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  1. Since each sub-pixel has its own emitters you wouldn't require an analog connection. It would be a digitally addressed grid just like an LCD and could natively use the same signals it could. Given that almost all of the advantages of this technology are shared by OLED (high contrast, no backlight, low response time, wide viewing angles) I doubt we'll ever see this come back. There just isn't enough advantage to displace the now reasonably established place in the market for OLED. The only advantage I even see is that the phosphors will probably last a bit longer. There wouldn't be an advantage to going back to analog signals. GPUs have always created a digital image and only turned it into analog signals if that is how it was to be output. The main work of a GPU is all of the parallel processing needed to build an image, in effect all of the light interactions that occur in virtual 3D space with multiple virtual lighting sources and virtual objects. The actual creation of display signals after that 3D processing is turned into a 2D image is a small part of a GPUs job that has had the option of both digital and analog output from the same GPU for several decades.
  2. Musk is correct that is the point of a nozzle (though that is immensely simplified, and not a new concept since it is rocket design 101). Basically a nozzle takes high temperature fluid and turns it into high speed fluid with large amounts of kinetic energy (see de Laval Nozzle). Temperature is random particle motion in every direction, while kinetic energy has a common velocity vector. In other words a nozzle is what forces the randomly moving particles to move (mostly) in the direction we want them to. A simple cylinder isn't going to do much in terms of shaping the direction of a fluid's velocity vectors, though you can certainly create magnetic fields with the convergent-divergent behavior you need, just with more complex shapes. As far as high thrust is concerned, the answer is that you can have a higher thrust plasma thruster such as VASIMR, though even at max thrust it is only 5 Newtons. This is much higher than the 0.327 N of the NEXT ion thruster (itself a noticeable improvement over prior ion engines), but a long way from the 110 kN of an RL-10 hydrolox engine and a really long way from anything that will launch you from the sea-level on Earth. The high energy requirements of a high thrust plasma/ion engine are difficult to meet. You also have the usual problem of needing a lot of reaction mass for a high thrust engine which increases the mass you need to take with you. Plasma/ion engines are really good at accelerating exhausts to high velocity which makes them poorly optimized for high thrust operation. It is more energy efficient to get more thrust by throwing more reaction mass than by increasing velocity, but increasing the reaction mass means you have more mass to move so rockets are actually better off devoting energy to higher velocities. Plasma engines are doubly impacted when trying to increase thrust since you need to increase both reaction mass and energy generation/storage mass (chemical engines have the advantage that their reaction mass is also their energy storage mass). Antimatter gives you really dense energy storage and a lot of energy to work with which does help a lot, though you still need to deal with waste heat and you still need reaction mass. You could do a higher thrust plasma engine using antimatter as an energy source, but the rocket equation still holds true and you would have an exponentially smaller spacecraft if you take the high exhaust velocity, low reaction mass, low thrust approach.
  3. Another negative impact of the square-cube law is that expander cycle rockets are limited to ~300 kN of thrust. This is because the surface area over which you can extract heat grows slower than the volume you need to fill with fuel and at some point you can't extract enough to run the pumps to fill the volume.
  4. Floating point is already logarithmic, and already represented by a pair of integers (plus a sign bit). The most common representation is IEEE 754 which defines several formats, but consists of a sign bit, significand, and an exponent with a pre-defined base. When you use a float data type it is (usually) a 32 bit representation with 1 sign bit, 23 significand bits, and 8 exponent bits with a base of 2 (making the exponent the whole number portion of log2(N) ). Converting this into a base 2 number looks like this N = (-1)(sign bit) x significand x 2(exponent) which is very similar to scientific notation except in base 2 since binary computers naturally operate with a base of 2. IEEE 754 does define a base 10 representations as well, though they are recent and if anyone uses them I'm not aware of it. Basically you won't save any time because this is already what we do. On the other hand you have managed to come up with a perfectly viable approach with a long history of working. Base e is not likely to work well. Since it is an irrational number a computer needs to approximate it to some number of digits. Computing the log base 2 of a number can be computed with a fairly simple circuit, log base 10 is more complicated yet reasonable, and log base e is just an awful mess. P.S. I'm glossing over some details. There is more to this than is relevant to the discussion.
  5. The SpaceX environmental impact study includes a third party simulation of the exhaust products (page 169). Per the summary: Calculations were performed to estimate the far-field exhaust constituents of the SpaceX Raptorliquid oxygen-liquid methane (LOX-LCH4) booster rocket engine firing under sea-level conditions. Although the exit-plane exhaust is fuel-rich and contains high concentrations of carbon monoxide (CO), subsequent entrainment of ambient air results in nearly complete conversion of the CO into carbon dioxide (CO2). A small amount of thermal nitrous oxides (NOx) is formed, all as NO. The CO and NO emissions are predicted to be less than 0.024 lbm/s each, per engine under nominal power (100%) operation. No soot is predicted to be generated by this engine cycle. The CO and NO emission rates for the Super Heavy has been estimated to be no more 0.788 lbm/s each. The predicted sea-level CO and NO emission rate for the Starship upper stage are estimated to be no more than 0.168 lbm/s each. Table 3: Thrust Chamber Nozzle Exit Species Mass Fraction from VIPER Simulation Species Mass Fraction CO2 0.39950 H2O 0.41333 CO 0.12071 O2 0.054752 H2 0.007462 OH 0.0035882
  6. I know this isn't the Raptor, but Scott Manley did a detailed video on the F-1 engine startup procedure that was pretty interesting.
  7. The EM Drive has been reasonably well debunked at this point. Dresden University of Technology did the tests that debunked it for most of the mainstream. They used a rig with very accurate force measurements and the ability to reorient it. Based on their observations most have concluded that the thrust measured is just inadequately shielded EM fields interacting with Earth's magnetic field. There are a number of tests that back this up, but probably the most convincing is that when they attenuated the radio waves going into the resonance chamber the thrust did not change. A far more interesting question is whether it was worthwhile investigating a fringe hypothesis like this with public funds. I tend to say yes since there was enough evidence that something was going on to warrant looking and we can't be closed off to all things contradicting established theories, though I don't think continuing investigation is warranted (at least not with public funds). Having said that the EM Drive always fell in the "extraordinary claims require extraordinary proof" category and it never delivered more than vague indications until we arrived at a more plausible explanation.
  8. Putting fuel into a rocket engine does not create momentum. Momentum is conserved, you can't create it though you can exchange it in interesting and useful ways. The overall system has the same momentum it started with. Basically if you were to take the vector sum of the momentum of the rocket and the rocket exhaust it would add up to its starting momentum (at least in a vacuum where we can treat this as the total system we're analyzing). A rocket doesn't work by creating momentum, but by dividing it in a controlled manner between the remaining mass of the rocket and the exhausted mass so that the velocity vector of the remaining rocket mass increases in a specific direction. To recapture all of the propellant you must undo this which means that the rocket and exhaust must end up with a net velocity vector of zero and as long as they remain together this means the rocket will not move. You could of course recapture a portion of the propellant and exhaust some of it. You would decrease your change in velocity relative to just exhausting all of it, but it would give you a variable thrust engine with consistent cooling characteristics. This gives us the only reason I can think of to pursue this dubious enterprise. You could create an engine that had a relatively high initial thrust until it ran low on propellant which then switched to recapturing its working fluid (no longer propellant, now coolant) and used the waste heat in a photon rocket to continue accelerating for as long as you have nuclear fuel (at an obscenely low rate of acceleration).
  9. Chemical rocket engines have very high thermal efficiency, bordering on ideal. An efficient chemical rocket has about 70% thermal efficiency. Combined gas and steam turbines used in some maritime applications are about 65% efficient. Jet engines have about 40% thermal efficiency. Gasoline engines are about 30-35% thermally efficient, diesel can reach about 40%. The low efficiency of piston engines is the reason electric cars make sense. Batteries have about 1/10th the energy density of hydrocarbons, but are much more efficient at converting that energy into usable work (90% vs 35%), so you can still get a useful range out of them in spite of the huge initial disparity (though it is large enough that piston engines still have longer ranges unless you devote more mass to batteries). Where rocket engines do poorly is overall propulsive efficiency, which includes converting that usable energy into propulsion. This is because rockets need to carry all of their reaction mass with them. The most efficient way to propel something is to move a large reaction mass with a small, but opposite velocity. This is because momentum is m*v meaning an increase in either mass or velocity has an equal change to momentum, but kinetic energy is 1/2*m*v2 meaning that increasing velocity requires significantly more energy, so the most energy efficient route is to use larger reaction mass and smaller velocity. Rockets can't use a large reaction mass for higher propulsive efficiency because this increases the amount of mass that needs to be moved which negates the advantage of using a large reaction mass, so it is ultimately more efficient for a rocket to devote that usable energy into a high exhaust velocity and reduce the amount of exhaust mass. Aircraft, boats, and cars all have the advantage of a constant supply of reaction mass they don't need to carry so they can devote their usable energy to moving a large reaction mass. NOTE: All of these percentages are approximate and most are on the high end of the range.
  10. LightSail 2 has successfully demonstrated solar sailing. It has raised its apogee by 2 kilometers using a solar sail for thrust, a momentum wheel for orientation, and electromagnetic torque rod for desaturation. http://www.planetary.org/blogs/jason-davis/lightsail-2-successful-flight-by-light.html
  11. Actually there is an interesting proposal to use in space construction to build something on this scale. I'm not sure how likely it is to actually be built, but it does allow for some interesting possibilities.
  12. In this case voltage, current, and resistance vary significantly with time and you also have to worry about impedance since we're dealing with an AC circuit with reactive components (see https://en.wikipedia.org/wiki/Ohm%27s_law#Reactive_circuits_with_time-varying_signals). I'm pretty sure the voltage will jump as high as it is going to get when you disconnect that switch. While it is superconducting you won't lose energy to resistance (at least through the inductor), but that will change when you quench (lots of energy dissipated as heat). That's assuming your capacitor doesn't burn out the moment you disconnect your supply. You can get the conditions to power fusion using inductors and capacitors to boost voltage since Farnsworth-Hirsch fusors commonly use high voltage flyback transformers (with ordinary inductors) to drive them. Unfortunately high voltage fusors generally don't reach an energy positive point. They are useful as neutron sources and research, but not useful for doing net positive work. The electric and magnetic fields of the plasma would change very quickly with time. This is one of the major hurdles of fusion, once you get it started the plasma generates its own electromagnetic fields that counter the beautifully orchestrated EM fields you used to get them to fuse in the first place.
  13. Essentially you're talking about a boost converter, using the inductor as both the energy storage and the switching element. Using magnetic quench instead of a transistor for the switch is interesting, but probably not terribly efficient. Generally a boost converter is switched at a very high rate to minimize losses, which wouldn't be practical with magnetic quench since the time to re-cool the superconductor would be very long.
  14. This type of station probably wouldn't be for satellite refueling. It would be for launcher fueling. For example you launch into a rendezvous orbit with minimal fuel left, dock, refuel and then continue to GEO, Lunar, or Mars orbit. This exponentially decreases the size of your rocket (or exponentially increases your payload capacity). If you did want satellite refueling, NASA has researched refueling satellites before and they did operate on the assumption that they wouldn't be provisioned for refueling which was proven to work on an ISS mission (Robotic Refueling Mission), though it wasn't a real satellite just a representative example. Chances are you wouldn't have the satellite come to you, but instead send out a tug with just as much fuel as you need to resupply it (see Space Infrastructure Servicing). Methane will be used by Vulcan's first stage (ULA), New Glenn's first stage (Blue Origin), and of course Starship (SpaceX). However, you do have a point since only Starship's orbital stage is methane so only it could benefit directly from methane in orbit. Having said that generating hydrogen from methane is relatively easy (pretty much all commercial hydrogen is produced this way anyway). You would need to liquefy it, which is difficult, but if you have the lead time, power, and cooling systems entirely doable. ULA's ACES upper stage is planned to have refueling provisions which would be able to benefit from a hydrolox refueling station. A fuel depot can afford the extra mass for active cooling, because they don't need to worry about their dry mass/wet mass ratio to the extent a spacecraft maximizing delta-v needs to. The real problem a fuel depot needs to overcome is economic. They need to have enough clients to justify the large up front cost and ongoing overhead. This means either it needs to be cheap to launch and operate or you need a high volume. If we go to the moon and stay for a prolonged period (or even just have an active tourist industry) you probably have the volume to justify it, but until then there probably isn't enough GEO, Lunar, Mars orbit launch volume to make this economically viable (ignoring the case where it is heavily subsidized, which it probably could be).
  15. Definitely a dubious prospect. The engineering challenges are a huge hurdle and even after you solve them, the things it could launch force them into a pretty small niche. It does have one advantage over a lot of other non-rocket space launch systems: you can conceivably change your launch azimuth. A gun or linear accelerator approach would almost certainly be a fixed installation, but this one could change the release point or even rotate the whole launch system into the proper orientation (since it must be movable). Still like most non-rocket space launch systems it probably makes a lot more sense on an airless moon where you don't have an atmosphere in the way and you can scale down the system to something you can practically build because the orbital velocities are lower. Scott Manley did a video on them about a year ago. No huge surprise that a lot of the potential problems mentioned earlier in the thread were brought up, but he added few more and threw in a little bit of interesting history relevant to the topic.