Enthalpy

Not the sought answer, sorry... On the European continent, the networks are synchronized, and because transmission delays shift the phase, 3-phase transformers with extra windings adjust the phase for smooth connection. That is, to phase A add the proper amount of phase B or C to get in-phase with the rest of the grid. DC under the channel because of the stray capacitance. I can't tell if the 3-phase grids are synchronized between the British Isles and the continent. DC is also better over long distances against ohmic losses and becomes easier presently in the GW and MV range; in the 70's for Itaipu it was badly difficult. Presently, offshore wind turbines transmit a few MW with DC for the same reason. It's even more meaningful because modern wind turbines run at variable speed (less variable than wind speed) so they make DC at some step.

Many high-pitched woodwinds, say one octave over a soprano, were tried. Only the piccolo flute is commonly used. The others are quite difficult to play, because the reed is too small and because the emission and intonation are bad and the timbre very hard. At least the timbre and intonation result from the too short air column, which doesn't filter enough the high harmonics and is exceedingly sensitive to the reed's susceptance. Switching from C# on the saxophone's first register to the next D on the second register improves both, by resonating the second mode of a longer air column (this improvement results also from losses matching the reed and mouthpiece better). So I propose to build high-pitched woodwinds that use only the second mode and higher, consequently with a longer tube. A cylindrical tube would look very long for a high-pitched instrument, so I describe conical instruments like the tárogató, saxophone or oboe - extrapolation is easy. Sopraninos would be feasible but as long as altos. A piccolo is as long as a soprano to play an octave higher. As the pitch demands, the bore is very narrow, especially as compared with the length. The modes 2 and 3 are closer to an other than 1 and 2, so fewer tone holes suffice. Fine, since my proposal has extra holes to use cross-fingerings on most registers so high notes reflect well and are easy to emit. Here's a description of the holes and fingerings. 8 tone holes make only the main closed-to-open transition for 9 notes and overtones; the sketch doesn't show the unused mode 1. 6 holes suffice if the higher registers begin at the bell as on the clarinet, but that's uneasy. The holes are narrow enough for a soft timbre, wide enough to emit the higher registers in tune, evolving with the position: similar to a clarinet. Both thumbs operate them all alternately with 8 keys, like the little fingers on the Boehm clarinet. The already described keyworks http://www.scienceforums.net/topic/107427-woodwind-fingerings/?do=findComment&comment=999559 synchronizes the covers. The four higher covers can be closed at rest and the lower four open at rest. A separable joint with the lower four holes (and four transmissions) is one natural choice. The narrow bore and the small reed and mouthpiece shall excite the second mode when only these holes are open. One optional long and narrow octave hole, operated for instance by the right index' proximal or middle phalange, would stabilize this mode. A separate set of 9 cross-fingering holes combine with the tone holes to produce the upper registers. They are independent with one finger each, except that for instance the left index operates also the highest hole with the proximal or middle phalange. Covers closed at rest ease playing, though coverless holes are cheaper. These holes are narrower to reflect the wave partly: only several holes including the tone holes make a good reflection. They must also be lossy enough to spoil the unwanted modes and can consist of several narrower holes under a common cover. Four tone and cross-fingering holes can occupy nearby positions at the tube, though three works too. The cross-fingering holes are expected nearer to the pressure nodes and the half-wide tone holes higher on the tube. Here blue means a closed hole. The corresponding key action varies. The number of lone open holes increases regularly with the modes: Zero for mode 2 (but optional octave hole) One for modes 2+3 and 3+4 Two for modes 3+4+5, 4+5+6, 5+6+8 and 6+8+9 Three for modes 8+9+10+12 The reflection improved by more open holes eases the emission of high notes. The low-intonating mode 7 isn't used; combine with the slightly high modes 6 and 12? The fingerings don't limit the range; written F# is already ambitious. An aspect sketch and hints to the construction may come some day. Marc Schaefer, aka Enthalpy

Don't tinker with hydraulic fluids if you want your circuit to work longer than a few hours. The hydraulic pump fails after few weeks if you don't make a complete hydraulic fluid, with anticorrosion, defoamer, viscosity index, and so on and so forth. I know it from experience. Water-polyglycol mixtures are available commercially ("hydrolube" is one trade name among many) and already made for hydraulics uses. Instead of "water density", it would be better to accept the density of existing hydraulic fluids if possible, especially oil. There are many. Check manufacturers and Wiki for "hydraulic fluid" and "brake fluid".

SpaceX: nobody know what their plans are. What they tell at AIAA meetings and Press conference is designed to make buzz. You don't even know if they plan to go to Mars. So you should not deduce any technical choice based on their claims. More generally, science and technology can't work on rumours, assumptions, impressions, interpretations of supposed reasoning by other people. It boils down to "how". You decide how you realise a function and convince with shapes, figures... that it's realistic. Anything else would fit in an annual conference of space frenzy, but would not be science nor engineering. Here you accumulate bizarre deductions on wrong hypotheses based on dubious claims. The result isn't convincing. I've already provided figures about the travel time to Mars using the sunheat engine. Why add your impressions to this and lead to wrong conclusions? Check my figures, and if they're wrong, tell us where and why. Ah, and I'd prefer fewer acronyms. I know that my fellow engineers and scientists love to use and misuse them everywhere. It could be by imitation, to look like a true one, but it's very bad practice.

Even before the mechanism for release and catch, I want to see how the tether is built. A description for a mechanical engineer, you know: what material, what shape, how much stress at 1680m/s tip speed and what mass. I remind that tethers of carbon nanotubes are science-fiction, and their performance essentially unknown. The best existing material is graphite fibre. Then, you might provide details about residual speed and height.

You might want to re-think this. But not the main difficulty anyway. The low-orbit speed is 1680m/s around the Moon and rotating a part with that tip speed is extremely difficult. I emphasize that we have no carbon nanotubes is significant amounts, nor do they have interesting properties as a rope up to now. The best materials is graphite fibre composite, which would require a thick base to attain such a tip velocity. That means: tons of rope for kg at the tip. Then, I want to see convincing details about the residual height and speed, and how the payload survives the landing. Such detailed descriptions could make science. Until then, all these rotavators remain science-fiction. ========== The other aspect is that a lunar base must be buried or shielded in some way, and then it keeps naturally a good temperature during the two night weeks. Electricity for other uses can come from batteries: a few tons suffice.

The Moon's escape speed in 2380m/s, so the smallest velocity, dropping from low orbit, is 1680m/s. Nothing keeps its shape at this speed, and I don't imagine how a "grazing" impact is achieved nor what it brings concretely. Effect on the Moon: the same as any impact, it makes a crater, wide but not very deep, open to the sky, the radiations and the meteorites. Long effort before it's something usefu, and I don't see why we should add craters on the Moon since there are already enough ones.

Power is not torque.

Glass too. More precisely borosilicate, commonly called Pyrex, so heat differences won't shatter it. I don't see affordable alternatives, so you must live with the fragile material. Here too: proper kind of glass and adequate shape. Avoid concave sharp edges and long thin parts.

Some boats have 400Hz too. Trains get electricity at 25Hz in Switzerland and 16Hz2/3 in Germany. Other parts of the world have other frequencies than 50Hz and 60Hz. Just for fun (when you're not involved): Japan has (or had) different electricity systems among the islands. And for fun too: The Itaipú dam produces electricity, 50% for Brasil and 50% for Paraguay. But since Paraguay covers all its needs with 2% of the production, it sells the rest to power-hungry Brasl. Of course, to let Brasil pay, the switch and power meter are located in Paraguay, so the current first goes there, then crosses back. Little difficulty : Brasil has its current at 60Hz there but Paraguay at 50Hz and the 10 alternators from 20 match. The choice was to transport everything in DC to São Paulo. ---------- Frequency limits: for a computer power supply, no worry. The input is a resonating circuit that often guarantees both frequencies and voltages. Most electronic equipment won't see the difference. But electromagnetic machines do make the difference, because d(phi)/dt depends on F. A transformer for 60Hz may over-saturate its iron core at 50Hz hence draw too much current. A synchronous or asynchronous motor runs at the wrong speed, and this changes the counter-electromotive force, which may not match the main's voltage.

Thanks DrP! PVC and PVDC look reasonable but I'm confident I recognized the odour when I burned the polymer. I smelled like burning paraffin, which polyolefins do and also polymers containing oxygen like hot glue gun. The flame and lack of smoke also hint to chlorine-free material. NMR: I have a university in the vicinity with a chemistry department. Whether they're interested in my tinkering? At least, reproducing the synthesis would be easy.

Do you see any chance that I got a sort of polyketone, just one -CH2- shorter than the usual one obtained from CO and C2H4? At least the flame's smell was compatible with C, H, O but not with Cl. Resembling PVDF, maybe the short polyketone is ferroelectric too? It depends on how the chains arrange in the solid and on the temperature. The usual polyketone, with one -CH2- more, is too symmetric to be ferroelectric. A ferroelectric material keeps a permanent polarization after the application of a strong electric field. Then, it behaves similarly to a piezoelectric material, or even better in most applications. Uses as memory devices were investigated too. The short polyketone would avoid fluorine in the production and destruction. And if my teenager tinkering really produced it, then it's facile. Marc Schaefer, aka Enthalpy

The Sabatier reaction is known, yes. Engineering is an other story. As soon as 50% of the hydrogen doesn't make methane, the conversion to methane needs more hydrogen than if you burn it directly in the rocket engine. And then you must transport the plant there and operate it, plus land the crew at the proper location. Once again, "they have their reasons" is not a receivable argument for me. Guesses are nothing. How do you achieve it, how heavy is it? Your "energy density" is just irrelevant. You should re-consider the mass of a gas tank. Put figures on it. Without figures, there is no science nor engineering. You mistake liquid ammonia with an ammonia solution. And on crop, it kills regularly. Putting 10t on 100t in a launcher would be insane. Refuelled: how? "Short hop": how far, how much propellants, obtained how? How do you reach such bizarre conclusions? "Seems, probably, probably". What script, delta-V, mass? The whole attempt makes me uneasy. The general impression is that you have less expertise on the topic than would be necessary and hope to compensate it by software found on the Web and by compiling documents. On a project that has never been done before, assembling existing data doesn't bring a solution. ========== You might want to explore the possibility of bringing water from a main-belt comet to Martian orbit and electrolyse it there to make propellants for a descent-ascent module and for a return module. I checked there how much can be transported http://www.scienceforums.net/topic/76627-solar-thermal-rocket/?do=findComment&comment=757109 addenda and corrections followed http://www.scienceforums.net/topic/76627-solar-thermal-rocket/?do=findComment&comment=757663 I didn't put figures on such a Mars trip. and in case you still consider the opposition mission, you could evaluate if this radiation shield brings something http://www.scienceforums.net/topic/80982-shield-astronauts/ for which you'd have to evaluate the improvement on Solar radiation and check if the extrasolar one is acceptable.

I stand by my figures, especially the thrust versus concentrator size. Whether they fit the decisions and policies of an administration is no proof for anything. Nor do I need nor seek bad designs elsewhere to consider them as limitations for other attempts. I'm not interested by a refractor concentrator. No perceivable usefulness, so its mass and losses are no hint to anything. Yes, more Isp needs more power. The sunheat engine allows to adjust the trade-off in flight, but I've seen no clear usefulness. From the trials cited in 20160003173.pdf: An inflatable concentrator is bad for high focus temperatures. I take a rigid one. Several concentrators per engine are dangerous for the craft or vessel and difficult to test. Sunlight can't make the proper temperature on Earth. How did they figure such a thing? Their results reflect that. Their nozzle is too small. They have no ruminator. It remains to see if their colder faceplate radiates little, and how much heat is lost through conduction to the faceplate. I don't understand the alleged advantages of the refractive secondary concentrator. But its obvious drawback is to limit the temperature. The Isp improvement through dissociation results from absorbed heat primarily, not from the average molecular mass. Their mass estimates are way off. A Gso launch does save a lot through sunheat engines. Yes, fairings must increase. Or better, make a separate sunheat stage, as I suggested here. They only consider Leo-to-Gso missions, too bad. => Many bizarre choices, misconceptions and half-thought designs. This led to wrong conclusions. => This is why I don't seek figures elsewhere to decide if a potential technology is interesting. Concentrate light on solar cells: The light is filtered by wavelength, and then the efficiency of the solar cell is hugely better. 40% refers to the power intercepted by the concentrators. Light with bad wavelength is rejected. When used at Saturn or even Neptune, no overheating to fear. Not only is the sunheat engine extremely performant, it's also the sole and only solution beyond chemical propulsion.

The bassoon is by far the woodwind most in need of better fingerings, but also the most difficult to improve https://en.wikipedia.org/wiki/Bassoon Heckel made the last significant change a century ago. It starts at Bb like many woodwinds but the second register begins higher and toneholes go to F, so the first register spans 20 notes plus Heckel's three holes for high notes. Its cross-fingerings span a major twelfth for a total of three octaves and a major sixth - the official range for which standard fingerings shall intonate decently; most bassoonists tell "four octaves", "four and a half", or "five". Many of the tone holes are tiny; some are very long too (about 60mm, almost a quarter wavelength at high notes) hence inductive and sit consequently very high on the tube, working almost like an ocarina. Consequently, the bassoon has the most complicated keyworks, with many connections, alternate fingerings, and keys where you don't expect them. A fingering chart for the Heckel system: http://davidawells.com/resources/fingering-charts/ 9 and 4 keys at the thumbs, so charts show the left front, left rear, right front and right rear keys - part of bassoonists' snobbery. Note the flicked keys, half-open hole, four keys pressed simultaneously by one finger, resonance keys, numerous holes closed at rest, a cover for three tiny holes at once, and writing on bass, tenor and treble keys. Detailed views there: http://www.clarissono.de/CssArchiv/CssTerminologie/CssTermFagott/FagottTerminologie.pdf This is how the range splits, including 16 holes able to open while the next lower is closed: These fine people tried to put big tone holes at the proper places, often on a wider bore, and didn't succeed: Triebert. His failed bassoon attempt is exposed at the Brussels museum. Sax. His failed bassoon attempt is exposed at the Paris museum. Gautherot. His sarrusophone sounds... It doesn't resemble a bassoon. Guntram Wolf, during the computer era. He didn't market his bassoforte. So let's see what can be done with the narrow tone holes and bore that double reeds demand. But since I want no closed tone holes below the closed-open transition, the hole positions and dimensions (aka "scale") will differ. This affects cross-fingerings and needs an important development time. Hole diameters and lengths should vary slowly with the position. Consistent sound quality needs narrow holes at the throat, but I'd have holes of decent length with predictable effect on high notes. Presently, inductive holes let the beginning of the upper register sound half a tone higher than flute logic tells; could this be a tuning goal? ========== Here each upper finger closes one cover open at rest or opens with the proximal or medium phalanx one other cover closed at rest. The second set of keys is adjusted to each musician. Each thumb can close 1 to 6 of the lowest covers, so the musician alternates the thumbs like little fingers on the clarinet. Both thumbs manoeuvre the register key(s) too; adding some near the reed shall help play the contraforte http://www.guntramwolf.de/downloads/contraforte_e.pdf Does a fourth tone hole fit at the wing joint's top? Then all the fingerings can slip half a tone higher and the thumbs manoeuvre one cover more. Here are fingerings for the first and second registers. And these would be fingerings for the upper register according to simple flute logic which the bassoon does not follow due to its narrow tone holes: it tends to play cross-fingerings half a tone higher or more. So the diagram is merely an indication that these fingerings offer flexibility for cross-fingerings and cover the whole range - they even overlap nicely. The Heckel bassoon needs action at the thumb covers for some high notes. With thumb covers all open, I hope it's unnecessary here. As this fingering is highly regular, it lets choose a steady progression of hole diameter, length and position, which shall permit sound colour, ease of playing and intonation uniformly good. ========== I'm half pleased with the bassoon fingerings I propose here. They need many transmissions between the joints. Don't disassemble the instrument and fold it more? But I like the bassoon shape. Are they convenient? Unclear to me, and difficult to assess on the paper. But they bring holes all open below the transition, positions and diameters of tone holes that vary regularly, fully flexible and regular cross-fingerings for the upper register. Marc Schaefer, aka Enthalpy

An other bassoonist playing the same sonata on a Heckel system instrument: https://www.youtube.com/watch?v=joKtwJL1Xq8 He has a softer sound (and plays damn well too). The difference with the narrower French bassoon remains.

The cor anglais and baritone oboe have a pear-shaped bell https://en.wikipedia.org/wiki/Cor_anglais https://en.wikipedia.org/wiki/Bass_oboe and to my ears, the resulting sound is seducing for five minutes but boring thereafter. So I suggest, independently of the fingerings, to build them with the oboe's conical bell to get its narrow dark sound, and soften the lower notes using the same small holes near the bell as the tárogató has, as depicted there: http://www.scienceforums.net/topic/107427-woodwind-fingerings/?do=findComment&comment=1004315 Marc Schaefer, aka Enthalpy

More thoughts about galling and protective oxide layer. The efficient oxide layer correlates suspiciously with the tendency to gall. It may be the property best correlated to galling. For instance tantalum and titanium are horrible, chromium and stainless steel too, Al-Mg alloys are bad but Al-Cu decent, while most Ni and Cu alloys are decent to good. But there are strong exceptions. Silicon bronze Cu-Si4 is known to gall badly and makes no protective oxide. And among the austenitic stainless steel, much-demanded improvement results from keeping the oxide-forming Cr and replacing most Ni with Mn, which changes very little in the corrosion behaviour. Further improvement, at the Nitronic alloys, results from adding 4% Si to the kept Ni, Mn and barely reduced Cr, which also keeps a very protective layer. So this seems a wrong direction too.

http://www.scienceforums.net/topic/76627-solar-thermal-rocket/?do=findComment&comment=1007124 Where did you see such a thing? A strong electric engine? Why?

On Mars, oxygen would be produced from the CO2 atmosphere, for the crew and maybe the engines. Demonstrators exist already that electrolyse CO2 in a hot ceramic. Trials on the Moon would be too different. Short stay: your choice, your good right. Methane can't be liquid above 191K, whatever the pressure. It demands active cooling on the too warm Mars. Storing gases is excluded because the tanks are too heavy for space travel. Even if burying in the chilly Martian soil, some fuels like RP-1 "kerosene" would freeze; concentrating sunlight is a better option, and low-freezing fuels a safer one. The density of rocket propellants isn't a primary concern. Hydrogen serves on most launchers, even at the first stage on Delta. Produce methane on Mars: smart people for sure, but nevertheless I say it's a bad idea. Very difficult, and bringing a bit more hydrogen is much simpler, safer, probably lighter. Remember hydrogen must be brought and stored to produce methane anyway. Glider and escape: have a look at the IXV. Put it atop a launcher without fairing but with an escape rocket on top. Accurate landing: a mission to Mars was lost recently because of inaccuracy. 18 successes on Earth prove less than 95% reliability for that single failure cause. "We landed the crew too far from the return vessel and can't send them anything timely" would be disastrous. Zubrin's team foresees a rover but neglects the lack of highways and the insufficient radiation shield. Other companies exist outside SpaceX, with engines for varied fuels. The RD-170 pushes 8MN with RG-1. Methane is negligibly more efficient but much more dangerous, while RP-1 doesn't catch fire with a lighter. And please forget ammonia, it is t-o-x-i-c, didn't you know? "If you're saying that chemical rockets are more efficient than solar thermal for LEO to staging area": No, I didn't.

Hi both, It is done for nickel-cobalt alloys. These elements have very close properties, including the redox potential. Instead of pulses, I'd use currents, which can be regulated exactly too. I had hoped, but never tried, to run the multiple-sources deposition for long enough that the bath gets richer in the metal more difficult to deposit due to the difference in redox potential. At some point, and if the metals aren't too different so some equilibrium is reached, the proportion of dissolved source must impose the proportion of the deposition. I'd have put the desired target only then. Though, I've heard only of Ni-Co, not even Ni-Cu, so the process can't be easy. What does exist is a deposited layer that incorporates other elements from the bath, and not only metals. Contractors can embed particles of Ptfe in Ni for instance.

Hello dear friends! Heterojunctions are produced by deposition (often epitaxy) of a semiconductor on an other to achieve excellent components. Silicon being the most commmon material, Si1-xGex is used as a material with a different bandgap, despite the drawbacks of germanium: lattice constant very mismatched, main electron valley in <111> direction versus <100>... As opposed, the GaP crystal is known to resemble Si closely: same zincblende lattice (called diamond when the atoms are identical), lattice constants matched to 500ppm, main electron valley in <100> direction too. GaP's bandgap is also bigger and differs more from Si, nice. http://www.ioffe.ru/SVA/NSM/Semicond/Si/index.html http://www.ioffe.ru/SVA/NSM/Semicond/GaP/index.html http://www.ioffe.ru/SVA/NSM/Semicond/Ge/index.html So it is seducing to produce epitaxies of GaxPxSi1-2x on Si. The less distorted crystal should conduct better, and the valley in <100> direction should accept a bigger proportion x. Since these heteroepitaxies aren't common up to now, many difficulties must arise; I try to address one here, the exactly equal amount of Ga and P. It won't happen naturally because Si crystals readily host the small P atoms but not Ga, and the resulting doping in Si must be so huge that no component can be built. My suggestion is to use an already formed GaP single-crystal as an epitaxy source. Semiconducting GaP is exactly balanced, perfect for a usable epitaxial layer. I imagine something like a short-pulsed laser could evaporate GaP to keep the proportion, and evaporate Si from an other source, for simultaneous deposition on the epitaxy target. The GaP source may evaporate one element more easily at the beginning, despite the laser pulse atomizes a volume of solid with almost no selectivity. The initial surface of GaP may also be less clean. The answer is to have a shutter and begin the deposition some time after beginning the evaporation. If the evaporated P and heavier Ga atoms fly to the epitaxy target for 100µs and 150µs (as an example) after the laser pulse, the epitaxy composition may fluctuate over the time hence the depth. The answer is a pulse repetition rate much faster than said 100µs. As 100µs flight time may spread as a 50µs Gaussian, 50ns repetition rate will smooth the distribution to far better than 1ppm. The evaporation rate of Ga and P differ at the epitaxy target, which shouldn't hence be too hot. Well, maybe. Marc Schaefer, aka Enthalpy

To accelerate a craft for weeks, the sunheat engine uses an energy amount impossible to store. But to raise or lower an apoapsis, escape a celestial body or get captured, the smaller energy for short kicks can be obtained during idle time and stored, as already noted on Jun 10, 2014: http://www.scienceforums.net/topic/76627-solar-thermal-rocket/?do=findComment&comment=810218 More details now. ========== Lithium-polymer batteries can store 475kJ/kg more or less. Before a kick, the concentrated light can be split by wavelength and sent to small solar cells of varied bandgaps for >40% conversion. http://www.scienceforums.net/topic/76627-solar-thermal-rocket/?do=findComment&comment=826983 Other uses welcome the efficiency and collecting area far from the Sun. To raise the apoapsis in Earth orbit, each sunheat engine without storage consumes 20kW during 1200s. A battery providing as much energy to double the force weighs 50kg. That's worse than adding one ~30kg engine. But: Fewer engines are easier to deploy. Operation during an eclipse season gains time and provides flexibility. Electric pumps for the propellants making the escape chemical kick justify 100-150kg batteries if starting with 18.5t at Leo, so 8 sunheat engines get 30% more energy per kick at zero extra mass, and the added thrust can concentrate on the best 1000s. At Mars (1.52AU) the battery is already lighter than the additional engine, at Saturn (9.58AU) the battery advantage would be 50*, if 1200s kicks were meaningful there. Other uses cherish the good electricity production at the outer planets. 700W from 8 concentrators at Saturn. The combination isn't a resistojet, because direct heating by sunlight is kept, as it avoids the wasteful conversion to electricity. Far better for the long pushes. The engine can use the same chamber for both modes or not. The described regenerative insulation methods apply. ========== Melting a metal stores heat too. Simpler than making electricity first, but heavier, and they probably dissolve their tungsten container. Tmelt Hmelt K kJ/kg ------------------- 3290 Ta 159 2896 Mo 286 ? 2750 Nb 288 2506 Hf 143 ------------------- One hope is to find some eutectic of tungsten with one or several other elements giving the desired melting point, as inspired by Sn-Pb-Ag solder not dissolving Ag. I didn't find credible data about Hf-W nor Nb-W eutectics, only calculated data; Mo-W and Ta-W seem to make no eutectic and be fully miscible. ========== Melting a ceramic stores more heat. Beware data is inconsistent. BeO is toxic, and B is expected to corrode W. More complex formulas are possible. Mixes shall bring missing melting points. Tmelt Hmelt Hform K kJ/kg kJ/mol --------------------------- WO2 -285 Ta2O5 -409 NbO -406 --------------------------- 2988 ZrO2 706 -550 2915 MgO 1920 -602 2703 SrO 674 -592 2500 Y2O3 463 -635 2318 Al2O3 1071 -559 2247 ZnO 860 -351 2218 MnO 767 -385 --------------------------- The last column shows the heat of formation per mole of oxygen atoms. If the melt's metal binds more strongly with oxygen, it could be compatible with W; computing the chemical equilibrium would be better if data exists. For water propellant at a lower temperature, container candidates are Nb or better Ta, possibly with W coating on the melt side, and some ceramics. As heat storage keeps the engines hot for months, the temperature should rather be 2700K or 2600K. With the ceramic fully molten, 2800K remains possible during week-long accelerations. MgO stores 4* more energy than a battery and is 2* lighter than an added engine for perigee kicks. The advantage increases at the outer planets. ========== The freight transport to the Moon took 10 months of perigee kicks with 10 sunheat engines http://www.scienceforums.net/topic/76627-solar-thermal-rocket/?do=findComment&comment=1007124 Let's replace 4 sunheat engines by 120kg of MgO heat storage: the 1.55* stronger kicks gain 3.5 months, and thanks to the shorter kicks' efficiency, we land 2% more mass. Marc Schaefer, aka Enthalpy

Well, there are many possible options (plus the ones still not thought at), and even more combinations. I doubt that propellants produced on the Moon and brought to Earth-Moon Lagrange point are any cheaper than if brought from Earth. And until I see a convincing proposal, I consider all cannons and variants are unusable. You had initially the intention to evaluate a short stay mission. Its big delta-V constraints everything else, so you might begin with these figures and their implications on the propellant mass and so on. The speeds differ a lot from the Hohmann transfers illustrated in the second post. Please note that my xls supposes no flyby at Venus, but most scenarios seem to gain from it. And... I don't see any advantage in a short-stay mission, while the drawbacks are huge. Are you the last person putting time in it? Methane and oxygen need active cooling to store in the Martian atmosphere, and I suppose in Earth and Mars orbit too. Once you have active cooling (a vital technology for space exploration, we should have had it for decades, wake up!), hydrogen is possible too; it's only a matter of tank mass and cooler difficulty. Here's a well insulated tank http://www.scienceforums.net/topic/60359-extruded-rocket-structure/?do=findComment&comment=761740 But if sticking to dense fuels, some are about as efficient as methane, safe on Earth and won't freeze on Mars http://www.chemicalforums.com/index.php?topic=56069.msg297847#msg297847 http://www.chemicalforums.com/index.php?topic=56069.msg272080#msg272080 (images only if logged in) while the toxic oxidizer Mon-30 is storable on Mars. Aerobraking brings an awful lot, both at Mars and Earth. You must decide if aerobraking from the transfer speed or from orbit. If aerobraking from a fast transfer, you need wings to achieve downlift so the vessel stays in the atmosphere long enough to permit a bearable deceleration. It's probably not compatible with sunlight concentrators, so some choices are hard. But it has already been combined with a capture by Mars rather than landing. In my scenario, the crewed vessel aerobrakes, the preset modules don't. And you must decide whether the capsule or plane serves again at Earth. If presetting hardware at Mars, you must decide whether on orbit or on the ground. Meeting on the ground suppose to land accurately, which is a risk, while orbiting hardware can be redundant and landed where and if needed. My opinion is very clear. If producing propellants on Mars, you should check what power it takes over how long just to make oxygen. Ouch. Solar energy would need many big concentrators. And I consider methane is far too difficult and risky, while a little bit more hydrogen can be brought from Earth and consumed at the engines. Much safer, probably lighter than the methane plant. http://saposjoint.net/Forum/viewtopic.php?f=21&t=1953#p36418 If meeting at Lagrange point (why? Isn't an elliptical Earth orbit better?) I'd bring much mass there by the craft with sunheat engine and little by the vessel with chemical engine: the astronauts, their radiation shield, their beds and suits, water and life support - but probably not propellants. And I have nothing against the Raptor, but it may be oversized for Earth escape, whose kick can last 600s: compute with the consumption rate. I found a few RL10 are strong enough, they burn the same hydrogen as the sunheat engine and offer a better ejection speed than methane. A chemical engine is more efficient to escape Earth (it gains like 20-30%). I've evaluated the best share there http://www.scienceforums.net/topic/76627-solar-thermal-rocket/?do=findComment&comment=818683 which you can compare with the sunheat engine alone there http://www.scienceforums.net/topic/76627-solar-thermal-rocket/?do=findComment&comment=1009859 it gains 20-30%, interesting. The same holds at Mars! You choose if you use the same engines at Mars. And for a Hohmann Earth-Mars, the optimum is "nearly all' the transfer speed by the chemical engine, which translates to "all" since the optimum is wide, the sunheat engine only raising or sinking the apoapses. But an accelerated or a lowered perihelion transfer does use the sunheat engine during the transfer.

I've re-read my documents, and the sunheat engine raises and lowers apoapses with kicks at periapses. This is more efficient than spiralling, but longer. In my scenario, the manned vessels escape Earth or Mars by chemical propulsion (oxygen and hydrogen) to go fast, they accelerate by sunheat engines, and aerobrake at both destinations. So the transfer differs from presetting the return vessels and the descent-ascent modules on Martian orbit, which is slow. The manned vessel meets the preset hardware on Martian orbit. I don't use any Lagrange points nor in-situ propellants. My scenario depends on no prior activity on Mars nor on landing at an accurate location, and offers redundancy. Maybe other scenarios save some launch mass, but check the risks too. If planning to use propellants produced on Mars or the Moon, consider burning hydrogen brought from Earth and producing only oxygen locally. It's almost as efficient as producing methane if the yield were 100%, and it's way simpler. No overcomplicated heavy plant brought to Mars. Electrolysis of dioxide in hot ceramic produces the oxygen, proven technology. http://saposjoint.net/Forum/viewtopic.php?f=21&t=1953#p36418 obvious choice to my eyes. ---------- Hydrogen versus methane: the transit time improves very slowly with the delta-V and the specific impulse. It's better to save mass instead. Aerobraking, sure. Even more so if the transfers are accelerated. Transfer times: the figures by SpaceX are surprising. They may correspond to very favourable configurations of Earth and Mars. Anyway, don't compare them with other estimates that base on circular orbits. It would be wise to run a computation with SpaceX' figures, to check by how much they cheated optimized their example. Please keep in mind that the announcement by SpaceX was part of a show. Nobody knows outside the company if they're serious about a Mars mission, nor whether the Raptor engine is meant for the BFR, or rather for a smaller launcher - nor how much soot plagues their gas generator at the Raptor. For Tesla's gigafactory, Musk had said "car batteries" but meanwhile he sells them for home and grid storage. About landing the Falcon 9's first stage on a barge, which is an overclever enabling solution, they didn't tell in advance, and once everyone saw it, they told "temporary solution".