Over at Pharyngula the claim is that the tooth structure and muscle attachments on the jaw indicate the strength that is characteristic of a carnivore, not a scavenger.
I have had a look at your blog and note that you have mainly concentrated on America.
I have a few reasons for this.
I can get fairly good energy data for the USA; data for the world as a whole is another matter.
The USA is the single biggest energy consumer on earth, and changes need to start at home.
Any change in the technology mix in the USA is bound to affect what is offered overseas; all major auto and power companies are multinationals.
It scratches my personal itch.
I encourage others to take up aspects of the issue for which I have neither the time nor the inclination.
Take for example if china went into anarchy due to rising oil prices and modern production stopped in china. Then the production for American goods goes to America and requires energy to run, the energy supply needs to increase by the same amount else the personal energy allowed for each citizen will probably go down.
I doubt this. The imports from China include lots of inexpensive consumer electronics and textiles. If these disappeared, they would not be replaced on a 1:1 basis; prices would go up and consumption would go down. I'd say that production would return to Taiwan and Japan, if the plants hadn't been physically moved to the mainland; perhaps India would be able to pick up some of the slack.
The "embodied energy" issue is one reason I advocate a carbon tax; you ought to have a price signal for the amount of carbon that each activity or purchase represents.
You would somehow have to get the soda water back to the hydrogen producing facilities(or the hydrogen to the soda water), which may be a non-trivial energy cost (including building infrastructure).
The hydrogen proponents' model already includes taking hydrogen to every filling station (either piping it or producing it on-site). Run CO2 and hydrogen through a reactor and you get methanol; all you need is a source for the CO2 (see this Linde document and the various reports listed here but especially #11), and if you can get the CO2 for the effort of connecting a hose to a tank it should be pretty easy. The tankage requirements are much less demanding than for hydrogen; hydrogen cars are using 5000 PSI today and may go to 10,000 PSI, while soda water should keep well at only a couple hundred PSI even when hot.
The Linde report lists an average price of $150/metric ton, with the price sometimes going to or below $100/metric ton. The density of methanol is 0.7914, so a metric ton is 2786 liters or 736 gallons. If the processing cost is $100 per metric ton, the cost of the methanol over the hydrogen would be less than 14 cents per gallon of alcohol.
The real problem with a scheme like this is infrastructure. You not only need the hydrogen supply network, you need a fleet of vehicles set up to perform carbon capture and the filling stations able to offload their carbon and transform it to alcohol. This isn't trivial. The infrastructure problem is the reason I've been pushing the plug-in hybrid as the one way to make an immediate dent in US petroleum needs; we already have an electric grid that is underutilized much of the day.
Absorbing CO2 "as needed" means collecting it from a very dilute state and processing a great deal of atmosphere to do it. This requires capital, and the reduction in entropy of the CO2 means that energy has to be expended (and dumped as waste heat). Plants collect lots of carbon over their growing season, but the entire carbon-fixing capacity of the biosphere is not very far ahead of our dumping of fossil carbon.
"Collecting car poop" can range from impossible to nearly trivial, depending on the technology you assume for the car. For instance, an Otto-cycle vehicle would be a very difficult target for sequestration. On the other hand, if you use a direct-reacting methanol fuel cell, you would be able to store the reaction products (CO2 and H2O, as highly charged soda water) in a tank much more easily than you could store the hydrogen required to supply the same amount of energy. Reactors to convert CO2 and H2 to methanol are off-the-shelf technology. It appears to me that an almost-hydrogen economy which uses methanol as the hydrogen carrier for mobile uses is more practical than the model of the purists.
I was going to make this point if nobody else had...
Microorganisms have little use for molecular hydrogen; what are they going to do with their hard-earned energy, vent it as gas? Fixing carbon for energy and structure is their goal, and fats and carbohydrates are nearly perfect for those needs. (Fatty acids and hydrocarbons are very similar chemically.)
Using molecular hydrogen for e.g. vehicular power is problematic; we could learn something from plants if we used carbon as a carrier for hydrogen instead, and just recycled (rather than dumping) the carbon.
You're certainly right about the relative power capacities of electric cable vs. tension cable. I'm not about to run numbers but I suspect that they don't get toward parity until you get up to Löfstrom Loop speeds.
Sea-basing the Gyromills means you have much more expensive support requirements, transmission cabling, the works. Skywind mentions cities all over the North American continent, so I doubt they are restricting themselves to off-shore sites; for their initial trials, perhaps.
So long as the gyromill is controllable (and a 4-rotor machine should be controllable as long as it has 2 opposed rotors operational) it should be able to auto-rotate to a landing from anywhere. With a bit of planning you could even lay its cable down more or less where you wanted it.
The real problem is when you have a failure which causes an "uncontrolled descent into terrain", or worse, an "in-flight airframe failure". Such possibilities are why you wouldn't site these things in populated areas (and ought to zone all land in the potential debris landing area as agricultural). Fortunately, there is one hell of a lot of land in the USA which meets this description. Trust me on this; I just drove from Wichita to Chicago, and huge swaths of KS, MO and IL are almost ideal. So are most of TX, NM, AZ, CO, UT, NV, WA, OR, WY, MT, ND, SD, IA, MN, WI, NB, big parts of OH and MI... and that's just land I've been across personally in the last 10 years.
They've got some graphics here which might illuminate things for you.
The issue which gets me is the tension in the up-side of the cable. If it is moving upward at 10 m/sec (about 22 MPH) a 100 megawatt system would require 10 million newtons of tension in the cable. That's about 2.25 million pounds! You could cut the tension if you could increase the cable speed (power = force * speed) but it's not obvious how you could get it to more than than the wind speed (even by flying the kites back and forth crosswind). Flying a kite down through a layer of calm air wouldn't present problems, but pulling one up through calm air to reach a wind means the cable would have to support its own weight plus the becalmed kites and their air drag.
The gyromill concept may have more mechanical complexity but it seems like it would deal with those problems a bit better.
Jamming and kickback are engineering details. Someone neglected to put spring or elastomeric dampers in the load path (none of the designers were fly fishermen, I'll bet). Those failures probably could have been prevented at a relatively low cost, but nobody gave them the thought or engineering analysis to have them dealt with. Look at your own list of examples; are you really claiming that we aren't wiser now?
A long, massy tether has the advantage that it has to be tapered and the amplitude of any wave will be attenuated as the thickness of the tether increases; waves will also be partially reflected at discontinuities such as joints between segments. Really, what are the difficulties here?
Avoiding resonant excitation of vibrational modes, e.g. by the 2/rotation tidal forces.
Snubbing shocks from sudden changes in load can be done passively (elastomeric dampers) or actively (piezoelectric elements in the load path). Magnitude of shocks can be limited by e.g. using magnetic grapnels for picking up loads and limiting the maximum force to values which will not overload the tether.
Trapped gas isn't going to be an issue with a skyhook which has nothing nearby to arc to. Magnetic propulsion can't fail; ISS has serious issues with the open conductors on some of its solar panels and F=IxB isn't about to be repealed. Last, a serious effort isn't going to founder on trivial budget considerations like two (three?) of your examples.
A solar sail can provide thrust on a vector from the Sun-spacecraft line, with the magnitude equal to max thrust times the cosine of the angle.
You can vector your thrust because you're not just absorbing the incoming light, you are bouncing (most of) it away again. The thrust is the difference in the momentum of the incoming and outgoing light. For instance, if you angle the sail at 45 degrees to the incoming light, the light coming in on the radial vector departs on the circumferential vector, and your thrust is half outward and half circumferential.
Perforated material laminated to vehicle rear windows to provide shade, maintain battery charge (esp. for hybrids) and power vent vans on hot days. Minuscule thickness means negligible weight penalty.
Adhesive-backed, encapsulated cells in roll form for direct application to membrane or raised-seam metal roofing turns any smooth roofing surface into a solar roof.
Solar hat fans.
Solar fairings for bicycles which charge the electric assist batteries.
Electric awning for fishing or pleasure boats, powers trolling/cruise motor.
If you can assume 120 kcal/cm^2/year, (1390 kWH/m^2/yr) a panel at 7% efficiency will yield 97.6 KWH/m^2/year. If the panel generates its rated output at 1000 W/m^2 insolation and costs 1 Euro ($1.34) per peak watt, each square meter costs $93.80 and returns about 10% on the capital investment (assuming 10 cents/kWH power, which may be much cheaper than daytime/afternoon rates when the panels would be generating). If you can get money at 6.5% this would be a good investment. If you can get money at 6.5%, pay with pre-tax dollars and use the output to displace post-tax expenses, it's a no-brainer.
... and I need to post more, because I should know that I can't assume anything about the background of the people here (even when they are posting on space matters).
It's not an issue of power.... It's an issue of propellant.
Damping torsional vibrations is relatively easy; you've got a magnetic field you can torque against, and passive coils will damp out rotation just fine (they're used to de-spin some passively-stabilized LEO satellites). East-west vibrations can be damped using current through the tether (additional plasma contactors will be required to allow the current to vary in different segments). Not sure how you'd handle north-south vibrations, but I have neither given it thought nor done research.
If you need to provide make-up thrust of 1 N through the segment between 120 km and 400 km, which is moving at an average forward velocity of ~1400 m/sec (figuring 10 m/sec/km), that is 1400 watts plus losses. Compared to the tens or hundreds of KW you'll need to reboost in compensation for net upward traffic, drag comp is nothing.
Even the relatively tiny tethers we've tried in space have had big problems with severing, accumulating currents, the works.
If you are referring to the TSS, it failed because of poor design and defective electrical isolation between the tether proper and the reel mechanism. This was relatively easy to foresee and prevent, but nobody did the work.... A skyhook in free space wouldn't have those particular issues. It would, however, be a great place to use the properties of conductive buckytubes.
1e-5 tesla field times 1400 m/sec is 14 millivolts per meter; over the 280 km segment that dips below 400 km, that's only about 4 kV. I doubt that this is going to be a big headache, especially if the tether is segmented and charge pumps used to keep each segment at close to the ambient voltage level (each charge pump would be in an insulated segment). For each difficulty there are probably several ways to address it; we should be flying a few so that we can get engineering experience.
What are those units, Newtons? (Notice that I listed units on everything, because I don't think anyone should have to ask me for further explanations in order to reproduce, or find errors in, my results.) Incidentally,.57 cm^2 is the cross-sectional area; the diameter was about.85 cm.
Okay, suppose you have 0.28 N of average drag. At a speed of 7050 m/sec (about 16,000 MPH) the required reboost power is... less than 2 KW. (In actuality it's much less. The draggy parts are at low altitude and moving at low speed, so the F dot v is considerably smaller than the center-of-mass velocity would suggest.)
The solar array on Deep Space One was capable of about 2300 watts. If you have a significant excess of up-traffic over down-traffic, you'll need tends or hundreds of KW to replace the lost energy and angular momentum. I can't see a couple KW of power demands for drag makeup being an issue. (Of course, if you're trans-shipping stuff to the Moon and back, you could always launch chunks of iron on the down path and play catch-and-drop with the skyhook to replace the losses to the upward traffic, with a little extra mass thrown in for lagniappe.)
The point about a braided tether being bigger than a solid one is well taken, but you probably don't need to spread it out in two dimensions; one will do, and that one can be aligned in the direction of motion. Nor do you need huge coatings; a sputtered layer of gold will do for UV and conductivity, and heating would be insignificant. (How much heat would you generate with 2 KW of drag?) There are a lot of icky technical issues that you'd have to deal with, but do you really thinkk there are any showstoppers in the basic physics? I don't.
I started to check some of your figures and found gross errors starting with your atmospheric densities. My CRC Handbook of Chemistry and Physics (55th ed.) lists density values almost an order of magnitude lower than your calculator does for the lower altitudes:
100 km 8.0e-7 kg/m^3
120 km 5.0e-8 kg/m^3
150 km 3.0e-9 kg/m^3
Et cetera. I found this a bit odd, so I decided to confirm with the Standard Atmosphere table in the CRC Handbook of Tables for Engineering Science, 2nd ed. This book yielded these figures from table 7-3:
100 km 5.0e-7 kg/m^3
200 km 3.3e-10 kg/m^3
400 km 6.5e-12 kg/m^3
Table 7-5 lists temperatures, molecular weights and pressures rather than densities, but we can calculate density from rho = mw*P/RT. I get similar figures for the 600K exospheric temperature table (calculated using oocalc):
120 km 380.0 K 26.77 g/mol 2.30E-005 mb 1.95E-008 kg/m^3
140 km 483.9 K 25.40 g/mol 5.92E-006 mb 3.74E-009 kg/m^3
160 km 535.0 K 23.90 g/mol 2.00E-006 mb 1.07E-009 kg/m^3
180 km 561.1 K 22.32 g/mol 7.80E-007 mb 3.73E-010 kg/m^3
200 km 574.1 K 20.79 g/mol 3.36E-007 mb 1.46E-010 kg/m^3
250 km 593.7 K 17.85 g/mol 5.53E-008 mb 2.00E-011 kg/m^3
300 km 598.4 K 16.06 g/mol 1.19E-008 mb 3.84E-012 kg/m^3
400 km 599.9 K 11.30 g/mol 9.91E-010 mb 2.25E-013 kg/m^3
Second, you assume that the skyhook would go down to 100 km. I did not say this, I said 120 km (roughly the altitude that SS1 actually reached); this knocks 1.5 orders of magnitude off the maximum
air density as well as cutting the speed of the segment below 400 km. If this remains a problem, the pickup could be moved up to
150 km and knock another 1.2 orders of magnitude off the density and another good fraction of the airspeed.
Third, you assumed a very large width for the skyhook. The tensile strength of both standard grade carbon fiber and Spectra is about 3.5 gigapascals, and a 3.3 ton vehicle accelerating at 3 G would weigh roughly 100 kN; at a 100% safety factor the cross-sectional area required would be only 0.57 cm^2, or a circular cross-section about 0.85 cm across. There's another half order of magnitude for you, assuming that you don't elongate the cross-section and align it with the direction of motion to cut drag further.
Fourth, the skyhook only dips into the atmosphere for a small part of each rotation, and only when it is at perigee while it goes through vertical alignment. Keeping it in an elliptical orbit and avoiding the atmosphere when not required would further reduce the average drag.
In conclusion, you should revisit your calculations using better data and more realistic assumptions.
A cable moving through hypersonic velocities at 100km will be experiencing drag like crazy.
Except that it wouldn't be moving at hypersonic velocities; it would be accelerating hard, but it would barely be moving at all.
If you consider 3 G as the acceptable limit for people, a skyhook with its end stationary at the lowest point and the center of mass moving at 16,000 MPH (allowing for altitude and some excess velocity) would need to extend 1738 km from the center of mass. Re-entry interface for the Space Shuttle is considered to be 400,000 feet; if the lowest point is 120 km (~394,000 feet), by the time it gets to 100 miles the tip of the skyhook would only be moving upward at about 3450 MPH and forward at roughly 380 MPH. These are very low speeds compared to the orbits of satellites, and it would be going in and out roughly endwise compared to the earth; the drag would be correspondingly small.
Heck, even docking operations with relatively "stationary" targets are really hard to perform in space as-is, let alone a target that will be, relative to you, dipping down and then pulling away.
I expect this to fall out of our anti-missile technology. A guidance system which can "hit a bullet with a bullet" will be able to plot an intercept to a highly cooperative grapnel moving at a much lower speed, and nothing says that you can't carry fuel for a few seconds of thrust at 3 G to perform the attachment at zero relative speed.
I can't see how you store that energy in spinners...
It's like a gravity-assist maneuver, with the cable substituting for gravity. The skyhook's high-energy state is an elliptical orbit, its low-energy state is closer to a circular orbit. The ends of the skyhook are moving relative to its center of mass (of course). When a piece of cargo comes from high orbit, it comes by on a tangent to the path of the high end of the skyhook as it whips by. The cargo carrier latches on, which shifts the center of mass of the skyhook toward the cargo end; the CoM is both higher and faster than it was just before. The cargo rides the end around to the low side of the arc (carrying the center of mass with it), where it detaches. At the moment of detach, the CoM of the skyhook is now both higher and faster than it was just before the detach. Energy is conserved, angular momentum is conserved, and all the energy lost by the cargo has been gained by the rotating skyhook.
... or how spinner energy can launch anything off Earth.
You can't, but you could pick up vehicles on sub-orbital trajectories and send them into space. Think about Space Ship One as an Earth-Luna transfer vehicle.
Incentives matter, because perverse incentives (expensive high-mileage vehicles combined with cheap fuel don't reduce fuel consumption) are proven failures.
I'm with you on the the nuclear thing, but I'm not so sure that coal powerplants feeding partially-electric cars are such a bad thing compared to the status quo. (Anything you can do to change the mix of generating sources changes the CO2 emission from grid-connected transport right along with it; this is easier than re-engineering the vehicle fleet.)
Where did I put that envelope... ah, here. Suppose you have a car that gets 30 MPG, gasoline is 6.167 pounds/gallon and is 12/14 carbon by weight; 12 pounds carbon converts to 44 pounds CO2, so the car would emit 0.646 pounds CO2 per mile. Suppose instead that you have an IGCC powerplant running at 40% efficiency (that's 8530 BTU/kwh), burning pure carbon at 14,000 BTU/lb. It emits 2.23 lb CO2/kwh (pessimistic, coal has considerable volatile matter). If it feeds a plug-in hybrid consuming 250 WH/mile at the plug, that's 0.558 lb/mile. That's not spectacularly better, but it's still an improvement.
You can do much better than the coal-plant-charged PIH with hybrids like the Honda Insight, but if you start putting wind or solar power into the car-charging mix the plug-in hybrid is going to kill any petroleum-powered vehicle for CO2 emissions.
Good point about the metal byproducts (even if the metal wasn't easily refined, a metal/rock mixture might be a semi-ductile and vacuum-weldable material for building blocks, and I'd mod you insightful if I had pionts), but shipping to LEO doesn't require rotating skyhooks; aerobraking is more than sufficient.
One problem with rotating skyhooks is that anything that's long enough to keep accelerations comfortable for people passes through the inner Van Allen belt too much. You're either going to be limited to cargo, or have to think of a different scheme. (Not that it hasn't been done already.)
Why should taxpayers pay for hybrid research? Let the car companies do that.
Taxpayers should help push the car companies, by paying higher fuel taxes (which can subsidize hybrids and plug-in hybrid infrastructure) among other things.
Unless you have a crop which is far more productive than corn, E85 is just a boondoggle.
It currently produces only 1.34 BTU of ethanol for each BTU of fossil inputs. This means each gallon is about 75% fossil energy.
The tax subsidy for ethanol is currently $1.90/gallon, or about $7.60/gallon of non-fossil energy. (And you thought petroleum was expensive!)
Even if all the corn grown in the USA was converted to ethanol, it wouldn't feed our motor fuel needs.
Taxpayer funds currently devoted to ethanol subsidies should be immediately diverted to programs which actually reduce petroleum consumption, such as hybrids.
I personally doubt those clouds would last very long- clouds have a tendency to come back to earth as rain....
When they're being produced at 15-20 miles up in the air, they would. And the problem isn't just the clouds, it's the humidity; the higher up in the stratosphere (which increases in temperature with altitude, which is why it's stratisfied) you produce the water, the more water the air can hold. Normally water is kept out of the stratosphere by the cold trap at the bottom, but creating free H2 shortcuts that natural barrier in the same way that chlorofluorocarbons bypass the normal mechanisms which prevent free halogens from getting to the ozone layer.
Don't forget that certain types of electric engines also PRODUCE ozone.
Ozone is produced in electric sparks, as you find at the commutators of certain motors. Commutatorless motors (induction motors, brushless DC motors, switched reluctance motors, etc.) are not ozone sources.
Bush already cancelled the PNGV (the Clinton administration program to produce an 80-MPG full-size car, due to have delivered right about now) in favor of a hydrogen car program that won't deliver for another 14 years.
Who's paying for this delay in government progress toward freedom from terrorist-loving oil producers? The US taxpayer, that's who. In the mean time, GM and DMC have gotten with the program and
decided to produce hybrid drivetrains, and most if not all hybrid systems can be adapted to become partially grid-powered plug-in hybrids with the addition of bigger batteries, different energy-management algorithms and a charging system. Such cars would not require wiring beyond a standard extension cord until their all-electric range got upwards of 30 miles, while even short all-electric range could eliminate an enormous fraction of motor fuel consumption.
In other words, industry is about to do incrementally what the current administration appears to be trying to prevent by demanding all-or-nothing leaps.
Big Coal and the utility companies would go ape over this. Oxygen-blown IGCC plants already produce a great deal of hydrogen in normal operation (the syngas product is a mixture of H2 and carbon monoxide), and coal is roughly 1/4 the cost of oil per BTU. Utility companies operating IGCC plants for power would be able to tap off syngas during off-peak hours and scavenge the hydrogen, which creates a bigger market for their product as well as the coal producers.
On the other hand, if we get solar hydrogen either by algal production or artificial chlorophyll-like photolytic molecules, we could get rid of the market for most fossil fuels.
Bacteria have normal defense mechanisms
on
Seaweed Antibiotics?
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· Score: 3, Informative
Antibiotics are not the only things that bacteria have to contend with; they are food for many organisms in the wild, and they have defense mechanisms that they trigger when they are numerous enough to take advantage. The formation of biofilms is one such action.
Bacteria detect this critical density by sensing molecular emissions from other bacteria. If you make a molecular antagonist for the receptor site that is used to sense these molecules (a molecule which binds to the receptor but does not activate it, like Naloxone binds to opiate receptor sites without activating them) you can shut down the molecular signalling and stop the problematic bacterial behavior. This doesn't kill the bacteria so much as it leaves them with their defenses down.
Incidentally, molecular jamming appears to be able to defeat certain antibiotic resistance mechanisms. One can imagine a triple-threat treatment for resistant infections: antibiotic, biofilm and antibiotic resistance jammers and viral bacteriophages. The staphyllococci wouldn't know what hit them.
The guy who wrote TFA seems to have an over-inflated idea of what his material will be able to do:
... the semi-glazed interior can provide an airtight membrane.
Ah, no. No sane person is going to trust their atmosphere to a brittle material like that, especially when it is held down by powder. One leak could literally blow a hole through the material providing the weight, leading to rapid or even explosive decompression.
Luna has been under a rain of meteoroids for billions of years, and has a fair amount of nickel-iron bits mixed into it. You can literally extract these with a magnet. If I was looking to build a pressure membrane on Luna I would make it out of stainless steel, not ceramic.
Slashdot Mirror
Over at Pharyngula the claim is that the tooth structure and muscle attachments on the jaw indicate the strength that is characteristic of a carnivore, not a scavenger.
- I can get fairly good energy data for the USA; data for the world as a whole is another matter.
- The USA is the single biggest energy consumer on earth, and changes need to start at home.
- Any change in the technology mix in the USA is bound to affect what is offered overseas; all major auto and power companies are multinationals.
- It scratches my personal itch.
I encourage others to take up aspects of the issue for which I have neither the time nor the inclination. I doubt this. The imports from China include lots of inexpensive consumer electronics and textiles. If these disappeared, they would not be replaced on a 1:1 basis; prices would go up and consumption would go down. I'd say that production would return to Taiwan and Japan, if the plants hadn't been physically moved to the mainland; perhaps India would be able to pick up some of the slack.The "embodied energy" issue is one reason I advocate a carbon tax; you ought to have a price signal for the amount of carbon that each activity or purchase represents.
The Linde report lists an average price of $150/metric ton, with the price sometimes going to or below $100/metric ton. The density of methanol is 0.7914, so a metric ton is 2786 liters or 736 gallons. If the processing cost is $100 per metric ton, the cost of the methanol over the hydrogen would be less than 14 cents per gallon of alcohol.
The real problem with a scheme like this is infrastructure. You not only need the hydrogen supply network, you need a fleet of vehicles set up to perform carbon capture and the filling stations able to offload their carbon and transform it to alcohol. This isn't trivial. The infrastructure problem is the reason I've been pushing the plug-in hybrid as the one way to make an immediate dent in US petroleum needs; we already have an electric grid that is underutilized much of the day.
"Collecting car poop" can range from impossible to nearly trivial, depending on the technology you assume for the car. For instance, an Otto-cycle vehicle would be a very difficult target for sequestration. On the other hand, if you use a direct-reacting methanol fuel cell, you would be able to store the reaction products (CO2 and H2O, as highly charged soda water) in a tank much more easily than you could store the hydrogen required to supply the same amount of energy. Reactors to convert CO2 and H2 to methanol are off-the-shelf technology. It appears to me that an almost-hydrogen economy which uses methanol as the hydrogen carrier for mobile uses is more practical than the model of the purists.
Microorganisms have little use for molecular hydrogen; what are they going to do with their hard-earned energy, vent it as gas? Fixing carbon for energy and structure is their goal, and fats and carbohydrates are nearly perfect for those needs. (Fatty acids and hydrocarbons are very similar chemically.)
Using molecular hydrogen for e.g. vehicular power is problematic; we could learn something from plants if we used carbon as a carrier for hydrogen instead, and just recycled (rather than dumping) the carbon.
Sea-basing the Gyromills means you have much more expensive support requirements, transmission cabling, the works. Skywind mentions cities all over the North American continent, so I doubt they are restricting themselves to off-shore sites; for their initial trials, perhaps.
The real problem is when you have a failure which causes an "uncontrolled descent into terrain", or worse, an "in-flight airframe failure". Such possibilities are why you wouldn't site these things in populated areas (and ought to zone all land in the potential debris landing area as agricultural). Fortunately, there is one hell of a lot of land in the USA which meets this description. Trust me on this; I just drove from Wichita to Chicago, and huge swaths of KS, MO and IL are almost ideal. So are most of TX, NM, AZ, CO, UT, NV, WA, OR, WY, MT, ND, SD, IA, MN, WI, NB, big parts of OH and MI... and that's just land I've been across personally in the last 10 years.
The issue which gets me is the tension in the up-side of the cable. If it is moving upward at 10 m/sec (about 22 MPH) a 100 megawatt system would require 10 million newtons of tension in the cable. That's about 2.25 million pounds! You could cut the tension if you could increase the cable speed (power = force * speed) but it's not obvious how you could get it to more than than the wind speed (even by flying the kites back and forth crosswind). Flying a kite down through a layer of calm air wouldn't present problems, but pulling one up through calm air to reach a wind means the cable would have to support its own weight plus the becalmed kites and their air drag.
The gyromill concept may have more mechanical complexity but it seems like it would deal with those problems a bit better.
A long, massy tether has the advantage that it has to be tapered and the amplitude of any wave will be attenuated as the thickness of the tether increases; waves will also be partially reflected at discontinuities such as joints between segments. Really, what are the difficulties here?
- Avoiding resonant excitation of vibrational modes, e.g. by the 2/rotation tidal forces.
- Snubbing shocks from sudden changes in load can be done passively (elastomeric dampers) or actively (piezoelectric elements in the load path). Magnitude of shocks can be limited by e.g. using magnetic grapnels for picking up loads and limiting the maximum force to values which will not overload the tether.
Trapped gas isn't going to be an issue with a skyhook which has nothing nearby to arc to. Magnetic propulsion can't fail; ISS has serious issues with the open conductors on some of its solar panels and F=IxB isn't about to be repealed. Last, a serious effort isn't going to founder on trivial budget considerations like two (three?) of your examples.You can vector your thrust because you're not just absorbing the incoming light, you are bouncing (most of) it away again. The thrust is the difference in the momentum of the incoming and outgoing light. For instance, if you angle the sail at 45 degrees to the incoming light, the light coming in on the radial vector departs on the circumferential vector, and your thrust is half outward and half circumferential.
- Perforated material laminated to vehicle rear windows to provide shade, maintain battery charge (esp. for hybrids) and power vent vans on hot days. Minuscule thickness means negligible weight penalty.
- Adhesive-backed, encapsulated cells in roll form for direct application to membrane or raised-seam metal roofing turns any smooth roofing surface into a solar roof.
- Solar hat fans.
- Solar fairings for bicycles which charge the electric assist batteries.
- Electric awning for fishing or pleasure boats, powers trolling/cruise motor.
If you can assume 120 kcal/cm^2/year, (1390 kWH/m^2/yr) a panel at 7% efficiency will yield 97.6 KWH/m^2/year. If the panel generates its rated output at 1000 W/m^2 insolation and costs 1 Euro ($1.34) per peak watt, each square meter costs $93.80 and returns about 10% on the capital investment (assuming 10 cents/kWH power, which may be much cheaper than daytime/afternoon rates when the panels would be generating). If you can get money at 6.5% this would be a good investment. If you can get money at 6.5%, pay with pre-tax dollars and use the output to displace post-tax expenses, it's a no-brainer.Damping torsional vibrations is relatively easy; you've got a magnetic field you can torque against, and passive coils will damp out rotation just fine (they're used to de-spin some passively-stabilized LEO satellites). East-west vibrations can be damped using current through the tether (additional plasma contactors will be required to allow the current to vary in different segments). Not sure how you'd handle north-south vibrations, but I have neither given it thought nor done research.
If you need to provide make-up thrust of 1 N through the segment between 120 km and 400 km, which is moving at an average forward velocity of ~1400 m/sec (figuring 10 m/sec/km), that is 1400 watts plus losses. Compared to the tens or hundreds of KW you'll need to reboost in compensation for net upward traffic, drag comp is nothing.
If you are referring to the TSS, it failed because of poor design and defective electrical isolation between the tether proper and the reel mechanism. This was relatively easy to foresee and prevent, but nobody did the work.... A skyhook in free space wouldn't have those particular issues. It would, however, be a great place to use the properties of conductive buckytubes.1e-5 tesla field times 1400 m/sec is 14 millivolts per meter; over the 280 km segment that dips below 400 km, that's only about 4 kV. I doubt that this is going to be a big headache, especially if the tether is segmented and charge pumps used to keep each segment at close to the ambient voltage level (each charge pump would be in an insulated segment). For each difficulty there are probably several ways to address it; we should be flying a few so that we can get engineering experience.
Okay, suppose you have 0.28 N of average drag. At a speed of 7050 m/sec (about 16,000 MPH) the required reboost power is... less than 2 KW. (In actuality it's much less. The draggy parts are at low altitude and moving at low speed, so the F dot v is considerably smaller than the center-of-mass velocity would suggest.)
The solar array on Deep Space One was capable of about 2300 watts. If you have a significant excess of up-traffic over down-traffic, you'll need tends or hundreds of KW to replace the lost energy and angular momentum. I can't see a couple KW of power demands for drag makeup being an issue. (Of course, if you're trans-shipping stuff to the Moon and back, you could always launch chunks of iron on the down path and play catch-and-drop with the skyhook to replace the losses to the upward traffic, with a little extra mass thrown in for lagniappe.)
The point about a braided tether being bigger than a solid one is well taken, but you probably don't need to spread it out in two dimensions; one will do, and that one can be aligned in the direction of motion. Nor do you need huge coatings; a sputtered layer of gold will do for UV and conductivity, and heating would be insignificant. (How much heat would you generate with 2 KW of drag?) There are a lot of icky technical issues that you'd have to deal with, but do you really thinkk there are any showstoppers in the basic physics? I don't.
100 km 8.0e-7 kg/m^3
120 km 5.0e-8 kg/m^3
150 km 3.0e-9 kg/m^3
Et cetera. I found this a bit odd, so I decided to confirm with the Standard Atmosphere table in the CRC Handbook of Tables for Engineering Science, 2nd ed. This book yielded these figures from table 7-3:
100 km 5.0e-7 kg/m^3
200 km 3.3e-10 kg/m^3
400 km 6.5e-12 kg/m^3
Table 7-5 lists temperatures, molecular weights and pressures rather than densities, but we can calculate density from rho = mw*P/RT. I get similar figures for the 600K exospheric temperature table (calculated using oocalc):
120 km 380.0 K 26.77 g/mol 2.30E-005 mb 1.95E-008 kg/m^3
140 km 483.9 K 25.40 g/mol 5.92E-006 mb 3.74E-009 kg/m^3
160 km 535.0 K 23.90 g/mol 2.00E-006 mb 1.07E-009 kg/m^3
180 km 561.1 K 22.32 g/mol 7.80E-007 mb 3.73E-010 kg/m^3
200 km 574.1 K 20.79 g/mol 3.36E-007 mb 1.46E-010 kg/m^3
250 km 593.7 K 17.85 g/mol 5.53E-008 mb 2.00E-011 kg/m^3
300 km 598.4 K 16.06 g/mol 1.19E-008 mb 3.84E-012 kg/m^3
400 km 599.9 K 11.30 g/mol 9.91E-010 mb 2.25E-013 kg/m^3
Second, you assume that the skyhook would go down to 100 km. I did not say this, I said 120 km (roughly the altitude that SS1 actually reached); this knocks 1.5 orders of magnitude off the maximum air density as well as cutting the speed of the segment below 400 km. If this remains a problem, the pickup could be moved up to 150 km and knock another 1.2 orders of magnitude off the density and another good fraction of the airspeed.
Third, you assumed a very large width for the skyhook. The tensile strength of both standard grade carbon fiber and Spectra is about 3.5 gigapascals, and a 3.3 ton vehicle accelerating at 3 G would weigh roughly 100 kN; at a 100% safety factor the cross-sectional area required would be only 0.57 cm^2, or a circular cross-section about 0.85 cm across. There's another half order of magnitude for you, assuming that you don't elongate the cross-section and align it with the direction of motion to cut drag further.
Fourth, the skyhook only dips into the atmosphere for a small part of each rotation, and only when it is at perigee while it goes through vertical alignment. Keeping it in an elliptical orbit and avoiding the atmosphere when not required would further reduce the average drag.
In conclusion, you should revisit your calculations using better data and more realistic assumptions.
If you consider 3 G as the acceptable limit for people, a skyhook with its end stationary at the lowest point and the center of mass moving at 16,000 MPH (allowing for altitude and some excess velocity) would need to extend 1738 km from the center of mass. Re-entry interface for the Space Shuttle is considered to be 400,000 feet; if the lowest point is 120 km (~394,000 feet), by the time it gets to 100 miles the tip of the skyhook would only be moving upward at about 3450 MPH and forward at roughly 380 MPH. These are very low speeds compared to the orbits of satellites, and it would be going in and out roughly endwise compared to the earth; the drag would be correspondingly small.
I expect this to fall out of our anti-missile technology. A guidance system which can "hit a bullet with a bullet" will be able to plot an intercept to a highly cooperative grapnel moving at a much lower speed, and nothing says that you can't carry fuel for a few seconds of thrust at 3 G to perform the attachment at zero relative speed.I'm with you on the the nuclear thing, but I'm not so sure that coal powerplants feeding partially-electric cars are such a bad thing compared to the status quo. (Anything you can do to change the mix of generating sources changes the CO2 emission from grid-connected transport right along with it; this is easier than re-engineering the vehicle fleet.)
Where did I put that envelope... ah, here. Suppose you have a car that gets 30 MPG, gasoline is 6.167 pounds/gallon and is 12/14 carbon by weight; 12 pounds carbon converts to 44 pounds CO2, so the car would emit 0.646 pounds CO2 per mile. Suppose instead that you have an IGCC powerplant running at 40% efficiency (that's 8530 BTU/kwh), burning pure carbon at 14,000 BTU/lb. It emits 2.23 lb CO2/kwh (pessimistic, coal has considerable volatile matter). If it feeds a plug-in hybrid consuming 250 WH/mile at the plug, that's 0.558 lb/mile. That's not spectacularly better, but it's still an improvement.
You can do much better than the coal-plant-charged PIH with hybrids like the Honda Insight, but if you start putting wind or solar power into the car-charging mix the plug-in hybrid is going to kill any petroleum-powered vehicle for CO2 emissions.
One problem with rotating skyhooks is that anything that's long enough to keep accelerations comfortable for people passes through the inner Van Allen belt too much. You're either going to be limited to cargo, or have to think of a different scheme. (Not that it hasn't been done already.)
- It currently produces only 1.34 BTU of ethanol for each BTU of fossil inputs. This means each gallon is about 75% fossil energy.
- The tax subsidy for ethanol is currently $1.90/gallon, or about $7.60/gallon of non-fossil energy. (And you thought petroleum was expensive!)
- Even if all the corn grown in the USA was converted to ethanol, it wouldn't feed our motor fuel needs.
Taxpayer funds currently devoted to ethanol subsidies should be immediately diverted to programs which actually reduce petroleum consumption, such as hybrids.Who's paying for this delay in government progress toward freedom from terrorist-loving oil producers? The US taxpayer, that's who. In the mean time, GM and DMC have gotten with the program and decided to produce hybrid drivetrains, and most if not all hybrid systems can be adapted to become partially grid-powered plug-in hybrids with the addition of bigger batteries, different energy-management algorithms and a charging system. Such cars would not require wiring beyond a standard extension cord until their all-electric range got upwards of 30 miles, while even short all-electric range could eliminate an enormous fraction of motor fuel consumption.
In other words, industry is about to do incrementally what the current administration appears to be trying to prevent by demanding all-or-nothing leaps.
On the other hand, if we get solar hydrogen either by algal production or artificial chlorophyll-like photolytic molecules, we could get rid of the market for most fossil fuels.
Bacteria detect this critical density by sensing molecular emissions from other bacteria. If you make a molecular antagonist for the receptor site that is used to sense these molecules (a molecule which binds to the receptor but does not activate it, like Naloxone binds to opiate receptor sites without activating them) you can shut down the molecular signalling and stop the problematic bacterial behavior. This doesn't kill the bacteria so much as it leaves them with their defenses down.
For a bit more information on this, see this Wired article.
Incidentally, molecular jamming appears to be able to defeat certain antibiotic resistance mechanisms. One can imagine a triple-threat treatment for resistant infections: antibiotic, biofilm and antibiotic resistance jammers and viral bacteriophages. The staphyllococci wouldn't know what hit them.
Luna has been under a rain of meteoroids for billions of years, and has a fair amount of nickel-iron bits mixed into it. You can literally extract these with a magnet. If I was looking to build a pressure membrane on Luna I would make it out of stainless steel, not ceramic.