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satnet

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  1. SpaceX could never launch humans without FAA/NASA approval. If it is from US soil there are treaties in place that make the US responsible. Even if they launch from international waters as a US company the government has oversight. If they launched without it they would probably lose every government contract overnight and every commercial contract shortly thereafter. They aren't foolish enough to do it. Anything can be human rated if you can demonstrate that you have sufficient forethought into survivability. Looking at commercial crew the expectation will probably also include un-crewed demo flights to empirically demonstrate safety. You can never make it perfect, but you can demonstrate adequate forethought and margin in your design, which is as close as any engineering endeavor gets. Having seen something similar before makes it immensely easier, but is not a prerequisite.
  2. Their main point is about cryogenic storage and transfer, but reusability was a stated criteria for selection (which necessitates fuel storage and transfer). SpaceX was unique in selecting LEO refueling, but all of the proposals had some variant of this. It is unprecedented, but one of the points of Artemis is to set this precedent. I do think the national team had decent hardware proposed, but I can't say they've handled this well. I expected the protests, but this just not putting their best foot forward. They seem to have decent engineering, but management and marketing could use improvement.
  3. Removing the transmuted elements is actually a feature of thorium reactors. They are self-enriching as a result which means that you fully utilize the thorium instead of leaving it as unprocessed waste (uranium rods actually still have a lot of viable fuel left when they are taken out of service, but no one wants to re-enrich them to a usable rod). They are also passively safe because they can make it so if it gets too hot it melts a plug and drains into storage tanks where it will shut down without the moderator. For a deeper dive I highly recommend the Illinois Energy Prof's video:
  4. I believe you're thinking of ZBLAN fiber optics. It is a legitimate improvement in the quality over manufacture in 1g, but I believe it isn't economical at current prices.
  5. I just ran across a good video by Anton Petrov with details about Ingenuity's first 4 flights and a few technical details about the helicopter itself. Highlights: All primary objectives are completed (successfully). We have actual video of some of the flight maneuvers downloaded from Perseverence. They plan to use it as a scout for as long as it can keep up (they will only fly once a week or so, which I presume is the reason it will fall behind). Perseverance will now get the majority of time and effort. The 4th flight was a success, but did have another instance of the software glitch that they needed to workaround before the first flight.
  6. There are numerous lawsuits over government contract awards in both directions that prove otherwise. SpaceX is also working on vertical integration which as far as I know has zero commercial applications (certain classified payloads require this).
  7. I think even Elon would agree Starliner will carry crew sooner. The reason Boeing is getting so much flak is because they said "according to our organization's engineering practices Starliner is ready to carry humans". It then had serious (though not life threatening) problems. They then stated that they had never done a full integration test, something that I can scarcely imagine and yet they acted like it was no big deal. Starship is still in the pathfinding/experimentation phase when mishaps are acceptable because it is meant to find the problems early before they are serious and SpaceX has never characterized it as done or even fit for cargo much less humans. Boeing's engineering judgement is in doubt because they overstated their readiness in the final phase, while SpaceX appears to have a solid grasp on what "ready for production" means even if they have a few more explosions on their way to getting there. I would like to see Boeing succeed (they employ a lot of people where I live) but they haven't exactly inspired confidence lately. Starliner will fly and be certified but they paid a heavy cost in schedule and goodwill for cutting a 24 hour integration test.
  8. You remember correctly, they use hydrogen peroxide as a fuel, which is non-toxic but does spontaneously decompose at an appreciable rate even without a catalyst.
  9. 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 coincide with my interests rather than their normal monthly issues, which might bias my perspective. I would also recommend looking at Smithsonian's Air & Space magazine. Obviously it is more focused and has more of a history point of view than scientific, but could foster an interest in engineering. IEEE Spectrum is another pretty decent option for engineering. It tends to be reasonably technical, but still covers things that are of general interest.
  10. 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 is handling crew rotations. In the long term Boeing does have a contract to launch Starliner and there are ample political and practical reasons why that will be seen through and we have every reason to believe Russia will continue (every time someone suggests retiring the ISS they say they'll just undock their modules and continue on their own). From a technical standpoint there isn't a reason why SpaceX couldn't handle crew rotations (as far as I know), though production capacity could be a limiting factor. They can't handle all ISS operations, specifically refueling, but crew rotations are possible. As it stands right now all it would take is the grounding of Soyuz and this actually would be the case until roughly June 2021 (assuming Starliner performs flawlessly from here on and the hypothetical Soyuz grounding lasted that long). From a political and practical standpoint it is almost certain that this wouldn't be allowed to persist. At a minimum Russia would insist on launching crews both for their own national pride and also to maintain the international ideal of the International Space Station. With respect to Starliner, it gives us a backup in case some flaw is found in Crew Dragon, which is a very practical reason to keep it given the history that lead to the commercial crew program in the first place. On the political front Boeing has a lot of contracts with NASA and the government at large and employs a lot of people.
  11. 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 a lot of material. Rockets launches are few enough that economies of scale don't necessarily apply, so just having fewer infrastructure pieces may be a net reduction in cost even if a dedicated machine might be faster/cheaper per piece made. It is hard to say whether this is a gimmick or game changing tech at this stage, but there is definitely a lot of interesting things happening in rocketry these days.
  12. 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 like Babylon 5 where non-military ships require well controlled jumpgates rather than being able to achieve high speeds on their own. 2. Anti-gravity and spacestations - If anti-gravity fields require a lot of power then space stations can still make sense. It really depends on the rules you create for your anti-gravity drive whether it really kills space stations. You can also make a plausible case for space stations as orbital habitats (maybe to handle overpopulation or just to give humanity a backup option) even if anti-gravity makes it easy to get to orbit. Having said that, good science fiction extrapolates from existing science to a place that is logical enough that it doesn't require a lot of explanation to to achieve "suspension of disbelief". There are certainly a lot of tropes in science fiction that are extremely common, but actually don't make a lot of sense based on current science. These are usually because they were tropes before the science was established or more often because they fix a common need in narrative story telling. Examples: 1. FTL - While there are some vague theories about how this can be achieved, most require negative energy and other things that may simply not exist. It does however make it plausible for the same crew to see more than one planet in their lifetime, so we generally accept it. 2. Transporters (Matter->Energy->Matter type) - The Heisenburg uncertainty principle makes this highly unlikely. The fact that this involves containing the same energy as a matter/anti-matter detonation of equivalent mass also stretches credibility. Star Trek at least had the Heisenburg compensators as a nod to those in the audience who knew why it probably wouldn't work. 3. Telepathy - The idea of one brain naturally interfacing with another is pretty far-fetched. Doing it wirelessly is even more so. I will however give Babylon 5 credit for having a semi-plausible explanation (direct genetic manipulation by a more advanced species rather than a naturally emerging trait). 4. Energy Shields - We know of nothing that could allow anything like an energy shield to exist. They do however make it possible to have space battles that aren't just ships firing missiles beyond visual range at one another (though the Expanse proves that can be cool too if you know what you're doing). 5. Knew elements with fantastic properties - No matter what planet you're on the atomic elements are the same (different ratios for certain, but the same elements). You aren't going to another planet and finding new elements, that will probably happen in a lab. If the proposed "island of stability" exists you might be able to create heavier elements, but they will almost certainly have the properties you can extrapolate from their position on the periodic table. Also my recollection is that the stability is relative and they are still short lived, just not the femtosecond lifetime you might expect. You can definitely get some materials with unexpected properties, but the trope is usually a new atomic element. Really you need to keep your audience engaged and keep from pulling them out of the story while they try to make sense of your concept. This usually means not straying too far from the rules we have come to know in our everyday lives with some plausible extrapolations. You should also try to avoid creating rules that contradict existing laws (over-unity energy production for example). Probably more than anything you need to be internally consistent (once a rule is introduced don't change it) and you should probably avoid creating rules that obviously only exist purely to satisfy the needs of your narrative.
  13. 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.
  14. 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.
  15. 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.
  16. 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.
  17. 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
  18. 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.
  19. 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.
  20. 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).
  21. 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.
  22. 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
  23. 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.
  24. 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.
  25. 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.
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