wumpus

I figured that, and it is also clear that he makes a clear difference between blowing up his gear (which is much more expendable than his heart) and being shocked directly. But the point of the thread is that three phase is typically used for hazardous levels of power. Being careless with the voltages inside a computer is relatively safe (just don't short a car battery or you will learn just how high current can get), being careless with three phase can leave you dead.

First, be careful. While it certainly helps to be reminded of the obvious, you won't last long in the field while that big a danger to yourself (says the guy who worked with a Senior Electronic Engineer who was missing the use of the fingers in his left hand thanks to using a band saw the wrong way. Let's just say the technicians kept the engineers away from the power tools much more zealously for awhile). Second: three phase motors have another large advantage as the sum of the voltage between each two rails is constant (the sum of all three together is zero, but circuits rely on two inputs). This allows a three-phase motor to deliver smooth power instead of the 120Hz impulses of single phase (in practice this was pretty irrelevant. Single phase and gasoline engines can simply add a flywheel to smooth out the power, but it becomes much more relevant in modern application where the inverter is only generating power for the motor [because it essentially is part of the motor]). Finally, his description of "brushless" vs. "induction" motors is all wrong. "old fashioned" (i.e. 20th century and the Edison vs. Tesla battles up to domination by switching power supplies). DC motors had brushes and used electromagnets to pull permanent magnets (or vice versa). The brushes were needed to switch the electromagnets on an off and/or switch polarity. AC motors were "induction motors" and used electromagnets on both sides. They were tied to 3600rpm (or a close integer multiple, I think a 3 phase motor would get thee times that) thanks to the fixed frequency coming from the generator. I think there was also a pretty hard limit of ~30hp (22kW) power limit on AC motors (although I'd think you could get the thing going with a system of kludging relays into square waves for frequencies ~6Hz or so). DC motors should be more powerful without starting motors or other kludges, but I'm sure they had similar issues at some power level. Modern motors of the 21st century: Brushless: Just like the old fashioned type, except that transistors control the output into the motor instead of brushes. In practice also expect the control circuits to include most of the parts for a DC-DC converter to send just the right power to the right places. Also these motors tend to use rare-earth elements to make wildly more powerful permanent magnets. Generally the powerful rare earth magnets allow for a more compact motor. Induction: Just like the old fashioned type, except that instead of getting power from the generator as AC, they produce the AC directly (and if powered by AC you can expect this to be first converted to some DC rails used to power the AC inverter, and anyone designing the inverter will nearly always design this in three phase [unless cutting cost and indifferent about efficiency] to balance out the draw against those DC rails). This allows the motor to produce maximum torque at zero RPM and let a Tesla move the car with 800hp (or whatever "plaid" produces. The old ones would just have enough torque to move the motors at 30hp and need a clutch once going). The other benefit to induction motors is that it is far easier to use them as generators while braking. - note: I suspect that "old fashioned induction" motors to never quite die out for low power sources that operate at a fixed speed with an AC supply. Brushed DC motors are already dead as the life expectancy of a brushless motor is much higher and the cost already low (the volume just isn't there for a cheaper brushed motor). PS: no matter what his shirt says, a full wave bridge rectifier is drawn like the following (are Canadian drafting standards that different?): Note to Canadians: is that bit with the meter and the outlet remotely right? In the US we run a single pair of wires from the breaker box to multiple outlets. What is shown in the video implies a breaker for each plug in each outlet. Pretty expensive, but it does have a small advantage. Is there an option to plug in two plugs and get three-phase power?

ULA can still pick up the juicy no-bid DoD and NRO launches. I'm sure Bezos has enough political baggage that the Military Industrial Complex can still get things done the old way. On the other hand, maybe he keep building new Amazon headquarters (or extend the competition) and make senators in finalist states steer business his way. He's finding he has more power than just margins.

The delta-v for a London-Sydney flight might as well be the same as to orbit. NYC-China should need 90% of that. NYC-Paris will be 75% (which might get away without staging). If you have the opportunity to have a layover in orbit with the 20 hour flight replacement will you take it? It will barely nudge the delta-v requirements... PS: don't run out of ignition fluid...

I expect that Verizon and Comcast (and other non-US communication companies) paid a lot more for the same volume of last mile (and last km) connectivity. And Starlink has a much better idea of how many customers they can expect. For a business project dreamed up to justify a Mars rocket, this one seems pretty good. Not sure if you can round up 250 passengers for a single exorbitant intercontinental trip.

It was tested against the bullets of the day (and possibly a weak one at that, but at close range). The point was that the meaning of the word changed and the original meaning was forgotten. The "proof" in the word literally meant the proof of the dent that it could stop a bullet, not that it could stop all possible (and later) bullets.

The word literally means "tested at close range with a gun, and typically still has the dent to prove it" [ok, so this is probably now definition #3 or #4, but it is where the word comes from]. Of course, that pretty much died out with the renaissance and more powerful muskets. It is hardly "no such thing", more like "bulletproof armor won't help you at all against modern firearms". This concludes today's etymology lesson.

I don't think you'll see metal expanding things ever work on Earth (outside of movie SFX). SCUBA has been holding on to propellers for years to get where they want to go. Is the propwash too unpleasant for wingsuits, or is it insufficiently cool compared to jets? I suspect the main point of winged flying is getting youtube views, so coolness is probably the big selling point.

The three phases are supposed be 120 degrees apart and shouldn't add up to 400V unless you start out close to 300V per rail. The big dangers are a wet environment (like when washing the machine), the issues that these things tend to be connected to inductive loads (if you disconnect a circuit in such a way that you become part of the circuit, the thing will attempt to maintain current regardless of your resistance. This will be lethal), and the dangers of the delta (no neutral) configuration (all rails can float relative to ground). The problem isn't "three phase". All else considered, it is probably one of the safer means of transmitting power (compared to single phase and DC transmitting similar amounts of Watts). The catch is that three phase is almost always used for high power devices and is a clear signal that you need to be careful.

It isn't that the human body isn't aerodynamic: look up wingsuits. It is that it the "aerodynamic mode" (superman position) doesn't lend itself to takeoff and landing. There's also the issue that even the glide ratio of a wingsuit implies a pretty high thrust out of an engine: you wind up with a similar issue as the Isp issue with the jetpacks. I suspect "the chance to fly around" will be a big draw for space tourism. I'd guess Icarus style in the lunar indoors would be most popular, but jetpacks might also be popular. But hardly enough of a draw at today's (and possibly with BFR) prices.

How big are those "wet workshops"? Skylab had a maximum stay of 88 days and would take roughly 9 Saturn Vs worth of fuel to haul it to Mars and back (no lander included). Obviously something more Salyut sized would work better, but you still are venturing into unknown shielding territory. NASA stuffed John Young and Micheal Collins into a Gemini capsule and left them in orbit for as long as it would take to go to the Moon and back. Unless you are expecting to build and man a Salyut sized craft (preferably with the same crew) for the years it would take a Mars mission than this is going well beyond the Apollo program. Granted, this might mean that such an extended mission might go up in the mid 70s and a full on Mars mission could be scheduled for 1980, but don't forget the relentless small steps that appear to be the hallmark of successful space programs. SLS isn't going to Mars. Being cheaper than a program that isn't going to Mars says absolutely zero about capability to go to Mars. You might as well say they can go to Europa. Show me a BFR and what cargo it carried to orbit and you would have a point. But I *did* admit they can transport the kg to Mars (Falcon Heavy certainly should change things on its own). But that does absolutely zero to getting the money to fund the project (something Musk has bailed from, spacex will only provide the transportation) and all the rest of the spacecraft (the habitat needed to go to Mars, the lander/return craft, any systems needed for assembly in space). Remember that the cargo is typically *significantly* more expensive than the launcher. These are expensive. COuld I ask WHY we still have this strikethrough but that has plauged this forum since the "update"?

Apollo could send an Apollo capsule to Mars and possibly return it. Finding astronauts willing to live in such a state is another issue (kerbals don't seem to mind, just keep the snacks coming). The other big difference is while a human managed to stay in Mir for 500 days, that was only after the launch of 9 Salyut [the whole station, not just crewed missions] launches (including some thrown in the memory bin) and the needed experience. I don't think that the ISS can survive 500 days without resupply, including specific needed parts. To get to Mars, you need a whole lot of money, you need the capability of delivering the required mass to Mars, and you need the ability to survive for nearly 3 years with no material support. Spacex has barely started to complete one of those requirements. I think you could get the job done with Falcon Heavy and an ion-based system, although it would take a decade or so and you would need to launch the Mars habitat early (which is one of the critical "unknowns" right now). Spacex is of course insisting that BFR is needed for Mars, and would certainly make things easier. I have strong doubts that BFR will significantly reduce the pile of money needed. Trans-Mars spacecraft and ground habitats will be even more expensive than BFR. The next clear stage is a space habitat: the earth bound Mars simulator and ISS are great ideas, but a Lunar-orbiting system would be far superior as it would be getting all the trans-Mars radiation that is a current unknown. It would also allow supplies to be sent on a similar schedule to ISS, although at far higher cost (hopefully Falcon Heavy is up to that job). There is a long way to go to be ready for Mars.

They got the "soft landing on water" long before they landed on the barge.

or how about "How not to land a booster": https://www.youtube.com/watch?v=bvim4rsNHkQ I somehow doubt that BO is going to build their first orbital-capable booster with a 99% chance of successful landing (not anything you can walk away from, but enough to reuse the engines). It seems that their market certainly includes those who take paper/powerpoint rockets at their word. On the other hand, they certainly seem likely to shake up the rocket world. I doubt ULA and the SLS program are going to be happy explaining their continued high costs. Spacex has an orbiting ISP to pay for the BFR, I wonder what type of manifest New Glen is supposed to have.

Compared to most other turbopump driven liquid engines, it certainly has a less complex job. Of course, being the first hydrogen engine produced in the US, it was almost certainly over-engineered. It also (current editions) appear to contain two RL-10s, when it "should" work better with a turbopump with multiple nozzles (it is limited by the ability to heat hydrogen to drive the turbopumps).

I really have to question your math. From everything I can find, it takes at least 3km/s delta-v to get to the Moon (note that NTRs are likely to have issues getting much from Oberth thanks to low thrust and start/stop issues). Apollo 11 took 51 hours and 49 minutes to get to the Moon. They used a free-return trajectory so they had a pretty much a standard Hohmann trajectory (or at least similar time expended). Average distance to the moon is 384,000km. time: 186540 seconds. distance: 384000000m. Effective radial velocity: 2058m/s. There is no way adding 450m/s (each way) to 2058 is going to cut your time by 2/3s (you'll get an 18% improvement). You will need upwards of 8km/s delta-v to the moon and another 4km/s for coming home (assuming you are willing to aerobrake at those speeds: most of your incoming speed will be thanks to your LEO delta-v). A NTR can easily get twice, possibly three times the Isp of a hydrolox engine, but that means that you can get at most 3 times the delta-v with the same mass ratio as hydrolox (and don't forget that NTRs will have some nasty dry mass). I suspect that either you meant 1/3 (and then forgot about braking) or got said information from someone who made such a mistake. Brachistochrone trajectories are favored for hype (and distant Sci-Fi flavor). There is certainly a lot of benefit in a small excess of delta-v for long journeys (especially for Mars and beyond), but the cost adds up quickly.

Ouch! RL10s appear to be some of the most simple liquid [turbopump] rockets ever designed, being expander cycle. I wonder if political pressure keeps Orbital from manufacturing it themselves (I'd assume that they can get the plans from NASA and could modernize them).

In KSP your best bet is to go into the "cheat menu" and turn off gravity. Take your vehicle and launch it perfectly horizontally (the spaceplane hanger will do wonders, although you might need launch clamps to keep it off the runway), and see how long it takes to slow down, this should at least give you indications of air resistance at that speed regime and altitude (subsonic, transonic, and supersonic should behave differently, although it might require Ferum to get this right). Notes from NASA: https://spaceflightsystems.grc.nasa.gov/education/rocket/flteqs.html More: https://www.grc.nasa.gov/WWW/K-12/airplane/dragco.html (I deleted a more ground-biased example that I wrote. Stick to NASA's explanation). Also, your gravity losses are relatively easy: (TWR-1)/TWR. If you are doing a relatively natural "gravity turn", you should be able to substitute (cos(angle of attack)(TWR-1))/TWR. But now you have a nasty calculus problem that requires you to also already know the path you are taking, not to mention the complexity of the aero-fixed equation. Don't expect to be able to be able to come up with a "God equation" that lets you specify an ideal rocket.

Reducing time to the Moon by 2/3s would require something like 2-3 times the fuel needed to go to the Moon. It would also reduce time going to Mars by an equal ratio (which might well be worth it). The only reason I could imagine for such a stunt would be to get a cargo carrier back before all the hydrogen vented out. Not that I would be all that surprised if people decided to take the "fast route" once NTRs were up there, but it isn't a very good reason to dig into all the political and technical problems for NTRs.

Do you really want to be in a confined environment with multiple large tanks of hyrdazine and NTO? I'd imagine there are enough things that can go wrong in a submarine without bringing something like that aboard.

A mountain launch during dawn/dusk plus lights should give nearly unlimited visibility (especially near Denver: Denver is basically the westernmost bit of prairie before the Rockies. Visibility is basically limited only by how much air you can peer through (you might want to try going a bit north or south to avoid too much air/light pollution). Of course, you would have to be careful about elevation issues. In practice it would likely be more like a missile (depends on thrust) than an aircraft (depends on lift). The scaling factors would require far more thrust than crewed supersonic aircraft that you end up building a missile engine. I also suspect that non-turbine engines would work well as compression fans for said jet (especially at supersonic speeds), making supersonic thrust that much harder. Can you build a supersonic compressor without scaling up your RPM to turbine speeds? Wouldn't the same issues that plague low-power turbines also be a problem?

As far as I know, "all solid" rockets use multiple stages. Pegasus uses 3, the tiny solid Japanese orbital rocket used 3-4, the peacekeeper missile used 3 (+ hypergolic navigation/MIRV), minotaurs seem to use at least 4 stages (wiki is weak on specific minutemen data), typically solid. The same argument can be used for liquid, although to a lesser degree. Generally speaking, SRB's lower Isp means more stages and g-force buildup is less of an issue. Granted, you can avoid gravity losses much easier by starting with high g-forces, which makes the buildup that much worse, but low g-forces don't seem to be driving launch vehicle development.

A lot depends on if you save anything on fuel thanks to the lack of air resistance in flight. Last I heard, you only saved fuel compared to mach 3 flight, pretty much killing the idea of suborbital cargo at least as long as we are limited to chemical rockets based on methods listed in Ignition!. I also can't imagine the BFR ever being safer or remotely as efficient as the Concorde, which doesn't help make it common in the modern world (not the US and EU, maybe China is more bold).

367 satellites a year. One per day (with way too much overtime). I'd assume that is comparable to shipping 60k Tesla Ss a year, not trying to mass market a Tesla 3. Mass production is the first thing that made Musk stumble. I have no reason to suspect that Spacex can't do the BFR. Judging from the FCC application (and spacex's love of vertical integration) they would be directly responsible for getting all 2,213 birds (initial run is 1,600) manufactured. It won't be good having two constant sets of crisis going on in the same company (not saying that anything is going *wrong* with BFR, just that it is a major project pushing their limits as a company and is going to have plenty of moments of crisis and handling them).

Starlink plans to have 83 specific planes (inclinations) used. While some will be more full than others, with ~2000-4000 satellites total it seems that even a BFR wouldn't fill a single plane in a launch. Inclination changes would presumably be a single burn to insert all birds into the same plane. I'm curious to see how much mass a block 5 FH can lift to LEO (with arbitrary inclination changes). The current FH can't lift much beyond ~68 tons to anywhere (limited by structural support), but there was obviously a chance to change that in block 5. I suspect that Elon Musk didn't hedge his bets at all and that this is purely a job for BFR. For those wondering about the business: 200,000 people coughing up $50 a month (the only figure I've seen, but it certainly would be competitive in the US. Developed nations might have cheaper ISPs that are harder to undercut) for 10 years will provide a billion dollars (ignoring interest. That will be a large chunk of any calculations considering sunk BFR costs and the four year launch plan). I'm sure there are significant non-infrastructure costs, but still that has to be the biggest cost of an ISP and the biggest barrier to competition. We also don't know the NRE and production costs of the satellites. I sure nobody has ever tried to build 4000 copies of one spacecraft. Why do I get the feeling that Spacex is all over this research and that ULA won't use it without additional NASA/DoD/US govt funds specifically earmarked for a composite tank?