Enthalpy

Admitting that the two wavelengths come from the laser and both are doubled, this implies that they are emitted at different times. If simultaneous, the doubler would create a third frequency which is the sum of both - in addition to the double of each. That is, [cos(w1t)+cos(w2t)]2 contains cos2(w1t), cos2(w2t) and cos(w1t)*cos(w2t) which expand into cos(2w1t), cos(2w2t) AND cos[(w1+w2)t] Since lasers tend to produce many frequencies erratically, even if they have only one transition, this explanation is natural. By the way, the difference between both frequencies is only 2.6THz, or 115µm, far less than the ambient temperature, meaning that the transition is naturally wide enough to lase at both wavelengths. Lasing makes emission lines much narrower than spontaneous emission, but occasionnally the oscillation can hop from one cavity mode to an other within one lasing transition that is wide enough. This is prevented in more expensive lasers. Did you open the pointer to observe if both wavelengths exist before the doubler?

Do you have the budget for gadolinium? Research papers use other materials. Do you believe Gd is better?

If an inverter that produces sine waveforms of MW at kHz is too difficult, I figure it can make nearly square waveforms. In that case, I'd drop the refinements that induce a quasi-sine voltage at electric machines: split coils, shared slots, variable gap... One coil per pole, one slot per pole and phase, wide magnets shall induce a nearly square voltage. Keep maybe some slot skew. Then the power components can switch once per output period to apply the rail voltage when the induced voltage has reached its plateau. During the voltage transitions, current flows through the flywheel diodes. 2 phases from 3 (or 4 from 5, or 6 from 8...) provide power at any time. The sizing advantages of three-phase current are lost, but the square waveform compensates them. Optimized timing between one phase switching off and the next switching on can reduce noise. If the slot inductance hampers the current rise, drive the switches shortly before the voltage plateau. The rail voltage must adapt to the rotation speed and the required torque - indicated by "Buck" on the sketch. At least near cruising speed, I'd synchronize the voltage regulator with the phase switches. The nearly-square induced voltage applies also - more easily - to a generator that feeds an input rectifier. Marc Schaefer, aka Enthalpy

Launching from Baikonur, Zenit achieves an orbit inclined 51.4°; a third stage brings to 1500m/s below geosynchronous orbit the satellite, leaving the same effort as from an equatorial transfer orbit. I suggest here a smaller third stage, as it starts from low-Earth-orbit already and attains the geosynchronous orbit directly. Its electric pump fits the many ignitions (~5 burns at perigee, 2 at apogee) and small thrust (10kN) that, with 60 bar in the chambers and four D=1.0m nozzles, extract Isp=3985m/s=406s from RG-1 and oxygen . Zenit-2 places 12940kg on the inclined low orbit. Correcting the inclination then lets the apogee cost 2500m/s instead of 1600m/s, while the perigee still takes 2500m/s, so the 8775kg propellants leave 3690kg. A truss of welded aluminium tube, 330mm wide and 2mm thick, holds the payload and the engines to the previous stage and contains the fuel. Polymer belts hold the oxygen balloon tank, made of brazed 150µm thin steel covered with foam and multi-layer insulation, to the truss; electric motors compensate the thermal expansion. The tanks with belts and insulation weigh 236kg, or 27kg/t of propellants. The 10kN four-chamber engine, with one set of pumps and actuators, plus verniers and their bladder accumulators, shall weigh 200kg. Existing Lithium-polymer accumulators weigh 142kg, the inverter 8kg, summing 350kg for the pumped engine. Sensors, radiocomms, control and their energy are to fit in 100kg. Three halves of separation actuators weigh 75kg. Sum 129kg unaccounted items, and the stage puts 2800kg in GSO . This is more than the DM-SLB followed by a pressure-fed apogee engine at the satellite, and it saves one stage. This design adapts to Falcon and others, and can be considered for hydrogen. Marc Schaefer, aka Enthalpy

I'm not sure at all that a 70% concentration burns. Far less so a 50% concentration.

The gear can be avoided. Again 2082kW as the PW127M, but the wide ring motor rotates directly at 20Hz. At D=1000mm hence 62.8m/s, the 3mm thick Neodymium magnets (happen to be Thyssen-Krupp 340/88) need only 0.15mm graphite winding and achieve 1.02T in 1mm radius gap. With 66 poles and 132 passes 205mm long, each of the three phases gets 1726Vpk induced in the single turn. The 6mm*3mm wires get 1mm thick insulation; the slits may need some potting in addition, especially at altitude. Diameter, mass and losses can be optimized against an other. At this speed, a squirrel cage would have been possible. The present design is wider than the gas turbine but only as tall. The motor's ring weighs about 280kg alone. Its ohmic losses are 42kW or 2%, but as it saves the gear's mass, maintenance and 1.5% losses , I prefer it. Marc Schaefer, aka Enthalpy

As sqrt(stiffness/density), where the stiffness must match the wave: shear, Young, Young with no side expansion allowed... The observation surprises me. Cold work alone should not change the stiffness, and the density less so - but maybe the material is special? Austenitic stainless steel can transform into martensite by cold work, and martensite is stiffer and lighter than austenite. The effect is even more important with many polymers, for instance polyamide.

Hello, heirs of James Clerk, Nikola and the others! It is well known, but by too few people : in an electric machine, only the force means losses and heavy parts, the speed comes for free. When a motor or generator runs quickly, say 50 or 100m/s at a power plant, it is smaller than a turbine. Quick machines with rotating permanent magnets use to hold them in a tight sleeve of strong steel to counter the centrifugal force. I propose to wind a composite of graphite fibres around the magnets instead of the steel sleeve. Graphite fibres are lighter than steel and produce less eddy current losses where they cross the stator's windings; better, while the accurate diameter of a steel sleeve is difficult, fibres are commonly wound tight over varied cores, even with a pre-tension useful here. A unidirectional composite looks best here, and pre-impregnated graphite is usual at wound pressure tanks for instance - other fibres may emerge. Some thin elastic material below the magnets can prevent cracks. To run at 200m/s, 5mm thick magnets weighing 7500kg/m3 need 1.5mm of graphite composite withstanding 1000MPa - or scale both thicknesses. Neodymium magnets like Thyssen-Krupp's 300/110 still achieve 0.78T through the graphite plus 1.5mm radial gap. I already described a small electric motor turning a rocket engine pump, there http://www.scienceforums.net/topic/73571-rocket-engine-with-electric-pumps/#entry734225 and http://saposjoint.net/Forum/viewtopic.php?f=66&t=2272&start=80#p41298 the following one outputs 2083kW like the PW127M gas turbine that moves the ATR-72 and other successful planes. http://www.pwc.ca/en/engines/pw127m http://de.wikipedia.org/wiki/Pratt_%26_Whitney_Canada_PW100 http://en.wikipedia.org/wiki/ATR_72 The motor rotates at 255Hz, so a gear drives the propeller at 20Hz - but a turbofan would need none. 5mm thick magnets at D=250mm run at 200m/s. The 355mm long stator has 3 phases and 18 poles. The windings are one turn of square 5mm*5mm copper that makes 36 passes through the shared 54 slits. The induced coil voltage is 1726Vpk (reduce the length if I botched a cos30°...) and the current 804Apk, nice for an inverter supplied with 3kVdc maximum. Coil resistance is 13mohm (or a bit more as the skin depth is 1.4mm at 2292Hz) so ohmic losses are 13kW or 0.6%; core losses are small with the proper material. This electric motor weighs ~120kg, is ~400mm long and 312mm wide , while the PW127M is 660mm wide and ~1.2m long without the gear, and weighs 481kg with the gear. Direct retrofit, though we still lack proper fuel cells. Marc Schaefer, aka Enthalpy

Do metals displace another according to reactivity? I thought this was primarily a matter of solubility of the salts. In addition, many metals have various oxidation states, so the reactivity "of a metal" is too vague.

Knowing that quarks don't go alone, can black holes create them? I expected electrons, mesons, baryons... to be created.

Violonists would naturally follow a scale of no-beat, but must learn to play accordingly to Bach's tuning. This makes very little difference on a perfect fourth, fifth... but a big one on both thirds. In some pieces, if the violonist follows his natural hearing, he accumulates the small differences and gets completely out of tune after one line.

Many conversions are not reversible. Direct Sunlight on a light bulb, get nothing at the terminals, as one example. The heat produced by radioactive waste is used at one place in China. Negligible amount of energy as compared to the reactors that produced the waste, significant added risk.

I firmly believe such EM weapons exist already and are commonly used but don't rely on any sensitizer. Thus, they are non-specific and block rather the whole brains, serving to let targeted people get seizures or wound themselves by falling. Nasty enough. Don't rely on me to make spook weapons worse than they are already. I'm happy to have not taken part in the ones developed in 1991. Probably used against me in 1992 and 1995. Recently, open research played with vaguely similar toys activated by light - which is of course impractical as a weapon.

To my surprise, rechargeable batteries are as light as primary ones, and would ease trials of the engines. Li-ion can fit the long burn of an apogee stage, perhaps a perigee stage, but seemingly not a booster, and already caught fire on aeroplanes, cars, laptops. Li-polymer exist for 4min discharge (15*C) - fits a booster. Polyquest-Enerland developed one series, but does A123 Systems still sell them? http://enerland.en.ec21.com/ "RC series" Toshiba developed an other series for <5min operation including at cold http://www.toshiba.co.jp/about/press/2007_12/1101/SCiB.pdf Altair Nano makes something, but what? http://www.altairnano.com/ Fortunately, hobbyists give more data about batteries and fast discharge http://www.aircraft-world.com/prod_datasheets/polyquestxp.htm http://www.conrad.de/ce/de/product/238913/Top-Fuel-LiPo-Akku-222-V-2500-mAh-40-C- Li-polymer meant for permanent 40*C, or discharge in 90s! http://www.conrad.de/ce/de/product/269802/Graupner-LiFePO-4-Akkupack-165-V-4000-mAh-35-C-Stecksystem-G35-EH Li-FePO4 meant for permanent 25*C, or discharge in 144s! From data at Conrad, Li-polymer would bring 455kJ/kg at a reasonable pace; if snap discharge drops the mean cell voltage to 3.45V, the battery would still bring 424kJ/kg. Data for Polyquest batteries at aircraft-world.com even tells 509kJ/kg slow, 475kJ/kg fast. The safe Li-FePO4 (through Conrad) still brings 371kJ/kg at moderate pace. As a complete launcher would use >10 tons of batteries, these can be tailor-made, say from prototypes a manufacturer didn't market. Here we can accept fewer cycles and a faster self-discharge, which uses to enable a faster discharge as well. And for sure, the pumps, electric motors and inverters would be new designs, saving much mass over the cited research paper's figures. ----- Li-S and Na-S work only hot - I dislike that... I'd even prefer some Li-O2. Inject the product in the main chamber. ----- How difficult would be a light fuel cell? It needs to operate for few minutes, can work at 600°C or 1400°C, get hydrogen at 100bar... At an apogee stage, providing only 50kW in 100kg, it still outperforms a lithium battery, and car prototypes have already such fuel cells. Marc Schaefer, aka Enthalpy

To illustrate electric pumps, this launcher puts 3.0 to 8.3t in geosynchronous orbit directly. It can also send 9.0t or 2.8t towards Mars and Saturn directly, or without the upper stage, put 8.2 to 25t in low-Earth-orbit. The upper stage burns 12.1t of hydrogen-oxygen at 30bar, expands in D=2.15m to achieve 75kN and Isp=4565m/s. Balloon tanks within a taller fairing would gain almost 300kg payload. The lower central stage burns 54t of hydrogen-oxygen at 40bar, expands in D=3.0m to achieve 650kN and Isp=4352m/s. 4 Vinci or 6 RL-10 chambers, with short nozzles, can replace the single one, and share a set of actuators and electric pumps, later maybe turbopumps. Each booster burns 52t of Pmdeta-oxygen at 110bar, expands to 0.35bar in D=2.0m to achieve Isp=3304m/s in vacuum and, at sea level, 1.2MN and Isp=2594m/s. 2, 3, 4, 6 boosters, or 6 followed by 2, match varied payloads. The launcher's strongest pump takes 5.0MW shaft power. The boosters connect at the reinforced upper section of the lower central stage. Boosters share a fastening with each neighbour at the core. The core of extruded aluminium profile spreads the push and pull forces by shear; a small internal truss prevents bending. All skins consist of extruded profiles as I describe elsewhere. Batteries are still Li-MnO2 despite the uncertain peak power, but that's a matter of 30kg/t weighing 1/3 more. All empty stages weigh less than 102kg per ton of propellants. Here all tanks start full even with two boosters, but bigger tanks would widen the adaptation range. Marc Schaefer, aka Enthalpy

For a small propellant throughput, say at an apogee stage, a screw pump is more practical than a centrifugal one. An accurate screw profile limits leaks. For a small screw like D=20mm, a (pair of?) accurate tailor-made tool can cut the profile, just like a fastening screw is cut: sketched here for turning; milling is possible. Notice the tool cuts the outer diameter as well, so the whole profile is precise and easy to measure. The stator and rotors will likely receive some protective layer against oxygen and wear; if thin Ptfe-impregnated nickel is acceptable, its thickness can finely adjust the parts' diameter. Or etch the parts (electro-) chemically for the last few µm. Electric Discharge Machining is one alternative here to chip-cutting. The screws' outer edge can comprise several crests instead of one, separated by grooves, to reduce the leak. The whole profile must be designed accordingly. Pump specialists may know more tricks, perhaps even seals. A thick stator deforms very little at 300b. Marc Schaefer, aka Enthalpy

This has very practical implications for geologists, who use extremely sensitive gravimeters to guess what lies in the ground (in fact, they prefer to use differential apparatus to remove these perturbations). Their instruments show with great precision the variation of g (is that g?) over one metre height, for instance. http://en.wikipedia.org/wiki/Gravimeter Tidal force is the first perturbation for gravimeters and must be accounted for very precisely. Its influence exceeds by far the observed effects of deposits. Since Moon's distance varies a lot (+-6.5%) so does its effect (+-20%) and this change demands an accurate evaluation.

1/c2 is just how heavy energy is. Any form of energy, not just nuclear one. Kinetic energy has that mass, and this includes heat. Electrostatic energy has this mass, and this includes nuclear fission: when uranium splits, the fragments get their speed from the electric repulsion of the protons. The energy of strong interaction, which attracts protons and neutrons together in a nuclear fusion, has this mass. Even gravitation energy has... But nuclear energy is more concentrated than chemical or thermal energy, at our usual human scale (gravitation can be more concentrated than nuclear energy at astronomical scale). So concentrated that the relative variation of mass is easily measured, like 0.1%, while it is far less with other forms of energy. That's why the mass variation is commonly used to compute energies of nuclear or particle reactions but not elsewhere. Just a matter of usable quantities, not of nature.

Researchers in Buenos Aires and Roma have already studied electric feed for propellants: http://www.dima.uniroma1.it/STAFF2/jpp12r3.pdf They evaluate masses identical to mines, within computing noise. - They take rechargeable lithium technology and properly observe the peak power of existing cells. - I carefully match the rotation speeds of the pumps and the specially designed motors. - The dear reader makes the smart and astute synthesis. My strong feeling is that electric propellant feeding will exist on apogee stages or satellites, because it's easily developed, and among the possible solutions (as a turbine would be too small), it brings a big performance improvement. At lower stages, it's rather a good, simple and cheap solution, which brings a launcher early to the market, before a more efficient turbine cycle possibly replaces it. Marc Schaefer, aka Enthalpy

I have never seen an astronomy satellite that works without pointing at the observed object (except Hipparcos) and I consider pointing is too difficult for a first satellite. Because of that, my satellite (Sara, from the club Esieespace) had no attitude control and we were suggested a topic in radioastronomy that did not need any attitude control, luckily enough. Without attitude control, but with a team of 9 people seriously skilled, enthusiast, and used to work together, Sara took 3 years and exhausted us. In case you're alone, I consider that a nanosatellite: - without attitude nor orbit control - without any precise thermal control - with a supercapacitor instead of chemical batteries, which eases the temperature range, and Solar cells - or better, with a primary battery instead, and working for a few days or weeks is more than enough difficult. That's what I had in mind when suggesting to test an atmospheric reentry shield. Don't forget the extra work associated with the interfaces and discussions with the launcher: it took us one man. Also, piggyback launch on Ariane cost then 200k$, the rest of the budget was alike. Maybe you could touch a word with Guy Pignolet. He's in La Réunion and has instigated several nanosats in schools. He speaks English and has a Website.

The best design I see is like at the video: wind the weight's rope around the input shaft, then have a series of simple gears. To me, the design challenge is rather to keep dust out of the gears and bearings, protect the first shaft from shock if the weight falls from a few decimetre height, ensure lubrication - or dry run capability, which is usually worse. Also unusual with a series of gears: make it simple to assemble and repair. Ensure safe operation for users and hardware on open and short circuit. Try to find an old clock powered by a falling weight, and observe it. You could consider tooth belts instead of gears. They resist dust better.

Thanks for your interest! And please forgive the late answer, I had no electricity for two days. You're absolutely right that the pumps need much power over a short time, so they must be fed by some chemical means. The secondary battery already in the satellite and full happens to suffice, which is excellent news, as this battery can be later re-charged by the Solar panels, so electricity for the pumps needs no extra mass. That's why I compute with a higher chamber pressure if the apogee rocket engine is part of the satellite rather than the launcher: enough energy is available at no extra mass, and pressure improves performance. Supercapacitors are still heavier than chemical batteries. Secondary (=rechargeable) batteries can fit quick discharge, but use to weigh more than primary ones do - I didn't check that with recent technologies. And I agree that the Li-MnO2 I've seen can't be discharged within few minutes; I just suppose that thinner electrodes and electrolyte enable that - take a different technology if not. ----- I extrapolate centrifugal pumps from RD-170's liquid oxygen ones. http://www.lpre.de/energomash/RD-170/index.htm (section Турбонасосный агрегат) The outlet pressure varies as density*square(linear speed). I keep the diameter/(blade height) ratio and make this area*speed proportional to the volume throughput, where I keep the fluid's radial speed proportional to the impeller's tangential speed. In some cases, the pump is symmetric, to double the relative blade height, reduce the impeller's diameter and increase the angular velocity, in favour of the electric motor. This design could be improved, especially the fluid's radial speed, but at least the direct extrapolation looks safe to my eyes. Or isn't it? Maybe I should not extrapolate to hydrogen. As the electric motor can run at 200m/s and is lighter then, fast impellers at oxygen and dense fuel would improve, which suggests some kind of axial pump instead, like at a booster pump, but I suppose cavitation is very difficult to avoid at the inlet then. ----- I give a mass for the screw pump. http://en.wikipedia.org/wiki/Rotary_screw_compressor The one I consider runs really fast at 418Hz as compared with 60Hz or 25Hz usually, and that makes it lighter. I consider it possible because it has no seals at the rotors, only at the low pressure side of the shafts. The throughput results from volume*frequency, and the mass from the size. 20µm radial clearance is easily achieved by machining (details later); because oxygen is very thin, leak speed is limited by inertia, or (10 steps) 9.6bar = 0.5*d*V2 with d=1141kg/m3. The leak isn't brilliant, but a thread profile more hollow would reduce the leaking area, and more turns would reduce the pressure per step. Centering the rotors needs adjustments, like eccentric parts to hold the shafts. Thermal expansion isn't critical: less than 24µm over the radius for steel and 200K, before stator-rotor matching. Put the pump within its oxygen inlet line?

This must be possible in an atom, at a transition between two orbitals. Essentially all available energy, in this case electric energy reduced by kinetic energy, must convert into a photon. Less easy for an unbound electron, since radiation is inefficient at low energy. But if the initial energy is highly relativistic and the electron looses nearly all of it in the collision with a nucleus, nearly all must convert into a photon. In an X-ray tube, emitted photons can have about the energy of the incoming electrons, but most have less, because most collisions are not head-on.

Hello dear friends! As an alternative to heavy pressurized tanks and to complicated turbopumps, an electric pump can feed the propellants in the chamber(s). Conceivable at small chemical thrusters, where a high pressure improves the efficiency and injects enthalpy from the Solar panels. ----- Scale up: electronics can control 1MW motors from the main's voltage. A 70% efficient centrifugal pump brings then 72kg/s of oxygen and farnesane C15H32 to 96b; expansion from 80b to 0.02b in a 2.6m nozzle to push 260kN with Isp=375s, enough for the main engine of a 30t upper stage. Rotating at 780Hz in vacuum, the motor is small. Its rotor can be a permanent magnet of Magnetoflex 93, D=250mm L=200mm. The D=350mm 3-phase 8-pole stator loses <1kW in its braided "Litz" wires and 70W in the Nanoperm magnetic circuit; it's cooled by the fuel. The motor weighs 140kg. It accelerates in 30s. The safer Li-MnO2 primary battery brings ~650kJ/kg in the too quick discharge. The stage bringing 5900m/s would burn 24t; at full thrust, this would require a 470kg battery (20kg per ton of propellants), but throttling is easy, useful, and lightens the battery. The battery is easy to integrate and welcome for the gimbal actuators, the igniters... ----- Pressurized steel tanks for the same 24t but with only 36b in the chamber, throttling to 20b, would weigh 1930kg and provide 13s less Isp. Graphite tanks could weigh about 1100kg. A gas generator cycle could waste 42kg per ton of propellants, later ejected at 1500m/s thus counting as 35kg/t - but this equivalent overhead is ejected all the way and a battery supposedly not. Staged combustion is more efficient. ----- Scale up further: power components control 6MW railway engines. This would provide 1MN thrust with 120b in the chamber, enough for 115t at a second stage or 70t per 6MW slice at a first stage. ----- Smaller roll and vernier engines can also have electric pumps, for instance at a solid engine stage. For a lander or descent-ascent module, I like the ease of starting and restarting electric pumps. ----- Fuel cells would have been fantastic for a hydrogen-oxygen engine with electric pumps, but are still too heavy. Marc Schaefer, aka Enthalpy ===================================================================================== At an RL-10B equivalent with electric pumps, injectors shall drop 17% pressure and pumps be 65% efficient, then the shafts need 145kW and 399kW, and the motors cumulate 80kg. The Li-MnO2primary battery weighs 36kg per ton of propellants, a bit less by throttling. This is mass where not desired, and an expansion cycle performs better, but the electric pump is simpler. The battery mass is a good surprise, this is how I compute it: 1kg of oxygen-hydrogen m5.88:1 occupies 2.8dm3 as liquids boiling at 1 atm. Because no turbine is needed and I forgot the drop in the cooling jacket, the pumps must bring the propellants to 52.3b at the injectors. The power electronics shall be 97% efficient, the motor 99.9%, the pumps 65% because of hydrogen. 23kJ of electricity is used per kg of propellants. Li-MnO2 batteries use to store 240Wh/kg = 864kJ/kg or 33Ah*2,7V/355g = 904kJ/kg at room temperature http://media.duracell.com/media/en-US/pdf/gtcl/Technical_Bulletins/Lithium%20Technical%20Bulletin.pdf http://www.saftbatteries.com/doc/Documents/primary/Cube656/FRI_M62.2cf814ca-1181-4dc6-85f1-7c679f35054c.pdf but are meant for multi-hour discharge. Winding the electrodes and electrolyte thinner must permit a faster discharge (and self-discharge); I take only 650kJ/kg because of the redesign. Hence the 36kg per ton of propellants. This extra mass is similar to a gas generator cycle because both energy sources are chemical, and both happen to be equally inefficient. 36kg/t is as much as the Shuttle's external tank, alas, so a lower pressure is probably better. Throttling permits to reduce the pump pressure at the end, saving energy. Li-SOCl2 and others are lighter, fit fast discharge, cold... but they catch fire, explode or emit toxic gas if crushed or pierced. I don't want half a ton of them over 20t of explosive gas. ----- The power electronics needs a special design cooled by the fuel. An eight-pole motor at 780 Hz (46,800 rpm) needs three-phase at 3120 Hz so the electronics makes probably a 1/3 - 2/3 waveform instead of a sine by pwm. The motor is exotic. Its permanent magnet rotor is uncooled; Magnetoflex 93 with HV=950 rotates at 613m/s, key to the tiny design. A stepper motor would accept more banal materials but demands vacuum, and might combine with the impeller - maybe perhaps. ===================================================================================== Many hydrogen engines for upper stages offer no roll control. Vernier thrusters control the roll, the launcher's attitude at spacecraft separation, the precise injection speed to orbit. Instead of toxic and less efficient hydrazine, these thrusters could use the hydrogen and oxygen, but they must operate after the main engine shuts off, and a restartable extra turbopump is too complicated for them. Propellants at ~1.5b from the tanks may cavitate and need bigger thrusters. Electric pumps would improve this. This holds for other propellants as well, but pressure vessels are especially bad for hydrogen, hence the pumps. As roll actuators, they could push only when needed, saving further electricity hence battery mass. A positive displacement pump can be considered here. A thruster taking 5b hydrogen-oxygen exists already at DLR. For this purpose? Marc Schaefer, aka Enthalpy ===================================================================================== Many communication satellites are put by the launcher on Geosynchronous Tranfer Orbit and reach Geo-Synchronous Orbit with a 1600m/s kick by their MMH+N2O4 apogee motor. While better than solids, these motors use inefficient propellants pressure-fed by heavy tanks to burn at a low pressure. Electric pumps would improve. The satellite shall weigh 4000kg including the engine - wherever this one is. The nozzle is 0.6m wide. 1600m/s are brought in 2000s, needing about 4kN. Hydrogen-oxygen in the satellite improves most. The satellite's existing battery loaded by Sunlight brings all electricity (75MJ) for 100b in the chamber, hence the Isp and inert mass. Though, the hydrogen takes a 1.7m sphere. The sphere can be multilayer-insulated and held to a truss by polymer straps. Hydrogen-oxygen in a launcher's special stage takes an extra battery of 16kg/t to achieve only 20b. No big improvement over a Vinci stage for instance, but some launchers (Zenit, Falcon...) could then offer GSO delivery to satellites without an apogee motor or to replace MHM. Syntin-oxygen in the satellite can burn at 250b, or even more if the apogee kick is spread over several orbits. A strained amine is as efficient as Syntin and possibly cheaper. Syntin-oxygen in a launcher's special stage burns at good 80b. All-kerosene launchers may prefer it. The gain over MMH is still impressive. Space probes have similar needs, for instance to get captured by Saturn. A cryocooler can keep the propellants liquid. Un pensamiento para Don Hugo. Marc Schaefer, aka Enthalpy ===================================================================================== An oxygen screw pump fits a 4kN apogee motor burning Syntin. http://en.wikipedia.org/wiki/Rotary_screw_compressor Its two rotors can have (before optimization) D=20mm and a core of d=16mm, a single thread of 10mm pitch and 50% solid, for instance of nearly-sine profile. Drive at 418Hz and 3.3N*m (8.6kW) achieves 96bar and 669cm3/s if efficiency is 75%. With 10 screw turns in 100mm length, oxygen inertia lets it leak at 41m/s; 20µm radial clearance limit the leak to 104cm3/s - less if the pump is smaller. The stator and rotors need roughly matched temperatures and expansion coefficients. Turning or milling tools are made to the desired tiny profile. The pump weighs about 3kg. The electric motor can have a D=40mm L=60mm rotor (only 53m/s) with four poles of Nd-magnets held by a steel sleeve. The three-phase stator then looses about 60W. The motor weighs 2.5kg. Example of an electrically pumped apogee stage: Marc Schaefer, aka Enthalpy ===================================================================================== A main hydrogen-oxygen stage pushing 1MN with 40bar in the chamber(s) is feasible with battery power. The impeller for the hydrogen centrifugal pump for 33kg/s or 467dm3/s at 48bar has for instance D=214mm (not optimized), its channels are 19mm high, and it rotates at 503Hz. If 60% efficient, it needs 3.9MW and 1.2kN*m at the shaft. I won't detail the booster pump. The electric motor can have 10mm thick Nd-Fe-B magnets moving at 200m/s at the D=126mm L=400mm rotor, held by a 3mm thick sleeve. The 3-phase 4-pole (or more) stator loses about 20kW in its coils with few turns of rectangular wire, and the motor weighs 200kg. The traditional sleeve is cold-rolled austenitic steel. It could instead be helix-rolled and welded Maraging sheet to offer permeability. But for precision, and to reduce eddy currents in the sleeve, I'd prefer the same 3mm wound of unidimensional graphite prepreg. Thin elastic material can fit between the steel core and the magnets. A stepper motor, with a D=400mm L=50mm rotor and overlapped phases and coils, may work and weigh 70kg, but I won't invest more time to check this attempt. The oxygen pump can have symmetric inlets, then D=174mm lets it rotate at 165Hz, so a ring motor can have D~380mm with many poles and be flat - I won't detail it. The magnets cost 1000€ per motor. 80t of propellants need 2.7t of Li-MnO2 batteries, which sell for ~50€/kg in small amount. Marc Schaefer, aka Enthalpy ===================================================================================== A booster burning 225:100 of O2:Pmdeta expanded from 110b to 0.35b in a D=2.4m nozzle to produce 2MN and 337s @vac needs 419kg/s and 367dm3/s of oxygen. The centrifugal pump with symmetric inlets can rotate at 217Hz with a D=204mm impeller; being 72% efficient, it receives 6.75MW and 4.95kN*m from the shaft. (Click to magnify) A corresponding electric motor has 10mm thick Nd-Fe-B magnets moving at 200m/s on D=290mm. 3mm thick wound unidimensional graphite composite holds the magnets. 18 poles allow 16mm thin iron at the stator and the hollow rotor, and a single turn (36 passes, 36 grooves, 3 phases) of D=8mm twisted "Litz" wire gets 1.7kVpk induced, while 2.0kApk take 12 big IGBT. Copper looses some 50kW and the motor weighs 160kg for almost 7MW: it's lighter than a gas turbine. On an aeroplane, it can drive a fan directly, or a propeller through a gear. We still lack light fuel cells. Marc Schaefer, aka Enthalpy

The cheap and practical way to hydrogen gas is to buy it in a bottle. You noticed ammonia is a nasty poison, didn't you?