No, you do not apply your force in an "upward" direction in order to increase orbital altitude. Remember the old saying, "In orbit, forward means up, back means down". A forward thrust increases the orbital angular momentum and energy, and results in a higher orbit. An upward thrust would just increase the orbit's eccentricity.
For more info, see Bates, Mueller, and White, "Fundamentals of Astrodynamics". BMW is the Honda Civic of astrodynamics textbooks (cheap to buy, effective, and still useful 10 years later).;)
As far as the calculation of the energy loss, I chose to calculate it directly from the dv/dt given by NASA. The fact that this is different from the 1km/week difference is likely due to the fact that the dv/dt increases as the station dips further into the atmosphere. If we are talking about a steady force which is applied constantly, then we can simply use the dv/dt and not worry about having to let it dip for a week before trying to return it to it's original orbit. This accounts for the factor of about 4 difference.
Superconducters would not really be necessary, as it is not hard to get a 90+% efficient electromagnetic system. But, yes, if you shield it from the sun, you might be able to cool it quite effectively.
The problem is that the tethers get damaged by micrometeors. A small comparison graph of the degradation rate of single and interlinked tethers can be seen near the bottom of http://www.tethers.com/Hoytether.html. IMHO, this means that other (non-tethered) means of magnetic propulsion may be worth investigating, as there is nothing unique about the tethered geometry which makes it advantageous for magnetic propusion.
Ok, first, what's up with the moderation on this post? Currently it is -2 Overrated. WTF? Who did TigerNut piss off?
A similar proposal was made by Ben Bova years ago, and I'd be surprised if he was the first. I don't know why pclminion thinks it would be such a hard calculation:
The eccentricity of the orbit is 0.0002300, so we can treat it as effectively circular.
mass of station: approx. 140 metric tons = 280,000 kg average orbital altitude: ~380 km orbital radius: velocity: ~7700 m/s Mean motion: 15.70869555 rev/day Decay rate: 1.60710E-04 rev/day^2 loses a kilometer a week altitude corresponds to an power loss of: ~(1/97745)*(0.5)*(280,000 kg)*(7700 m/s)^2/86400 seconds = 990 Watts call it a kW
to replace this power loss requires a force of F=Power/velocity force needed: 1 kW/7700 m/s = 0.13 newtons earth's magnetic field: approx. 1 gauss=10^-4 T Force = 2piR*I*B*turns, R*I = 207 ampere*meters*turns assume a desired voltage drop of 100 V, and that gives us I= 10 A assuming 100 turns this gives us a coil of radius 0.2 meters.
I would be surprised if the station did not have a spare kilowatt of power available. As far as aiming the coil so that the magnetic field is in the proper direction relative to the earths magnetic field, 3 coils could be used and power changed between the 3 to create the proper net field.
I have also worked with BF3 neutron detectors around high electrical fields, and I have also seen noise effects on the detector. In my experience, the counts which were caused by electrical disturbance only occurred during nearby spark-out incidents. If you were working indoors without high electrical fields present, it is most likely that your spikes were caused by the lightning neutrons, and not by the electrical effects. This of course, presumes that the neutron events that DYAIZA saw were not actually broadband noise events. My Russian is rusty, so I haven't checked out the original paper to see if that might be the case.
With regards to cold fusion, I used to hang out on sci.physics.fusion back in the day, when cold fusion was still fairly controversial and Jones, Blue, Mallove, and others would discuss their experiments. I have always thought that the interstitial energy explanation was the correct one, and I think it should be brought up whenever cold fusion is discussed. The claims of excess energy never seemed to take into account the energy of putting the hydrogen into the interstices, and the process of doing this was always the bugaboo when discussions of "If it works, why don't you build an engine" came up.
I do think that using the so-called "cold fusion" process as an energy storage mechanism could be interesting.
Maybe what we need is the MLAA (Music Listeners Association of America).
Fight fire with fire.
The EFF handles many different issues, many of which go over the head of the average American. But an organization which exists solely to protect peoples right to listen to music would be easy for most people to understand, especially when the RIAA is taking actions like it has in recent years.
I wonder if the hardware manufacturers who keep getting dictated to and sued by the RIAA would like to join as associate members...
Sundown: The Vampire in Retreat
on
Review: Darkwatch
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· Score: 2, Interesting
I've seen a few good suggestions posted, but the king of this "relatively untapped genre" would have to be Sundown: The Vampire in Retreat, starring David Carridine (from Kung Fu) as Dracula and Bruce Campbell (from Evil Dead) as Van Helsing.
Not that it's a good movie or anything (it's not), but if you've ever seen it, it does define the "Vampire Cowboy" genre more than most things out there.
That's strange, I thought that when I didn't pay the maintenance fee on my last patent that it went into the public domain. I'd be glad to hear it's still in force.
Patents may have their problems, but at least the length of time and the requirement of maintenence fees to keep them in force are appropriate.
As an intellectual property owner, I worry when Congress goes overboard in an attempt to "protect intellectual property holders' rights". Yes, I like that what I create can benefit me. However, when other people use IP as a cudgel to abuse people, it makes me worry about the stability of the whole system. If you were an aristocrat in France in 1780, wouldn't you be a little concerned about the other aristocrats who beat and starve the peasants? They might just have a revolution.
I highly agree that electromagnetic launchers would be damn useful. I also think that most people are thinking of using them in the wrong way. Let me explain:
Due to high acceleration, electromagnetic launchers are probably not the best choice for launching humans or delicate equipment. Rockets are likely to be cheaper for this for the time being. In order to have a launcher which would be useful for human launches, the launcher would have to be very long, and thus very expensive. However, a launcher which was designed for bulk transport would not need to be very expensive at all. This is because, unlike in a rocket, the majority of capital expense stays on the planet. In order to have a cheap (and thus, likely to be actually built) system, you want to minimize the expense involved in building the launcher. One of the best ways to do this is to reduce the size of the projectile. People tend to think of launchers as firing something about the size of a Gemini capsule or Space Shuttle. However, if the launcher is going to fire a projectile the size of a coke can, a much smaller launcher could be built. Electromagnetic launchers can have very high fire rates - why launch one large projectile when many small ones will contain the same mass and use the same energy?
The atmosphere of course puts limits on the size reduction of the projectile. A large or dense projectile loses a smaller proportion of its energy to drag. However, if we make the launcher small enough to put on an airplane, then we can launch from the stratosphere for a fairly low cost. This would enable the use of small projectiles without too much energy loss to atmospheric drag. I would expect the cost of a launcher to be less than the price of an airplane which could mount one. Lets assume it is a plane similar to a 727. A 727 has a payload of about 50,000 kg including fuel. Let's say that 10,000 kg of that is projectiles, with the rest of the payload being used to carry the crew, the launcher, and the fuel for the plane and the launcher. To get to LEO, the fuel for the launcher would be about 2 times the mass of the projectiles, so that works out about right for a short flight. Assuming a fire rate of about 1/sec for 1 kg projectiles, the payload of the plane would be shot in about 3 hours.
So, presuming we had a bulk launcher which cost $20 million and could launch small projectiles into LEO at not much more than the cost of fuel, the price per kg would likely be on the order of $10/kg. Of course the launcher could only be used for launching bulk materials, but as an example:
A Delta 4 heavy rocket delivers a payload of 23000 kg to LEO at a cost of about $170 million. If we were to take that same $170 million and put $20 million into a plane-based launcher, $50 million into various upkeep costs (personnel, ground site, the inevitable bureaucracy), and $100 million into launch fuel, you could put 10 million kg into LEO. It would take a year of flying 3 flights a day with the launcher plane to put this much mass in orbit.
Of course, the mass would not be a nicely formed satellite or spaceship, but the point is that for the same cost, you get to put 4300 times the mass into orbit. 100 million kg is about twice the mass of a WWII battleship like the Bismarck, and is plenty of mass to build an orbital factory to turn some of that mass into something useful. In addition, metal encapsulated fuel pellets could be sent into orbit - fuel in orbit is worth much more than fuel on the ground.
This sort of project would only take a few million to get off the ground, and if things don't work, then you have the opportunity to retool your system, which is not as easy with exploding rockets. The real challenge lies in making the projectiles go where they are supposed to so they can be gathered in orbit to be used.
Auditor: So you plan on putting your spacecraft inside a General Products #3 Hull? Me: Yes, it's the most indestructible thing we know. Auditor: But what happens if you run into a moon? Me: No problem, we have a sophisticated stasis field to kick in in case of impact. The ship and crew would be unharmed. Auditor: But what if you are shot with a laser? The General Products hull is transparent to visible light. Me: We have a coating which instantaneously becomes mirrored if the light intensity exceeds a certain value, plus the internal bulkheads provide protection. Auditor: What if you crash into a ringworld? Me: Uh... we've got a backup set of flycycles to fly the crew out in case of a serious crash. Auditor: Yeah, but what if you run into a rogue anti-matter moon? Me: The hell? But the chances of that happening are... Auditor: But it could happen right? Ever heard of Beowulf Shaeffer? Me: Well, sure it's possible but... Auditor: (Checks FAIL on his report)
Another former non-tokamak fusion researcher here.
I agree. The biggest problem with the large tokomak designs is the scale, and hence price tag, required for a self-sustaining reaction. The large price tag and long construction times mean that prototyping is essentially a decades-long process subject both to political whims and the need to be used for years after it is built just to make the building of it worthwhile.
Imagine how fast computer science would advance if each new motherboard required an act of Congress.
The real need in fusion is not for more money. The big money has been squeezing out the small money for my entire lifetime. We need smaller, easier prototyped designs that take at most a year and $1 million to build. It's the only way the art will advance.
I remember emailing back and forth with Paul Koloc back in the early nineties and commiserating about how DOE just wasn't interested in non-tokamak designs. I thought that things got better after the Bussard letter (hey, where's Baldrson at?), but I guess not. Paul is probably the world expert on ball lightning, but I'm still not sure that ball lightning is a good means of producing fusion. Should he be funded? Hell, yeah! His programme is magnitudes cheaper than ITER, and we'd definitely get our money's worth of science out of it.
In case it makes you feel any better for not being picked ahead of Carrot Top for Celebrity Poker Showdown, here is a little (true) story for you:
A friend of mine is friends with Carrot Top. A while ago, they were waiting in line at Wal-Mart together. They get up to the checkout, and the checkout lady looks at Carrot Top and says, "You know, you really look like that Carrot Top guy from TV... I mean... no offense."
I'm sure you are already familiar with the work of Leik Myrabo , but in case you aren't, you ought to check out his stuff. He is the big pioneer in this area (ref. 3 on your correct link).
You are right that huge savings can be had by separating the power source from the vehicle - Myrabo was writing about this 20 years ago. Most of the energy used by a rocket is used to elevate the fuel to the altitude at which it is burned. If the energy is supplied to energize a propellant (such as vaporized water as suggested in your link), the amount of propellant can be much less than the amount of burning fuel would be. Unfortunately, Myrabo has focused his more recent efforts on rather weak air propelled engines which haven't had much punch.
Because the real limit in terms of how much propellant is needed depends upon the specific energy (and thus the temperature) to which the propellant is energized, it is best if the propellant is heated to a very high temperature. For these purposes, an concentrated ultraviolet light source would work as well as a laser, and would likely be much cheaper than a fairly efficient laser of high power. Also, if a laser is used, the best case scenario would be if the photon energy corresponded to a particular energy jump in the target propellant, similar to the way an excimer laser is used. In the case of simply heating the propellant, material considerations will limit the amount you can heat the material (i.e. at some point, your water vapor will melt the nozzle). However, in the case of the excimer laser, a solid propellant could be used which would not suffer from heat transfer from the solid/gas interface, which means really high specific energies could be used.
I agree that we want the same thing, but disagree on the approach. I do think the CEV is a step forward. However, I doubt that the savings from the reduction in launch costs are going to go into the development of new launch technologies. And I also don't think that the only 5x reduction in launch costs is going to be enough to spur the development of a true space industry. It might put us to where the Russians are right now, albeit a bit more up-to-date. I don't see how another launch system like the ones we have now (to within an order of magnitude) is going to spur the economic development of space. Are we going to mine asteroids with CEV, or beam solar power? I doubt it; it doesn't have the economics for it. So why not put that money towards developing something that makes those activities economically feasible?
I'm just hoping that at some point NASA will decide to draw a line in the sand and say to congress "Look, we need something better. We are going to go on a fast development course and develop a reliable launch engine with a specific impulse in the 2000+ second range. We need this, and we are going to do it."
I'd love it even more if a private company would do it. I don't see that coming from the biggies though - they love spending government money, but not their own.
I really do think that the cost of the design does matter a lot. If it costs $1 billion to develop an engine, not a lot of prototypes are going to be built, the development is going to be slower as a result, and only a few players are even going to have the choice of whether to develop it. This is the case with most (but not all) of the types of engines you have listed. Fusion has this same type of problem - it's hard to do engineering experiments when it takes ten years to go from idea to prototype test. A design which costs $1 million to test will very quickly exceed a design which costs $100 million to test. We have too many $100 million ideas and not nearly enough $1 million ideas.
I'm not sure that I would call NERVA a success, although it certainly wasn't a failure either. "Needs work" is the grade I'd give it.
How much of the earth can be fashioned into something useful? It's also not a lump of refined metal that self assembles into struts and bulheads...
The only things the earth has in plenty that the moon does not are air and water. Anywhere you go in the inner solar system you need to bring these, aside from the poles of Mars. Fuel can be just energy and reaction mass. Solar energy is fairly plentiful on the moon, at least for half of the month. Storing this energy as separated oxides makes sense, both from an energy storage standpoint as well as a fuel and refining one. I think Rei as already addressed much of that, although I think an engine could be made from lunar regolith if enough energy were available. I wonder what the energy payback time is for refining lunar regolith to make iron+oxygen, then using the iron to make solar thermal heaters? Something to think about. I'm not sure what would be a good available working fluid - I'm sure someone has already done some work on this.
Don't get me wrong - I'm not trying to dissuade people from supporting space efforts. See that little blue dot next to my name? I was into nuclear engines long before I ever found slashdot. However, I don't trust NASA to complete what it starts. I've lived near the Cape for too long. If we have so many great designs on the drawing board, we ought to build a few. Unfortunately, it seems like the capital, either political or monetary, to build them isn't easy to find. To me, that says that the designs aren't really that great. Building prototypes is the most important step of R&D - and I was saying that we need to build better engines before spending $umpteen billion in space. The money would be better spent on building better engines, because history has shown that once NASA has a launch system that functions, no matter how shitty, their budget will be set to whatever they need to keep it barely functioning. Any development past that system will be stuck on the drawing board indefinitely. We've been stuck with the shuttle for the past 30 years - ask yourself what kind of launch system you want to be stuck with for the next 30. I expect the CEV program will have all the good stuff cut out of it - so look at what the minimally functional version of the CEV program looks like, and that's what we will get. I'd rather see $1 billion go to advanced engine development so when a system is used it works great, than to see that same money go to build a single component in a system which doesn't work so well. Perhaps you are right that we need to have activity in space to spark economic demand and hence R&D. However, until someone builds an advanced engine (anyone, of any design) we are effectively stuck in the vacuum tube age of space, on the ground floor level of any Space Moore's Law. We need that first semiconductor to advance.
You referred to this as a chicken and egg problem. In the real world, the chicken and egg problem was solved by whatever came before the chicken laying a mutant egg, which became the chicken. Until we lay that mutant egg, we will be stuck being pre-chickens.
Oh great, I've stretched my analogies so far I have Moore's Law mutant chickens! I'd better get some lunch. Mmm... chicken!
Using your previous analogy of IBM, back in the days of only 6 computers, I would argue that you can't have the Fairchild without the Semiconductor. If you look to that as an example, you will see that only once the R&D was completed in the lab, did the industry grow beyond a single-expensive-item, government-subsidized industry, like the one we have with space right now.
I think you make an excellent point, one I have been saying myself in various ways for the last 10-15 years. When I was saying "we ought to develop cheaper means of getting into orbit before we try anything really ambitious in space", I wasn't saying "we" as in NASA, but rather "we" as in The Human Race. NASA will never do anything useful in space until the Shuttle dies. Politically, they can't afford to kill it, and they can't afford to do anything else while it is around.
I agree that the best way to bootstrap the launch industry is to develop a cheaper way of getting into space. I'd be working on this myself if I didn't already have a million things to do - I have some very fun ideas involving high Isp "excimer plasma rockets" which I'd love to try out. I think that the industry needs a technological leap before we can really have growth in the industry, in the same way that the invention of the transistor sparked the semiconductor industry. What I am saying is that money spent on developing a new launch technology is going to go much farther than money spent on rockets or infrastructure. And when I say new technology, I mean something really new, not just another chemical rocket. Chemical rockets can certainly be made better and cheaper, but they will not give the powers-of-ten leaps which are really necessary for true advancement. It takes on the order of 100 MJ/kg to get something into a good orbit. Current launch systems spend $1000+/kg to do this. 100 MJ is 28 KWhr, or about $3 worth of energy. Yes, I think we could better.
Well, if we are ever planning on building a space infrastructure, do you happen to know of any place closer to Earth that has 10^19 tons of building material that doesn't cost $1000/lb to put into space?
At current technology levels, that makes the moon's mass worth on the order of $10^25, or ten trillion trillion dollars. Cool, eh?
Personally, I think we ought to develop cheaper means of getting into orbit before we try anything really ambitious in space. But if we are going to use our current chemical rocket technology to build an infrastructure, we aren't going to be able to afford to send enough mass into space to build anything of a reasonable size. So why not withdraw some mass from the Moon's bank account? It's close, we know how to get there, and it has more rocks than some continents. 100 tons of building material in space is worth a lot.
A list of common thermonuclear fusion reactions with various elements can be found here
The links on the page lead to the rest of the NRL Plasma Physics formulary, which has lots of useful info on fusion-related stuff.
As far as how far this one method can be pushed, this design is basically a very compact neutron generator. This type of design suffers from the problem that the electrons in the target on average absorb the majority of the incoming particle's energy before it hits an ion and fuses. This is because the electrons in the target are very cold (from a plasma physics point of view) and cold electrons are light mass and absorb energy easily. Consider it similar to trying bowling in gravel - the little gravel pieces absorb so much energy from the bowling ball that it is really hard to knock over a pin. Even if you got 10 new bowling balls every time you knocked over a pin, you would still run out of balls pretty fast if you only hit a pin one out of every 1000 balls.
About ten years ago I accidentally made a neutron generator, similar to the one in the article, although without the cool little pyrocrysal accelerator. I was working on a beam collision fusion project (where the idea is to have two recirculating ion beams which cross and collide, avoiding the electron energy absorption), and instead of the beam recirculating, it was hitting a titanium wall. We started getting neutron counts, and when we measured the energy, they were 2.45 MeV, which meant they were fusion reactions. We thought everything was going well, until I tried a control experiment where we blocked the beam recirculation path. We still were getting neutrons. We found out that the deuteron beam was depositing deuterium on the titanium wall, and the incoming deuterons were fusing with the deuterium on the wall. Another back to the drawing board moment...
I hope the filterers use the fact that the.xxx is a TLD to filter, and don't just filter everything with an xxx in it. At work, our company uses one of those stupid filters which just matches keywords with any part of the url, and it drives me crazy when I want to look up stuff in the lanl arXiv. Yes, I realize that you can look it up through the arxiv.org url, but if the link is an xxx.lanl.gov one, I have to take the time to work around the stupid filter to get my work done.
Not mention how agravating it was when I found my google search for "quantum computation" was blocked. It turned out that "puta" (I believe that's Spanish for whore) was blocked. Great! I can't look up a search for "computation" on the friggin' Internet!
Yes, I have complained to the sysadmin. It gets changed, but always changes back after a while. I've gotten tired of dealing with it.
Slashdot Mirror
No, you do not apply your force in an "upward" direction in order to increase orbital altitude. Remember the old saying, "In orbit, forward means up, back means down". A forward thrust increases the orbital angular momentum and energy, and results in a higher orbit. An upward thrust would just increase the orbit's eccentricity.
;)
For more info, see Bates, Mueller, and White, "Fundamentals of Astrodynamics". BMW is the Honda Civic of astrodynamics textbooks (cheap to buy, effective, and still useful 10 years later).
As far as the calculation of the energy loss, I chose to calculate it directly from the dv/dt given by NASA. The fact that this is different from the 1km/week difference is likely due to the fact that the dv/dt increases as the station dips further into the atmosphere. If we are talking about a steady force which is applied constantly, then we can simply use the dv/dt and not worry about having to let it dip for a week before trying to return it to it's original orbit. This accounts for the factor of about 4 difference.
Superconducters would not really be necessary, as it is not hard to get a 90+% efficient electromagnetic system. But, yes, if you shield it from the sun, you might be able to cool it quite effectively.
Thanks for the great explanation Moofie. ;)
The problem is that the tethers get damaged by micrometeors. A small comparison graph of the degradation rate of single and interlinked tethers can be seen near the bottom of http://www.tethers.com/Hoytether.html. IMHO, this means that other (non-tethered) means of magnetic propulsion may be worth investigating, as there is nothing unique about the tethered geometry which makes it advantageous for magnetic propusion.
Sorry, my mistake. 140 metric tons = 140,000 kg. Please cut my estimate of power loss by a factor of 2.
:(
Sorry, I'm an American. I'm used to thinking ton = 2000 lbs, and I fucked it up because I was in a hurry.
When will America switch to metric?
Ok, first, what's up with the moderation on this post? Currently it is -2 Overrated. WTF? Who did TigerNut piss off?
A similar proposal was made by Ben Bova years ago, and I'd be surprised if he was the first. I don't know why pclminion thinks it would be such a hard calculation:
The eccentricity of the orbit is 0.0002300, so we can treat it as effectively circular.
mass of station: approx. 140 metric tons = 280,000 kg
average orbital altitude: ~380 km orbital radius: velocity: ~7700 m/s
Mean motion: 15.70869555 rev/day
Decay rate: 1.60710E-04 rev/day^2
loses a kilometer a week altitude corresponds to an power loss of: ~(1/97745)*(0.5)*(280,000 kg)*(7700 m/s)^2/86400 seconds = 990 Watts call it a kW
to replace this power loss requires a force of F=Power/velocity
force needed: 1 kW/7700 m/s = 0.13 newtons
earth's magnetic field: approx. 1 gauss=10^-4 T
Force = 2piR*I*B*turns, R*I = 207 ampere*meters*turns
assume a desired voltage drop of 100 V, and that gives us I= 10 A assuming 100 turns this gives us a coil of radius 0.2 meters.
I would be surprised if the station did not have a spare kilowatt of power available. As far as aiming the coil so that the magnetic field is in the proper direction relative to the earths magnetic field, 3 coils could be used and power changed between the 3 to create the proper net field.
The lightning neutrons that RenoX referred to are here: http://www.physorg.com/news6674.html
I have also worked with BF3 neutron detectors around high electrical fields, and I have also seen noise effects on the detector. In my experience, the counts which were caused by electrical disturbance only occurred during nearby spark-out incidents. If you were working indoors without high electrical fields present, it is most likely that your spikes were caused by the lightning neutrons, and not by the electrical effects. This of course, presumes that the neutron events that DYAIZA saw were not actually broadband noise events. My Russian is rusty, so I haven't checked out the original paper to see if that might be the case.
With regards to cold fusion, I used to hang out on sci.physics.fusion back in the day, when cold fusion was still fairly controversial and Jones, Blue, Mallove, and others would discuss their experiments. I have always thought that the interstitial energy explanation was the correct one, and I think it should be brought up whenever cold fusion is discussed. The claims of excess energy never seemed to take into account the energy of putting the hydrogen into the interstices, and the process of doing this was always the bugaboo when discussions of "If it works, why don't you build an engine" came up.
I do think that using the so-called "cold fusion" process as an energy storage mechanism could be interesting.
Maybe what we need is the MLAA (Music Listeners Association of America).
Fight fire with fire.
The EFF handles many different issues, many of which go over the head of the average American. But an organization which exists solely to protect peoples right to listen to music would be easy for most people to understand, especially when the RIAA is taking actions like it has in recent years.
I wonder if the hardware manufacturers who keep getting dictated to and sued by the RIAA would like to join as associate members...
I've seen a few good suggestions posted, but the king of this "relatively untapped genre" would have to be Sundown: The Vampire in Retreat, starring David Carridine (from Kung Fu) as Dracula and Bruce Campbell (from Evil Dead) as Van Helsing.
Not that it's a good movie or anything (it's not), but if you've ever seen it, it does define the "Vampire Cowboy" genre more than most things out there.
That's strange, I thought that when I didn't pay the maintenance fee on my last patent that it went into the public domain. I'd be glad to hear it's still in force.
Patents may have their problems, but at least the length of time and the requirement of maintenence fees to keep them in force are appropriate.
As an intellectual property owner, I worry when Congress goes overboard in an attempt to "protect intellectual property holders' rights". Yes, I like that what I create can benefit me. However, when other people use IP as a cudgel to abuse people, it makes me worry about the stability of the whole system. If you were an aristocrat in France in 1780, wouldn't you be a little concerned about the other aristocrats who beat and starve the peasants? They might just have a revolution.
What the heck are these guys doing that's going to require somewhere between 40,000 and 200,000 man-years of effort?
I don't know.
It sounds like a pyramid scheme to me.
I highly agree that electromagnetic launchers would be damn useful. I also think that most people are thinking of using them in the wrong way. Let me explain:
Due to high acceleration, electromagnetic launchers are probably not the best choice for launching humans or delicate equipment. Rockets are likely to be cheaper for this for the time being. In order to have a launcher which would be useful for human launches, the launcher would have to be very long, and thus very expensive. However, a launcher which was designed for bulk transport would not need to be very expensive at all. This is because, unlike in a rocket, the majority of capital expense stays on the planet. In order to have a cheap (and thus, likely to be actually built) system, you want to minimize the expense involved in building the launcher. One of the best ways to do this is to reduce the size of the projectile. People tend to think of launchers as firing something about the size of a Gemini capsule or Space Shuttle. However, if the launcher is going to fire a projectile the size of a coke can, a much smaller launcher could be built. Electromagnetic launchers can have very high fire rates - why launch one large projectile when many small ones will contain the same mass and use the same energy?
The atmosphere of course puts limits on the size reduction of the projectile. A large or dense projectile loses a smaller proportion of its energy to drag. However, if we make the launcher small enough to put on an airplane, then we can launch from the stratosphere for a fairly low cost. This would enable the use of small projectiles without too much energy loss to atmospheric drag. I would expect the cost of a launcher to be less than the price of an airplane which could mount one. Lets assume it is a plane similar to a 727. A 727 has a payload of about 50,000 kg including fuel. Let's say that 10,000 kg of that is projectiles, with the rest of the payload being used to carry the crew, the launcher, and the fuel for the plane and the launcher. To get to LEO, the fuel for the launcher would be about 2 times the mass of the projectiles, so that works out about right for a short flight. Assuming a fire rate of about 1/sec for 1 kg projectiles, the payload of the plane would be shot in about 3 hours.
So, presuming we had a bulk launcher which cost $20 million and could launch small projectiles into LEO at not much more than the cost of fuel, the price per kg would likely be on the order of $10/kg. Of course the launcher could only be used for launching bulk materials, but as an example:
A Delta 4 heavy rocket delivers a payload of 23000 kg to LEO at a cost of about $170 million. If we were to take that same $170 million and put $20 million into a plane-based launcher, $50 million into various upkeep costs (personnel, ground site, the inevitable bureaucracy), and $100 million into launch fuel, you could put 10 million kg into LEO. It would take a year of flying 3 flights a day with the launcher plane to put this much mass in orbit.
Of course, the mass would not be a nicely formed satellite or spaceship, but the point is that for the same cost, you get to put 4300 times the mass into orbit. 100 million kg is about twice the mass of a WWII battleship like the Bismarck, and is plenty of mass to build an orbital factory to turn some of that mass into something useful. In addition, metal encapsulated fuel pellets could be sent into orbit - fuel in orbit is worth much more than fuel on the ground.
This sort of project would only take a few million to get off the ground, and if things don't work, then you have the opportunity to retool your system, which is not as easy with exploding rockets. The real challenge lies in making the projectiles go where they are supposed to so they can be gathered in orbit to be used.
Auditor: So you plan on putting your spacecraft inside a General Products #3 Hull?
Me: Yes, it's the most indestructible thing we know.
Auditor: But what happens if you run into a moon?
Me: No problem, we have a sophisticated stasis field to kick in in case of impact. The ship and crew would be unharmed.
Auditor: But what if you are shot with a laser? The General Products hull is transparent to visible light.
Me: We have a coating which instantaneously becomes mirrored if the light intensity exceeds a certain value, plus the internal bulkheads provide protection.
Auditor: What if you crash into a ringworld?
Me: Uh... we've got a backup set of flycycles to fly the crew out in case of a serious crash.
Auditor: Yeah, but what if you run into a rogue anti-matter moon?
Me: The hell? But the chances of that happening are...
Auditor: But it could happen right? Ever heard of Beowulf Shaeffer?
Me: Well, sure it's possible but...
Auditor: (Checks FAIL on his report)
We missed you in the original thread, Jim.
Another former non-tokamak fusion researcher here.
I agree. The biggest problem with the large tokomak designs is the scale, and hence price tag, required for a self-sustaining reaction. The large price tag and long construction times mean that prototyping is essentially a decades-long process subject both to political whims and the need to be used for years after it is built just to make the building of it worthwhile.
Imagine how fast computer science would advance if each new motherboard required an act of Congress.
The real need in fusion is not for more money. The big money has been squeezing out the small money for my entire lifetime. We need smaller, easier prototyped designs that take at most a year and $1 million to build. It's the only way the art will advance.
I remember emailing back and forth with Paul Koloc back in the early nineties and commiserating about how DOE just wasn't interested in non-tokamak designs. I thought that things got better after the Bussard letter (hey, where's Baldrson at?), but I guess not. Paul is probably the world expert on ball lightning, but I'm still not sure that ball lightning is a good means of producing fusion. Should he be funded? Hell, yeah! His programme is magnitudes cheaper than ITER, and we'd definitely get our money's worth of science out of it.
Wil,
In case it makes you feel any better for not being picked ahead of Carrot Top for Celebrity Poker Showdown, here is a little (true) story for you:
A friend of mine is friends with Carrot Top. A while ago, they were waiting in line at Wal-Mart together. They get up to the checkout, and the checkout lady looks at Carrot Top and says, "You know, you really look like that Carrot Top guy from TV... I mean... no offense."
I know exactly what you mean.
Although, I figured they would have saved an announcement this important for September
Thank you, that was the most interesting post I've seen on /. in quite a while. I'm sorry I don't have mod points today.
I'm sure you are already familiar with the work of Leik Myrabo , but in case you aren't, you ought to check out his stuff. He is the big pioneer in this area (ref. 3 on your correct link).
You are right that huge savings can be had by separating the power source from the vehicle - Myrabo was writing about this 20 years ago. Most of the energy used by a rocket is used to elevate the fuel to the altitude at which it is burned. If the energy is supplied to energize a propellant (such as vaporized water as suggested in your link), the amount of propellant can be much less than the amount of burning fuel would be. Unfortunately, Myrabo has focused his more recent efforts on rather weak air propelled engines which haven't had much punch.
Because the real limit in terms of how much propellant is needed depends upon the specific energy (and thus the temperature) to which the propellant is energized, it is best if the propellant is heated to a very high temperature. For these purposes, an concentrated ultraviolet light source would work as well as a laser, and would likely be much cheaper than a fairly efficient laser of high power. Also, if a laser is used, the best case scenario would be if the photon energy corresponded to a particular energy jump in the target propellant, similar to the way an excimer laser is used. In the case of simply heating the propellant, material considerations will limit the amount you can heat the material (i.e. at some point, your water vapor will melt the nozzle). However, in the case of the excimer laser, a solid propellant could be used which would not suffer from heat transfer from the solid/gas interface, which means really high specific energies could be used.
I agree that we want the same thing, but disagree on the approach. I do think the CEV is a step forward. However, I doubt that the savings from the reduction in launch costs are going to go into the development of new launch technologies. And I also don't think that the only 5x reduction in launch costs is going to be enough to spur the development of a true space industry. It might put us to where the Russians are right now, albeit a bit more up-to-date. I don't see how another launch system like the ones we have now (to within an order of magnitude) is going to spur the economic development of space. Are we going to mine asteroids with CEV, or beam solar power? I doubt it; it doesn't have the economics for it. So why not put that money towards developing something that makes those activities economically feasible?
I'm just hoping that at some point NASA will decide to draw a line in the sand and say to congress "Look, we need something better. We are going to go on a fast development course and develop a reliable launch engine with a specific impulse in the 2000+ second range. We need this, and we are going to do it."
I'd love it even more if a private company would do it. I don't see that coming from the biggies though - they love spending government money, but not their own.
I really do think that the cost of the design does matter a lot. If it costs $1 billion to develop an engine, not a lot of prototypes are going to be built, the development is going to be slower as a result, and only a few players are even going to have the choice of whether to develop it. This is the case with most (but not all) of the types of engines you have listed. Fusion has this same type of problem - it's hard to do engineering experiments when it takes ten years to go from idea to prototype test. A design which costs $1 million to test will very quickly exceed a design which costs $100 million to test. We have too many $100 million ideas and not nearly enough $1 million ideas.
I'm not sure that I would call NERVA a success, although it certainly wasn't a failure either. "Needs work" is the grade I'd give it.
How much of the earth can be fashioned into something useful? It's also not a lump of refined metal that self assembles into struts and bulheads...
The only things the earth has in plenty that the moon does not are air and water. Anywhere you go in the inner solar system you need to bring these, aside from the poles of Mars. Fuel can be just energy and reaction mass. Solar energy is fairly plentiful on the moon, at least for half of the month. Storing this energy as separated oxides makes sense, both from an energy storage standpoint as well as a fuel and refining one. I think Rei as already addressed much of that, although I think an engine could be made from lunar regolith if enough energy were available. I wonder what the energy payback time is for refining lunar regolith to make iron+oxygen, then using the iron to make solar thermal heaters? Something to think about. I'm not sure what would be a good available working fluid - I'm sure someone has already done some work on this.
Don't get me wrong - I'm not trying to dissuade people from supporting space efforts. See that little blue dot next to my name? I was into nuclear engines long before I ever found slashdot. However, I don't trust NASA to complete what it starts. I've lived near the Cape for too long. If we have so many great designs on the drawing board, we ought to build a few. Unfortunately, it seems like the capital, either political or monetary, to build them isn't easy to find. To me, that says that the designs aren't really that great. Building prototypes is the most important step of R&D - and I was saying that we need to build better engines before spending $umpteen billion in space. The money would be better spent on building better engines, because history has shown that once NASA has a launch system that functions, no matter how shitty, their budget will be set to whatever they need to keep it barely functioning. Any development past that system will be stuck on the drawing board indefinitely. We've been stuck with the shuttle for the past 30 years - ask yourself what kind of launch system you want to be stuck with for the next 30. I expect the CEV program will have all the good stuff cut out of it - so look at what the minimally functional version of the CEV program looks like, and that's what we will get. I'd rather see $1 billion go to advanced engine development so when a system is used it works great, than to see that same money go to build a single component in a system which doesn't work so well. Perhaps you are right that we need to have activity in space to spark economic demand and hence R&D. However, until someone builds an advanced engine (anyone, of any design) we are effectively stuck in the vacuum tube age of space, on the ground floor level of any Space Moore's Law. We need that first semiconductor to advance.
You referred to this as a chicken and egg problem. In the real world, the chicken and egg problem was solved by whatever came before the chicken laying a mutant egg, which became the chicken. Until we lay that mutant egg, we will be stuck being pre-chickens.
Oh great, I've stretched my analogies so far I have Moore's Law mutant chickens! I'd better get some lunch. Mmm... chicken!
Using your previous analogy of IBM, back in the days of only 6 computers, I would argue that you can't have the Fairchild without the Semiconductor. If you look to that as an example, you will see that only once the R&D was completed in the lab, did the industry grow beyond a single-expensive-item, government-subsidized industry, like the one we have with space right now.
I think you make an excellent point, one I have been saying myself in various ways for the last 10-15 years. When I was saying "we ought to develop cheaper means of getting into orbit before we try anything really ambitious in space", I wasn't saying "we" as in NASA, but rather "we" as in The Human Race. NASA will never do anything useful in space until the Shuttle dies. Politically, they can't afford to kill it, and they can't afford to do anything else while it is around.
I agree that the best way to bootstrap the launch industry is to develop a cheaper way of getting into space. I'd be working on this myself if I didn't already have a million things to do - I have some very fun ideas involving high Isp "excimer plasma rockets" which I'd love to try out. I think that the industry needs a technological leap before we can really have growth in the industry, in the same way that the invention of the transistor sparked the semiconductor industry. What I am saying is that money spent on developing a new launch technology is going to go much farther than money spent on rockets or infrastructure. And when I say new technology, I mean something really new, not just another chemical rocket. Chemical rockets can certainly be made better and cheaper, but they will not give the powers-of-ten leaps which are really necessary for true advancement. It takes on the order of 100 MJ/kg to get something into a good orbit. Current launch systems spend $1000+/kg to do this. 100 MJ is 28 KWhr, or about $3 worth of energy. Yes, I think we could better.
Well, if we are ever planning on building a space infrastructure, do you happen to know of any place closer to Earth that has 10^19 tons of building material that doesn't cost $1000/lb to put into space?
At current technology levels, that makes the moon's mass worth on the order of $10^25, or ten trillion trillion dollars. Cool, eh?
Personally, I think we ought to develop cheaper means of getting into orbit before we try anything really ambitious in space. But if we are going to use our current chemical rocket technology to build an infrastructure, we aren't going to be able to afford to send enough mass into space to build anything of a reasonable size. So why not withdraw some mass from the Moon's bank account? It's close, we know how to get there, and it has more rocks than some continents. 100 tons of building material in space is worth a lot.
A list of common thermonuclear fusion reactions with various elements can be found here
The links on the page lead to the rest of the NRL Plasma Physics formulary, which has lots of useful info on fusion-related stuff.
As far as how far this one method can be pushed, this design is basically a very compact neutron generator. This type of design suffers from the problem that the electrons in the target on average absorb the majority of the incoming particle's energy before it hits an ion and fuses. This is because the electrons in the target are very cold (from a plasma physics point of view) and cold electrons are light mass and absorb energy easily. Consider it similar to trying bowling in gravel - the little gravel pieces absorb so much energy from the bowling ball that it is really hard to knock over a pin. Even if you got 10 new bowling balls every time you knocked over a pin, you would still run out of balls pretty fast if you only hit a pin one out of every 1000 balls.
About ten years ago I accidentally made a neutron generator, similar to the one in the article, although without the cool little pyrocrysal accelerator. I was working on a beam collision fusion project (where the idea is to have two recirculating ion beams which cross and collide, avoiding the electron energy absorption), and instead of the beam recirculating, it was hitting a titanium wall. We started getting neutron counts, and when we measured the energy, they were 2.45 MeV, which meant they were fusion reactions. We thought everything was going well, until I tried a control experiment where we blocked the beam recirculation path. We still were getting neutrons. We found out that the deuteron beam was depositing deuterium on the titanium wall, and the incoming deuterons were fusing with the deuterium on the wall. Another back to the drawing board moment...
I hope the filterers use the fact that the .xxx is a TLD to filter, and don't just filter everything with an xxx in it. At work, our company uses one of those stupid filters which just matches keywords with any part of the url, and it drives me crazy when I want to look up stuff in the lanl arXiv. Yes, I realize that you can look it up through the arxiv.org url, but if the link is an xxx.lanl.gov one, I have to take the time to work around the stupid filter to get my work done.
Not mention how agravating it was when I found my google search for "quantum computation" was blocked. It turned out that "puta" (I believe that's Spanish for whore) was blocked. Great! I can't look up a search for "computation" on the friggin' Internet!
Yes, I have complained to the sysadmin. It gets changed, but always changes back after a while. I've gotten tired of dealing with it.