Enthalpy

It's the projected antenna's area that count. Cone, parabola.. don't chance anything. At 40AU, pointing to Earth instead of the Sun multiplies by cos(1/40 rad) or 0.9997: who cares.

Sensei mistook W for W/m2. I politely corrected the claim. Is that worth two negs? If this computation needs an explanation: Sunlight power density is a mean 1367W/m2 at one AU (=Sun-Earth distance), hence 0.838W/m2 at 40.4AU. The craft exposes to sunlight its D=2.74m antenna (5.90m2) and the RTG (5% of the antenna's surface), together 6.19m2. The incoming sunlight (my original wording) on this area at 40.4AU is 5.2W. Done, thanks! Though, this paper brings little scientific material, it's more a compilation of what other people say. But it's nice to know than Anderson, the maint author of the 1998 paper to which Turyshev contributed, disagrees with Turyshev's 2012 claim that thermal recoil would explain the anomaly.

Coefficients of friction depend on the contact pressure, but slowly. Between the Earth and the Moon, it won't make a significant difference. But if the contact pressure changes a few magnitudes, the coefficients of friction change easily by a factor of 3, so the measures should always tell the experimental context to be useable.

430km/h, both with turbofans and turboprops http://en.wikipedia.org/wiki/A%C3%A9rotrain on a special track. A bumpy terrain wouldn't be the same game. 400km/h makes turboprops an obvious choice, as they're more efficient at this low speed. Commuter aircraft prefer them.

I can't tell for your country, but liquid nitrogen is easy to get here in old Europe. If the supplier doesn't want to deliver a litre, just go to the next lab (chemistry, microelectronics, and so on) with a container made of polystyrene foam and kindly ask to fill it. High-temp superconductors are still uncommon presently, worse in the form of wires, and even worse as womewhat malleable material. This is one big hurdle to their banal use. You might try your luck at the producers ( www.suptech.com , Bruker HTS GmbH , and several more). Though, it may be difficult. Somewhat easier would be a superconducting thin film, rather than wires. At liquid helium temperature, many metals superconduct. Liquid He is a bit expensive, and if improperly stored or used, is quickly lost. Though, if you really need wires, this may be an easier route. CERN has published online an excellent introduction to superconductivity by Sonneman within a "quench analysis" document but apparently it's gone. You might read other courses online.

If seeking the same moderate pressure and performance, a hydrogen staged combustion cycle is simpler than a gas generator cycle. A single stage hydrogen pump after the (not represented) 20b booster pump achieves 123b in the pre-chamber, and the smaller pumping power leaves 103b in the main chamber, which gives the same performance as a gas generator cycle. The hot gas' maximum expansion speed can be shared as 691m/s and 421m/s in the single-stage turbines that power pumps with 528m/s and 141m/s tip speed. Single stages simplify turbines and pumps. Gas generator cycles exploit much faster hot gas through several stages. We can also accept some liquid leaking into the hot gas if this flows in the drawn direction, which makes seals easier. Matc Schaefer, aka Enthalpy ========================================== Few days ago, Ariane's member states agreed on a new definitive design for Ariane 6, with one solid and two hydrogen stages. It's probably the best architecture without designing a new liquid engine. ---------- The Vulcain 2 kept from Ariane 5 is an old and not quite simple design. While better industrial organization and production methods can make it cheaper than now, at some point it will reach a barrier. The staged combustion design suggested just above may be cheaper than the gas generator cycle. It differs from the MC2000E option for Vulcain 3 by its lower pressures and higher pre-chamber temperature. An other option would push the central stage with 7 Vinci chambers with D=1.3m nozzles and one common set of turbopumps and actuators. The chambers are kept as they are, the turbines and pumps are sqrt(7) times bigger, the angular speeds sqrt(7) times smaller like the resonant frequencies. This gains 10s isp over a Vulcain 2, saves the gas generator, and Vinci's turbopumps are much cheaper. ---------- I hope the designers of the integration and launch buildings will leave room for a wider body, and at the launch pad for more solid boosters, to keep the future open. The sunheat engine brings more to satellites and space probes than any variation of chemical rocket engines http://www.scienceforums.net/topic/76627-solar-thermal-rocket/ and it prefers wide fairings, so extra room at the integration and launch buildings would be smart. Marc Schaefer, aka Enthalpy

I didn't write W/m^2. You did. I wrote "The incoming sunlight is 5.2W at 40.4AU".

Hi Sensei, I don't remember having read about such an experiment, but so much has already been made... My bet is that in 2014, as we have a model that predicts sound speed accurately, isotopic separation would be considered expensive for a limited result. It's worth it for superconductors, to check once if phonon speed influences the transition temperature of a new material or not. If you want to try, may I suggest you other gases? Deuterium is much easier to separate from protium than the isotopes of other elements are, so heavy water is commercially available at reasonable price. the relative mass difference is also better. You could make measures in water vapour, at +100°C or at a lower pressure. You could also compare CH4 with CD4, whose masses offer a ratio of 1.25 instead of 1.06 for chlorine. Both gases are less dangerous than chlorine. You could even compare H2 with D2. The speed of sound in liquid heavy water must already be measured.

Stopping the shuttle with bungees permits to start a new flight immediately, but is difficult to design and bring to run, much so because the behaviour of reused parts during a 180km/h contact is hard to imagine, as I know from crash-test hardware at 120km/h. Since immediate restart is a compelling advantage for a drop tube but is a design risk, I believe the designs should be tried and improved in a tight iterative process before the costly vertical tower is built and freezes to the propulsion and vacuum options. I propose to test horizontally the shuttle's propulsion and stopping, on a purposely built short track with one catapult-brake at each end. Beyond the sketched parts, the trial track needs bunkers at least around each end, fast video, data acquisition and more. Much can be tested, repetitively, not necessarily everything nor at the same time: Propulsion and stopping. Bungees' behaviour, adjustment, (not sketched) setting drive. (Not sketched) the rake and the rewind drive. The railway, wheels, suspension. The vacuum bubble and its seals. The drag compensation engine and its control, with a track long enough. Marc Schaefer, aka Enthalpy

Photons emitted or received have the same effect. This is necessary for momentum conservation: light carries some momentum opposite to the emitter's recoil, and transfers it to the target. Other interpretations wouldn't conserve the sum of momentums of the emitter plus the light, the light plus the target, or the emitter plus the target. Even better than a theory or a principle, the momentum of light is observed at spacecraft, with an interesting accuracy. Both received and emitted light, both visible and far infrared. At geosynchronous satellites, radiation pressure uses to be the main external torque, parasitic or useful since many satellites use it to stabilize themselves. Radiation coming from outside the Solar system isn't probable. First, it would need a significant strength to explain the Pioneer anomaly, but we observe radiation at so many wavelengths without noticing that. The anomaly gets significant as compared to our Sun's radiation pressure near Saturn's orbit, where sunlight is still stronger than any lamp. Then, both Pioneers observed the same deceleration (one craft more accurately than the other) despite going to different directions after the Saturn flyby. That makes an explanation by unidirectional radiation more difficult. But if isotropic, radiation towards the Sun would re-emerge at the opposite site, cancelling the effect out - unless it stops at the Sun. In his latest opinion: "Support for the thermal origin of the Pioneer anomaly", arXiv 1204.2507 Anderson claims (and I don't agree) that 45% of the anomaly is recoil from heat emitted by the equipment, 35% heat emitted asymmetrically by the generators without influence by the antenna, and 20% due to propagation or being within the uncertainties. One basic difference (besides detail arguments) is that I checked if the speed curve could be fit by radiation recoil, while Anderson made a fit on the acceleration curve. The acceleration curve is more tolerant, because it accepts misfits always in the same direction within the uncertainty, while these small misfits accumulate on the speed curve to make it impossible to fit. The curvatures differ, see message #4. So I dont' tell "Turyshev's model is wrong" (I have discrepancies with some paint degradations; things like that) but rather "the model doesn't pass a more stringent test".

When the construction of ITER began, the cost estimate had already swollen to 14G€ - a lot in absolute terms - and presently it seems to be around 36G€, while the project is only at its beginning. At that price, it is perfectly normal that governments and parliaments check if the investment brings us somewhere. Unfortunately, I haven't seen any sort of answer to the problem of pollution by the neutron multiplicators. While ITER is a demonstrator which doesn't have to answer every detail of a working production reactor, I feel this is a fundamental problem with a very serious potential to make the whole attempt useless, so having no answer worries me. For far less money, we would know how to store electricity, and then wind turbines make already cheaper electricity than uranium reactors.

Tritium is too scarce in Nature to feed fusion reactors. It must be produced, and this problem for full-scale production of electricity by fusion reactors is not solved. Presently, the demand is small, for experimental fusion reactors and for nuclear bombs of "boosted" design, that is, nearly all bombs. The uranium reactors provide it, part at Candu reactors, part at normal water reactors where it is a minor product of normal operation, and could be obtained in bigger amount by introducing lithium. This path wouldn't be viable to get much electricity from fusion reactors, as it takes many big uranium reactors to supply one small fusion reactor, cancelling its usefulness. Alas, all methods to obtain significant amounts take big flux of neutrons, which means a nuclear reactor, so the developers of ITER have realized that the reactor must regenerate the tritium it consumes, using tritium breeding blankets https://www.iter.org/mach/tritiumbreeding http://www-fusion-magnetique.cea.fr/gb/cea/next/couvertures/blk.htm One D-T fusion provides one neutron, and one neutron absorbed by lithium makes only one T, too little to compensate the losses, so the answer by ITER's proponents is to multiply the neutrons: the 14MeV fusion neutron is to hit a lead nucleus which emits more neutrons, and these are captured by lithium. Problems: Whether such a blanket can really breed as much tritium as the reactor consumes is doubtful. No better multiplier seems to exist (except 235U and 239Pu...), as beryllium is too scarce. 3He could be a better target than Li but it's badly scarce on Earth, and mining the Moon for it is really a bizarre idea: it's very scarce there as well, the technology doesn't exist, and, well, the alternative is just wind turbines on Earth. Neutron multiplication by lead is dirty. Very dirty: about as much as uranium fission for the same electricity. My estimates are there http://saposjoint.net/Forum/viewtopic.php?f=66&t=2450 I had invited Poitevin, the designer of ITER's demonstration blankets, to answer my arguments, but he didn't, so we ignore if he has some. The main change is that the documentation about neutron-lead reactions has disappeared from the Web. Copies exist, fortunately. To my understanding, this problem is fundamental. Not just a matter of technology for which we could hope progress; it's as dumb as counting neutrons. Presently, I suppose no solution exists, and without a solution, nuclear fusion is useless. Why invest tens of G€ in a technology known to be polluting in case it works in many decades, while we have renewables at hand right now and cheap? The brilliant people working on fusion would better develop good methods to store electricity at the grid scale, we need that. It's a huge disappointment, sure. Other methods of fusion aren't better off: laser fusion doesn't target anything else than D-T since all others are much more difficult; magnetized target fusion has the same difficulties as the others; maybe perhaps the Z-striction could consume other fuels, but that's very hypothetical, and production of electricity is not the main goal of this machine; people there have let known recently that a net energy gain would take a machine some 4 magnitudes bigger than their big thing.

http://www.cem.msu.edu/~reusch/OrgPage/bndenrgy.htm beware they still have kcal (=4184J) at MSU.

Vacuum vessels are a common thing, but building one light enough to buoy in the atmosphere hasn't been made up to now, to my knowledge. I believe it is possible (not easy!) and give hints there http://saposjoint.net/Forum/viewtopic.php?f=66&t=2520 in short: graphite composite is strong and light enough for the purpose (very few metals too, but they're more difficult to use). The difficulty is to avoid buckling, because the compressed structure is very hollow. I suggest to hae a very heterogenous structure, with a few beams (possibly as an icosahedron) holding reinforced foils that resist traction only.

In the usual bad books, yes.

OK, now the correct values of coefficient of friction are moved to speculations. Just for info: - I'm possibly the only one here who measured a coefficient of friction - I used friction coefficients for several years in my job - The figures I cite are in every book for mechanical design - Such decent books cite the pressure used to measure the coefficient, to be meaningful - Have a look at the fastening torques for screws. That's something observed more than once a year. Sorry, but I give the proper figures here, which are the commonly accepted ones.

You should put figures on the weight lifting method. What mass, what height to store how much energy. Figures are the stupid reasons that wreak havoc so many fantastic ideas, especially at renewable energy. You could check it (I haven't) for a wind turbine floating on the open Ocean, since depth is available there - don't forget the cable's cost. One affordable means to lift weight is to use water that you don't pay and store it in a huge basin for which Nature has provided all the walls except the tiny dam you add across the vally. Then, the price is correct. Unfortunately, it needs water, mountains, uninhabited valleys. I do like Prof. Garvey's underwater bags to store compressed air http://www.physforum.com/index.php?showtopic=21016&st=0 alas, no drawings there, sorry for the huge mess. Good reason to prefer ScienceForums. Batteries can work. Their cost is more or less acceptable. Their efficiency isn't that good. The amount of lithium accessible to Mankind is short, but a Japanese university tries to make them with sodium instead: may they succeed. I describe there how I imagine flywheels to be cheap and efficient: http://www.scienceforums.net/topic/59338-flywheels-store-electricity-cheap-enough/ they're presently my preferred method.

Your font size is getting as unnecessarily fat as a Stirling engine. Stirling engines are inefficient and huge, that's why sensible designs avoid this fashion.

Pure nonsense. 90% efficiency demands a hot source >10 times hotter than the cold sink, that is, >3000K on Earth. No materials enables a piston engine at 3000K. That's bare fact. In a turbocharged piston engine, the turbocharger passes about the same power as the reciprocating part of the engine, but it's nearly 100 times lighter. A Stirling engine is much bulkier and heavier than a gasoline engine. A turbine needs far less maintenance than a piston engine. That's exactly why airliners switched to turbines. Power and mass were perfectly acceptable with piston engines. As for the high tech, you should check what kind of effort was needed before seal rings could be made for the pistons, or bearings between the crankshaft and the rods, and so on. Again: I had a Stirling engine 100m from my employer and observed it often enough. It's bigger than a truck engine for just over 10kW. The comparison with a turbine is immediate.

You have not understood. The difficulty is not 3D rendering. Sorry I have to repeat. Molecular modelling software computes atom positions (or tries to) according to the atoms' interactions. This cannot be done once: in ring or cage molecules, the bonds don't have their usual length nor angles. Steric hindrance prevents it as well. Even the links to other atoms influence the length to one atom. This is exactly what users expect from such a software. For constant bond length and directions they'd take any general 3D drawing software. Obviously, you ignore what molecule modelling software does, and much about molecules as well. Why make definitive claims on the topic then? Molecular modelling is the difficult task. 3D display is negligible in comparison, and no-one cares whether this trivial part of the job is optimized or not.

Many charges flow to and from Earth, over which cosmic rays are a tiny part. For instance, an energetic particle arriving in Earth's atmopshere will create many particle pairs there, of which some must be capable to leave Earth. And you have the solar wind, whch I'd say is the biggest contributor - if it's not the ionization of the upper atmosphere by Sun's UV light. Earth is approximately neutral because an excessive imbalance would result in a stronger electric field that would help the excess charges leave and retain the minority charges stronger. A strong voltage at Earth would already be noticed, since it would change the mean energy of the electrons that arrive. Since Earth's capacitance is small, a limited voltage means a small net electric charge, for sure tiny as compared with the number of electrons and protons that constitute the Earth. R=6370km make only 700µF, so 100kV imbalance (for no reason, but >1022kV would be noticed) make only 71C or 4e20 electrons. Earth weighs 6e24 kg so it contains 4e51 protons and neutrons, over 1e51 electrons. Pretty much neutral.

The angular and magnetic momenta can only have discrete values in any direction, so the image of a magnetic vector with a definite direction is approximate. QM doesn't use this vocabulary - at least in courses and textbooks - and I fear (unsure!) such a description would be inaccurate. Sorry I can't make a definite statement about this: I've no clear mental image of the intrinsic angular and magnetic momenta in QM. Anyway, the descriptions I've seen up to now don't tell about an orientation of the momenta (which must be impossible to measure), they tell only about the probabilities of every value along one direction. Though, the final result resembles a set of probabilities computed from a vector orientation.

Methane is produced on a daily basis in many farms. That's existing technology. As opposed, methanol has presently no broad commercial circuit because it's a poison, and ethanol is not obtained from waste up to now. If it were any necessary, methane could be liquified. That was difficult in the 19th century, not now. A 1 ton piston engine cheaper than a 10kg turbine? No.

Answering to my: " Measured efficiency is worse for Stirling engines than for vapour turbines. " Stirling's measured efficiency is worse than a vapour turbine, at any scale. And if a Solar setup provides a low temperature, it's badly conceived. In addition, a Stirling is huge. Wrong choice, whatever the size. But the observed inefficiency is an excellent reason to abandon this bad choice. Yes they are. Nobody pays for sunlight nor wind. The collecting area does cost, and a turbine makes best use of it. But since sunlight is free, and land is much cheaper than a sunlight concentrator, comparing the necessary area doesn't bring farther. The net result is that ethanol from sugar cane is cheap enough to run cars with it at the scale of Brazil, while other renewables don't propel cars up to now.

Measured efficiency is worse for Stirling engines than for vapour turbines. And since renewables are free but their conversion costs, efficiency isn't the primary concern. In seriously engineered Solar thermal plants, the conversion uses turbines. Ethanol: it would be nice if this already worked practically. Much research is done on the topic. Presently, fermentation of sugar (beetle, cane) gives ethanol, fermentation of vegetables gives methanol, a lower-value poison. Researcher's aim is to get the preferred ethanol from waste rather than food; until this works well, methane is the best fuel obtained from biomass.