Enthalpy

I don't know. I only remember that when observing Venus in a small refractor, blurring increases very quickly as the Sun heats the ground still minimally, so in a sunny day it would be brutal, many many arcseconds.

Reaction engines must eject mass, here downwards, to achieve a pull, here lifting the shield. Though, the ejected mass must first be carried by the rocket engine. Ion engines are about the least bad and they're not up to the task. Let's say the engine expels ions at 720km/s. If it uses 1kg propellant, it achieves 720,000 N*s, and if adjusting the thrust to 10N to lift this 1kg, it can hover for 72,000s or 200h. If it uses 1t propellant, it achieves more N*s, but since it needs more force to lift the heavier propellant, it still hovers for 200h at most. (OK, the mass diminishes over the time, it would be an exponential, blah blah who cares). That's why we introduce this "specific impulse", which characterizes the propellant and engine independently of the propellant amount: here it's 200h. After 200h, the shield would fall back to Earth, impractical. Since this is for the best available rocket engine, I consider this option is out. Not that masts would be practical... I only checked that for 300km height they can carry their own weight.

The shield diverts the flux away from the conductor, but this doesn't change the force on the loop+shield. You proposed to check the induced electromagnetive force, and this is an excellent approach. A net force, hence power and energy, needs an emf as the loop moves, but an emf in the loop results from a variation of the flux, so a permanent force over the distance would need to accumulate more and more flux in the loop from a uniform external induction, which won't happen. As a consequence, even with the shield, we get a force only from the change of external induction with the distance and position versus the planet, and because the variation happens over a long distance, the net force is small. The torque on a loop is more significant as a rotation changes the flux over a short path, and this torque is used by some spacecraft.

Good idea to put tokamaks in fiction and fantasy, because, err, well. Wiki is rather reliable. It contains mistakes, but others sources too, and we must live with that. 1: yes. 2: D-T, short for deuterium-tritium, because this is the only mix we can hope to use in any foreseeable future. D is available in seawater. Alas, T isn't widely available. 3a: I vaguely suppose that the plasma is too thin to absorb infrared well, since pictures show it almost transparent in visible light. Also, we have efficient means to make concentrated microwaves; in infrared it would need a powerful and efficient laser, which isn't easy. For instance, an IR heater like in a bathroom is colder than the plasma, hence it wouldn't heat the plasma. 3b: The comparison with an oven isn't too bad. You can also imagine that the microwave EM field lets the plasma's electrons wobble, and as a they collide with more speed then, it makes heat. More complicated and detailed explanations exist, sure. 4: The induction is strong, several tesla. It's more or less the maximum possible when the tokamak is designed, keeping in mind that a tokamak has many design constraints that prevent being optimum in every aspect. 5: Yes, any flame is a plasma, but at a lower temperature like 1000K instead of 100,000,000K, so very few atoms are ionized in a flame, while nearly every atom is in a tokamak's plama. Because of that, containing a flame with a magnetic field won't work, as the means of action are too scarce. 6: It depends, sorry... Sometimes it's trivial, for instance a stone absorbs visible sunlight and emits infrared due to its temperature. Sometimes it's a complex and inefficient technology, for instance a 146nm laser taking a room and several M$ to emit 50W. No common answer nor method exists.

Gears are a matter for specialized companies. Designing a gear that lasts for hours is a matter of experts. Machining a gear takes special tools (available from tool producers, sure). Then, you need special materials and heat or surface treatments. Even at a mechanical engineering company, designers wouldn't draw a gear, but instead specify the parts to be bought, possibly after advice from the specialized company. Gears are standardized. They are grouped in compatible families through their "module", which isn't exactly a pitch; the module comes in standardized series and must match for long and smooth operation. https://en.wikipedia.org/wiki/Gear Once chosen, the module defines completely the tooth profile and, with the number of teeth, the wheel diameter. So to my opinion, you're seeking too much detail, since a good gear is both bought and standard. All you must define is a module (tooth size) and the number of teeth at the wheels. Note that the numbers of teeth are normally chose mutually prime to reduce the wear, so equal numbers would be avoided. A reasonable approach would be to seek an online gear catalogue to check that existing gears transmit the torque, speed, power you want.

Some general remarks. BiotechFusion, if you want to learn some electromagnetics and electric machinery, go on. If instead you want something that works properly within a limited time, buy it. Generators are cheap, often you find some used ones for free, you'll save months of disappointment, because EM isn't trivial and takes its time to grasp. Presently you're many months away from building a usable generator. You could acquire "Electric machinery fundamentals" by Stephen Chapman. Not more complicated than it needs, nice pictures, but it's the level of engineering students. Or accept a less numerical but much more "hands on" understanding - which has as much value to my eyes, and in my opinion should be acquired before the numerical approach - and buy yourself an experiment kit for electromagnetism. The universal and justified choice is to build (AC) alternators and, if DC is desired, put diodes. Diodes are very cheap and reliable - much more so than the additional parts in a (DC) dynamo. Nobody would have a single diode: buy a bridge, it makes use of all alternances. 4-diode bridges for single-phase AC to (rippled) DC, 6-diode bridge for three-phase AC to (rippled) DC. Same size and price as a single diode.

That would need more information about the generators, yes. Combining several generators can be difficult. In single and three-phase AC, synchronization is vital, both in frequency and in phase, in series connection too (when possible). In DC and AC, if the generators give roughly a constant voltage, this voltage must match accurately, or you get worries. Often, generators and loads are meant for some standard voltage, so series connection is seldom possible. About fault tolerance: it depends on the expected or more probable failure mode. Many parts, including apparatuses with windings, fail as a short-circuit rather than an open circuit. But anyway, with big apparatuses, you must take corrective actions in the circuit if one fails. You can't leave a short-circuited transformer or alternator in operation nor in the circuit.

A liquid propellants launcher stage made of wound graphite composite seems light and feasible, at least on the paper. To compare, I take the same triple-chamber Vinci stage over a P120, recently estimated with metal balloon tanks in a truss. D=3.6m, H=3.9m and H=9.2m tanks make the stage but longer than a P120, so the same machine shall wind the liquid stage, but wider if needed. The balloons are wound first, as for a solid propellant but thin. They are assembled with temporary kernels, and the cylinder's inner skin is wound. ° Intertwining some strands from a ballon and the skin isn't mandatory (shear 100kPa) but seducing. It may need several strand spools with independent movements, as for waving. Balsa (or foam) core is glued on the inner skin. Foam can fill slits. The cylinder's outer skin is wound. It may require a different matrix polymerized at a milder temperature. A liner is put on the balloons' inner face. ° Perhalopolymer is known. ° Nickel, cobalt and alloys can be deposited. ° Or deposit the liner on the balloon's kernel first, before the balloon is wound. ---------- The oxygen balloon is 870µm thick (1350g/m2) to break at 550kPa, the hydrogen balloon 500µm (775g/m2) for 310kPa. Can the machine for solid stages wind that thin? At least, carbon fabric composite plies exist with 110g/m2. Buckling at 4.1MN determines the cylinder. Linear buckling theories are known (...by too few people) to fail, so I take an axial force of 0.68Ee2 from my experiments confirmed by: Nasa's SP-8007, "Buckling of thin-walled circular cylinders" hence the sandwich with quasi-isotropic (is that optimum?) skins. The graphite inner and outer skins are each 500µm thick, contributing E=170GPa as 250µm in each direction. The balsa core is 12mm thick. The sandwich is worth an e=6mm sheet of isotropic E=170GPa. The compressive stress on 2*250µm is 730MPa. The balsa core insulates the oxygen enough, and the hydrogen gets additional 10mm foam over the outer skin. The quasi-isotropic inner skin would contract freely by some 3ppm/K but the core suffices to hold it: radial 8kPa in the balsa stretch the inner skin and compress the outer skin by 60MPa azimutally. Well, fibre composites aren't that simple, but here margins are big. ---------- The insulated ballons and the H=15.4m cylinder weigh 48+140+479 = 667kg. The same functions with metal took 225+335+718 = 1278kg. Gained 611kg, wow. The dry stage weighs 1927kg with graphite, that's excellent 47kg per ton of propellants. The truss wastes diameter, wound graphite doesn't. The small compressive stress suggests that one skin and omega stiffeners, or a graphite truss, may be lighter. Though, good joints at the nodes of a graphite truss aren't obvious, while the manufacture of a wound stage is widely automatic. Being manufactured by the same plant as solids, wound graphite stages could have the historic merit to eventually convert Europe to liquid propellants. Marc Schaefer, aka Enthalpy

I had suggested for fixed-wing aircraft to produce electricity by a few combustion engines and use it where many propellers or fans are more efficient. Several companies and agencies work on it presently. This is even more interesting for multi-rotor helicopters like hexacopters. Much simpler than the cyclic pitch of single-rotor helicopters, they use fixed-pitch rotors whose independent speeds let pilot the craft. Electric motors are cheaper and more flexible to run the rotors. A combustion engine driving a generator is an alternative to limited batteries and to cold hydrogen. The combustion engine can be a gas turbine, with which an alternator cooperates nicely http://www.scienceforums.net/topic/73798-quick-electric-machines/#entry737931 an airliner Apu would fly a big hexacopter. It can also be a turbocharged Diesel burning kerosene, or pretty much any combustion engine. Marc Schaefer, aka Enthalpy

Blurring is often worse than the 1 arcsecond I took, because this holds for a bad observation site during nighttime. Daytime makes it worse. How much can be filtered out? Unclear to me. Adaptive optics makes miracles for astronomy. From before-after comparisons, I'd say they gain a factor of 10. That would bring 1arcsecond blurring from 40mm to 4mm at the target, and then big headlines get clear. Notice that this blurring in mm at the target doesn't worsen with the observer's distance.

Who said graphene or nantubes block microwaves perfectly? At least I didn't. We can make masts to carry a shield, or at least their strength can carry their own weight. The best choice today is graphite composite, with optimistic 1550MPa compression strength and 1550kg/m3 density, so at 10m/s2 its section multiples by e every 100km. To reach 300km (or is there a better choice?) the basis must have a 20x bigger cross-area than the tip. The shield can then weigh as much as the truncated part of the masts. Then, there are some worries and limitations, for instance with the wind, the cost, and so on. Pulling the shield under rockets would not be possible. The best chemical rockets offer isp=470s, which means that the propellants can lift their own weight for 8 minutes only. Ion engines do it for 200 hours.

Even if a Medusa were feasible, its specific impulse isn't up to the task. At 100,000s=1Mm/s you can accelerate and then brake the vessel to 2Mm/s or very little more. 5Ly to the next star still take 1500 years. Same worry with nuclear fusion.

Heavy elements, not particularly strontium, absorb X rays better, even if the layer is thinner to compare at identical number of electrons or at identical mass. This is because the electrons near to a big nucleus absorb more energy to expel - as the square of the number of protons. Lead glass is very transparent when new, but I expect it to get yellow then brown under intense irradiation like ordinary glass does. Cerium-doped glass resists yellowing, strontrium maybe has the same advantage.

Ouch.

If your measure tries to determine a location, then you can use a measuring particle whose position is better known than an atom's diameter and observe how frequently it interacts with the electron. Then you tell "the electron was there with that much probability". And after a successful interaction, you know that the electron has started its new life from a smaller volume. But you can want to measure the momentum instead, and then the measure and the interaction would not tell where the electron is. One reason is that the measuring particle, with its well known momentum, has a badly known position. So "measure" does not imply a position better known afterwards, and even less a point position. If an interaction did occur, we know that the particles' attributes have concentrated within the volume range, or the momentum range, or the energy range... that is compatible to both the measured and the measuring particles. Some attributes can't be split, that's an excellent reason to keep the idea of particle. A point is not necessary for interactions, and for that purpose it can be dropped. In fact, interactions are computed over both particles' volumes, like Laplacian[Psi(r1, r2, t etc)] and q1q2/(4pi*eps*|r1-r2|) for an electrostatic interaction, leading to a density Psi of the particle pair as a function of r1, r2, t etc - except that it's pretty much unsolvable by hand. Or in a quantum well or a superlattice, the electron that absorbs or emits a photon is delocalized over many atoms before, during and after the event, and the photon interacts over that size. QM courses use to begin with the double slit experiment, alas, which is misleading. I feel important to meditate instead the orbitals observed by an atomic force microscope http://www.zurich.ibm.com/st/atomic_manipulation/pentacene.html (search AFM pentacene) It's all the time the same electron pair at the CO molecule that senses the same electron pair making the Highest Occupied Molecular Orbital at pentacene.

"Sail" is already used for other modes of propulsion, but personally I don't care. Computing by the flux through the loop holds in many cases. It suffices that the current is conserved over the turn, and then magnetic material doesn't change it. This hold in DC, as well as when the circuit is clearly smaller than a quarter wavelength. It would become uninteresting at higher frequency, when for instance a radiowave induces current in a reception antenna. If you consider an electric motor or generator, they do have magnetic material and are computed by d(flux)/dt. In fact, it is highly desired (and achieved) that the machine's flux does not pass at the conductors, since the varying induction there would induce eddy currents in the copper, creating big losses. The conductor slots are designed to keep the flux and the induction away from the copper. Same for a transformer. With equations: https://en.wikipedia.org/wiki/Maxwell%27s_equations rot(E) = -d(B)/dt holds always, whatever the materials and shapes, and so does voltage = -d(flux)/dt whether there is a metal around the loop or not, whether the flux passes through a core or not. In some cases, for instance a straight antenna, the path closing a voltage loop isn't clear so this law becomes less useful. But in DC or at frequencies low enough, current paths are closed, and integrating the voltage along them is generally the fertile approach.

I'd say that if it's transparent in one direction, so is it in the other. It doesn't even depend on the kind of passive material. Though, this must hold for energy transmission. "Transparent" may be more subtle, like "no blurring", which isn't so easy to answer.

Does it? In weak measurements, thinking of a particle helps little. In a first approach, you could keep from "particle" that some attributes come in integer numbers, for instance the charge. But if for instance you imagine that an interaction is local, you can forget it. "Know why", I don't think so. It's a theory, not far at all from direct observation, that works very well.

This EM drive does not work. The claimed figures are not plausible. What's within science is a thrust equal to P/c where P is the emitted EM power and c is 3*108m/s. 4.7MW would push 16mN, oh good. So you can forget the vessel to Mars. What makes sense within physics is, for instance: Chemical propulsion. Bulky, lengthy. Nasa's Vasimr and other ion engines, provided they have enough power and the corresponding cold sink. Variants exist with similar performance, the Vasimr's development is more advanced. My sunheat engine http://www.scienceforums.net/topic/76627-solar-thermal-rocket/ But with an SLS-sized rocket and reasonable engineering, I got sensible figures only for a pair of 50t vessels http://www.scienceforums.net/topic/83289-manned-mars-mission/ Solar sails, if we can build them much, much bigger than presently, and much bigger than a rugby pitch too http://www.scienceforums.net/topic/78265-solar-sails-bits-and-pieces/ they need serious development, for which no path is known A few more, which look less promising. So to write a story that is (necessarily) a strong extrapolation but makes scientific sense, you might choose wild upscales of an ion engine or of the sunheat engine. Very important too: don't concentrate on the propulsion of a single manned vessel. All propulsion methods better than chemical have a tiny thrust, so taking advantage of them is much a matter of scenario. Use slow efficient transfers to preset unmanned hardware at Mars.

The Ieee 754 is widely available and described. Unfortunately, the problem is not the binary representation of 0.25, which is exact, but the conversion from the string "0.25" to a binary float, which is allowed to be inaccurate within the tolerance, is expected to be inaccurate because of the conversion algorithm, and which I observed to be inaccurate in Javascript. ---------- Can someone tell what goes wrong with the other line? i % 32 And first, how does Java behave with the double float and the int?

The fuel cells for the previous estimates provided 1kW/kg, but they have progressed to 2kW/kg: https://en.wikipedia.org/wiki/Toyota_Mirai which eases everything at aeroplane design. At the 255t supersonic airliner, fuel cells weigh 77t instead of 154t. Still not reasonable, but it becomes feasible. The subsonic frames were already feasible, they improve. The Atr72-42 chimera improves its freight capacity from 3.4 to 5.4t. The Piaggio 180 Avanti gains 500kg.

Fuels cells make progress, and quickly. Three years ago they provided 1kW/kg, now the one powering the Toyota Mirai claims 2kW/kg https://en.wikipedia.org/wiki/Toyota_Mirai which eases electric helicopters quite a bit.

The new EDF plant in Britain would be of the newer type, EPR. Which doesn't make it safer to my eyes: - Obviously, nobody in France knows to build a reactor presently. The last adaptation was made four decades ago, from a design bought from the US company Westinghouse. The knowledge is gone, adios, bye-bye. - It will necessarily contain software hence be unreliable. At least, France's existing reactors have switches and needle displays. The good part of it is that EDF is nearing bankruptcy because of the EPR disaster, many people at the company call it foolish to build two more reactors at Hinckley Point - the financial director resigned loudly because of that. Alas, both governments want to proceed. I wasn't very confident of ASN (the supervisor) as they had let obvious design mistakes pass through which were detected by their Finnish and British equivalents - like, overpressure expelling the control rods, or circuits serving both for control and surveillance. Now it seems that they have downplayed the situation or didn't achieve to get the true information. Hey, I first asked publicly on May 31, 2009 whether the EPR would ever run - just because it was already abnormally late at Olkiluoto. Meanwhile, 3 more construction sites have been started, 1 is in discussion, none is operational, Areva would already have closed in a market economy, EDF has bought the activity which may kill the company - and no government has taken the proper decision. It's too late to stop, but tomorrow it will be worse.

Here are second stage details and two optional upper stages for higher energy missions. The launcher matches Falcon-9's performance with limited development and looks cheap. It could replace Soyuz if this weren't lese-majesty. The P120 is designed for 3 and 2.5 stages launchers, so its thrust drops little: I take 2.5MN at shutoff from A62 needs. This imposes a too strong acceleration on a too heavy upper composite. My sailback booster is an alternative http://www.scienceforums.net/topic/65217-rocket-boosters-sail-back/ ---------- Second stage The truss transmits 4.0G when the P120 goes empty: worse than aerodynamic moments. To break at 4.1MN, it uses AA7022 tubes, Ri=34mm Ro=35.8mm, welded as 18 nodes per 0.8m stage, and weighs 718kg of which 79kg separate with the first stage. Its node diameter is 4.2m to host the 3.6m balloons; aluminium tanks welded at the truss would improve that. The surrounding shell weighs 163kg but is thrown away earlier. The balloon for 34.9t oxygen is of 250µm to 500µm (bottom) thick steel and 10mm foam hold by polymer belts. It weighs 225kg. The balloon for 9.0t hydrogen is of 280µm steel and 15mm foam that gives 500s to ignite this stage after the tower's arms open. Hold by polymer belts, it weighs 335kg. Four 750N engines control the roll while the P120 pushes, adjust the orbit and orientation after the second stage shuts off, and deorbit it. Fed from the main tanks over 10bar pumps powered by 5kg Li-poly batteries, they total 10kg. The three-chambers Vinci shall weigh 700kg with the frame, common actuators and upscaled turbopumps. The small D=1.25m nozzles bring Isp=4345m/s=443s and 171kN; thin niobium seems possible for the uncooled section to save much mass. 300kg electronic equipment, a 50kg payload adapter and 200kg undetailed items let the dry stage weigh 2459kg, or 60kg per ton of propellants. This puts 9.1t in Leo. ---------- Chemical upper stage It starts in orbit or almost and pushes 10kN only, taking 3 kicks at perigee for most missions. Multilayer insulation of the tanks spares active cooling. The truss is of welded aluminium tubes with 12 nodes per 0.8m stage. The lower part has Ri=29mm Ro=30.4mm of AA7022, these 82kg stay with the second stage. The upper part has Ri=25mm Ro=26mm of AA7020 and weighs 80kg at the third stage. The D=2.6m sphere for <=595kg hydrogen has 90µm steel (15kg), 45mm foam (48kg) that give 500s to leave the atmosphere after the tower's arms open, and 10 plies multilayer insulation (8kg) to give 50 days vacuum operation, long enough to land 1.9t on the Moon with but bigger tanks. Polymer belts (1kg) hold it to the truss. The Ro=2.0m Ri=1.2m torus for <=4739kg oxygen has 60µm steel (12kg), 10mm foam (13kg) and 3 plies Mli (3kg). Polymer belts (7kg) hold it. Maybe the oxygen would fit in the truss instead. The engine has electric pumps, better for that size and easier to develop http://www.scienceforums.net/topic/73571-rocket-engine-with-electric-pumps/ that bring 2.1kg/s of 796:100 O2:H2 to 100bar in the chambers, using 88kWe from a 114kWe 60kg fuel cell as the Toyota Mirai has - less pressure and a lighter cell would improve if available. More thrust is also possible, to target Jupiter for instance. https://en.wikipedia.org/wiki/Toyota_Mirai The fuel cell diverts 0.8% of the flux expanded separately. Four D=1m niobium nozzles expand to 20Pa for combined Isp=4842m/s=494s, wow. The engine shall weigh 30kg plus the 60kg fuel cell. 100kg electronic equipment, a 50kg payload adapter and 50kg undetailed items let the dry stage weigh 479kg, or 89kg per ton of propellants. ---------- Sunheat upper stage Thanks to Isp=12424m/s=1267s, it brings heavier payloads to farther destinations than the chemical upper stage but slower. http://www.scienceforums.net/topic/76627-solar-thermal-rocket/ Leo to Gso takes only 40 days by six engines with the inefficient spiral transfer; a year long Hohman would transfer more. The 300km Lunar orbit gets the same payload but after over a year. A transfer towards Mars needs a bigger tank than shown, and to a Martian orbit more so - but a better option would combine a chemical engine to leave Earth and capture at Mars, letting the sunheat engines change the apoapsis as described on Jul 27, 2014 in the linked thread. Gso, Lunar and Martian transfers consume hydrogen from time to time, and taking an adjusted fraction as a gas suffices to regulate the tank's pressure. Operations at a remote planet need a cryocooler during the trip. The truss is to break at 1.1MN compression to transmit lateral 2G to the payload and hydrogen. With 18 nodes per 0.7m stage, it uses welded AA7020 tubes with Ri=22mm Ro=23mm and weighs 243kg. The D=4.2m h=4.4m ellipsoid for <=2900kg hydrogen has 150µm steel (68kg), 30mm foam (84kg) that give 500s to leave the atmosphere after the tower's arms open, and 30 plies Mli (61kg) that permit 40 days wait in vacuum. Polymer belts (4kg) hold it. Six D=4.2m engines shall weigh 156kg together. 100kg electronic equipment, a 50kg payload adapter and 50kg undetailed items let the dry stage weigh 816kg. Marc Schaefer, aka Enthalpy

For solubility, you have to check the nature of the intermolecular forces (which are not just stronger and weaker), and at both the solvent and the candidate solute. Because a solution or mixture needs to solvent and solute to attract an other, but it also needs to separate some solvent molecules, and possibly some solute molecules if they were a liquid or solid. Thermal energy helps to mix both species but to a limited extent. Many people want to explain capillarity by the mere surface tension, but I suspect that the nature of the intermolecular forces at the liquid and solid, and their compatibility, is impotrant too. Beware non-mainstream paragraph.