With a superconducting recirculating LINAC driven FEL, I expect you could get 10-25% wall plug efficiency, but the present systems are way below that because there has so far been no need to optimize efficiency. OTOH, a superconducting linac on a moving platform like a ship raises all sorts of technical issues (for example the cavities are typically suspended by wires.......).
BTW: the above is a guess. Would take a real design study to get a solid number.
You are right that the mirror will be destroyed pretty quickly, but for a short time it will be reflecting light back at the ship.
The 1 second was my assumption. I was thinking that the main advantage of the FEL over a conventional gun was the faster travel time for use against nearby fast-moving targets. In that case I think you need a really fast response time. I guess it depends on whether we are talking about inbound missiles or boats. For a boat, I agree you have lots of time, but then I don't see an advantage of the laser over a chain gun. For a missile you probably don't have much reaction time - probably only a few seconds if its a low altitude cruise missile. If you do have time, then again it seems a chain gun would work.
You are also right that adding ablative shielding to missiles will add weight. It would take some work to figure out how much is needed against a MW laser for a ~sonic speed missile.
I help design and commission the world's largest FEL (SLAC / LCLS) - they are quite complex and finicky machines. The FELs the navy is considering are a different type of machine (most likely superconducting recirculating linacs like the TJNAL FEL) but they remain very complex machines (Operating a SC linac on a rolling ship sounds very difficult to me).
Its not impossible to imagine one that could be kept ready for rapid use (1 or 30 seconds doesn't make a lot of difference), but it will be a LOT of work.
I have a reasonable understanding of the technology, but freely admit that I know nothing about the military application.
Interesting. Do you have a feel for how much power drills how big a hole how fast? I would have thought that the wood would carborize and that would tend to protect the under layer, but I believe any actual data you have.
Its a tricky problem to figure out how fast you can drill a hole. The energy is all absorbed at the surface. You are right that some material melts, but once the hole is much deeper than it is wide, it will be difficult for the molten material to get out. You could easily wind up with a jet of boiling metal exiting the hole, and probably blocking the input beam (I don't know if dense iron vapor is transparent, but I expect not). All this really is just an aside - the main application doesn't involve drilling through very think metal plates.
Corner cubes - I'd need to work out how big a cube you would need to reflect a blinding beam back at the ship. It might take as little as the reflective paint that is used in some signs - but it might need larger reflectors. The cubes don't need to be very good - just 3 crossed pieces of metal - you don't need to reflect perfectly, just get a modest amount of the beam back.
Of course you could use a low power guide beam to detect reflectors and then not fire the main beam - but that would increase the targeting time.
I don't see this as an intermediate option. Its very likely to blind the crews, and maybe kill them if the engines explode, this really isn't a non-lethal weapon. Isn't a warning shot followed by a conventional lethal attack better?
If the attacking boat has a corner cube reflector there is a good chance of blinding people on the defending ship. Since the system needs to be ready for use without warning, the crew would need to always wear laser goggles.
You can protect a missile with an ablative shield - the sort used for re-entry vehicles. This doesn't need to be high tech - wood works surprisingly well (used by the Chinese for spacecraft years ago).
You could use a more diffuse beam to blind the crew of an attacking boat, but I think that violates the Geneva convention.
I'm also very skeptical about the 1MW -> 20' of steel / second. At a kilometer away, you probably have a spot size of around a centimeter. (it depends on wavelength, optics, etc, but that is the right ball park. Iron vaporization energy is 300KJ/mole or about 6KJ/gm. A 1cm long by 10M piece of iron is 1000 cc's or ~10^4 grams. So that's 60MJ to vaporize, or a minute, not a second to burn through. Of course the plume of iron vapor will disrupt the incoming beam so it will take a lot longer. This also assumes you can keep the beam perfectly focused.
The is also the question of whether a complex device like an FEL can be kept always ready to fire within a second. The light is much faster, but its not clear that when you include the time to ready and aim the weapon that the time to hit the target is faster than for a high speed gun.
I have personally observed interference from a camera (Nikon D70) on the navigation instruments on my Bonanza (caused the VOR needle to jump - we were in visual conditions at the time so it wasn't a problem). Of course airliner avionics is better - but we need the odds of substantial interference to be about 1 in a million for it not to be a safety risk.
It is true that many passengers fail to turn of electronics, but remember that the transmit power adds from all the devices. It is possible that 400 cell phones on a plane would be a more serious problem than the few that weren't turned off.
The wikipedia article says just how large an amount of negative energy is needed, for a reasonable sized spaceship it is in universe masses.
Such a drive would also violate causality - since you can arrive before your light cone. (if you accelerate to a new frame and do it again, you wind up in your own past). This has nothing to do with how you travel FTL, only that you arrive faster than light.
Calculations like this are a very interesting way to study general relativity and the structure of space-time, but they really don't represent realizable technologies.
If it takes ~3 hours to move a clock from 1 location to the other, (by air, then need to get down into the mine). ~1e4 seconds. If you want 10ns (1e-8), you need clocks that are matched to 1e-12. Good frequency standards are better than this, Relativistic time dilation goes as roughly v^2, so at 100M/s, you are seeing effects at the1e-13 level not too bad, so its not impossible.
There are practical issues - portable Rubidium clocks are't good enough. Atomic Hydrogen and Cesium clocks could do it, but I don't know how much the accelerations during transport will change their stability.
It isn't a bad idea though - but not trivial to make it work.
Then of course there is still the problem of getting the distance correct - not as easy as it sounds since the detector is deep underground without GPS reception.
I mostly use XFCE now. It feels like a small step backwards from Gnome 2, but that's a lot better than the huge step backwards for gnome 3 and the other cell-phone UIs. I'm also someone who does a lot of work on a desktop and who needs multiple windows. I may have a spreadsheet, a mechanical drawing and a web page all referring to the same thing. I have big monitors, why shouldn't I have everything I want on the screen at once. Then - I can have my email on another desktop so I can get to it (and the other associated windows) all at once.
I really tried to like Unity on Ubuntu - but I'm just no where near as efficient.
If they are going to operate below 18,000' (as is very likely), they will also be in airspace that has VFR (visual flight rules) aircraft. These aircraft are (in most areas) not required to be in contact with air traffic control and operate under "see and avoid" rules. If drones are significantly smaller than aircraft, they will be more difficult to see and become a collision hazard.
They could of course choose to change the VFR rules in the US, but that is a major change to the way aircraft are operated.
As long as people are really aware of the issue, I'm not bothered. I consider everything posted on facebook to be completely public - the equivalent of making a statement to the news media. I then only provide information that I do not mind being associated with my identity by any organization. I apply the same thinking to posting on slashdot.
I think it depends a lot on the type of job. Hiring an airline pilot based on their skill at flying a (realistic) aircraft simulator is not a bad idea. Hiring a sales person based on their interaction with a computer program is probably completely wrong.
While computerized testing has all sorts of problems, so does standard HR hiring. I think the extent to which you can use tests depends completely on the type of position you are hiring.
I think the traditional view is that it is a combination of radioactive decay and heat left over from the formation of the earth. Not counting recent global warming, the earth is on average loosing energy as heat from both these sources is radiated into space. That may be a much larger change in relative mass than the other effects discussed here.
A very good point. Any idea of what limit they can put on fission power generated in the earth's core?
There might also be some information from seismometry - woudl a 5-mile diameter high density central core be noticable (I don't have any feel for the resolution of these techniques).
I would think that if there is significant heat generatio in the inner core, it could only be carried by convection and that would quickly dilute (or more likely prevent from forming) any central reactor. This is just a guss though - my intuition may be very broken on these scales.
Knowing that an atomic bomb was possible motivated other governments to develop one (through espionage or R&D). Keeping the technical details of how to make an atomic bomb secret is one of the reasons that small non-government groups have so far not developed one. In this case I think that making it difficult to find out how to create a super-deadly virus will reduce the chances that small groups will try to create one.
I think there is a real anti-correlation between well funded competent organizations and desire to do widespread destruction.
It would be very surprising if the US really tracked every flip anti-american comment made anywhere in the world on any social media.
Something here just doesn't add up.
Someone needs to do the experiment - tweet some threatening, anti-american comment then see if the let you into the country. Nothing like a controlled experiment.
The decision to go into space depends entirely on your goals. It is easy to imagine a stable, sustainable, happy human population on earth. We are no where close to that yet, but it is a goal that we can reach for, and I think achieve.
I can also imagine a goal of human expansion into space. The solar system is with reach of easily foreseeable technology. It might take centuries to ready fully self-sufficient colonies, but again they don't require impossible technology. Interstellar is more difficult, but speeds of a reasonable fraction of C are imaginable with nuclear propulsion or laser driven sails. This is too slow, but not a lot too slow, and maybe practical if we can extend human lifetimes.
There is no question that an expanding human race is a much more difficult goal, and a much more dangerous one: It will involve the development of technologies that could wipe out humanity, and even if we succeed we might meet something dangerous out there.
Technology only develops if it is needed: if we want improved space technology we need to work on space travel, just waiting for something to develop isn't likely to succeed. Compare the progress from 1950-1970 when we were actively developing space to the almost complete lack of progress from 1990 to 2010.
We have a choice: stay here where it is safe and comfortable, or see what wonders and horrors are waiting on a billion billion worlds throughout the universe.
The main LCLS X-ray laser also works without mirrors, but it has so much gain that the final beam is pretty close to transform limit in the transverse - almost a coherent as a conventional laser.
Grazing incidence mirrors work well - we use them to steer the main X-ray beam. The mirror system we have works up to 24 KeV X-rays but with shallower angles you could go higher.
You can also use crystals to reflect X-rays over large angles - even 180 degrees using Bragg diffraction. The limit here is that the X-ray beam needs to be almost exactly a single wavelength.
We treat the X-ray safety in a way similar to the high energy beam safety at the lab. Shielding, interlocked doors, monitoring, etc. For the soft X-rays in this experiment there is very little risk, they don't go far through air, but for hard X-ray operation we need to use more protection.
Slashdot Mirror
With a superconducting recirculating LINAC driven FEL, I expect you could get 10-25% wall plug efficiency, but the present systems are way below that because there has so far been no need to optimize efficiency. OTOH, a superconducting linac on a moving platform like a ship raises all sorts of technical issues (for example the cavities are typically suspended by wires.......).
BTW: the above is a guess. Would take a real design study to get a solid number.
You are right that the mirror will be destroyed pretty quickly, but for a short time it will be reflecting light back at the ship.
The 1 second was my assumption. I was thinking that the main advantage of the FEL over a conventional gun was the faster travel time for use against nearby fast-moving targets. In that case I think you need a really fast response time. I guess it depends on whether we are talking about inbound missiles or boats. For a boat, I agree you have lots of time, but then I don't see an advantage of the laser over a chain gun. For a missile you probably don't have much reaction time - probably only a few seconds if its a low altitude cruise missile. If you do have time, then again it seems a chain gun would work.
You are also right that adding ablative shielding to missiles will add weight. It would take some work to figure out how much is needed against a MW laser for a ~sonic speed missile.
I help design and commission the world's largest FEL (SLAC / LCLS) - they are quite complex and finicky machines. The FELs the navy is considering are a different type of machine (most likely superconducting recirculating linacs like the TJNAL FEL) but they remain very complex machines (Operating a SC linac on a rolling ship sounds very difficult to me).
Its not impossible to imagine one that could be kept ready for rapid use (1 or 30 seconds doesn't make a lot of difference), but it will be a LOT of work.
I have a reasonable understanding of the technology, but freely admit that I know nothing about the military application.
Interesting. Do you have a feel for how much power drills how big a hole how fast? I would have thought that the wood would carborize and that would tend to protect the under layer, but I believe any actual data you have.
Its a tricky problem to figure out how fast you can drill a hole. The energy is all absorbed at the surface. You are right that some material melts, but once the hole is much deeper than it is wide, it will be difficult for the molten material to get out. You could easily wind up with a jet of boiling metal exiting the hole, and probably blocking the input beam (I don't know if dense iron vapor is transparent, but I expect not). All this really is just an aside - the main application doesn't involve drilling through very think metal plates.
Corner cubes - I'd need to work out how big a cube you would need to reflect a blinding beam back at the ship. It might take as little as the reflective paint that is used in some signs - but it might need larger reflectors. The cubes don't need to be very good - just 3 crossed pieces of metal - you don't need to reflect perfectly, just get a modest amount of the beam back.
Of course you could use a low power guide beam to detect reflectors and then not fire the main beam - but that would increase the targeting time.
Now if we could mount MW lasers on Segways we'd fix the problem of them running over old people.
I don't see this as an intermediate option. Its very likely to blind the crews, and maybe kill them if the engines explode, this really isn't a non-lethal weapon. Isn't a warning shot followed by a conventional lethal attack better?
FELs do usually use rare earth magnets, but the total amount of material isn't very large compared to disk drives and other commercial uses.
If the attacking boat has a corner cube reflector there is a good chance of blinding people on the defending ship. Since the system needs to be ready for use without warning, the crew would need to always wear laser goggles.
You can protect a missile with an ablative shield - the sort used for re-entry vehicles. This doesn't need to be high tech - wood works surprisingly well (used by the Chinese for spacecraft years ago).
You could use a more diffuse beam to blind the crew of an attacking boat, but I think that violates the Geneva convention.
I'm also very skeptical about the 1MW -> 20' of steel / second. At a kilometer away, you probably have a spot size of around a centimeter. (it depends on wavelength, optics, etc, but that is the right ball park. Iron vaporization energy is 300KJ/mole or about 6KJ/gm. A 1cm long by 10M piece of iron is 1000 cc's or ~10^4 grams. So that's 60MJ to vaporize, or a minute, not a second to burn through. Of course the plume of iron vapor will disrupt the incoming beam so it will take a lot longer. This also assumes you can keep the beam perfectly focused.
The is also the question of whether a complex device like an FEL can be kept always ready to fire within a second. The light is much faster, but its not clear that when you include the time to ready and aim the weapon that the time to hit the target is faster than for a high speed gun.
I have personally observed interference from a camera (Nikon D70) on the navigation instruments on my Bonanza (caused the VOR needle to jump - we were in visual conditions at the time so it wasn't a problem). Of course airliner avionics is better - but we need the odds of substantial interference to be about 1 in a million for it not to be a safety risk.
It is true that many passengers fail to turn of electronics, but remember that the transmit power adds from all the devices. It is possible that 400 cell phones on a plane would be a more serious problem than the few that weren't turned off.
--- Joe Frisch
The wikipedia article says just how large an amount of negative energy is needed, for a reasonable sized spaceship it is in universe masses.
Such a drive would also violate causality - since you can arrive before your light cone. (if you accelerate to a new frame and do it again, you wind up in your own past). This has nothing to do with how you travel FTL, only that you arrive faster than light.
Calculations like this are a very interesting way to study general relativity and the structure of space-time, but they really don't represent realizable technologies.
If it takes ~3 hours to move a clock from 1 location to the other, (by air, then need to get down into the mine). ~1e4 seconds. If you want 10ns (1e-8), you need clocks that are matched to 1e-12. Good frequency standards are better than this, Relativistic time dilation goes as roughly v^2, so at 100M/s, you are seeing effects at the1e-13 level not too bad, so its not impossible.
There are practical issues - portable Rubidium clocks are't good enough. Atomic Hydrogen and Cesium clocks could do it, but I don't know how much the accelerations during transport will change their stability.
It isn't a bad idea though - but not trivial to make it work.
Then of course there is still the problem of getting the distance correct - not as easy as it sounds since the detector is deep underground without GPS reception.
I mostly use XFCE now. It feels like a small step backwards from Gnome 2, but that's a lot better than the huge step backwards for gnome 3 and the other cell-phone UIs. I'm also someone who does a lot of work on a desktop and who needs multiple windows. I may have a spreadsheet, a mechanical drawing and a web page all referring to the same thing. I have big monitors, why shouldn't I have everything I want on the screen at once. Then - I can have my email on another desktop so I can get to it (and the other associated windows) all at once.
I really tried to like Unity on Ubuntu - but I'm just no where near as efficient.
If they are going to operate below 18,000' (as is very likely), they will also be in airspace that has VFR (visual flight rules) aircraft. These aircraft are (in most areas) not required to be in contact with air traffic control and operate under "see and avoid" rules. If drones are significantly smaller than aircraft, they will be more difficult to see and become a collision hazard.
They could of course choose to change the VFR rules in the US, but that is a major change to the way aircraft are operated.
As long as people are really aware of the issue, I'm not bothered. I consider everything posted on facebook to be completely public - the equivalent of making a statement to the news media. I then only provide information that I do not mind being associated with my identity by any organization. I apply the same thinking to posting on slashdot.
I think it depends a lot on the type of job. Hiring an airline pilot based on their skill at flying a (realistic) aircraft simulator is not a bad idea. Hiring a sales person based on their interaction with a computer program is probably completely wrong.
While computerized testing has all sorts of problems, so does standard HR hiring. I think the extent to which you can use tests depends completely on the type of position you are hiring.
I think the traditional view is that it is a combination of radioactive decay and heat left over from the formation of the earth. Not counting recent global warming, the earth is on average loosing energy as heat from both these sources is radiated into space. That may be a much larger change in relative mass than the other effects discussed here.
A very good point. Any idea of what limit they can put on fission power generated in the earth's core?
There might also be some information from seismometry - woudl a 5-mile diameter high density central core be noticable (I don't have any feel for the resolution of these techniques).
I would think that if there is significant heat generatio in the inner core, it could only be carried by convection and that would quickly dilute (or more likely prevent from forming) any central reactor. This is just a guss though - my intuition may be very broken on these scales.
Knowing that an atomic bomb was possible motivated other governments to develop one (through espionage or R&D). Keeping the technical details of how to make an atomic bomb secret is one of the reasons that small non-government groups have so far not developed one. In this case I think that making it difficult to find out how to create a super-deadly virus will reduce the chances that small groups will try to create one.
I think there is a real anti-correlation between well funded competent organizations and desire to do widespread destruction.
It would be very surprising if the US really tracked every flip anti-american comment made anywhere in the world on any social media.
Something here just doesn't add up.
Someone needs to do the experiment - tweet some threatening, anti-american comment then see if the let you into the country. Nothing like a controlled experiment.
I hope that the news media follows up on this and we find out if it is as outrageous as it sounds.
The decision to go into space depends entirely on your goals. It is easy to imagine a stable, sustainable, happy human population on earth. We are no where close to that yet, but it is a goal that we can reach for, and I think achieve.
I can also imagine a goal of human expansion into space. The solar system is with reach of easily foreseeable technology. It might take centuries to ready fully self-sufficient colonies, but again they don't require impossible technology. Interstellar is more difficult, but speeds of a reasonable fraction of C are imaginable with nuclear propulsion or laser driven sails. This is too slow, but not a lot too slow, and maybe practical if we can extend human lifetimes.
There is no question that an expanding human race is a much more difficult goal, and a much more dangerous one: It will involve the development of technologies that could wipe out humanity, and even if we succeed we might meet something dangerous out there.
Technology only develops if it is needed: if we want improved space technology we need to work on space travel, just waiting for something to develop isn't likely to succeed. Compare the progress from 1950-1970 when we were actively developing space to the almost complete lack of progress from 1990 to 2010.
We have a choice: stay here where it is safe and comfortable, or see what wonders and horrors are waiting on a billion billion worlds throughout the universe.
The main X-ray laser is about a mile long. We are working on breeding bigger sharks......
The main LCLS X-ray laser also works without mirrors, but it has so much gain that the final beam is pretty close to transform limit in the transverse - almost a coherent as a conventional laser.
--- Joe Frisch
SLAC
Grazing incidence mirrors work well - we use them to steer the main X-ray beam. The mirror system we have works up to 24 KeV X-rays but with shallower angles you could go higher.
You can also use crystals to reflect X-rays over large angles - even 180 degrees using Bragg diffraction. The limit here is that the X-ray beam needs to be almost exactly a single wavelength.
--- Joe Frisch
We treat the X-ray safety in a way similar to the high energy beam safety at the lab. Shielding, interlocked doors, monitoring, etc. For the soft X-rays in this experiment there is very little risk, they don't go far through air, but for hard X-ray operation we need to use more protection.
-- -Joe Frisch