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  1. Discover is probably the best bet for your kids. I once had a Scientific American subscription, but over time I came to the same conclusion @kerbiloid did and dropped it. SciAm is still probably a better option if you want something deeper than Discover that is still reasonably kid friendly. Science is probably not going to be the best option unless your kids already have a deep interest and you're trying to nurture it. You might also consider National Geographic. They tend to be more multidisciplinary than you might expect, though I tend to pick up their specials when they happen to coin
  2. There are two International Docking Adapters installed, which is what Crew Dragon uses. Cargo Dragon uses the common berthing mechanism to dock, so it doesn't use the ports used for crew operations. You should clarify what you mean by "near future" because Starliner hasn't been cleared while Crew Dragon has, so for the short term SpaceX is already handling all American launched crew rotations, though there are of course Russian launches as well. Looking at the schedule SpaceX is handling the next two rotations, and Soyuz is handling the third, so for certain values of "near future" SpaceX
  3. There is a fair chance that 3D printing this particular part is a gimmick. Having said that if I give them the benefit of the doubt I can come up with a few possible reasons. There is more that goes into the tanks of a rocket than you might think. They are pressure vessels and often structural. Rocketry is so mass sensitive that I'm sure that getting it to the point where it has enough material to match the safety margin and no more is generally the goal. Also I remembered this post when discussing Vulcan's manufacturing where it was apparent that traditional manufacturing involved a removing
  4. Here's the thing with sci-fi: You can get just about any concept to make sense with the right rules for your fictional world. No concept is truly DOA, though some things require more work than others to make believable. Your list definitely has concepts that require a fair amount of work to really make sense, but it isn't impossible. For example: 1. Private ownership of starships - If "planetary shields" are a thing you could allow private ownership because you now have a defense (of course now you need to explain how shields can exist). There is also the option of doing something li
  5. 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
  6. 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 ve
  7. 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.
  8. 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 scientifi
  9. 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 forme
  10. 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.
  11. 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 inter
  12. 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
  13. 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
  14. 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
  15. 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.
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