Enthalpy

Then it's only a matter of wording. By "decay" one usually understands "through radioactivity". Humans have some means to act on nuclides, typically by particle bombardment, which is less inefficient than X-rays. It is done at research labs, for instance to produce energetic neutrons in big amounts from a proton beam and investigate the effect of neutrons in materials. Or in particle colliders, usually for other purposes. Though, the faint probability to hit a nucleus, and the big chances to have accelerated a particle for no result, mean that nuclide reactions provoqued that way are not usable on commercial scale - if this is your intention. For instance, a 100MeV proton beam on a target of natural lithium makes neutrons, triton, alphas and the like. At big energy and money expenses for very little produced amounts, and technology won't improves that radically. Up to now, the only action from humans on nuclei on a big scale is through neutrons. They require no minimum energy to meet a nucleus and are produced abundently by uranium and plutonium fission. So to say all the man-made nuclides (in significant amounts) result from neutron irradiation at nuclear reactors. If someone could find a way, sensible economically, to produce some radio-nuclides without the special nuclear reactors, that would be extremely useful. Some nuclides are wanted by medicine and are produced by 3 to 6 reactors worldwide; some of these reactors are dangerous ruins, and when one stops, worldwide supply is short. The day-lived nuclides must be transported across the planet to the hospitals before decaying. Not satisfactory at all. One other nice task, as soon as someone finds how to command radioactivity, would be to exploit the decay energy of 40K. Abundent in the Oceans, no radioactive waste... Except that no-one has found a way.

Ouch. Ouch again. Alas, no. The mean value of all angles would be zero for a sphere, and so would have been the drag according to this theory. There is no decent theory to evaluate a drag coefficent in subsonic flows. Drag coefficients are essentially experimental. One reason is that liquid flows are complicated and unsteady, one other is that body elements interfere. Well-trained aerodynamics designers can give their gut evaluation to 0.01 accuracy, which is better than software does. Things improve at supersonic flows, for which several theories can make sensible predictions, and even finite element software achieves meaningful results.

Zeon23445, maybe you could define more precisely what kind of "robots" you mean? Some people understand autonomous androids, which are not close to be useful in daily life. Other already call "robot" a computerized arm that paints a car according to a memorized path, and these are common now and under strong push to progress further. For instance the trucks that move individual containers on the ground at Hamburg's haven are fully automatic. Or the cleaners at some metro stations in Paris. Robots with this extent of autonomous operation will expand.

Thanks for your interest! You're perfectly right, the extruded aluminium panels make a skin strong enough to be exposed to the wind, and naked foam is used on launchers to insulate cold tanks. I should have made it clearer. The throwaway shell of message #40 is only for stages sensitive to wind, and was meant for the Esc-B variant suggested in message #38. This one has naked satellite junk like multilayer insulation, very useful to store propellants until the apogee kick(s) while foam would let evaporate some propellant costly brought to orbit, but the better insulation consists of 6µm thin plastic films superimposed and demands a protection. Having foam, then multilayer insulation (MLI), then again foam is surprising, is it? We might perhaps have the multilayer insulation directly at the tanks, then only one layer of foam, if possible thrown away, but I see no good design nor operation then. At hydrogen's 20K, only helium and hydrogen are still liquid - air gases liquefy or freeze. The MLI at 20K would require vacuum (I believe this exists for small helium tanks, but is heavy and very special stuff) or be swept with hydrogen or helium all the time that the tank contains hydrogen. This is a difficult and costly operational burden; I prefer to keep 64+41kg foam at the tanks (this foam would be uneasy to throw away through the truss anyway) for simple and safer launch operations. With the foam directly on the tanks, once the hydrogen replenishment is stopped and the tank pressurized, one has 30 min in the atmosphere before a vapour valve must be opened. That's comfort. Once in vacuum, 8+6kg MLI give one week with no propellant evaporated. Foam alone would weigh a tonne to keep the propellants until the apogee. At launchers where hydrogen and oxygen tanks have a common head, a polymer honeycomb is said to work well. The gas in the combs freezes as hydrogen fills the tank, and they say this material keeps its shape and stays airtight; then vacuum in the combs insulates the tank. I may be wrong to distrust airtight polymers; then this honeycomb would be an alternative to foam.

Some biodegradable polymers are polylactic acid (commonly available for 3D printers) and polycaprolactone: http://en.wikipedia.org/wiki/Polylactic_acid http://en.wikipedia.org/wiki/Polycaprolactone Polylactic acid makes items not resistent to heat, chemicals... nor to biodegradation, but you seem to like that. Would it be any suitable for gloves? Not as a protection against chemicals - this looks like a generic restriction for biodegradable gloves. In any case, you should consider to copolymerize the biodegradable part with NBR, instead of mixing it after polymerization.

The terrestrial proportion of 3He is 1.37ppm http://www.webelements.com/helium/isotopes.html http://en.wikipedia.org/wiki/Helium so for a significant thickness, the container's top would better be very narrow. That's a tiny proportion, but producing 3He is seriously difficult, especially because it swallows neutrons passing by - these neutrons used to produce it. It also takes patience, since the decay of 3H is typically on the route. Some people suggest to consume 3He in fusion reactors instead of the unavailable 3H, but: - Tokamaks are nowhere near using 3He, which is hugely more difficult than 3H - 3He could regenerate 3H in blankets there, but it needs one neutron per tritium just as lithium does, and only one neutron is created per consumed tritium... Neutron multipliers may work some day, but maybe not, and these would pollute as much as a uranium reactor does. Yuk. - These same people add: no 3He on Earth, but let's extract it from Moon's regolith, where it is hypothesized to be... Two impossibilities and a hypothesis, engineering works better on stronger bases.

Forces are diffuse at Ariane's Esc-B upper stage, so a light truss is easier to design with a lighter material than with a stronger one of equivalent strength-to-density ratio, hence the choice of aluminium AA7022. Magnesium alloy improves a bit over aluminium. AZ80A in T5 temper offers: 1800kg/m3, E=45GPa, 0,2% proof stress = 275MPa (tension) and 240MPa (compression). This gives about the same specific strength as AA7022. The AZ80A can be extruded, machined, welded; turn the tubes to the optimum thickness, leaving extra material fot the weaker weld seam (if equivalent to F temper: tension 250MPa, compression unclear). Magnesium doesn't burn, as know people who tried. The magnesium truss shape can keep aluminium's design; just put more thickness, and adapt the diameters a little bit. Because magnesium's density fits this particular task better, the design can fully exploit the specific strength, which saves 100kg roughly over AA7022. ---------- A truss of stronger but denser materials is difficult to design here. Titanium alloy Ti-Al6V4 would provide 4430kg/m3, 113GPa and 1030MPa (hardened condition) to 828MPa (annealed, maybe attainable at good weld seams). This exceeds aluminium and magnesium by far, almost equalling steel, but demands very short and narrow truss elements which make a cylindric truss too thin and make it weak against buckling through elliptic deformation. As it looks, long wide truss elements must themselve be trusses - not obvious to design nor produce. Isogrid tubes as truss elements are an other option. NiCoMoTi 18-9-5 steel's specific strength equals Ti-Al6V4, and 18-12-5 outperforms it, but it's even harder to exploit. Improving over AZ80A would be a performance. Also, it demands a heat treatment after welding, difficult at this size - or an other, heavier assembling method. ---------- Graphite composite is an obvious choice for light and strong design, excellent here as well. Exploiting the full strength would be about as difficult as for titanium, but even though the limit won't be reached, gaining mass is easy, because the material outperforms the others so much. Marc Schaefer, aka Enthalpy

Usual Hydrogen to deuterium to tritium via neutron capture does work, but deuterium's section for neutron capture is very small. 3H converts to 3He spontaneously, yes. 3H is normally produced from lithium: http://en.wikipedia.org/wiki/Tritium#Production And: why should someone want to produce 3He by a nuclear reaction? It's a naturally occurring nuclide, and it separates spontaneously from 4He at 2K. Just cool enough, get one layer on top of the other, how easy.

My dear visionary and megalomaniac human fellows, you've probably heard about Solar sails, one attempt among many to exceed chemical rockets performance, these being inconveniently slow for hopping through our Solar system and beyond. Solar sails want to catch the light of our Sun to obtain a thrust which would indeed improve on rocket speed if the sail is big, the complete spacecraft light, and the push long enough. http://en.wikipedia.org/wiki/Solar_sail http://www.jspec.jaxa.jp/e/activity/ikaros.html http://planetary.org/ As far from the Sun as Earth is, incoming light has a pressure of 4.5µPa and reflected light as much, so accelerating any significant spacecraft mass requires sail areas at least in the square hectometre range which, to keep their own mass low enough, must be few micrometres thin - the very reasons why we still don't use Solar sails as the main propulsion of every spacecraft. Of course, I couldn't refrain from throwing a few thoughts at the engineering challenge. ===================================================================== One standard design of Solar sail has few long booms (or masts) that hold the film at its apices. The stiff parts of the sail are less long for the same film area, hence less difficult to build light. At identical boom length, a square provides the maximum area-to-length ratio, letting call the design "square sail". A pentagon loses 5% ratio, a hexagon 15%, and the drop accelerates. Though, if testing the deployment of a hectare-class sail on the ground, for which buildings limit the size, more sectors enable a bigger sail. I propose to try at a time just one sector between two booms. A continuous film can protect the payload against Sunlight, which is mandatory very near to the Sun; elsewhere we can split the film in sectors. As a wind-free building, I take a roofed soccer or rugby stadium: 100m*70m of flat lawn, where we can float or hang the booms and the film for the test. This is bigger than all Solar sails built up to 2013, and the building is still decently common. The best sector orientation on the lawn is (...with luck): Sector base parallel to lawn's diagonal for a triangular sail; Sector base parallel to lawn's length for a square, pentagon, hexagon; Sector side parallel to lawn's length for a heptagon, octagon; Sector height parallel to lawn's length for a nonagon to dodecagon and more; At some farther number, the sector's height is better parallel to the lawn's diagonal. The resulting area varies irregularly with the number of apices. 5 is a good blend. 10 is a remote optimum, with much boom length. Marc Schaefer, aka Enthalpy ===================================================================== A nice innovation on the Solar sail Ikaros is that it uses Lcd surfaces as an attitude control. That is, by making these eccentric surfaces more or less reflective, radiation pressure is controlled there, which creates a tilting moment. But Lcd have some drawbacks. They consume some electricity permanently, since the polarity must be reversed regularly to avoid wear-out. They are sensitive to sunlight, needing some protection. My proposal is to replace them on Solar sails by a thin electrochemical cell, as the one I described in EP0564012: http://www.freepatentsonline.com/EP0564012.html http://www.freepatentsonline.com/EP0564012.pdf which needs no organic material and should thus be more resistant to UV. This patent has meanwhile been granted (and should hence be available in English) and abandoned, so its technology is public and free. I never prototyped it. Making it work reversibly many times could require development. I also considered it as a thermal control surface for spacecraft. Marc Schaefer, aka Enthalpy ===================================================================== Producing 3µm polyimide film is easier than I first thought. Just take 7.5µm film and make it thinner. All right, all right, this needs further explanation. You know the machines that metallize similar films? Their big vacuum vessel encloses two huge film rolls - the source and the destination - between which the film is moved in front of an aluminium vaporizer. Pump once, metallize kilometres of film. Now, take such an existing machine, possibly a decommissioned one. Replace the vaporizing component by an etching unit - I suppose plasma etch would be fine, reasonably fast and wouldn't deteriorate the remaining 3µm thickness, as opposed to wet or gaseous etching. Adapt the pressure accordingly. And then, add thickness sensors before and after etching and build a feedback loop to control etching speed. Here you get the necessary precision that prevented thinner films from being laminated. As polyimide in this thickness range is semi-transparent to visible light, a dirt-cheap light attenuation sensor is enough. If needed, more sensors and etching units can be spread across the film's width to make the thickness uniform. You can also proceed in several steps, possibly by passing the film several times between the rolls. Add a metallic roll to stabilize the film-to-plasma generator distance if it helps. Add light shields between the plasma and the sensors, add wavelength filters, modulate the sensors' light source to protect against parasitic light. Blah blah, you already guessed all this. While this process may be too expensive for the most common uses on Earth (metallized polyester is used to wrap sweets) (and who needs 3µm film on Earth anyway) it looks really cheap for a Solar sail. Marc Schaefer, aka Enthalpy ===================================================================== An other way to make thin plastic film for the sail: Take a varnish, lacquer or similar. Pour it over a denser liquid, so the varnish floats on it and spreads. Proper amounts achieve really thin films, if the varnish takes enough time to dry. The method was used to make wing films for ultra-small model aeroplanes. Much thinner than 25µm. Polyimide varnish exists to coat high temperature transformer wires. Polyimide is dense, but some benign liquids are denser, like perfluorodecalin. To scale from 1dm2 to 1km2... Pouring and pulling continously the film to a coil as it dries can be an element of answer. Or maybe the varnish can be sprayed on an antiadhesive roll or film instead of poured on a liquid. A few crossed carbon fibres glued on the film would usefully stop the propagation of slits. I prefer the thinning machine already described, but it needs some investments. Marc Schaefer, aka Enthalpy

A light shell meant to cover a stage truss, as suggested in the Esc-B message, can look like this, depicted here with a release mechanism: A sandwich of foam and aramide fibre composite is cheap, light and resilient to shocks - but I have nothing against honeycomb. Supersonic flight demands stiffness. The foam is thicker only at ribs to save weight. To throw away the panels composing the shell, geared electric motors turn the screws that hold the panels. This worked well on several projects, and I prefer it to pyro devices: testable many times with the components that will fly, safe, easy storage and export. Throwaway panels should be bigger than individual holes in the rocket's truss. As alternatives, the payload fairing could be lengthened to cover the upper stage as well; this often reduces the bending moments on this stage and enlights it. Or a separate stage's shell can use the fairing's material and release mechanism. When the stage uses satellite junk like multilayer insulation, its shell can be thrown away at the same altitude as the fairing, say just after. Marc Schaefer, aka Enthalpy

You will receive the same frequency that you emit. Relative speed would change the frequency. The propagation medium does not. Source... This is so well known, I just can't think of one.

You mistake molten salt reactors with LFTR, whatever your reason is - many industries try to promote LFTR despite they know the obvious drawbacks. As is known, no single LFTR has ever run. --------------------------- And because LFTR would not attain the breeding threshold, they would always need a source of plutonium to supplement the 233U, which implies - Keep uranium reactors - Make usable only a tiny proportion of the thorium ore, as limited by the 235U available in uranium ore, which is necessary to produce plutonium. This is presently all the ambition of the Indian programme, the biggest and most advanced one. The same result is obtained by existing uranium reactors, both with boiling and with pressurized water. Some VVER already burn a mix of plutonium and thorium, to save some uranium ore. This cost a few millions and is operational now, instead of many billions for a hypothetical future result. --------------------------- There is more. A thorium reactor is built with a core that produces vast amounts of excess neutrons (as opposed to a uranium reactor) and breeder blankets or thorium to produce 233U. This design is much easier to tweak to produce plutonium, just by replacing the blankets with uranium. Changes are easier because the core's reactivity is less influenced, and then one fuel load give much ore available neutrons to make plutonium. As for weapons grade: this is nonsense. The answer is called a "booster" and is in every textbook. Anyway, replace the blankets more often and you get weapons grade if really needed. One more: two bombs have already worked using 233U - the one LFTR would breed without modification - instead of 235U or Pu. --------------------------- Again, the nuclear industry knows and understands these arguments perfectly. But subsidies are just so palatable!

Several people have considered this... But: - What happens the first time you trigger a quake? - If your "small" quake has consequences, are you responsible for them? Or will judges believe you avoided a greater one? - If a strong quake happens nevertheless, will you be responsible for not having prevented it? Or for having triggered it? That's discouraging, I know... Just compare with lava flows. In Italy, humans have been very successful in deviating them with trenches and dikes. This saved towns, but sometimes isolated houses had to be sacrificed to save towns. Guess what: people who had decided to save the town were condemned for the destruction of the isolated houses. Other example: the Rhine valley is active, though not often. In 1356 an earthquake completely destroyed Basel; once in 1000 years means 5% risks if you build a house for 50 years. Though, a geothermal pilot plant got worries for allegedly triggering a tiny quake (just after I proposed to work for this foreign company, figure that), which any decent house in the region should have withstanded. With sismologists recently condemned (in Italy) for not warning enough against potential earthquakes, I hardly imagine anyone wiling to take such legal risks. When one just lets Nature kill people as usual, he gets no worries.

Which confirms what I wrote: few molten salt reactors have been built, among which no LFTR has ever run. Not a single one.

Your "alternate universe" obviously doesn't obey the laws of physics. How should someone deduce anything about climate then?

Elemental hydrogen exists at giant planets, from which escaping is too difficult. Oxygen if often bound with silicon, metals, carbon... where hydrogen is scarce, like our Moon or asteroids. Oxygen and hydrogen are at the same place in the form of snow: ordinary comets, comets in the asteroid belt. Separating them takes much energy, but is simple enough that a robotic mission conceivably achieves it. There I describe how to bring a main belt comet to martian orbit (or Earth, etc.) before separating hydrogen and oxygen: http://www.scienceforums.net/topic/76627-solar-thermal-rocket/page-2#entry757663 this is the first time I see clearly how in-situ propellant can work. Ice exists at other places, but then very dilute (polar Lunar craters) or deep in the soil (Mars), which looks much more difficult with limited unmanned means. ----- Pmdeta is an amine very common in human industry: it's more widely available than RP-1, less flammable, marginally more efficient, fluid and dense, dirt-cheap - so I take it everywhere as a banal dense fuel. While its production on Earth is very easy (with ethylene, ammonia, acetone and the like) it's less suited to small robots, for which even the simplest hydrocarbons are already a challenge. Last time I considered fuel production on Mars from brought hydrogen and the atmosphere found there, my conclusion was to produce only oxygen locally, and burn hydrogen as-brought. ----- My Solar thermal rocket engine is an enabling technology for many missions and this one ejects hydrogen or, in special cases, water without prior dissociation. ----- Electric pumps are presently my preferred way everytime the (reasonable) battery mass is acceptable. Especially to bring back astronauts or samples from Mars, Moon and more, because I trust such an engine to start, and it brings performance unattainable to pressure feed.

Hardness is a property of a molecule, not of each element, and varies with the crystal form, the heat treatment, the deformation... Carbon, sulphur, iron... have very different hardness depending ont their crystallographic state. So even for solid elements it's impossible to define one hardness.

Ariane V's upper Esc-B is rumoured at 5950kg. This shattering dry mass reduces GTO (gesosynchronous transfer orbit) capacity, hampers GSO missions, nearly precludes transfers to Jupiter and beyond. Here's my alternative. This design has no structural tanks of extruded material, as it would complicate the excellent insulation that keeps hydrogen until the apogee burn. Polymer belts hold balloon tanks in a structural truss. A superinsulation that resists the wind would enable other designs. The elliptic hydrogen tank is of 200µm brazed maraging steel, plus 20mm foam so hydrogen warms by 0.6K after 10mn in air, and 5 plies of multilayer insulation for 0.07K after 10h in vacuum. It weighs 180kg with polymer belts. Already 10 plies would enable a week-long Moon mission; a 200 days Mars mission better has active cooling. Two torus for the oxygen shorten and lighten the stage. With 100µm steel, 10mm foam and 3 plies, plus the belts, they sum 123kg. Electric motors and screws can adjust some belts against thermal expansion. The outer part of the truss, similar at each level to the Soyuz interstage with 12 nodes, shall break at 6MN*m or 4.4MN. I couldn't check by hand the truss' global bucking, but only one nodes level (near the equator of the hydrogen tank) makes a straight cylinder. Welded (screwed at some places) AA7022 tubes make it, a section example being D100m*e2mm, summing 557kg. The inner part of the truss holds half of 24t oxygen and shall break at 2*5.5g; it stiffens also the outer part. AA7022 tubes there range from D70mm*e1mm to D80mm*e1.1mm, summing 163kg. 11kg of similar stuff hold the Vinci. The bistage conical adapter to an 8t payload is built the same way and weighs 35kg; heavier individual payloads to Leo or Gto have a special adapter. A shell on the truss protects the tanks from wind. Its sandwich panels have guessed 193g/m2 skins of aramide composite and 10mm foam thickened to 40mm ribs on 20% of the area. D5.4m*h6.0m weigh 121kg. The long Vinci is estimated at 280kg for want of manufacturer data, its actuators at 10kg. Vernier and roll engines (20kg) could burn gaseous hydrogen and oxygen at 1bar, or better, have electric pumps to burn the liquids at 25bar; as multiburn apogee engines, they would then outperform slightly the Vinci. They save separate tanks. Adequate chambers and nozzles exist at DLR. The separation belts, some auxiliary tanks and pipes account for 100kg; sensors, transmissions, control and steering for 300kg; unlisted items for 100kg. The dry stage weighs 2000kg, or 71kg per ton of propellants. With a second Vinci and dropable nozzle inserts for atmospheric operation you have a single-stage-to-orbit. Tanks holding more than here 28.2t would be nice, since this stage puts some 9.5t in GSO and 4.8t in transfer to Jupiter. Electric engines and screws can hold the shell panels, to drop 121kg just after the fairing, gaining as much payload. Maraging tubes would make a lighter (-150kg?) truss, but only if cut by laser or water jet to the shape of small frameworks; or make the tubes of carbon composite. Marc Schaefer, aka Enthalpy

Hello you all! Water saving basins are long known and used for water transport. Explanations at Wiki: http://en.wikipedia.org/wiki/Lock_(water_transport)#Water_saving_basins where I pinch RokerHRO's illustrations: Descending operation Ascending operation The equivalent for airlocks, with several air tanks at varied pressures, is possible and sometimes useful, to save energy and accelerate the airlock operation while limiting the peak pumping power. Is it already used? Highly possible. I didn't check that for long. Marc Schaefer, aka Enthalpy

Solar panels and ion thrusters have propelled a very nice JPL mission to pass by several asteroids. Chemical engines wouldn't have done it. Though, the acceleration is faint and provides too little speed within the time spent in good Sunlight to gain a good speed. There are species for which 5000 years and more are acceptable: bacteriae, fertilized spores... Some seem to survive in a favourable space environment, say within snow. Hence the opinion that life may spread among planets and even Solar systems. Though, the thread was rather about intentional travel. An intelligent mushroom maybe? Some (dumb ones) are reportedly thousand years old.

Leaking air tanks would eventually leave the train without brakes... But: - After an hour? I can't imagine it from sound hardware. - On nearly ALL wagons? A few wagons without leak would have stopped the train. - Normal practice, at least in Europe, demands to put a wedge on the track (I haven't found the English word) before abandoning a train. Let's hope the investigation will find convincing answers.

Combustion cannot bring a spacecraft to a remote star, because combustion rockets aren't good enough and stars are too far away. If it's for science-fiction, take fission rockets instead http://www.scienceforums.net/topic/78055-what-engines-and-fuels-would-interstellar-species-use-for-space-travel/#entry761035 or rather, just say "antimatter" and avoid giving too many details.

Travel would be faster for the travellers, as is known, but not for people staying on Earth and waiting for reports about the remote galaxy. And here I just react as an engineer and ask: "How"? Because, well, current technology achieves a few times 5km/s. I very proudly proposed one propulsion that will achieve few times 10km/s. Some processes (fission fragments' kinetic energy) for which no-one can suggest an implementation would conceivably achieve 3000km/s. That's still a factor-of-100 to approach c.

Not even YouTube suffices to make them work... No single LFTR has ever worked, despite India has invested much in them. Not even a convincing proof-of-concept exists. Every fast neutron reactor detonates like a plutonium bomb if hit by a big kinetic energy penetrator. Thorium reactors generally demand plutonium and nothing else to start, but don't produce it, so they can't replace uranium reactors. LFTR produce little actinides, but as much fission radioactive waste as uranium reactors.

Desalinate needs energy, even if not much. A tissue alone won't suffice: it needs some input, like Sunlight or digested food - my fear is that we're heading to a complete organism just to replace a pump and a membrane. Does it take stem cells to produce gills? Can't these grow exaggerately under quasi-normal conditions, say if you split the iniital tissue as it's still tiny? From all the fish we eat, can't we keep enough gills?