Enthalpy

The polarization could be worse than elliptic. The laser can perfectly emit light whose polarization hops randomly over time. For instance if gas molecules of random orientation lase, and no mirror nor polarizer forces the polarization within the cavity, then it looks just logical.

Though, industrial-scale biodiesel uses methanol. Does it react more easily maybe? Or is it cheaper where vegetable oil is available? The effect on viscosity and pour point must be small.

That story is extremely doubtful to be polite. First, the measurements are difficult to make. Then, one team made measurements at one place, and an other team on an other continent re-interpreted the data 20 years later, with some filtering, without seeing the disappeared experiment that had by far not been designed for the new claimed accuracy, nor interviewing the experiment's authors. The re-processed data contains fluctuations; the more recent authors analyze some fluctuations that confirm their claim and neglect others that don't. It's visible with naked eye on the curves. This does not fit science. The authors believe to see a seasonal variation and claim it must relate with Sun's distance, while billions of effects depend on the season. A scientist has taken the accurate curves of power produced by the RTG of a space probe that went both near Venus and Jupiter - a distance change better observable than Earth's eccentricity - to observe that the decay rate evolved exactly as expected. No effect of Sun's distance. When searching for a simple experiment that a students team could make on a satellite, I considered checking this "effect" versus the changing distance to Sun over an orbit. The radioactivity specialist I consulted answered to forget said claim. So: don't take this for firm evidence, and don't build any theory on such claims.

This was debated at the beginnings of quantum mechanics. The present consensus (with fringes as for any consensus) is that particles are random by their very nature, and the uncertainty does not result from our limited capability to observe or predict their behaviour. In other words, the particle(s) determines itself when it is "asked" to do so by the observation, but not before. One key hint was given by entangled particles. You can observe the random polarization of two entangled photons that can be vertical, horizontal, right, left... for both. Individually random but both are linked. If it worked anly for vertical vs horizontal, one could claim that the photons decided upon emission what polarization they choose. Then, right vs left detectors would detect 50% of the vertically polarized photons, 50% of the horizontally, without correlation at both detectors. But the same source of photon pairs gives the correlation with left vs right polarized detectors. Then, the simplest (there are other attempts) interpretation is that the polarization is really undefined until the pair decides for vertical, horizontal, right, left at the detectors.

----- Descent to Mars and ascent ----- This is a script from and to a 3390+400km Mars orbit (orbital=3362m/s) and the ground (3.711m/s[super]2[/super], escape=5027m/s, rotation ~180m/s), starting with 60t in orbit. ----- Propulsion The ascent engine pushes 180kN for 15m/s[super]2[/super] through four 0.8m nozzles; gases expand to 4.3kPa and 3445m/s=351s. The descent engine pushes 1050kN for 20m/s[super]2[/super] through four 0.8m nozzles; gases expand to 39kPa and 3010m/s=307s. Adding the ascent engine during the descent would land only 0.4t more but would test it early. The descent engine must be separated before ascent, the descent tanks preferably. A first propellants option pressure-feeds oxygen and 3,7,11-tri(methylaza)-tridecane. The fuel shall be storable on Earth and Mars, and produced easily http://www.chemicalforums.com/index.php?topic=56069.msg272080#msg272080 but it could be pentamethyl-dipropylene-triamine (Jeffcat ZR-40, Polycat 77, mp -78°C) or farnesane, phytane. Ascent oxygen would fit in a graphite fibre compact tank, multilayer insulated and hold by straps in a vacuum shell as in http://www.scienceforums.net/topic/73798-quick-electric-machines/#entry738806 1kg/day evaporation needs a few watts of active cooling. The descent oxygen needs no vacuum, only foam and multilayer insulation. Chamber pressure is 36bar dropping to 18bar, with helium stored at 90K and 240bar in graphite tanks. The ascent tanks and helium weigh an estimated 106kg/t of propellants if the ascent fuel is a radiation shield. Alternative propellants are Mon-33 (toxic) and farnesane, both storable on Mars, pumped by this cycle http://www.scienceforums.net/topic/83156-exotic-pumping-cycles-for-rocket-engines/?p=805383 the exhaust speed happens to be the same, the lighter tanks must compensate the pumps - the real advantage is the flexibility to arrange all tanks, preferably as radiation shields. ----- Descent A 216m/s kick de-orbits in a quarter turn, leaving 55.9t. The D=10m vessel aerobrakes from ~3700m/s with its 0.8t heat shield separated thereafter, then with a first parachute opened at 800-1000m/s, made of high-temperature polymer. Truly big parachutes, like three (plus redundancy?) D=27m, bring the fall to 100m/s. They weigh 3t and separate ~600m above ground, leaving 52.1t. The descent engine brakes to zero; this costs 123m/s. It then allows the pilot to hover three times 20s (233m/s together) and hop twice to a better location 200m away (130m/s together). Operations near the ground need 486m/s from the engine, which leaves 44.3t landed. This includes dry propulsion, the ascent module, three dressed astronauts, some shielding, equipment to improve the shields, mission and repair tools, mobility - and habitat and regenerative life support for two years, so this mass is easily used. ----- Ascent 12t lift off. A Hohmann transfer would cost 3840m/s without Mars' rotation nor atmospheric drag; with some orbital manoeuvres, I take 4100m/s, which leaves 3.6t in orbit - including dry propulsion, three dressed astronauts with some shielding, and souvenirs. Marc Schaefer, aka Enthalpy

I could have written something like "readers consider a theory to be certain as soon as they see it in a book". I thought it was clear enough. Just consider how many people in forums want to save the ether theory just for having read about it. Or how many people repeat that cubic centered alloys are brittle and face centered ones are ductile, just for having read or heard it, despite a quick check shows that there is no relationship. In the fields I know better, every book contains at least one plain big mistake. The best experts err - even ol' James Clerk himself about Crooke's radiometer. This should make us wary and keep our critical mind. But then, learning is believing, or nearly. There is no magic solution to this. ----- At least for the C/T, a group of scientists did meet and claimed that a meteoroid impact was the probable cause. Which surprised me, since scientists have to keep thinking individually. The good thing is that everyone can still voice a different opinion, and even this group may change its mind if it were necessary, like geologists did over tectonics.

QM is often similar to classical physics. For one, it has to give the same result in some circumstances where classical physics is excellent. Then, for photons, you can most often compute the field exactly as a classical wave, and add photon behaviour only at emission and absorption, only if needed. The equations for a photon's wave are the equations of electromagnetics. So much that most people allege that the E field is the photon's wavefunction - that's sometimes not enough.

Edit already... I implicitly supposed that a small amount of gas is introduced in the rifle and expands much over the bullet's travel. Swansont may have supposed that gas is replenished during the bullet's travel. Also, depending on the gas pressure in the rifle, carbon dioxide can be very far from an ideal gas, and then the gamma story doesn't hold as is. It gets complicated, and people introduce an artifical gamma which isn't a constant any more. And at 70bar and 300K, carbon dioxide would even be a liquid, nearly critical, which changes everything. http://encyclopedia.airliquide.com/encyclopedia.asp?GasID=26 http://encyclopedia.airliquide.com/images_encyclopedie/VaporPressureGraph/Carbon_dioxide_Vapor_Pressure.GIF

Pity, I thought you also wanted to put humans on Mercury before Mars since the mission is shorter - but this is a project very different from what you consider, for sure. Solar thermal engine: the idea takes time to percolate. Esa had made a design a few years ago, and it had some uneasy points, especially a transparent window for the concentrated light - I didn't check if they had catchers as good as mines for heat leaks. Then, operation at low chamber pressure, which dissociates some hydrogen, improves the isp from 800s to 1200+, which helps also. My concentrators+chambers look feasible. And I've described some pretty-cute missions which are more sexy than just Leo-to-Gso. So possibly my design and missions are more appealing than what Esa had. But it takes time for mission planners to realize what gets possible and what stays not, and re-think how to organize a mission. My first thoughts were in 2010 and I still learn how to use the toy, so someone who heard about the engine through indirect ways legitimately needs time. Manned Mars yes, I design a mission script presently. Mercury probably. For the Moon, the solar thermal engine may preset heavy equipment in orbit before people arrive there quickly, that is by chemical engines. J2-X: it's good stuff. It has the Isp of its thrust and nozzle area, so if one needs the MN, fine. For a bit less thrust, I wish four or six RL-10 chambers had a common turbopump and set of actuators. And for sure, performance results from adopting good propellants (pumped oxygen+hydrogen, or pressure-fed oxygen+kerosene, instead of tetroxide+hydrazine) more than individual engine performance. The ballon tanks I describe elsewhere enable it, even without active cooling for the duration of a Moon mission.

The work obtained in adiabatic expansion from the same initial pressure and volume depends on the gas' gamma. For a big expansion factor, the main effect is that the enthalpy available in the gas changes significantly with the gas: bigger with carbon dioxide, which has more degrees of freedom than a diatomic gas like air, hence stores more energy. The second effect is that the conversion of enthalpy to work is slightly less efficient - for a given expansion ratio - if the gas has more degrees of freedom.

As alternatives to a bulldozer, you may consider a conveyor belt (faster, but is it lighter?), or a machine that throws the regolith through vacuum on the base to be shielded. And I still hope 10m aren't necessary, but have no excellent reason for it. Is Mercury's soil texture known? To my knowledge, only orbiters have been near Mercury, and just a few ones. If a crew depends on regolith, this must be assessed before. Bringing a few 100kg samples back must not be very difficult. A one-craft mission with the solar engine can bring 300kg from several asteroids. By presetting the return module around Mercury, we must achieve the same from a robot. My personal interrogation is rather if a semi-autonomous robot can choose and obtain the samples as wisely as a geologist would. As far as I know, no human has ever lived from food grown away from Earth. Biosphere 2 achieved on Earth to grow food but not to remove the carbon dioxide from the air. My fears: - we still ignore how many and how varied organisms are necessary to sustain food growth over seasons - does the soil regenerate in a small closed environment? so an experiment in real size should first be conducted at a place where the crew can come back quickly, say in Earth orbit. Anyway, once air and most water are recycled, humans don't need so much supply; it can be brought by cargo. One could even produce simple food, like glycerine, from carbon dioxide and water - and Mercury's poles have water, they say.

Thanks for caring! If someone jumps in, just fine! If not, it doesn't worry me. My messages are rather descriptions, but on a forum, members don't need an additional invitation to discuss, do they? This young thread has been viewed 165 times as of today, so I imagine some readers have even come back.

The continuous faint push of the solar thermal engine makes bad use of the Oberth effect http://en.wikipedia.org/wiki/Oberth_effect Pushing near a planet is much more efficient, so that a strong short kick (possibly at slower exhaust speed) can be advantageous. The solar thermal engine can be operated with a higher propellant throughput for that, accepting less hydrogen dissociation and a lower temperature. It brings a modest advantage. An other option, combinable with the previous one, is to release some heat not obtained in real time from sunlight. For instance molybdenum absorbs 375kJ/kg to melt at 2896K, niobium 288kJ/kg at 2750K, or hafnium... Ceramics or salts may bring more options. How tungsten resists these is very unclear to me. As much heat as 1000s from a D=4.57m concentrator takes 60kg molybdenum near Earth, but just 2.2kg near Jupiter, where the usefulness is clearer. Or add heat from electric current, as in a resistojet. A safe Li-polymer battery store 475kJ/kg, other chemistries more - and better, spacecraft have already a battery. Electricity from sunlight is less efficient, so the continuous push better results from sunlight-to-heat, but lightweight and shared storage is attractive for kicks, especially near Jupiter or Saturn. Marc Schaefer, aka Enthalpy

What are the reasons for a crew to stay on Mercury during daytime? Fuel cells can provide electricity, and waiting for a good position of Earth and possibly Venus can be done elsewhere - orbiting Mercury when leaving for Earth isn't even useful with my solar thermal engine which wastes the Oberth effect. Nighttime has obvious advantages: fighting cold is easy (-50°C in Antarctica means a good coat) but heat would be very difficult, and the planet shields against Solar ionizing radiation. This leaves 80 terrestrial days on the surface. http://en.wikipedia.org/wiki/Mercury_(planet) So a mission that lands where night begins, makes a few pictures with a flag, grabs some stones, and scrambles before the day arrives, looks safer and easier. Or isn't it? 10m regolith, I hope it's less. Our terrestrial atmosphere is very efficient against even cosmic rays and weighs "only" 10t/m2, or about 3m sand - astronauts staying 80 days don't need the same protection as for 80 years on Earth. You had also considered landing at a pole: why not make a shield of water ice? It's easier to process and the lighter O+H produce less Bremsstrahlung than Fe+Al+Si+O.

Same answer here as on the other forum... Oxygen and acetylene serve to atomize calcium by heat, so you can observe its absorption. At 3000+°C there is no solid calcium, hydroxide, nitrate... I wouldn't call acetylene an oxidiser, nor would I put a specific number of water molecules around Ca2+.

I've put there an illustration of the slow (hence unmanned) transfer of heavy equipment (return vessel, descent-ascent module...) to Mars; it should look similar for Mercury, except for a potential Venus flyby: http://www.scienceforums.net/topic/83289-manned-mars-mission/#entry809990 Figures and spreadsheets are in the message before. One interrogation I have is about the radiation dosis suffered by a crew during a Mercury mission (besides the uneasy idea of living in an oven like Mercury). If - unsure! - the worst radiations emanate from our Sun and decrease with distance as R-2, but the transfer and residence times decrease as R-1.5, then the cumulated radiations would be worse over a Mercury mission than a Mars mission. I certainly agree that a shorter mission has other advantages: for the crew, the operation personnel, the public.

Illustration of the transfer of heavy equipment to Mars orbit: Very classical, except that the solar thermal engine uses several hundred kicks between the low and the elliptic orbits, and also pushes and brakes far from the planets. "Strong" indicates the times, one at each planet, where the Oberth effect multiplies a kick, so that specific impulse can be traded for thrust, say by operating the solar thermal engine in a high-flow mode. Marc Schaefer, aka Enthalpy

Random thoughts: - What you need is mechanical power. Wind energy seems cheaper for that than tidal or wave power. - The atmosphere is huge. Direct human influence has a worry of scale. You need huge and very efficient methods. - Moving air needs unnecessary power. You better rotate many parallel disks, soaken in water at their bottom, swept by wind at the top. Room humidifiers work like that. - Seek help from biology, it's cheap at a big scale. Just pump seawater to a plantation that accepts salty water and will evaporate a part. - The Ocean surface is already a huge exchanger with air. Dry air (Namib, Atacama) occurs when the surface water is cold. If you can immobilize the shallow water and warm it over some km2, you might save the active exchanger. A black plastic film 1m below the waves? Dark algae hold in place?

----- Preset 62t equipment on a 400km Mars orbit ----- The solar thermal engine does it over a 259 days economic Hohmann transfer. ----- Mars The vessel brakes much in advance and passes at 600km altitude with 125m/s below the escape speed, see xls: MarsCargoArrival.zip Arriving with asymptotic 2649m/s, capture to 3390+400km/58,000km costs 2727m/s. A 400km circular orbit takes 1245m/s more, with many 1000s kicks around periapsis only; I sum to 4200m/s. isp=1267s and 100kg/t inert mass let eject 26t hydrogen and start the deceleration with 91t. Fourty-four 10m concentrators push 216N near Mars, or 2.4-3.3mm/s2; it takes boring 160 days to the circular orbit, but the equipment is in place and tested before launching the crew. ----- Earth Climbing to a 6370+400km/194,000km from circular 400km takes 2994m/s, escape and acceleration to 2945m/s additional 2955m/s. The climbing kicks extend 1000s around perigee, and I sum to 6100m/s. EarthCargoDeparture.zip This consumes 62t hydrogen, starting from Leo with 159t. The same concentrators achieve 501N near Earth, or 3.2-5.2mm/s2, so climbing takes some 130 days before the Hohmann launch opportunity. ----- Variants? The RL-10B would start with 236t at Leo, with Oberth effect at both planets. The vessel could aerobrake at Mars, but not with the concentrators deployed, and retracting them all is challenging. Accelerate chemically, aerobrake at Mars, deploy the equipment's concentrators later? The start mass at Leo is similar. I prefer to have well-tested solar engines ready at Mars and avoid the risks of aerobraking. The solar engines could spiral faster to a high circular orbit than kick to an elliptic one, but this costs much mass. The last (first) kick near Earth (Mars) can be stronger to exploit the Oberth effect. Used for 1000s at isp=500s instead of 1267s, the Solar engine pushes 2.5x stronger but consumes hydrogen 2.52x faster. This gains 3% mass at Earth. The vessel could have a chemical engine just for that last kick, after the solar engine achieves the elliptic orbit. More complicated, but it does gain mass. A gravity assist at our Moon is more useful with the Solar engine's faint acceleration: possibly 16% mass gained, hard to compute by hand. Though, it takes a slow, very elliptic orbit before, imposes departure windows asynchronous with Mars, and constraints the Earth orbit's inclination. Marc Schaefer, aka Enthalpy

The universal question about alternative energy is: how expensive ? Because oil, gas are dirt-cheap, coal even more so. Basically, you obtain them from Earth and light them. Wave energy is not concentrated, so it uses to cost much hardware to extract little power. Many (many!) setups have been proposed, you might check at the patent office. It boils down very much to the Ocean area where you can collect waves from and the necessary amount of material. My impression is that no design can compete up to now, not even against nuclear electricity - and coal is way cheaper. Tidal energy looks better, because humans can exploit existing geographic features. With a thin and narrow dam, they have a huge reservoir, where all other sides pre-exist as an estuary. Adding a few bidirectional turbines is standard technology then. Existing demonstrators are old now, small and not proftable. More recent projects (Severn estuary in UK) wanted to be big and profitable, but I believe they're abandoned. Hydraulic turbines on the seabed do exploit tides, sometimes in addition to permanent currents. I have doubts about their cost versus power, since the necessary area and strength is much worse than wind energy for the same power. The French EDF buys and operates demonstrators - possibly because they're sure this one will never outperform nuclear electricity.

From the participants of that one thread, I believe to have seen nobody recently.

From the time of this thread, Phi for All is still active.

One thing that fascinates me with permittivity is that you can measure it at very low frequency (or at DC, say by electrostatic deflection of an electron beam) and, unless it results from slow processes (ion movement, molecule orientation, molecules clusters, like in liquid water), this DC permittivity still gives you the refraction index in the GHz range or even at optical frequencies. http://www.ioffe.rssi.ru/SVA/NSM/Semicond/Si/optic.html silicon : relative permittivity = 11.7 and optical refractive index = 3.42

Huma, I know now way of saying that in a pleasant way, it would only be circumlocution... You can't make a satellite without experience. The transmitter is only a small part of a satellite, but already a radiocomm design demands practical experience that takes years to get, and only outside a schoolroom. Buying parts for a satellite is usually impossible, because satellites have some constraints. Not necessarily difficult ones, but unusual. For instance PVC, the cable insulator, is excluded from any satellite design. Or the insulators used at connectors - manufacturers usually won't tell you or just lie. Then you have to cool the transmitter without air. (The often cited radiations, vibrations or reliability are smaller worry). And so on, and so forth. If you buy space-capable hardware, it costs a fortune, for being specially designed. If you buy a transmitter, it will be polluting, and the launch's main passenger will reject your satellite from the flight. Even if the transmitter got to orbit, it would probably fail from bad cooling. You might get an old space-capable transmitter offered, but then you would have all the other difficulties of a satellite. None is so big individually, but they interfere very badly: thermal design, mechanical design, possible materials... It takes people with a broad technical and scientific backgroud to answer these difficulties a consistent way. Big companies have it easier because they build always the same satellite or nearly, and have specialized teams - but this doesn't exist for small satellites, and then you're back to the early space exploration times, when a handful of people must reinvent much. And of course, practical projects are difficult. Every team fails at its first project. Then, at best, it tries again but with a project of more accessible difficulty. Knowledge can more easily be acquired, but a trained team is seldom and takes time. An existing team that has already built a sailboat has far better chances to build a satellite than a group of specialists without individual practical experience nor collective record. I regret the hard answer, but the only way to success is to choose a much simpler project. Since you're in electrical engineering, you might try to build a ground radio receiver for amateur satellites. That would be a (too?) hard project for a (good and big) group. Depending on the time available, just assembling the orientable antenna, connect a commercial receiver (for amateur radio), and possibly steer the antenna by a computer would be a better goal. Just to figure out: half a dozen of well-trained students (not a first project) would take well 3 months of intense work just for that ground station with steered antenna.

[Replied to my "there is no vacuum in a normal solid, since electrons occupy all the volume"] It's again our different representations of the electron. I say "the electron is the wave". If I don't misinterpret you, you say "the electron is permanently a point whose wave defines its position probability density". One reason I prefer no permanent point is that this permanent point can't be observed. If one tries to locate more precisely an electron, the wave is modified. So I feel more natural not to imagine a point in addition to the wave, but say rather that a wave can change its shape and size according to the environment. Then, "point-like" means that the quantities associated with the electron (charge, momentum...) don't split, whatever small the wave gets with our present technology. This is the necessity of particles, but not that they're points permanently. Numerically, it changes nothing. When integrating over a wavefunction, when we don't take the step of squared modulus, we can call psi the particle's amplitude there, or add that its squared modulus would represent a spatial probability density if an additional physical means were to locate the particle more accurately. ---------- An interesting point is that most interactions with a photon of eV energy don't reduce the size of an electron. The interaction doesn't happen at one point whose position can be determined by the wavefunction, but rather must be summed over the volume. For instance a valence electron that absorbs a photon near the bandgap energy to become a conduction electron is delocalized over many atoms before and after, and so is the photon. The photon couldn't bring the energy necessary to localize the electron in any band. Same with a single atom, or with nonmetallic bonds. A photon of moderate energy interacts with the electron over the whole electron's volume (or possible positions in the more usual formulation), as the photons lacks energy to localize the electron in a smaller volume. Or take an atomic force microscope. The atoms of the scanned surface and the sensing tip interact as diffuse electron clouds, deformed by their proximity. An interaction between two point electrons at fixed positions wouldn"t produce the picture. I certainly agree that everyone computes these examples by summing complex amplitudes over the volume. It's just that I feel unnecessary because not observable, and potentially misleading, to add the idea of a permanent point electron. ---------- As for the refractive solid, electrons take all the volume in my formulation - or in the more usual formulation, the possible positions of the point electrons occupy all the volume. Pictures use to represent atoms in a crystal as hard spheres for clarity, but with the biggest distance to the next nuclei being like 10% more than the smallest half-atomic distance, the fuzzyness of the electrons covers it easily. ---------- While the "permanent point" is more commonly claimed or implicitly suggested, I feel to be perfectly orthodox with "the electron is the wave". At least Schieffer used to write it exactly that way. Do I feel animosity by some members every time I write something that is a less usual formulation, especially that one? I should like to remind that "usual" does not equate to "true", and that misinterpretations of quantum mechanics are common. Just remember how many people want to see a Bose-Einstein condensate in the BCS theory of superconductivity, despite the authors ruled it explicitly. Below the frequencies that can be absorbed, atoms get polarized by light. This radiates without delay a local and mainly electrostatic field (call it a virtual photon if you wish). Then you get the lower wave impedance in a dielectric. As opposed, atoms radiating the photon with a delay would keep the vacuum's wave impedance.