K^2

No. There is no net angular momentum transfer and at equilibrium, no net work, as there is zero average movement in radial direction. All it's going to do is reduce orbital velocity for given distance by the tiniest of amounts and probably circularizes orbit over very, very long time.

I don't mean editor as a mod. I mean mods with an already modified tech tree. If you want to make your own tech tree, you really ought to be prepared to take an extra step and make a mod.

I can't imagine them making something that's simple, intuitive, and does everything it needs to do as a built-in tool. This feels like it should be left to mods.

There are exoplanets out there currently within the corona of their star that are cool enough to have liquid water on the surface. They probably don't, because they probably have their atmosphere stripped, but bellow surface, they can be habitable even by our, terrestrial standards. If you are happy calling that thriving inside a star, then you are technically correct, and we don't have a disagreement. But it's kind of like if you did Mars fly-by, skipped off the atmosphere, and then said you've been to Mars. Technically, sure... Nonetheless, if that's what you meant, I don't have any objective disagreement, just a subjective "meh" feeling about it. And exponent is an excellent model for the graph. You're just thrown off by a constant bias, which, as we've seen above, is pretty much irrelevant to planet's motion. If your model is exp(...) + constant, and constant is tiny, then you can just model it as an exponent. That place where density curve goes almost horizontal? That's the fun part. Planets touch that, and NOW they're heading into the star-proper. This is the only part that interests me from perspective of "What happens to the planet once it's inside the star." Until then, it might as well be in slightly harsher solar wind. And yeah, technically, since this is a log scale, exponent would look like a straight line, and you can see that within chromosphere there's a good chunk that is actually almost perfectly exponential. If you extend that line through the top of chromosphere and into the corona, you'll get a model that's good enough for rough estimates. Again, getting that density to within an order of magnitude will get you correct qualitative predictions, and that line looks like it'd do. So for modeling behavior of a planet falling into the star, I'm happy enough calling that an exponent until you hit photosphere.

I think I know where you learned to solve problems.

Checks out. Cd is going to be of order 1 for basically anything. You'd need a better model to get precision, but for order-of magnitude, just take it to be 1 and you'll always be in ballpark. Getting slightly larger number, but close enough. So one last step this needs to be formal is figuring out whether that actually is a lot or not. Best way to do this is to take this as energy loss and look at how that impacts orbit. On the following plot, I've taken specific force, multiplied it by orbital speed, and assumed constant energy loss. Then I plotted how the orbit decays with that energy reduction. I did actually bump up density to 10^-14 g/cm³, because that's the highest number I could find for coronal density of the current Sun, and I think you'll see why in a moment. The x axis is time labeled in years and y axis is semi-major axis in AU. So that's like 5% decay in a billion years. Thing is, if we don't get dramatically higher density at 1AU, Earth will be fine. I mean, yeah, atmosphere will be gone and surface scorched, but Earth will still be right where it's at now. No plunge into the Sun. So let me revisit the point of contention. I'm reading this as Earth actually becoming part of Sol proper, not just passing through its extended atmosphere. If all you meant was, "Earth gets bathed in Solar corona, and life persists somewhere within," yeah, maybe. But that's not actually being inside a star. Mercury is going inside the star. Venus is going inside the star. Jury's out on Earth, but if it does go inside the star, the descent is not going to be like the above. It can't, you've just demonstrated that. And what the above graph really tells you is that deceleration will be smooth and gradual, right up until the point that you start hitting denser pockets of stellar matter, and then it won't be fine and gentle anymore. That's a completely different profile. To get an idea of what the descent will be like in reality, you should model density as an exponent. Now, it's not a perfect model, but it puts you on the right track. And you can run the numbers, but actually, we already have KSP doing that for us. Sort of. The model for aerobraking is similar. Again, not for precision, but kind of order of magnitude sort of thing. Put a ship in circular orbit just skimming the atmosphere. It can actually hang there for a while, because drag starts out really low, but you also aren't getting any heating or anything else of note, and a light puff of engines will pull you straight out. That's what we're seeing above. But once you actually start descending, the process is very quick. You can hang on the outskirts for a long time, but not through your actual descent. And this will be the case for any planet spiraling into the Sun. Same goes for heating. While Earth is bathed in corona, the surface will be boiling, cooling everything down. Temperatures will be in high hundreds, possibly low thousands of K, but well within what we're used to dealing with. I'd have to take a look at heat conduction through rock to see how long the deep-living bacteria have, but I suspect it will be a while. Possibly long enough to outlive the Star if the Earth doesn't fall in. But if it does fall in, that final descent into the star is going to be brief and it's going to be violent. And the time between deep bacteria not even experiencing any changes and the planet being ripped apart into atoms is not going to give you enough time for any kind of evolution to work. So either Earth stays pretty much where it is in orbit, scorched, but not fundamentally changed, in which case, sure, there might very well be life surviving within it pretty much until the core freezes solid. Or Earth falls in, in which case, the ride will be short.

I've seen some recent papers from studies of other stars that suggest that we might have been severely underestimating extent of corona at red giant stage. I don't recall details, and whether that'd be relevant to our own Sun when it reaches that stage, but it might be enough to offset whether or not Earth, and possibly even Mars, end up decaying from their orbits due to drag. If I'll find anything useful, I'll add info. Right now, take that with a considerable quantity of salt.

It's dense enough to generate tremendous drag. Yes, heating from corona, while significant, will cause ablation over very long time scale, except, Earth isn't sticking there. Even in high corona, the orbit can be maintained on the order of decades, maybe centuries, not hundreds of thousands of years that you need. And once the planet gets to low corona, it will decelerate very fast. Most likely, it will break up. Sun's surface is right on the threshold of Roche limit for Earth-sized object (0.8R for rigid and 1.55 for fluid), and with a help of hydrodynamic forces of low corona, I'm pretty confident calling it. [Edit: I'm being silly. Of course, this is in relation to Sun's current radius. Once Sun becomes a red giant, Roche limit will stay well inside, so it's not a factor at all. Hydrodynamic forces might still break up the planet, but I'm not nearly as certain of it. Rest of the post stands.] Even if the Earth somehow didn't disintegrate due to combination of gravitational and hydrodynamic forces, it would decelerate very rapidly at that point, ending up literally sinking in much lighter hydrogen-rich atmosphere of the Sun. And as much drag as it's going to generate, it's not a very slow process. Add to that pressure and convective forces, and Earth has about as much of a chance as single ice cube in a hot cup of tea.

@Dragon01 How is that supposed to work, when atoms don't form molecules anymore?

I was with you up to this point, but here I have to call B.S. Even if hypothetically life can exist in a star, which seems very dubious from thermodynamic perspective, it can't be life that evolves from anything on Earth. First of all, because absolutely everything life here uses in one way or another relies on chemical bonds, which go away completely in Sun's atmosphere. Secondly, because while it starts out slowly, once the star expands sufficiently, the descent from, "Oh, it's really hot in here," to "Planet's becoming part of the star and chemical bonds are failing," is actually pretty rapid. So you are asking for an impossible adaptation to happen in impossibly short time, and this is not a case where two negatives cancel each other out. Now, if, say, Mars becomes habitable again due to temperature increase, some rock from Earth can end up there, (re?)seeding life. So Earth life can, indeed, survive demise of the planet itself even without Humanity's or any other civilization's help, but it would be via planet-hopping, not living inside a star.

That's how games are supposed to work. But then contracts happen.

Almost exactly twenty years ago, I remember splicing GPF gene into a plastid, using electrophoresis to find the correct size fragments, and adding these to e. coli to make a glowing test tube. It was an AP bio class, the whole experiment came in a kit, and things you could do with this technique were pretty limited, because there were no simple, generic ways to find sequences you wanted, but the basics were very similar to what you still do today. Don't get me wrong, stuff that's being done is still super impressive. From techniques for getting the exact sequence you want into exact place you want, to methods of sequencing. 20 years ago, electrophoresis was still the main way of gene sequencing! Something like 23 and Me seemed absolutely impossible. But writing was on the wall for the direction things are going. Given that at the time I had a flip phone with no camera, because that just wasn't a thing, and it was considered advanced because it could talk to mail server, watching things develop along side with electronics, some part of me is even disappointed with advancements in gene editing. It's not a rational part, but it's there, kind of like flying cars.

Well, you have to splice adenovirus' genes at a very minimum. The way this delivery method works is that there are known sequences on adenovirus' genome that mark beginning and end of a "payload". Normally, payload contains genes that when expressed make the capsid proteins, but you can put basically anything you want there instead. What they've done with Sputnik V is grabbed the sequence for one of the proteins on the surface of COVID that it uses to bind to cells, one they're calling S protein on the site, and placed that sequence in the payload of adenovirus. Now, I don't know if this applies to all adenoviruses or not, but the main reason adenoviruses got popular in gene modification is that they're good at sneaking payload into cell nucleus and getting it incorporated in the genes of the cell. This is useful when you want the cell to keep expressing a particular gene long after the therapy. It's possible that this particular variant of the virus doesn't do this, so in that sense, it wouldn't be splicing your genes. But there are other viruses in your cell that have no qualms about grabbing stray DNA like this and adding it to your gene sequence. Like another adenovirus that you're already infected with, and most people are. So it's not like you can guarantee that it won't be happening. Of course, this sort of thing happens naturally as well, but that never stopped people complaining about genetic modifications. And yeah, technically speaking, unlike some other forms of gene therapy, it's entirely unnecessary to try and incorporate the payload into human genome. All this really does is emulates infection without infecting you. The protein in question ends up on the surface of affected cells, and immune system will produce antibodies regardless of whether the S protein got there because you're infected with COVID, or because it was made from a snippet of code snack by adenovirus. I suspect, depending on the dose, fever and inflammation, possibly even pneumonia, are possible side effects, but you wouldn't get the same lung tissue scarring, so I don't think it's a problem for healthy individuals. Outside of something really out of the left field, the ways this can backfire that I can think of are that S protein sequence does get incorporated into your genome in enough of your lung cells to just continually trigger immune response. Then you either die of your lungs filling with fluid, or they pump you full of immunosuppressants, and you die of a cold, or something. The other possibility is causing false resistance, potentially turning people into carriers without symptoms, potentially making outbreak worse. Both of these are pretty unlikely, but the fact that these things do happen is the reason these kinds of things usually take a lot longer to test properly and safely. If there are no devastating side effects, however, I expect this to work. There's no way to tell how well it will protect any given individual, but if enough people get the vaccine, herd immunity will make short work of the pandemic. Which is probably why Russian gov't is willing to roll the dice on this. Economy is doing rather badly, which is always a risk of unrest, especially with what's going on in Belarus right now. On the other hand, if vaccine works and gets people back to work before neighboring countries, it's a great trade advantage. So the gov't might look at this as being worth the risk.

It does, actually. In fact, it makes it a lot worse. At sufficient speeds, things that aren't normally a type of ionizing radiation become ionizing radiation. Such things as interstellar dust, then hydrogen and protons of interstellar medium, and if you're going fast enough, light from distant stars. Coming up with a ship that can practically survive hyper-relativistic speeds is a nightmare. In fact, if you're traveling at 0.999999994c, which gives you time dilation factor of a little over 9,000, the microwave background radiation turns into X-Ray at an intensity of hugging a blue giant, and at 0.999999999999994c, when time dilation is over 9 million, universe shines gamma radiation at you at an intensity I'm scared to think about. Now, on a trip to Alpha Centauri, you won't encounter anything nearly so extreme. You just don't have time to accelerate to truly ludicrous speeds. For nearby stars, it's only interstellar dust you have to worry about. Everything else you can take on with modest shielding. But the moment you go beyond our immediate neighborhood, difficulty quickly ramps up.

Sand-like particle impact satellites pretty regularly. To do some damage, you need a ball bearing roughly a mm in diameter. You also want to hit something vital with good odds, and tidal forces will distort the grid, so lets say 100m radius at about 5cm apart? That's 400/m² * 31,415m² = 12.5M bearings, which is a little less than 100kg. Again, that's bear minimum, assuming you have good aim and can spread the bearings very uniformly. If you have a tech for all of that, you can probably build a kill vehicle with maneuvering engines that's going to be cheaper to throw at sats. If you don't, the amount of garbage you need to throw into orbit to hit something quickly increases. I think you're still better off with an active kill vehicle, regardless. Also, way less debris.

You severely underestimate the amount of correction you typically need. Even if you had exact orbital elements to start with, you're not going to hit a sat dead on. ICBMs can't hit with that precision without terminal correction, and their targets are stationary. Because of that, you don't know by how much you're missing until you're close enough to sight your target visually or with radar. Lets say you were 100km away when you were able to get a clean enough sighting/lock to determine that you're 50m off target. Very generous parameters. If you're going head-on in LEO, you have a 15km/s closing rate. So you need to move laterally 50m in 6.7s. That requires acceleration of 2.25m/s². Not a lot for a rocket, but you're not pulling that kind of acceleration with an ion drive. And chemical thrusters have a huge problems with precision. You're not going to dial in thrust precisely in that time. So instead, you want to fire multiple brief puffs, taking measurements and making corrections after each one. With modern manufacturing methods and the amount of computer power you can put on a rice grain, it's not exactly earth-shattering, but you're building something far more complex and expensive than a rock. Still, in today's world, putting the kill vehicle on the near-pass trajectory is probably the harder part of the problem. Terminal maneuvering can be solved for spherical horse in vacuum. Ascent to target trajectory requires corrections for atmosphere, gravitational anomalies, and tidal forces just to get you close enough to have a chance of intercept. Way more things that can go wrong for you, making it a very hard problem.

I don't think we've ever deployed anything via adenovirus broadly, but to be fair, that is becoming the standard way of delivering genetic payloads to non-stem cells for all kinds of gene therapy and has an excellent record so far. Given the sheer magnitude of risk if something does go wrong, I still consider this broad distribution with such small amount of testing to be irresponsible and unethical, but in terms of pure likelihood, it will probably be alright. If you'll allow me a Machiavellian moment, from perspective of anyone not living in Russia, having close relatives there, or being close to the border and risking being caught in border disputes if there is destabilization, this is all wonderful news. Because Russia is basically taking on the risk of stage 4 testing not only a COVID vaccine, but adenovirus as delivery method. Something we absolutely would not have for years without it. And if everything goes well for Russia, not only will every other country have similar vaccines within months, but it opens up doors for the rest of the world to develop cures for such things as lactose intolerance via very simple, very safe genetic mod, with the only known potential risk being adenovirus delivery itself. That is, of course, a very cynical take on situation, because an untold number of lives are on the line if this goes sideways. For these interested in more background, here is a video of a biohacker engineering his own version of adenovirus to cure his own lactose intolerance, as well as a follow up video on results.

Minor nitpick. Tides, yes. That energy is already "stolen" once you have a tide, so tidal generator just lets us make better use of it before it turns into heat, but you're still entirely correct on where it comes from. Winds are more complicated. Rotation of the Earth shapes direction more than strength of the winds. Coriolis Force, like magnetic fields, does no work, because it's applied perpendicular to the motion. It's responsible for formation of Cyclones, yes, but not for the energy stored in them. The energy still comes primarily from solar via thermal convection. Yes, there's tidal contribution to wind as well, but most of the wind energy is ultimately solar.

Science as progression never felt quite right in KSP from gameplay perspective, but I don't think it's a bankrupt concept. Just not terribly well implemented. I'm ok with some completely different progression system, though, one that has nothing to do with science. Regardless, I would like to still see things like thermometers and barometers in the game as functional parts. So I hope we get to keep some of the experiments in game, even if they aren't directly used in gameplay in any way.

So is hydrogen/oxygen in LH2 rockets by that measure. This isn't a useful distinction. Rocket fuel is just a way to store a lot of energy in one place, and whether that fuel was found naturally or had to be made hardly makes a difference, so long as there's efficient method for production. Yes, we aren't there with AM yet, but we'd have to be to be buildings ships powered by it. So distinguishing between natural fuel and "energy transportation mechanism" isn't really necessary.

I actually had no idea there were successful tests all the way back then. Good to know.

[snip] We are trying to do estimates of a physical quantity, namely yield of explosion in Beirut, using known methods. Dimensional Analysis is chief among these and resulted in early estimates. It has a big spread due to how sensitive the results are to measurements, but then we had more data and other methods were applied to refine the estimates. There is valuable discussion here about methods and results. Including bad estimates that result in errors, and that's fine. We sort through these and we try to figure out why these things don't work. That's scientific method. And this discussion is very valuable as an example of scientific method which is basis for this entire subforum. When I asked @sevenperforce where he got numbers I thought were suspect, it wasn't to make fun of him. It was a question in good faith. I took his equation, and I ran the math myself, and I found an inconsistency. Sometimes it goes another way. I follow someone's link, and I learn something new or discover a mistake in my own math. And that's valuable. This is why we're sitting here juggling numbers and estimates around instead of just talking about what a tragedy the explosion was. That's the whole point of having such a discussion, and it can only work when people act in good faith.

I didn't need to. I cited it. I freely admit, I had to look it up, but the reason we had initial estimates in place before destruction or seismic data is Dimensional Analysis which has been famously used to get estimates in Trinity tests and applied all over the place. That's the SIMPLE and WELL KNOWN math. So go ahead and tell me why dimensional analysis is wrong here. And again, your formula applied to Trinity Test provides a wrong answer. Please explain.

Look, the only bit of math you provided is in this post here. Now, I didn't want to touch it, because I know how that discussion goes. But because you keep claiming that you've provided evidence in another thread, here it is in all its glory. I'm going to set aside for a moment the fact that the fireball radius estimate is off by a factor of two. I've hinted a number of times to you that you should go back and actually measure against the map, but even then you refused. That alone would inflate your estimate by a factor of 8, as volume increases as a cube - almost an order of magnitude. But that's not even the worst part. You are using an estimate used to evaluate sub-sonic explosions. Literally the only place I've found this used in practice is depth charges, but this might also work for early WWII munitions and older. The core assumption is that fireball pressure is balanced against atmosphere. The problem with that is that there's a shock wave separating from the fireball, and there is gradient of pressure across any supersonic shock. That overpressure you kept mentioning? The one that goes into many times atmospheric pressure at fireball radius? That means your estimate of 1 bar is wrong by a factor of a few to lots depending on speed of supersonic wave. How do I know that there's a supersonic shock? Because I can measure buildings 500+ m away from the fireball that are reached within a second of shock wave separating from the fireball. I know you'll try to jump in and come up with some sort of reason why 1 bar is the correct value to use. But there's a simple test. You know how critical thinking works? If you have a hypothesis, apply it to a situation you can verify. If I take 20kT explosion, say yield of Trinity Test so that we have lots of data on it, and then I do the same math on it. Your doubling was arbitrary, but lets do the same thing and half the yield that we count towards fireball expansion. So just 10kT, then compute corresponding radius, we get that fireball should stop expanding, according to your math, at R = (10kT * 4.2GJ/T * 3/(4pi) / 1bar) ^ (1/3) = 460m. Actual fireball at ~20kT yield is measured to be about half of that radius. So we just found another order of magnitude error in yield. The actual physics of fireball expansion at supersonic speeds is that so long as the pressure is sufficient to keep accelerating shock wave, the fireball keeps growing. Once the pressure drops bellow that point, the shock separates. That pressure is rather high for a high speed shock. The specifics will vary from explosion to explosion. In case of a nuke, you can assume all energy is released pretty much at once for sake of simple math and use it as an estimate. Chemical explosions aren't as clean, and the fireball for the same yield will vary with the type of explosive due to that fact. This is why absolutely everyone has been using rate of expansion as a measurable and not the final size. So you are using a completely the wrong model with completely the wrong input resulting in two orders of magnitude of error [snip]

No historical background on this whatsoever, but without rifling and with gun powder charge varying from shot to shot, I don't know if actual sights will do any better than sighting along the body of the barrel and calling it good enough.