Enthalpy

On Earth, waste permits us to grow food in a closed material cycle, with Sunlight input. Alas, this has consistently failed in space up to now, and even in the Biosphere 2 experiment, big and on Earth. http://en.wikipedia.org/wiki/Biosphere_2 Until this closed cycle can be reproduced, an imperfect one looks possible. From energy and waste water and dioxide, we can produce chemically glycerol or other rudimentary food. Not healthy complete food, but it's a source of calories as good as sugar, and is permitted and used in industrial cookies. For a fraction of the waste, that would be a more valuable use than propulsion. Ion propulsion prefers heavy ions, and if possible of easily ionized atoms like xenon and rubidium, because ionization takes much energy adding to the useful one that accelerates the ions to propel the craft. Hydrogen, oxygen, nitrogen, carbon available in waste are not the preferred atoms for that use. Though, ion mass spectroscopy includes a generator of molecular ions, which are heavier than atoms. That might benefit to ion propulsion if feasible: waste is first converted to semi-big molecules like toluene, and these are ionized once and accelerated. Marc Schaefer, aka Enthalpy

Cyclers are just less straightforward than I thought. Their proponents are well aware of the limits and have already suggested workarounds for Mars - but not really simple with several vessels, sometimes a hybrid operation with aerobraking and slingshot; always with regular orbit adjustments and gravity assists. Having added all this, their interest becomes less obvious. Maybe your contacts could also tell how much a transfer to Mercury costs, in the nearly-vanilla scenarion, where only Venus provides gravity assist, only once per leg? Much easier to tell than a cycler, such a scenario permits a quick transfer and a short stay, and must cope with preset descent-ascent module and return module, using accessible propulsion technology. ---------- Back to ionizing rays. I thought the difficult ones were cosmic rays which are hard to shield, but scenarios to Mars worry about Solar storms, suggesting that Solar rays are the main danger. Hence I wonder about a mission closer to the Sun than Mars is. ---------- Here a hint to a thermal design near Sun and Mercury. to suggest that a spacecraft can maintain a decent temperature in any circumstance, because some directions can be protected against both Mercury's heat and against Sunlight. Beware this is just a sketch, and thermal design is tricky. Here I don't detail the temperature of the tips of the shaders, but they do radiate towards the cooling zone. Though, these questions are known in spacecraft thermal engineering. Maybe a mobile sunshade is necessary, hopefully not. My conviction is that a convincing solution, working in all circumstances near Mercury, must be feasible - and that I'd prefer to rely on a better thermal design than on a special orbit, for it offers better alternatives if something goes wrong. Same argument in favour of preset modules, which can be redundant. Marc Schaefer, aka Enthalpy

Hi Richard, welcome here! 14C datation doesn't apply properly to that short timescale. I though a different isotope method fits centuries better but I didn't find which one. For very recent items, you can search for radioactive fallouts from atmospheric bomb test. That would at least distinguish a medieval book from a recent fake.

Could someone explain me why chemists are so uneasy with diethyl ether? I understand it can form peroxides, is flammable, a bit toxic... But households use it commonly, and I haven't heard about so many related accidents in houses. 50mL suggested here are a small bottle as available from the drugstore. Ullage would limit the overpressure.

Nearly all electrons are already paired in a metal at room temperature. So are they in a plastic, a ceramic... Though, these materials are not superconductors, so the usual short explanation is just too short. Anyway, I don't see neither why a boson would travel unhindered.

The OP wrote: "I want it to be quite heavily based on fact."

Cooper pair: search for BCS theory. In BCS, electrons are said to pair because they deform the crystal. Some sort of pairing is to be more favourable, in combination with the deformation. No idea how this relates with spin.

Slightly different approach: as physicists working on steam engines observed that work, unburnt fuel, later electricity, and others, could convert into heat, and always into the same amount of heat, they found useful to call each one a "form of energy", with the sum of all forms being conserved. Then they added a second law telling that only a fraction of heat can be harvested as work, the rest staying as heat. Up to now I've found convenient to consider light as energy. Or maybe it's a matter of wording: energy is located where light is, not at the emitting nor receiving objects, during the propagation of light. During propagation, energy is stored where there is no object, in vacuum.

Crews aboard space stations presently live to an amazing extent in a closed materials cycle, to which Sunlight brings the energy. Water is recycled. Extracted from waste and exhaled humidity, purified, and reused as washing, drinking and cooking water. The bottom line is a net production of water resulting from food consumption by humans. Carbon dioxide is extracted from air. I'm not completely sure it's done, but getting the oxygen back is known technology. Again, food consumption by humans results in a net production of dioxide, or after processing, carbon. With the necessary energy input, reprocessing would leave carbon and water, or more easily, some compound of both. ---------- The amounts are small, in the order of 1kg per day and person, so they won't lift a spaceship from a planet. The available power also limits the rate of reprocessing. So my proposal would not be to transform the waste into a chemical fuel, but instead to use waste as a fuel for a high-impulse propulsion. Such a propulsion takes power, often as electricity, to eject the working fluid at a speed unattainable by a combustion. It's power-hungry but mass-saving, as compared to a combustion rocket. One example is ion propulsion. An other is a resistojet. Have a look at Wiki. The obtained thrust is faint, very few newton at best, but it lasts for long, enabling strong speed variations. As a beginning, it can serve at a space station: reduce the resupply need. It's just that existing engines are picky about their fuel. The benefit of using waste that way would be to save the fuel mass for the high-impulse propulsion. Instead of throwing water out and accelerating xenon, take only food on board, and accelerate the waste. It saves mass. Now I know what happened to Iapetus... Marc Schaefer, aka Enthalpy

What shall mean "heat" for two particles becoming none? What do you call "close enough" for photons? The ones we receive from distant stars are square light years wide. More generally: why formulate wild assumptions as claims?

This limit to cyclers is well-known, as is clear from Wiki's cyclers to Mars for instance. Their operation is, as a consequence, less favourable than one trip per synodial period. The best operation imagined is indeed to choose their period so that both planets permit a transfer whose apside line moves little. As this can only be approximative, well-adjusted planet flybys shall give the cycler the residual correction. Since the period needed for the cycler does not match a Hohmann transfer between both planets, its orbit around Sun is to pass by one planet but overshoot it. Of course, the relative speed increases a lot. And less frequent opportunities mean that a short stay on the distant planet requires an other cycler to come back.

The kinetic energy of rotation would create gravity. To be significant, it would require a rotation speed approaching c, which a piece of steel can't withstand, nor even a molecule of hydrogen. Then, the rotating matter would still be visible. Maybe very little matter would create much gravity if its speed is very near to c... I imagine only the gravitation of black holes to do this, and matter near their horizon is negligible as compared with the hole.

OK, go on without me. Good luck to understand QM through philosophical considerations and newspaper-class knowledge, if you hope such discussions will help you.

Mamma mia! Since when is h an energy? And: do you imagine a quantization independently of an object?

10 drops per litre, I say: no effect. Gasoline in Diesel isn't very harmful. Diesel engines are rather tolerant even without tuning; I ran mine with 1/3 rapeseed oil. They need fuel with low ignition temperature, reasonable viscosity and no particles; recent engines must run with low fuel-to-air ratio, which precludes vegetable oil. Better: my Diesel's user's manual tells I can run on plain kerosene, and that in cold winter, I can add up to 20% gasoline in Diesel oil to thin the fuel. Diesel oil in Gasoline is more of a worry, because Diesel must ignite easily and gasoline must not. Diesel oil would raise the cetene and lower the octane numbers. So don't exaggerate this one, since early ignition destroys an engine quickly.

The hypercube networks I suggest now keep feasible where a full matrix is too big. http://en.wikipedia.org/wiki/Hypercube With less wiring than a full matrix, they offer about the same throughput. Their latency may be worse, or maybe not, if smart serial links manage the destination addresses and the collisions. A hypertorus would have been possible as well; 3 processing nodes per loop outperform a hypercube, 5 save wiring. http://en.wikipedia.org/wiki/Hypertoroid#n-dimensional_torus Present supercomputers are hypertori with 100 nodes per loop, and users complain about data transfers. ---------- 131k processors for 1 petaflops fit in 4 person-sized cabinets. Each cabinet holds, stacked with 30mm spacing, 64 boards of 512 = 2*16*16 processors+Dram chips. The chips have at least 17+17 serial links out and in, of which 9+9 serve within the board and 8+8 go to connectors and, via cables, to other boards. The hypercube (or a hypertorus) lets group on a board one link from each of the 512 processors to a 512 signals connector and have one pair (for full duplex) of 512 signals cables between two board. Each of the 256 cards bears 2*8 connectors and communicates directly with 8 network neighbours - which can be geometrically remote, since we have 3 dimensions to arrange a board hypercube of dimension 8. There are no network boards, no cable spread nor confluence, and here no integral repeaters. The 25mm*10mm cables have 17 layers of 32 signals. The boards are >400mm wide, double the cumulated cable width, to accommodate the connectors and permit cables to cross an other. At the worst height, 84 vertical cables run within a cabinet, so 20% filling factor needs 0.26m wiring thickness. 2*2*64 = 256 horizontal cables run between the 1.9m tall cabinets, taking 0.17m wiring thickness. The 1m cables cost 5ns, as much as transmitting the destination address twice over a serial link. Connectors facing an other at one board's edge could carry the in and out signals to one other board, and then half of the boards could be upside down depending on the parity of their hypercube position. Or we could route the up- and down-bound cables clockwise, right- and left- anticlockwise, with all boards up, and their outbound connectors up left and down right. Arranging the boards in binary sequence according to their position in the hypercube seems better than in Gray sequence. Connector positions on a board would better not correspond to one dimension of the hypercube, but rather be allocated on each board to ease interboard wiring; the processors could sense it at powerup and adapt. The destination address of a message could begin with the chip address within a board, but with the board in the cables. All this mess is imperfectly clear to me, but must be known if big hypercubes have been built. At 3.8GHz, each 64b scalar Cpu+Dram chip shall draw 6W, because six 256b 3.6GHz cores need 130W presently - without the Dram but with wide fast interfaces. This sums to 800kW for the computer, 200kW per cabinet whose supply at the top can receive three-phase mains and distribute 48Vdc through 50mm*10mm aluminium bars. Quiet liquid cooling, managed at the bottom, is easy; transformer oil suffices. Signal cables can run from the boards' rear edge, while power and cooling can connect to the front edge and run at the cabinet's sides. ---------- 1M processors for 7 petaflops fit in 32 similar cabinets, here as 4 rows of 8. The 2048 boards widened to >550mm have now 11 pairs of connectors. 8 cabinets side-by-side need now 5*2*64 = 640 horizontal cables, or 0.34m thickness filled to 25%. 2*2*8*64 = 2048 cables plunge straight to the floor and run in it between the rows; they take 0.29m thickness filled to 40%; integral repeaters look necessary for these cables. This sums to 0.92m wiring thickness for 0.5m long boards. At 3.5GHz, each scalar Cpu+dram swallows 5W, and the computer 5MW. ---------- Tianhe-2 brings 55 petaflops: 8M scalar processors at 3.2GHz make the equivalent. A different arrangement accommodates the wiring: the boards are vertical, 1024 pieces in a row, and 8 pairs of rows achieve 16k boards. Personnel have alleys between the row pairs, power can run at the middle of the row pairs, cooling circuits below, and all wiring passes over the board rows and, between the rows, overhead. Rows are 31m wide for 30mm board spacing, and (gasp) 700mm wide for 2*14 connectors. Two rows, power, and an alley take 2.2m, so the machine is 18m long. Many cables have an integral repeater. 100ns in some cables are as much as 50 bytes data, or 320 Cpu cycles: special messages, like scaled indexed or bit-reversed access to 2kB of remote data, can be useful. Within each row, 682 cables fill 1.2m height to 20%. Start from hip height, add an access gap, and your reach the adequate height for the 10240 overhead cables, which fill 0.21m thickness to 40%. 4W per 3.2GHz scalar Cpu+dram let the computer draw 33MW, gasp. More Cpu running slower would improve; scalar ones are better used, but the network swells. A full matrix only at the boards would save Cpu pins, emulate a hypercube if wanted, and access disks if any useful; between the boards, a hypertorus would save cables, say as 510 nodes. ---------- How does the hypercube of scalar Cpu+dram compare with existing supercomputers, say at 55PFlops? The floor area is similar. The power consumption is almost double at 3.2GHz. The Dram capacity is similar. If a Cpu+Dram costs a bit more than a Dram chip in a module, then the computer price is similar. But what really changes: - 300PB/s Ram throughput (peta=1015) for easy programming. Addressing modes. - 2.5PB/s network throughput between any machine halves. - 300ns network latency. Existing supercomputers have workstation boards as nodes, but Ethernet is not a supercomputer network. - Scalar Cpu are more often efficient. For instance plain Lisp programmes are supermassively multitask but can't use the Avx. - Simple programming model! This machine would be just task-parallel, with no other limit nor difficulty. I'd say: easier to use well by more varied programmes. In short, more capable. Marc Schaefer, aka Enthalpy

I like the electric pump very much - for special purposes! At a perigee-apogee-escape stage it looks excellent in bare performance. For roll and vernier it's very nice. At a lower stage it only saves development time: rotate the pump with a motor first, later with a gas generator and turbine to save the battery mass. Whatever battery chemistry you want if it's safe! Catching fire like laptops or a recent airliner did isn't acceptable on a launcher neither. The battery must also deliver its charge in 2min (if fist stage), 10min (second) or 24min (escape stage). Li-polymer fills these criteria; others may improve, sure. Merlin 1D's thrust-to-mass is already excellent, hence difficult to improve. Maybe SpaceX want to keep the first stage's performance despite flying back, but other means can be easier than lighter engines: Have turbines of molybdenum alloy. The higher temperature gains 8s specific impulse. Rationale in http://saposjoint.net/Forum/viewtopic.php?f=66&t=2272 on Sun Nov 04, 2012 Gain 50kg/m3 with cis-Pinane (cheap), 3s with Pmdeta (cheap and dense - odour?), 9s with azetidine (volatile and flammable, but less than cyclopropane and methane), 7s with safer special-made simple strained amines (azetidine, diazetidine, diazaspiroheptane, all methylated or cyclopropyled: pick one for good liquid range including a flash point >+55°C). Strained hydrocarbons are less good and more difficult to produce. Have lighter tanks if possible. My extruded construction looks strong and cheap at least: http://www.scienceforums.net/topic/60359-extruded-rocket-structure/ magnesium (it doesn't burn) may fit the task better than aluminium. A gas generator that doesn't soot... but how, and how big a gain? 1000:358 of Ethylenediamine:Guanidine, without any oxygen, provided the recomposition to N2, CH4... wants to proceed? Different pumping cycle... That's an expensive development! My amine recomposition cycle http://forum.nasaspaceflight.com/index.php?topic=26952.0 (my 4th message on 02 October 2011) matches the performance of staged combustion and looks simpler. Have a good wing on the first stage to fly back. A scissor-type, for efficient subsonic back flight. The stage can still land vertically. Then the rocket engine doesn't have to brake the stage. Electric aeroplanes... I had suggested at Physforums an electric power transmission from the power plant to the fans, which meanwhile the big manufacturers work on. But without any kerosene engine, my feeling - within existing battery technology! - is that hydrogen and fuel cells are better, and even are excellent: http://www.scienceforums.net/topic/73798-quick-electric-machines/#entry738806 http://www.scienceforums.net/topic/75102-electric-helicopter/#entry747135 and following http://www.scienceforums.net/topic/79265-water-bomber/#entry772040 (the last sketches group)

My course was not useable. Learnt meanwhile. What I say about the cycler's apside line is that is does not follow the Earth-Mercury synodial period - unless there's some pice of luck I have not seen. The synodial period of 116 days corresponds to a transfer orbit that has every time a different orientation. Earth moves by 114° meanwhile, Mercury by 360°+114°, to offer a new Hohmann transfer opportunity that has turned by 114° - but the cycler stays on its orbit. If you wait 3 periods, the Hohmann transfer moves by 343°, too different from 360°. After 22 periods, you get 7*360° minus 3°, probably too much. Do I get properly that this is a fundamental issue? You might try (nothing simple) to use Mercury and Earth flybys to rotate the cycler's orbit, if any feasible. Or, very hypothetical, let a huge Solar sail rotate the cycler's orbit - but then, a cycler loses its advantage over a one-time transfer vehicle. In case the cycler can't be kept, you may consider a descent-ascent module and a return module preset on Mercury orbit. Gravitation assistance can put them there after years. Then, improved propulsion (Solar thermal for instance) preferably with one Venus flyby may bring a crew there and back. No local resource necessary

You can supply the filaments with DC to remove the hum. Having not compared with my own ears, but knowing how many crooks exploit the audiophiles, I won't risk an opinion about tube amplifiers nor their distortion. Nanodiamonds are still a research topic for electron emission. To my limited understanding, their bulk properties are nothing special; diamond has the advantage of sharp edges and peaks that concentrate the field to favour emission, and nanosize puts more peaks per area unit. Tungsten carbide or silicon carbide might be as good, but we happen to have a working process for nanodiamond. Don't expect a current density as good as a hot filament of thoria-coated tungsten. The present research goal is to make plasma screens, and people try hard to obtain locally the current needed by one pixel, while a hot filament provided the current for a whole screen. For more current, you might replace the rod by a wound filament - as is done with hot tungsten. Apart the higher resistance, it also concentrates the electric field while keeping some area. Put the nanodiamonds on the thin wound wire. The other limit of cold emission, as yet unsolved, is the sensitivity to absorption of residual gas. Field emitters in hard vacuum last for a quarter hour, then they absorb one gas molecule, and it's over. That's the very reason why electron microscopes use warm LaB6 cathodes. Their current isn't as nicely concentrated as from field emitters, but far better than hot tungsten, and they last long. An other use of emissive cathodes is to build micrometre-size vacuum tubes. Quick tubes have been demonstrated, integrated by hundreds on a single substrate, but here a cold cathode seems necessary, so the lifespan isn't solved. Marc Schaefer, aka Enthalpy

A cloth on the mouth, if any possible. Other methods are worse than ice cubes: dessicant in the mouth (hazardous!), cloth in the mouth (doubtful, hazardous, changes the voice). (Artificial portable) wind would remove the vapour quickly enough. If not, you need warmer outside air. Its humidity has no significant effect.

Your gas is not air: too light. At 15.2g/mol it's nearly methane, not ammonia nor neon - so it must be a mix. The exit temperature does need the exact Cp. If you knew the Cp (or Cv, or gamma, or atoms per stiff molecule): Kinetic energy converts into enthalpy, in adiabatic operation. Near 1bar 300K, gasses are perfect so you deduce the temperature rise from the enthalpy change, then deduce the rest from the temperature ratio. The step through temperature is nearly always the best. But this particular case does not need the exact Cp to get the exit pressure. You can keep the Cp as a parameter: - Deduce the temperature rise as a function of Cp. The rise is inversely proportional to Cp. - Write the pressure ratio as a function of the temperature ratio. - Observe that the relative temperature variation is small in your case, even for a monoatomic gas - So you can linearize the P variation versus T variation. - This linearized form is proportional to Cp, so both influences cancel out, and you don't need the Cp. The mass throughput is obvious at the inlet.

This is a newspaper-type approach of QM, which has a long history of making QM obscure. I won't participate.

And this is perfect, because the very nature of particles is to be probabilistic. This is the only surviving interpretation of QM presently, the others having been dismissed experimentally. Even better: what we call particle is a word put on the random behaviour of waves. It is because waves have the ability to concentrate at a narrower location (a detector pixel, say) despite being broad, or over a limited duration despite lasting long, or in one polarization despite having a random one, and more examples of choice, that we say "waves are also particles". Waves keeping spread while interacting would be classical. This doesn't suffice to model our world (historically: the photoelectric effect). We need the ability of wavefunctions to collapse. So complaining about particles being probabilistic is a blind alley. Particles are the random behaviour of waves, plus a way to account some conserved quantities.

OK, if the cycler's period is 4 Mercury orbital periods exactly, it works. Then the Polar orbital plane around Mercury will be parallel to Mercury's orbital speed around the Sun after 4.000 Mercury orbital periods. As the Hohmann transfer arrives and departs parallel to the Mercury orbit, the Polar orbit permit to arrive and leave properly. I wonder about the necessary accuracy between the periods of Mercury, Earth and the cycler. Maybe 10 or 20 days can be compensated once, at some cost, but what happens over time? I understand you want to re-use the cycler for many missions over years, so the cycler must remain synchronous with both, and accurately I would say. Does this allow a cycler orbit easily used to join Earth? Can the smaller vessel between the cycler and Earth spend a time short enough, with acceptable fuel expense, despite the orbit mismatch? (You might try to spread the orbit mismatch among Mercury and Earth). ---------- The Oberth effect is more favourable than this. It just tells that if your craft must have 11.0km/s speed to escape Earth from a low altitude (where your craft has already 7.8km/s if it's in orbit), and you want 7.5km/s above Earth's gravity well, then you only need 112+7.52=13.32 km/s near Earth. Plunging from L2, your craft would already have some 10.5km/s (to be checked) so it need just 13.3-10.5=2.8km/s added at perigee. It tells that fuel at L2 is more efficient than on low-Earth-orbit (provided it has not been brought from Earth...), because from Leo, the craft would require 13.3-7.8=5.5km/s. That's a factor of 2 in the mass. Is it worth mining the Moon? Err, only if the heavy mining machine sent there is lighter than the produced fuel! Note to all students: I nearly got thrown out of my engineering school for being so bad for physics, especially in orbital mechanics, so don't lose hope ---------- I'd like to get relieved from a doubt: Mercury orbits the Sun in 88 days Earth does it in 365 days So the cycler takes 211 days, because its semiaxis is the arithmetic mean, and semiaxis cubed give periods squared. Additionally: the cycler's apside direction is fixed, so it needs Earth and Mercury to be timely at its aphelion and perihelion. To my understanding, the synodial period is useable only if one can choose freely each time the orientation of the transfer orbit. How many orbits of Mercury, the cycler and Earth happen to synchronize? I imagine 4:1 aren't the whole story, it would need something like 16:7:4, which isn't very frequent. And how accurate must this be, if cumulating over time? Or did I miss something?

Hot iron powder? It will remove oxygen, but may begin a bit brutally. What speaks against liquid nitrogen you evaporate as needed? Get 1L from relations having a tank of it.