Terwin

Nothing can go faster than c (speed of light in a vacuum = 300 Mm/sec) Cherenkov radiation is due to particles going faster than light in a medium(usually water which is 225 Mm/s). So any particle that is shot though water at a speed higher than 225Mm/s will give off Cherenkov radiation. No need to go faster than c for this.

So for the first few prototype launches they are using as small of a door as they can manage because that makes it easier to seal while they continue to iterate on the design. Once they have a more final design it will likely be more worth-while to spend the design time needed to have a larger opening.

I don't see why not. You would need something to hide your plume from the surface while braking from orbital velocity towards a speed where you would not have significant friction heating.(Presumably you would do this over the day-side of the planet so scattered sunlight would reduce your visibility) Then do a controlled reentry where you keep your speed down and your radar-reflective surface intact until you are low enough for aerodynamic flight, at which point you can be just as stealthy as a B2 as you come down to land on a platform extended above the surface of the ocean by your secret underwater base.

Drones and autonomous transport/navigation are both currently in periods of rapid expansion. Transportation might well be the next industry where we go from 'most people participate' to 'a few specialists take care of everyone' like happened with farming. Sure there will be hobbyist drivers, just as there are hobbyist gardeners, but I could see a 'self-drive' license become a rare thing for which most people have little need. Automakers from Tesla to GM are working hard on autonomous driving, and drones are becoming both cheaper and more capable. (I think GM even had an 'autonomous personal transport drone' in their super-bowl ad for point and click in-city autonomous air transport) I would be surprised if these technologies were not a game-changers at the very least.

To me, that looked like a re-play with close-up specifically added to the tweet, not part of the original broadcast, so any audio would have just been a repeat of what was just said.

If you get the habitation up to 5 years(I think, might be 50 for non-pilots) then the home and habitation timers stop. At that point it is considered a full colony and adequate for long-term habitation. Colony supplies can still be used in the medbay to bring back unhappy kerbals, but at that point the only reason to run the colonization modules is if you have reproduction turned on. As far as I am aware, the exact ratio of colony supplies to additional time has not been published(and is likely dependent on your hab-time/seat configuration). 3.75m has a 'time multiplier' of 6 and a rate of 0.000833 colony supplies/sec 2.5m has a multiplier of 2 for 0.000278 CS/sec This may or may not be related to their crew capacity which matches the time multiplier, but as 278*3=834, it looks like the efficcency may be the same between them. At first glance it *looks like* you may be getting 2 seconds of additional hab-time per 0.000139 colony supplies, but this would need verification.(it might only be 1 second, especially if your timers are stopped) This would be roughly 1 CS per seat for every 2 hours(or 3/day per seat), giving possibly 2 or 4 hours of additional hab-time per unit of colony supplies. Note: med-bays only work on disgruntled kerbals, but look to use roughly twice as many colony supplies per seat/time multiplier, but may also be affected by the number of stars the scientist has, potentially making it more efficient than a colony bay with enough stars. note: these numbers were taken from a 1.4.1 release of MKS

Starship HLS plans to use "high‑thrust RCS thrusters located mid‑body to avoid plume impingement problems with the lunar regolith" when within 100m of the lunar surface. Not really mushroom shaped, and will still need elevators and such, but it sounds like even half way up Starship should be enough to avoid the primary issues. One thing we do not want, would be plume impingement on the body of the rocket itself, which is something that looks highly likely if we were to return to rockets with the fuel tank directly under the engine.

Do you like to eat? Personally, I am quite content for the people who are growing my food to focus on how to do that the best way possible and not waste time worrying about the (often) made-up problems of the people who want to eat it. There are a *lot* of rules and laws already in place for food producers, and agricultural technologies are constantly advancing. Even for a full-time farmer or rancher, that does not leave a lot of head-space to worry about the behaviors of all those people who *need* that food to survive.(not unless they want to neglect their livelihood which *always* has things that can be done to repair, maintain, or improve the results) If your greatest pathogen exposure is spending one hour per week with your family in a room with perhaps 20 other families who also have trivial levels of exposure, your concerns over something like COVID will be different from that of someone who spends 8+ hours each day in an office with people from 50-100 other families, each of which has children in different schools giving exposure to hundreds of other families with a potential transmission delay measured in minutes or single digit hours. TLDR: If you want someone to do something for *your* piece of mind that will not meaningfully benefit them, then you are the one that needs to do the convincing.

Can you provide any references/examples for bombs with multiple sequential fusion events? This is something outside of what I would expect and would like to know if I am mistaken. The reason fission is used to kick-start the fusion, is because you cannot fit other forms of ignition on a plane or missile. (the National ignition facility is large enough to hold 3 foot-ball fields for example)

I am pretty confident that an Orion can *not* SSTO, because if you are not in a vacuum, then a single shield plate will not protect you from the radiation of your bombs. (radiation will bounce off air molecules and sterilize your entire vessel unless you have hefty radiation armor protecting all parts of your vessel, making it too heavy to launch) Not just radiation but hot molecules can also bounce off of ambient air and provide enough heat to your vessel(that by-passes the pusher-plate) that will bake your crew, once again sterilizing the vessel(possibly melting it) long before it can get to orbit. Finally, the shock-waves of all those nuclear blasts will rip apart an Orion vessel in the atmosphere. Once again, this is not something you need to worry about in space because there is no ambient atmosphere to carry the shockwaves. Those three reasons an Orion cannot SSTO are only for traveling through an atmosphere however. For an Orion to launch from a surface(with or without atmosphere), it will need to be protected from the radioactive shrapnel caused by exploding a nuclear bomb on the surface of a planet. A pusher-plate will not be sufficient to shield from radioactive surface shrapnel, so you either need lots of additional shielding, or a rocket engine to get you far enough from the surface to prevent the surface shrapnel.(making it a tsto at the very best, and even that is only on airless bodies) Once again, we are talking about something akin to lighting a maltov cocktail behind your car for the purposes of propulsion instead of putting gas in the tank.

Yes. It is called nuclear energy, and it is very cool. It could address all of our energy needs for centuries into the future(possibly millennia if you include fuels other than uranium), but it is also a bogey-man that will summon al NIMBY protestors within a thousand+ miles, and is regulated to the point where it is no longer cost-competitive with coal and other fossil fuels. (one might almost see a conspiracy in that...)

If you shrink it further, you get a fusion pulse drive or fusion torch drive. Either of which would be far more efficient than this anitmatter-calayzed fusion Orion. I also rather suspect that liquid helium would work much better, be far less complex, and much more possible than trying to use metallic hydrogen in fusion. As has been explained again and again, a pusher-plate is *never* better than a rocket using the same energy source. A pusher-plate is a low-tech way to use a small fraction of an over-powered energy source. It was only ever considered because 1% of nuclear potential is better than 100% of chemical potential.

I am pretty sure that it would need to be at a point where a figure-8 orbit would be (more or less) stable. Larry Niven proposed ring-worlds which are basically a torus possibly with a shepherd planetary-core. I do not think that such a structure would be long-term stable however, and would eventually recoalesce around the planetary core back into a gas giant. (then again, the rings of Saturn are just a transitory feature, so perhaps such a gas torus would last a very long time)

If items of disparate components(like a shoe or bottle of Gatorade) are combined into a single object for determining if a gravity plate will affect it, why does it not include the surrounding air? If a 4 kg tank holding 65kg of water dissolves a couple kg of air(or co2 for carbonization) sitting on a 70kg tile, is it affected by gravity? What if most of that co2 has left solution but is heavy enough compared to the surrounding(very still) air, to stay as a layer on top of the water? Would a 65 kg scuba tank holding 10kg of compressed air be affected by a 70kg tile? What about a 69kg bath-tub that is large enough to hold 1.5m^3 (ie ~ 2 kg of air) but is open on the top? Does a fan in the compartment cause the tub to float? A helium filled balloon with 2kg of lifting capacity tied to a 70kg weight on a 70kg tile? The more details and stipulations you include in how something works, the more holes you open up. In StarTrek there is grav-plating and a grav-generator, and for some reason there is a neat little zero-g area half way between the grav-generator and the main power core. These things are not used for propulsion, presumably because impulse engines and warp drives are better. Even in-world explanations like 'I don't understand why, but the scientists say that it just does not work for propulsion, and all the engineers trying to prove them wrong have failed.' provide more detail than is really needed, but at least it does not open up any holes for the readers. Plot is what should be driving all of these decisions, physics(both real and imaginary) just get in the way. It does not matter to the story if the reason the generational ship is one-way is due to politics, financing, or physics when the MC is a 3rd generation colonist looking forward to standing on a planet for the first time in their life.

No worse than a multi-passenger buss dropping families off at specific bungalows at a resort. envision this: Starship docks, old residents board starship, maid-service works to clean/refresh habitat, then new residents board the mini-station, starship un-docks. Those with a stay of greater than (LS refresh duration) get 'maid-service' part way through their stay. With enough habitats, you can have daily flights that can also address any urgent issues for habitats that are not yet scheduled for return... (I would expect most holiday stays to be 1-2 days under this approach, because there is not a lot to do in a mini-habitat besides look out the window, but corporate/research teams could stay a week or two for micro-g research/production)

I think the national ignition facility has already reached 'theoretical break-even' where you only look at the energy received and the energy emitted, but as the lasers are no where near 100% efficient, and neither is the energy capture for what is mostly gamma rays, there is still a long way to go for a net energy surplus. For all we know, it may actually be impossible to produce a cost-effective energy surplus with one (or all) of the methods currently under development for fusion energy This is a goal that has ben pursued diligently for decades, and while we are pretty good at reliably igniting fusion with some methods(inertial confinement for example), others are still having problems(tokamak, stellarator). As far as I am aware, if we are working on a discrete fuel pellet, we can ignite it pretty reliably, but it is much harder to break-even with this approach. While potentially self-sustaining approaches(tokamak or z-pinch for example) have difficulty getting up to ignition temperatures without losing heat(like plasma leaks), or maintaining it once there(fusion by-products escaping with all of their energy, cooling the remaining plasma). In any case, each design requires different magnetic field strengths. Lots of links to follow here: https://en.wikipedia.org/wiki/Fusion_power

It looks like they are using a crane to move B4 off of the pad, any ideas as to why they are not using the chop-sticks?

And the cost is not having control over your buoyancy, which seems pretty major. (needing to wait until the air in your balloon is sun-heated also means waiting until the ambient air is also warmer and presumably reducing lift)

What is the expected change in the 5BY we are expected to have before the sun swallows both? Was do we think the orbit of the moon/rotation of the earth was ~4.5BY ago when they formed a stable system?

The spontaneously creating/destroying particles(called virtual particles I believe) will normally attract each other and annihilate, returning the 'borrowed' energy they came from. If there is a steep enough force gradient, one of these particles can be turned from it's course and instead follow the gradient(in the case of black holes, this would be gravity of course, with smaller black holes having a steeper gradient). With a black hole, the particle that is sucked in can never re-combine with it's sister particle, turning that sister particle from virtual to real. Because the energy to 'create' that new real particle must come from somewhere, the energy is considered to come from the black hole(presumably the sister-particle that falls in will annihilate with a particle inside the black hole, reducing the energy of the black hole) (I'm guessing the video explains this better however)

Now I know where they got the idea for false vacuum decay...

To the best of my understanding, metallic hydrogen is a form of solid hydrogen with a specific internal structure: http://ch301.cm.utexas.edu/imfs/#solids/metallic-solids.html There have been some experiments using super-chilled diamond anvils that have credible claims to having made solid hydrogen, and I think one of them even tried passing a current through it before it evaporated. So it is *possible* that metallic hydrogen has been created in a lab in microscopic quantities. The ISP benefit of metastable hydrogen is the fact that there is a huge energy released when metallic hydrogen decomposes into H2, and if there is nowhere else for that energy to go, you get *very* hot H2 atoms. Very hot translates to very fast for rocket exhaust, which in turn translates into very high ISP when you have very hot pure H2 exhaust. The down-side of this is that your thrust is low because your exhaust is very light. Metastable hydrogen would be great for inter-planetary transit, but might not even get an airplane off the ground. If you want a very high isp airplane, use a battery powered prop-plane. There is a miniscule amount of mass loss from the battery as the power drains from it, but you get lots of thrust by pushing against the air around your vehicle. I'm not even sure how to do the math, but I would not be surprised by an ISP over a million. (I think you use e=mc^2 for battery mass loss in this case) ISP matters most to rockets because once you are in orbit, (unless manned) you only care about mass-efficiency, and ISP is a measure of mass-efficiency. For airplanes, cost-efficiency is a much more important metric, and a fuel that would cost more than an equivalent weight of multi-carrot diamonds is not in any way cost-effective.

Do the QD connections require human assistance to connect? Any thoughts on the propellent aggregator keeping the fuel super-cooled? Would it likely even keep the fuel cooled aside from venting to keep the pressure reasonable? Presumably they would like to keep at least some fuel for extended periods(such as a buffer in case of losses during fueling), but I would expect cryogenic fuels to require active cooling and I do not recall hearing anything about that.

A flexible tube would probably require an EVA, and I believe the current plan for loading up the fuel depot only involves unmanned flights. Extending a prehensile fuel line sounds like a significant engineering challenge, and no relevant results pop up on google for the term.

So tungsten and DU pellets provide Looting deterrence as a fringe benefit? nice.