there was a heated debate on TV between Palin and some religious guy.
Followed by a superb "Not the Nine O'Clock News" satirical sketch: a heated debate between a devoted follower of the Church of Python and a Bishop about "The General Synod's Life of Christ" -- an obvious parody of the life of our comic messiah John Cleese -- even the initials are the same!
Nonsense -- sounds remarkably like a primitive version of the "flamed trellis" from A Fire Upon the Deep:
After a moment, Greenstalk said a little shyly, "There are theories. It's pure carbon, a fractal polymer. We know it's very common in Transcendent cargoes. We think it's used as packing material for some kinds of sentient property."
"Or perhaps the excrement of such property," Blueshell buzz-muttered.
The power distribution companies are just about the one group who really can afford to run private fibre. After all, they already HAVE cables connecting all the omportant sites, byu definition, and the technology to wrap a fibre around a power line is already well established.
And before someone makes the obvious comment -- it's already easy to route data around a line interrupted by a fallen tree or whatever. Harder to route gigawatts.
I agree, from my limited experience (we have about one diagnosed Asperger's student coming through our CS programme each year) and the information available this does seem worth looking into.
The point is that Asperger's is a fairly well-defined problem -- there are diagnostic tests and established forms of support. Also, at least in the UK it is recognised as a disability and you can get some extra support from various public institutions on account of it. If this is the case, you should be able to find fairly specific practical advice on how to support this student.
Anything you fire from the moon basically takes three days to arrive. You have loads of time to target and disable it.If you want to sneak in, you fire from close -- Cuba, say, or a submarine lurking at the edge of the continental shelf.
I think the "useful source of material resources" is kind of key. Using a space station for interplanetary vehicle construction means that the vehicle, the station, the scaffolding, the blast shield in csae the fuel goes up, etc. all have to be hauled up from Earth, at huge cost.
With a moonbase, you have space, a stable framework, and ample supplies aluminium silicate dirt, from which you might be able to refine something useful. Even if you can't, you can pile it up to provide bracing, shielding and the like.
If you just want to dock three or four pieces of Mars mission together you might as well just do it, in LEO with no station. If you really want to start building, you want to be somewhere with some ground to lean on.
Of course if Earth->orbit costs come down by a couple of orders of magnitude, for instance with an elevator, then it's a different game entirely, but I think we're probably 20-30 years away from that, if we're lucky.
As someone has already said, life does select C12 over C13. This isn't total, living tissue contains some C13, but less, proportionately than inorganically produced carbon compounds in the same environment.
Presumably C14 is even less favoured, so the C14 level in currently living tissue will be lower than that in the environment, but the dating works by comparing the levels in "fresh" material similar to the sample with the levels in the sample, so the living/non-living thing factors out.
In a rather chilling experiment a few years ago, someone took a group of professional long-distance lorry drivers. Sober, on average, they would confidently drive their lorries at 30+MPH through a gap 6 inches wider than the lorry, slow down for narrower gaps and refuse gaps narrower than the lorry. These men (I think they all were men) routinely drank 10 to 20 pints of beer at a session when socializing. The experimenters gave them 1/2 pint each and allowed time for it to be absorbed. Now, they would confidently attempt to drive their lorries through spaces 1/2" NARROWER than the lorry at 30+ MPH.
In other words they thought they were still safe drivers (and they were well under any blood-alcohol limit), but in fact they were dangerously overconfident.
I respectfully suggest that you are doing the same thing.
We have a pretty good idea of the historical variations in X, and a reasonably good probabalistic idea of the scale of likely variations over the next few hundred years. We also have a pretty good idea of the long-term (billions of years) trend in X (which is up).
Historically, variation in X does not plausibly explain the variation in mean temperature shown over last hundred years or so. Looking forward, it seems unlikely (although not impossible) that X will drop enough over the next hundred years to counteract the well understood change in fa/fb which will be induced by an increase in atmospheric CO2.
We don't understand changes in X very well, but we can see enough to be pretty sure that ignoring changes in fa/fb would be extremely unwise
CO2 is more than an insulator. It's a selective insulator.
It is transparent to most of the energy coming from the Sun, which gets through and is absorbed by the land and sea (but not by ice, which reflects just about all of it).
The warm land and sea then radiates heat. BUT, it is not nearly as hot as the sun, so it radiates at much longer wavelengths. CO2 is opaque to these wavelengths, so it absorbs this energy and re-radiates part of it downward.
A planet with a CO2 atmosphere (eg Venus) receiving the same Solar input as Earth would have a MUCH higher equilibrium temperature than one with a largely CO2-free atmosphere and significant ice cover (eg Earth). In steady state, each will radiate as much heat as it absorbs, but, the CO2-atmosphere planet will be much hotter.
Try http://books.nap.edu/html/climatechange/ (US National Academy of Sciences review).
The really detailed numbers are in http://www.grida.no/climate/ipcc_tar/ (which is about 1000 fairly technical pages. There are various summaries and the US report independently confirmed that they are reasonably accurate summaries,
Unfortunately, economics is rarely that simple. People make decisions as to whether to save money for later, or spend it now. The sum of those decisions has massive effects on the economy, by varying demand for consumer goods and supply of investment capital. The efforts of the economy to adjust to that demand involve hiring and firing people, building or not building infrastructure and so on, which has (at least) two effects:
1. It may make people more, or less, inclined to spend rather than save 2. It effects the efficiency of the economy, since once you have invested, in plant, or training or.... you waste that investment unless there is demand for your product.
1. Leads to feedback effects, that, if totally unchecked can lead to stock market crahes, wars, and other undesirable effectes.
2. Means that artificially stimulating demand (eg by breaking windows) can result in a larger net positive gain for the economy (by keeping a skilled window-maker in business so that he can make many windows in the time it would otherwise have taken him to retrain as a tailor and make one shirt).
Economics is NOT simple and NOT well explained by silly parables.
Read the full report, it's on-line. Four senior Computer Security Professors concluded that NO Internet and PC based voting scheme could be made as secure as current absentee ballot arrangements. Crypto strength is not the issue at all.
D/He3 is a potentially nicer that D/T in that it would produce far fewer neutrons. Instead almost all of the energy comes out as charged particles -- protons and alpha particles, which (a) can be steered with magetic fields (b) are more likely to stop inside the reaction, helping keep the heat in and (c) are much less prone to make anything they hit radioactive.
A D/He3 reactor could probably be designed to deliver most of its energy directly as electric current (by steering the energetic charged particles directly onto the electrode) rather than as heat, which would make it much more efficient and the lower neutron output would mean that the reactor didn't become so quickly radioactive, making it longer-lasting and easier to dispose of.
Still this whole plan is some way down the line, to put it mildly
Getting close to light-speed is also a problem. All rockets essentially work by converting some of the initial vehicle (the fuel) into energy and using it to accelerate another part of the vehicle backwards (the reactin mass), thereby forcing the remaining part of the vehicle forwards. This covers chemical rockets, ion drives, mass drivers, fission rockets of various kinds, project Orion and so on.
There is a simple equation relating the speed at which you can throw the exhasut backwards (in the ships rest frame), the proportion of the ship made up of fuel and reaction mass at launch time and the total delta-V which can be achieved. A slightly more complicated equation deals correctly with what happens when the exhaust velocity or the ships velocity approach light-speed and relativity plays a role.
Using this and imposing a ceiling of say.9999999 on the proportion of the launch mass made up of fueld and reaction mass (ie at least 1 part in 1 million must be payload) you can easily find that no chemical or fission based system can get you even close to light-speed because it simply doesn't convert enough of the mass of the fuel into energy. This basically leaves fusion (and you need a pretty efficient fusion plant, and you still don't do go very fast) or antimatter, which works just fine (in principle), or you need to cheat.
Cheating is a matter of not carrying all your fuel with you. You either leave it at home and get the folks there to ship you momentum in the form of a beam of something (photons, charged particles, smart bullets,.....) or you pick it up as you go along, which is the Bussard ramjet idea. Both have their problems. Antimatter and beam riders seem like the best ideas so far.
Don't be silly! We've known since Heisenberg that you can't tell where anything is and how fast it is moving at the same time.The XYZ people have to be lying about one or the other.
Steve
PS See also John Varley's "The Golden Globe". In particular see the description of the problems of giving directions on Oberon.
An ion drive is still nowhere near effective enough for a manned interstellar probe.You need a fairly pure fusion drive, or antimatter, or some flavour of beam-rider to get interstellar journey times down to a few years or decades without completely silly mass ratios.
You need an element which is easily ionized. you also want the individual ions to be pretty massive. A bonus is if the ionized version of the element is not too reactive. Early drives used mercury or cesium, but they had a habit of sticking to things and clogging them up, and had to be heated before they were ionized.
i'm pretty sure the cost of the xenon is negligible compared to almost any other cost around.
It'll be freight driven in large part. Drive your truck from the UK or Germany, or... down to some freight yard in Southern Spain roll onto a train (or maybe crane the cargo container onto a train, and unload a few hours later handy for all of West Africa. Take televaisions down and fresh fruit back. This could have a massive impact on the economy of North Western Africa.
The whole Silamarillion has far, far too much plot for one film. It's written in a very condensed style with little dialogue and not much description.
You might be able to fit the story of Beren and Luthien into one longish film without losing too much. A friend of mine once worked out a treatment for it a cycle of four longish operas. Similarly the story of Turin Turambar might work, or you could do something with the downfall of Numenor.
You'd need a really good writer though, because practically all of the dialogue would have to be written from scratch.On the other hand, you have much less detail from Tolkein to fit in or worry about leaving out.
Tidal generators are what I was thinking of, of course, but if you think large, most of the kinetic and gravitational potential of the solar system is in Jupiter, just as most of the other energy is the unfused hydrogen content of the Sun.Everything else is really just noise.
a) it's quite messy, dangerous and difficult to do safely. Not impossible, but neither easy nor cheap.
b) You turn a lot of moderately radioactive waste into a smaller amount of highly radioactive waste (purified fission products) and some reusable fuel (some of which is plutonium, which raises certain accounting and security issues) and in the process create a whole lot of medium level waste (irradiated machinery and such).
Neither is insuperable, but recycling is not a panacea
I'm a fan of fusion. If you look at the whole solar system, there are really only two large pools of energy -- light elements that could be fused and gravitational and kinetic energy in the planets orbital motion. Using the latter on a really large scale runs into a few problems with conservation of angular momentum, and also involves dropping Jupiter into the Sun, which is a but destructive, so it seems that fusion must be the way. Whether it is better to have one big central fusion reactor (as at present) and broadcast the energy (surely rather wasteful) or to distribute the generation more widely, I'm not sure. Breaking up the Sun into local sunlets might also be seen as a bit radical.
The economics of reprocessing don't work out too well though. It's horribly expensive to do, because you have do everything, including maintenance by remote control, and handle materials that are not only pretty radioactive, but thermally hot and chemically corrosive. The life of the machinery becomes quite short due to the harsh environment, and the used machinery is itself now medium-level radioactive waste, etc.
The only way to make it really economic is to put a very high price on the plutonium produced -- which can only be justified for weapons use, it's much more than any conceivable value as reactor fuel.
Re:What about intra-solar system signal repeaters?
on
Goodbye, Galileo
·
· Score: 1
It's an interesting idea, but the numbers just don't work out for covering the large distances across the Solar system. Let's try and work through them:
For the sake of easy numbers lets talk about the forthcoming Cassini/Huygens mission to Saturn, which is more or less 1 billion (10^9) miles away.
Now, suppose we wanted to reduce the distance between repeaters by a factor of 10, which would boost the signal by a factor of 100. At that point a 30ft antenna on the repeater satellite, would be as useful as a 300ft Deep Space Network dish on Earth, if, and it's a big if, we could put as good a set of amplifiers and signal processing equipment on the repeater (and power it) as we use on Earth.
So, we need a chain of repeaters 100 million miles apart. Most of them will have to be in solar orbit (there aren't enough planets). Since the time taken to orbit the sun varies with distance from the sun (28 years for Saturn, 12 for Jupiter, 2 for Mars, etc.), they will not stay nicely lined up. To guarantee 100 million mile ranges, you would need a "necklace" of repeaters spaced every 100 million miles or so apart around the orbit. So, for the first circuit inside Saturn, we need 2*pi*(900 million miles)/100 million miles = about 55 satellites. In total we would probably need upward of 300 of them, and this is just to give the same quality we get with 300ft antennae on Earth.
Basically the solar system is too big, and it's so much cheaper to make the antennae and amplifiers on Earth better, that inter-planetary relays is unlikely ever to win.
What does work is planetary relays: communications satellites in orbit around planets. They are so much closer to satellites exploring that particular planet that even quite small antennae give excellent communication (indeed, one can reuse technology developed for satellite phones, shuttle comms, and so on, on Earth). Then the commsat, with less other work to do, can carry a large antenna and powerful transmitters. With a few commsats you can also avoid irritating problems like not being able to talk to your landers when they're on the wrong side of the planet.
This is already being done for Mars, various ESA and NASA orbiters are relaying communications for various landers. In a small way, it was done for Jupiter and will be done at Saturn, in that the Gallileo and Cassini orbiters did (or will) relay data from the Jupiter entry probe and the Titan probe. It might be possible for the planned JIMO to be left in a suitable orbit to act as a relay for future probes. Since it will have nuclear power and ion engines it should be capable of long life.
As you say "we still need to develop the cheap carbon nanotube construction methods". These would have lots of applications beyond a Space Elevator, so its a pretty firm bet that people are already working hard on these in industry and academia all over the world. It makes no sense for NASA to commit to more than the odd design exercise for an elevator until this work is completed, and no sense for NASA to get into doing the work itself.
Better cheaper expendables and a small spaceplane to manage the only really difficult part (getting humans and delicate cargo down again) seems like a very sensible strategy for the next 10-20 years.
Slashdot Mirror
Followed by a superb "Not the Nine O'Clock News" satirical sketch: a heated debate between a devoted follower of the Church of Python and a Bishop about "The General Synod's Life of Christ" -- an obvious parody of the life of our comic messiah John Cleese -- even the initials are the same!
Does anyone have a transcript of this sketch?
The power distribution companies are just about the one group who really can afford to run private fibre. After all, they already HAVE cables connecting all the omportant sites, byu definition, and the technology to wrap a fibre around a power line is already well established.
And before someone makes the obvious comment -- it's already easy to route data around a line interrupted by a fallen tree or whatever. Harder to route gigawatts.
I agree, from my limited experience (we have about one diagnosed Asperger's student coming through our CS programme each year) and the information available this does seem worth looking into.
The point is that Asperger's is a fairly well-defined problem -- there are diagnostic tests and established forms of support. Also, at least in the UK it is recognised as a disability and you can get some extra support from various public institutions on account of it. If this is the case, you should be able to find fairly specific practical advice on how to support this student.
Anything you fire from the moon basically takes three days to arrive. You have loads of time to target and disable it.If you want to sneak in, you fire from close -- Cuba, say, or a submarine lurking at the edge of the continental shelf.
I think the "useful source of material resources" is kind of key. Using a space station for interplanetary vehicle construction means that the vehicle, the station, the scaffolding, the blast shield in csae the fuel goes up, etc. all have to be hauled up from Earth, at huge cost.
With a moonbase, you have space, a stable framework, and ample supplies aluminium silicate dirt, from which you might be able to refine something useful. Even if you can't, you can pile it up to provide bracing, shielding and the like.
If you just want to dock three or four pieces of Mars mission together you might as well just do it, in LEO with no station. If you really want to start building, you want to be somewhere with some ground to lean on.
Of course if Earth->orbit costs come down by a couple of orders of magnitude, for instance with an elevator, then it's a different game entirely, but I think we're probably 20-30 years away from that, if we're lucky.
As someone has already said, life does select C12 over C13. This isn't total,
living tissue contains some C13, but less, proportionately than inorganically produced carbon compounds in the same environment.
Presumably C14 is even less favoured, so the C14 level in currently living tissue will be lower than that in the environment, but the dating works by comparing the
levels in "fresh" material similar to the sample with the levels in the sample, so the living/non-living thing factors out.
In a rather chilling experiment a few years ago, someone took a group of professional long-distance lorry drivers. Sober, on average, they would confidently drive their lorries at 30+MPH through a gap 6 inches wider than the lorry, slow down for narrower gaps and refuse gaps narrower than the lorry. These men (I think they all were men) routinely drank 10 to 20 pints of beer at a session when socializing. The experimenters gave them 1/2 pint each and allowed time for it to be absorbed. Now, they would confidently attempt to drive their lorries through spaces 1/2" NARROWER than the lorry at 30+ MPH.
In other words they thought they were still safe drivers (and they were well under any blood-alcohol limit), but in fact they were dangerously overconfident.
I respectfully suggest that you are doing the same thing.
We have a pretty good idea of the historical variations in X, and a reasonably good probabalistic idea of the scale of likely variations over the next few hundred years. We also have a pretty good idea of the long-term (billions of years) trend in X (which is up).
Historically, variation in X does not plausibly explain the variation in mean temperature shown over last hundred years or so. Looking forward, it seems unlikely (although not impossible) that X will drop enough over the next hundred years to counteract the well understood change in fa/fb which will be induced by an increase in atmospheric CO2.
We don't understand changes in X very well, but we can see enough to be pretty sure that ignoring changes in fa/fb would be extremely unwise
CO2 is more than an insulator. It's a selective insulator.
It is transparent to most of the energy coming from the Sun, which gets through and is absorbed by the land and sea (but not by ice, which reflects just about all of it).
The warm land and sea then radiates heat. BUT, it is not nearly as hot as the sun, so it radiates at much longer wavelengths. CO2 is opaque to these wavelengths, so it absorbs this energy and re-radiates part of it downward.
A planet with a CO2 atmosphere (eg Venus) receiving the same Solar input as Earth would have a MUCH higher equilibrium temperature than one with a largely CO2-free atmosphere and significant ice cover (eg Earth). In steady state, each will radiate as much heat as it absorbs, but, the CO2-atmosphere planet will be much hotter.
Try http://books.nap.edu/html/climatechange/ (US National Academy of Sciences review).
The really detailed numbers are in http://www.grida.no/climate/ipcc_tar/ (which is about 1000 fairly technical pages. There are various summaries and the US report independently confirmed that they are reasonably accurate summaries,
Unfortunately, economics is rarely that simple. People make decisions as to
.... you waste that investment unless there is demand for your product.
whether to save money for later, or spend it now. The sum of those decisions has massive effects on the economy, by varying demand for consumer goods and supply of investment capital. The efforts of the economy to adjust to that demand involve hiring and firing people, building or not building infrastructure and so on, which has (at least) two effects:
1. It may make people more, or less, inclined to spend rather than save
2. It effects the efficiency of the economy, since once you have invested, in plant, or training or
1. Leads to feedback effects, that, if totally unchecked can lead to stock market crahes, wars, and other undesirable effectes.
2. Means that artificially stimulating demand (eg by breaking windows) can result in a larger net positive gain for the economy (by keeping a skilled window-maker in business so that he can make many windows in the time it would otherwise have taken him to retrain as a tailor and make one shirt).
Economics is NOT simple and NOT well explained by silly parables.
Steve
Read the full report, it's on-line. Four senior Computer Security Professors concluded that NO
Internet and PC based voting scheme could be made as secure as current
absentee ballot arrangements. Crypto strength is not the issue at all.
D/He3 is a potentially nicer that D/T in that it would produce far fewer neutrons. Instead almost all of the energy comes out as charged particles -- protons and alpha particles, which (a) can be steered with magetic fields (b) are more likely to stop inside the reaction, helping keep the heat in and (c) are much less prone to make anything they hit radioactive.
A D/He3 reactor could probably be designed to deliver most of its energy directly as electric current (by steering the energetic charged particles directly onto the electrode) rather than as heat, which would make it much more efficient and the lower neutron output would mean that the reactor didn't become so quickly radioactive, making it longer-lasting and easier to dispose of.
Still this whole plan is some way down the line, to put it mildly
Getting close to light-speed is also a problem. All rockets essentially work by converting some of the initial vehicle (the fuel) into energy and using it to accelerate another part of the vehicle backwards (the reactin mass), thereby forcing the remaining part of the vehicle forwards. This covers chemical rockets, ion drives, mass drivers, fission rockets of various kinds, project Orion and so on.
.9999999 on the proportion of the launch mass made up of fueld and reaction mass (ie at least 1 part in 1 million must be payload) you can easily find that no chemical or fission based system can get you even close to light-speed because it simply doesn't convert enough of the mass of the fuel into energy. This basically leaves fusion (and you need a pretty efficient fusion plant, and you still don't do go very fast) or antimatter, which works just fine (in principle), or you need to cheat.
There is a simple equation relating the speed at which you can throw the exhasut backwards (in the ships rest frame), the proportion of the ship made up of fuel
and reaction mass at launch time and the total delta-V which can be achieved. A slightly more complicated equation deals correctly with what happens when the exhaust velocity or the ships velocity approach light-speed and relativity plays a role.
Using this and imposing a ceiling of say
Cheating is a matter of not carrying all your fuel with you. You either leave it at home and get the folks there to ship you momentum in the form of a beam of something (photons, charged particles, smart bullets,.....) or you pick it up as you go along, which is the Bussard ramjet idea. Both have their problems. Antimatter and beam riders seem like the best ideas so far.
Don't be silly! We've known since Heisenberg that you can't tell where anything is
and how fast it is moving at the same time.The XYZ people have to be lying about one or the other.
Steve
PS See also John Varley's "The Golden Globe". In particular see the description of the problems of giving directions on Oberon.
An ion drive is still nowhere near effective enough for a manned
interstellar probe.You need a fairly pure fusion drive, or antimatter, or some flavour of beam-rider to get interstellar journey times down to a few years or decades without completely silly mass ratios.
You need an element which is easily ionized. you also want the individual ions to be pretty massive. A bonus is if the ionized version of the element is not too reactive. Early drives used mercury or cesium, but they had a habit of sticking to things and clogging them up, and had to be heated before they were ionized.
i'm pretty sure the cost of the xenon is negligible compared to almost any other cost around.
It'll be freight driven in large part. Drive your truck from the UK or Germany, or ... down to some freight yard in Southern Spain roll onto a train (or maybe crane the cargo container onto a train, and unload a few hours later handy for all of West Africa. Take televaisions down and fresh fruit back. This could have a massive impact on the economy of North Western Africa.
The whole Silamarillion has far, far too much plot for one film. It's written in
a very condensed style with little dialogue and not much description.
You might be able to fit the story of Beren and Luthien into one longish film without losing too much. A friend of mine once worked out a treatment for it a cycle of four longish operas. Similarly the story of Turin Turambar might work, or you could do something with the downfall of Numenor.
You'd need a really good writer though, because practically all of the dialogue would have to be written from scratch.On the other hand, you have much less detail from Tolkein to fit in or worry about leaving out.
Steve
Tidal generators are what I was thinking of, of course, but if you think large, most of the kinetic and gravitational potential of the solar system is in Jupiter, just as most of the other energy is the unfused hydrogen content of the Sun.Everything else is really just noise.
The problem with reprocessing is that
a) it's quite messy, dangerous and difficult to do safely. Not impossible, but neither easy nor cheap.
b) You turn a lot of moderately radioactive waste into a smaller amount of highly radioactive waste (purified fission products) and some reusable fuel (some of which is plutonium, which raises certain accounting and security issues) and in the process create a whole lot of medium level waste (irradiated machinery and such).
Neither is insuperable, but recycling is not a panacea
I'm a fan of fusion. If you look at the whole solar system, there are really only two large pools of energy -- light elements that could be fused and gravitational and kinetic energy in the planets orbital motion. Using the latter on a really large scale runs into a few problems with conservation of angular momentum, and also involves dropping Jupiter into the Sun, which is a but destructive, so it seems that fusion must be the way. Whether it is better to have one big central fusion reactor (as at present) and broadcast the energy (surely rather wasteful) or to distribute the generation more widely, I'm not sure. Breaking up the Sun into local sunlets might also be seen as a bit radical.
The economics of reprocessing don't work out too well though. It's horribly expensive to do, because you have do everything, including maintenance by remote control, and handle materials that are not only pretty radioactive, but thermally hot and chemically corrosive. The life of the machinery becomes quite short due to the harsh environment, and the used machinery is itself now medium-level radioactive waste, etc.
The only way to make it really economic is to put a very high price on the plutonium produced -- which can only be justified for weapons use, it's much more than any conceivable value as reactor fuel.
It's an interesting idea, but the numbers just don't work out for covering the large distances across the Solar system. Let's try and work through them:
For the sake of easy numbers lets talk about the forthcoming Cassini/Huygens mission to Saturn, which is more or less 1 billion (10^9) miles away.
Now, suppose we wanted to reduce the distance between repeaters by a factor of 10, which would boost the signal by a factor of 100. At that point a 30ft antenna on the repeater satellite, would be as useful as a 300ft Deep Space Network dish on Earth, if, and it's a big if, we could put as good a set of amplifiers and signal processing equipment on the repeater (and power it) as we use on Earth.
So, we need a chain of repeaters 100 million miles apart. Most of them will have to be in solar orbit (there aren't enough planets). Since the time taken to orbit the sun varies with distance from the sun (28 years for Saturn, 12 for Jupiter, 2 for Mars, etc.), they will not stay nicely lined up. To guarantee 100 million mile ranges, you would need a "necklace" of repeaters spaced every 100 million miles or so apart around the orbit. So, for the first circuit inside Saturn, we need 2*pi*(900 million miles)/100 million miles = about 55 satellites. In total we would probably need upward of 300 of them, and this is just to give the same quality we get with 300ft antennae on Earth.
Basically the solar system is too big, and it's so much cheaper to make the antennae and amplifiers on Earth better, that inter-planetary relays is unlikely ever to win.
What does work is planetary relays: communications satellites in orbit around planets. They are so much closer to satellites exploring that particular planet that even quite small antennae give excellent communication (indeed, one can reuse technology developed for satellite phones, shuttle comms, and so on, on Earth). Then the commsat, with less other work to do, can carry a large antenna and powerful transmitters. With a few commsats you can also avoid irritating problems like not being able to talk to your landers when they're on the wrong side of the planet.
This is already being done for Mars, various ESA and NASA orbiters are relaying communications for various landers. In a small way, it was done for Jupiter and will be done at Saturn, in that the Gallileo and Cassini orbiters did (or will) relay data from the Jupiter entry probe and the Titan probe. It might be possible for the planned JIMO to be left in a suitable orbit to act as a relay for future probes. Since it will have nuclear power and ion engines it should be capable of long life.
As you say "we still need to develop the cheap carbon nanotube construction methods". These would have lots of applications beyond a Space Elevator, so its a pretty firm bet that people are already working hard on these in industry and academia all over the world. It makes no sense for NASA to commit to more than the odd design exercise for an elevator until this work is completed, and no sense for NASA to get into doing the work itself.
Better cheaper expendables and a small spaceplane to manage the only really difficult part (getting humans and delicate cargo down again) seems like a very sensible strategy for the next 10-20 years.