likely, that a group may take advantage of covering weather that obscures it from satellite detection for some time.   Plus, there are more... aggressive ways to remove satellite observation from the equation.  

And there's the Prairie Masker system, a sonar 'cloaking' device that is already in service today.    It doesn't really jam anything, it just makes the sonar signature look like something the sub would normally ignore. 

25 minutes ago, K^2 said:

In order to talk about jamming strategies, we have to be talking in context of the sub relying on them, which precludes communication with outside sources. Again, if you think that's unrealistic, that's fine. But it's a separate discussion.

My point is, if you have a jamming system, it has to prevent the operators from being able to use their sonar systems at all.  That's the point of jamming.   Otherwise it's just a decoy or 'cloaking' device. 

Making a system that might work in a controlled setting is all fine and good, but it does not represent a real solution if it cannot be used in a real world setting. 

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6 hours ago, Gargamel said:

My point is, if you have a jamming system, it has to prevent the operators from being able to use their sonar systems at all.  That's the point of jamming.   Otherwise it's just a decoy or 'cloaking' device. 

Making a system that might work in a controlled setting is all fine and good, but it does not represent a real solution if it cannot be used in a real world setting. 

A sonar system that only shows you false targets without showing you real ones seems properly disabled. But if you want to split hairs on terminology, I won't argue the point. Lets call it, "Creating decoys using hardware more commonly used for jamming."

And the only limitations I'm setting is that subs don't talk to each other, and subs have a reason to rely on the sonar. You've provided me with the later in your previous two paragraphs, and I think we agree that subs communicating with each other would reveal them. So that's a real world scenario where this is useful.

It might be that the sonar signature masking systems are good enough to where you wouldn't want to bother with this. I have no idea what the state of the art on these is. In that case, *shrug*. If there is no reason to jam, there is no reason to jam better. Can't argue with that.

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