K^2

You don't. Your first order estimate is going to be that the ship just collided with hard surface and bounced off. You don't care about the details of the interaction. You do care about energy lost, which is a function of angle of incidence and impact velocity. To get that, you might want to run a bunch of simulations for with different starting conditions and fit an approximation formula to the results. This is sufficient to start solving for fly-by trajectories and come up with candidates for near-optimal solutions. Once you have these, you start actually numerically solving for a flight through atmosphere and adjusting parameters - basically, it's just a multi-variate optimization problem at this point, so you'd use a standard method. You will need to factor in lift in your simulation for energy lost estimate function and in final optimization. Aerodynamic forces are conventionally split into drag and lift. Drag is component of aerodynamic forces matching direction of relative wind and lift is component perpendicular to relative wind. The equations for both are very similar Lift = (1/2)CLρv², Drag = (1/2)CDρv², where CL and CD are lift and drag coefficients respectively. v is velocity of relative wind. ρ is density of air. Both CL and CD are functions of angle of attack and of mach number (more generally, velocity, density, and temperature of air stream, but modeling it as just mach number is surprisingly accurate). Generally, very non-trivial functions, so you'll have to have some fit formula. Typically, these would be obtained from full aerodynamic simulations, but there are a lot of ways to get a back of the napkin estimates that aren't bad. That's a whole topic in itself, though. So for the energy-lost simulation, I would probably select alpha for given mach number that gives you best glide ratio = CL/CD for given mach number and integrate flight through atmosphere with that for each choice of incident velocity and angle. Get your data, fit a formula, and use that to estimate energy-loss in your fly-by optimizer, treating each encounter with atmosphere as a hard, elastic impact. Once you have an approximate plane that works, you start simulating in earnest and optimizing all of your parameters, as well as making sure you don't exceed structural limits. Edit: If you're doing this in KSP, your best bet for getting accurate simulation is just spawning the ship under conditions of interest and going for it. If you get enough data points, you should have a pretty good estimate.

To Bill's point, the collision will not be perfectly elastic. You should treat it as a collision with an energy loss. Also, there are going to be severe limits on the angle of incidence if you want to skip out of the atmo.

Pretty sure that thing has the same creation story as A-10. "You know what that gun needs? Wings!"

Mars feels like a good industrial base. Low gravity and thin atmo means rail launch is viable. I'm just not sure if it's substantially better than Moon for it. For a colony world, Venusian cloud cities all the way.

Yeah, I couldn't imagine this is a new idea somehow. I'm more curious why nobody built one. Unlike NTR, this is scalable. At least, it scales down quite well. And unlike NTR, there are no regulations blocking something like this. I'm sure back in the 60s, somebody just said, "Why bother, just stick a nuclear reactor on it," as that was basically attitude towards everything, but why haven't we revisited the concept since?

Stop giving them ideas. So long as they keep trying to make killer robots humanoid, we have a chance.

Wait... Why aren't we doing this? No, I don't mean with dung, just in general. You can get 3,000K out of solar easy. That's plenty for NTR minus the N. (Sorry, @Nuke) I'm sure specific power will be, well, topical. But you should have the same 800s+ ISP that you get with NERVA if you feed hydrogen through it. And in principle, collectors don't have to be that much more complex than solar sails, it's just a mirror. To get 1N of thrust, you need about 0.15km² of solar sail. Or instead, you can eject 0.125g of hydrogen per second at 8km/s, which takes 40J/s. Even at 10% thermal efficiency, that's less than half a square meter of mirror, which is, well, trivial. Scaling up back to a 0.15km², that's 150MW of power, which at 10% efficiency still would be enough to give you more thrust than NERVA did. Somewhere in between, there ought to be a practical rocket.

You can recycle it into better fuels. Methane should be achievable. But the main weight is still oxidizer. I'm not sure you're saving enough to be worth the trouble.

Do you have a citation on that? We know that Kerbol is still there, and we know there is at least one other system. But do we have an actual confirmation that there are multiple systems other than Kerbol. And technically, all that Nate confirmed in this thread is that there is more than one system, which can still mean just the two total. Kerbol and the new system.

If you didn't see Transnistria (aka Transdniestria, Prednistrovie) mentioned and went, "Oh yeah, that makes sense now," you probably should read up on the region a bit. The famous Mythbusters quote, "I reject your reality and substitute my own," can be a state moto. It won't surprise me one bit if it turns out that these helicopters were fully certified in Transnistria.

Yeah, basically. But the instability bit is key. In summary, the moment you get anything inside a Kerr black hole, the interior collapses into something else, and I'm not aware of actual solutions that describe what it becomes. So in real world, the structures described by the video do not actually exist. What does exist may or may not be similar. One strong indication that there are substantial differences is that we haven't found any white holes in our universe. For that reason, anything with an exit to another universe seems unlikely, but a supermassive rotating black hole might still contain a pocket universe under its inner horizon, if, indeed, it has one. I don't have any high hopes for precise mathematical solutions explaining what's really happening inside a rotating black hole, but it might be possible to find a solution with numerical simulation, but starting with Kerr metric, perturbing it, and simulating collapse to a true ground state. Back when I was in grad school, that seemed entirely out of reach, but there has actually been a lot of progress on simulations with really big data sets in higher dimensions, so we might be getting close to the kind of compute power that this would take. Hopefully, we'll know exactly what sort of things are actually happening inside a rotating black hole soon.

This applies to a point mass falling in. Physics of a black hole swallowing something with substantial mass, like a neutron star or another black hole, is different. Black holes merge in finite time producing quite a gravitational splash that we can actually detect with LIGO. And, of course, anything that was close to event horizon when two black holes merge will also get swept up pretty much instantly from our perspective. That does make a close fly-by of a supermassive black hole both a legitimate way to time-travel forward and an extremely risky one, as it's very easy to get swept up by a gravitational wave of something else falling in. It's not about light speed. Time dilation at event horizon diverges to infinity. That's part of why event horizon is also called a coordinate singularity, which is different from true singularity at the center. From perspective of observer falling in, you reach Schwarzschild radius in finite time. From perspective of remote observer, it takes infinite time due to that time dilation. But this only works so long as the thing falling in doesn't have enough mass to alter the space-time metric with its own gravity.

If you want a precise answer, "because math." But if you are ok with a bit of hand-waving, Schwarzschild radius, which is as close as you'll get to a black hole and have a hope of returning, grows linearly with mass. Tidal forces are an inverse cube relationship with distance from the center and linear with mass. So the larger the black hole is, the lower the tidal forces at Schwarzschild radius. Sure, the black hole is more massive, producing stronger forces overall, but you are also that much further from the center, which is a bigger factor.

Rotating black holes are still a bit of a mystery. We have solutions for everything that happens above the event horizon - it's called Kerr metric, and it has some exciting properties. Like, it allows you to actually go "bellow" event horizon utilizing frame dragging in the ergosphere, which lets you steal a bit of an angular momentum from the black hole to escape from a distance you normally shouldn't be able to. The singularity of the Kerr metric is a ring that is infinitely thin but has finite radius. Unfortunately, Kerr metric is also known to be unstable in the interior region, which means that the interior of a rotating black hole is not cylindrically symmetric, and that means the singularity is probably not a perfect ring. Without solving for the interior metric, it's impossible to say what it's actually going to be like. If Kerr metric is very close to true solution, it might be as simple as singularity being an ellipse, but there are other possibilities as well.

Yeah, but you're saving with bringing a lot less oxidizer, which is a huge chunk of the fuel weight. So this might be a good trade. I was talking more about conventional LH2/LOX engine.

Highly efficient ascent profile requires very fine tuning of TWR along ascent. It peaks at about TWR of 3, which is great because that's also about as high as you want it to go for crewed ascent, as you point out, and it happens after you burn off some of the fuel. So if you start at 100% throttle with TWR a little under 2, and start gravity turn until you hit TWR of 3, you're actually pretty close to perfect ascent. But after that, you need to throttle way down. There are ascent profiles that let you ride the rocket at pretty close to 100% throttle, but they are way less efficient, bringing you up to 10-10.5km/s requirement in worst cases. That's often an acceptable trade off in staged rocket with kerlox or solid boosters, but it's really not good for SSTO. Which is why ability to throttle the engine is one of the major tech challenges to SSTO. And if you're combining that with something like aerospike to combat the change in pressure, you end up with a very complex and heavy engine.

Some of the proposals that Harold White and his team have looked into have at least some scientific basis, even if all are kind of out there. But there's also stuff like EM Drive, which I'm pretty sure only showed up on their radar because several other teams reported results on, and they had equipment to look into it. I think the article might have just talked about EM Drive because it made a bit of a buzz a while ago, but the actual interest is in things like quantum thrusters. To be clear, all of these ideas are highly speculative. The difference is that idea for EM Drive is based on a self-contradiction, so it could have only worked by complete dumb luck. Other suggestions are based on hypotheses of how vacuum works that are entirely ad-hoc at this point and aren't supported by any experiments, but that's how pretty much every theory starts out. Most of them end up being wrong, but you find out by testing. I do think the team kind of over-sell what they're really doing, but I guess that's how you get funding.

With good ascent trajectory you only need about 9.5km/s. So that's about 1.6x the exhaust velocity at 600s. So you only need 75% of your takeoff weight to be propellant. Very reasonable for SSTO. Honestly, even with just conventional rocket on LH2, ISP is pretty close to ideal. The two challenges that prevent SSTO from being the simplest way of getting to orbit is needing different nozzle bells for different altitudes and being able to maintain efficiency at full throttle and throttling down to about 10%. And the moment you start fiddling with using different engines for different parts of the ascent trajectory, two stage is just cheaper, and then you might as well go kerlox. If you have an engine that provides a weighted average of 600s throughout ascent and has the right throttle range, yeah, SSTO sounds like a good way to go.

The biggest problem with the fundamental concept of EM Drive is that the initially proposed explanation for why it was expected to work comes entirely from classical electrodynamics. And classical electrodynamics is built on Minkowski metric, which has certain space-time symmetries, which by Noether's Theorem lead to momentum being a conserved current, meaning you can't have a reactionless drive, and conservation of energy, which means that unless you're expending reaction mass, you at best have a photon drive which is horribly inefficient way to move about. So it's mathematically impossible for electromagnetic drive to operate as advertised. Either it doesn't work at all, or the reason it works has nothing to do with electrodynamics. And if it's the later, and we stumbled on something that produces thrust by a novel, unknown before method, entirely by chance, in which case, everything they've been trying to do to study it is kind of hopeless. Of course, it was extremely unlikely that it was ever a real effect at all. Noether's Theorem is actually a bit more general than just electrodynamics. It's kind of in foundation of all modern particle physics and cosmology. An entirely underrated theorem by an inexcusably underrated mathematician, Emmy Noether. The odds of us stumbling on symmetry violation or new force that exists outside of known symmetries by pure chance with something like EM Drive is astronomically low. Primarily, because we've spent a lot of effort intentionally setting up experiments to look for these things. So it being something trivial and unaccounted for was almost a given. I haven't actually heard any specifics since the craze in the news died down, but what @Nightside said about power cable sounds very plausible. Don't get me wrong. It's good that there are people out there who say, "Well, fine, but why did we keep measuring thrust?" and keep looking into it until they find satisfactory answer. It's good practice for when we go on to test things we're actually have doubts about, if nothing else, and sometimes, you discover a tangential effect that's of worth. But from perspective of whether EM Drive was a real deal, there was no reason to wait for a debunking. Despite how awesome of a discovery that would be, I'd be comfortable enough not even trying it, because that's how bad the odds of it being a real effect were.

That's not actually correct. It's important to understand that event horizon is a coordinate singularity, not a physical one like the singularity at the center. Event horizon is not a fixed surface, but rather is relative to your frame of reference. Physics is, indeed, undefined if you want to be at rest w.r.t. the singularity, which is impossible once you're bellow Schwarzschild radius, but a free-fall frame exists and is valid. What happens as you fall into a black hole is that the event horizon appears to flatten as you get closer, and then wraps around, creating what's known as Schwarzschild bubble around you. So rather than appearing to be bellow event horizon, which obviously can't work, it appears that absolutely everything in the universe is bellow the event horizon, which surrounds you fully. At no point do you actually experience crossing the event horizon. Also, from perspective of someone falling in, you make it to singularity in finite time. Of course, not in one piece. Even for supermassive black hole, whose "surface" gravity is quite manageable, allowing approach well within Schwarzschild radius, as you get closer to singularity, the tidal effects are still going to reach the point where they pull apart absolutely all matter. So the Schwarzschild radius is still that final judgement point - all trajectories bellow it lead to singularity in finite time. @WestAir To your original question, I actually don't know. I'm going to pull up some references and might need to crunch some numbers. Intensity of Hawking radiation encountered by a free-falling object should be calculable, but I'm not sure about correct frames of references for the few commonly cited formulas, so I'm going to have to look up a bit more detail on derivation, and hopefully, I'll be able to get back to you quickly with exact numbers. Edit: Depends on the mass of the black hole. The larger it is, the weaker the forces are at the event horizon. Supermassive black holes are actually perfectly fine to approach from perspective of the tidal forces.

It's worth pointing out, that more savvy and rational consumers would lead to the two coinciding a lot more often. But practice shows that people will absolutely re-buy DLC, no matter how much they grumble about it on forums. It's very similar to prisoners' dilemma. If all of us would stop buying re-hashed or intentionally cut from main game DLC, we would probably all get more for the initial purchase and better DLC. But that would mean giving up on at least some of the DLC that we find acceptably priced, even if we think it's unfair, which is the incentive for "defecting". And, of course, if enough people "defect" by buying such DLC anyways, there is no incentive for publishers to set up pricing any different. I'm pretty sure we'd still find things to up-sell people on, so even from perspective of someone who has potential to earn money from people buying more DLC*, I don't think it'd be such a bad thing if gamers actually made better purchasing decisions, but I can't offer anything like a concrete plan on this. It is note-worthy that public image and reviews are a factor in sales, and cutting something that customers and reviewers consider essential from the game is going to be detrimental. We've seen this plenty of times, so it's not entirely gloom and doom. There are feedback mechanisms in place that actually do work and protect gamers from egregious exploitation of downloadable content monetization. But once you've managed to make a game that manages to sell well, whether on merits or marketing, then there is really no incentive not to sell everything else piecemeal. * Yeah, it's mostly publishing house execs who are getting rich from DLC and enhanced edition floods, but bonus programs are often tied to games' post-release performance, so even rank developers have incentives to push more DLC.

Without servos and electric motors as core part of KSP2, it'd feel like major regression to me, personally. If any other parts of these expansions, or something similar to them, ends up in DLCs, I can live with it.

ShadowZone did a video with some thoughts and more gameplay.

Smart Delivery allows for simultaneous cert for XB1 and SX. Like I said above, it's a single SKU. But even setting that aside, certification is nowhere near this bad. If somebody's telling your cert takes 6 months, they're trying to sell you a bridge. It's a process, and the reason why PC builds sometimes get shipped very raw and unfinished, which sometimes also means early, but even then, it's nowhere near 6 months. Never having worked on KSP nor talked to anyone involved, I can't say for sure, but my best guess for why the lag is so large is because KSP UI is very different between PC and consoles, and UI is where a LOT of the bugs are coming from for a game like KSP. The PC is also clearly the lead platform, which means that while PC release is getting polish, the port team is just starting to work on UI for the new features. And yes, to update the UI, get all the bugs out, go through cert and release can open up a 6 months gap between PC and consoles. Very little of it is actually due to cert, and almost none of it applies to difference between console versions. If you have a working PS4 Unity game that passes cert, you have a working PS5 Unity game that passes cert. And passing a cert on that can take less than a week. If we were actually talking about console release getting delayed past the game's scheduled release, yes. It would make sense to release on current gen and delay the next gen until the consoles are out or possibly even longer. But there is no way PS5 or SX are getting delayed to fall 2021. That just isn't happening. I would say that even a simple delay isn't happening, because production of hardware takes time, and to be ready for a holiday release, both consoles have to be in production already. Sony is almost certainly going to be fine releasing with insufficient units to cover demand, and Microsoft would most likely have to do the same in response rather than delay. So we can be talking about a shortage, but even that would get resolved by fall one way or another. That kind of depends on demographic. Spending behavior among young adults suggests that they'll make cuts elsewhere more likely than not purchase the new console. You can take a look at iPhone sales as an indicator. Granted, a large segment of console sales is parents buying them for kids, and that will most certainly take a dive, but gamers are getting older and older as a demographic. I'm not saying situation is ideal for a console launch, but if you are expecting them to tank, you aren't looking at the right trends. Sony has released tech talks on the hardware they are using, and I know enough about how storage is used in games to tell you for a fact that what they're doing is going to make a huge impact*. The rest I can't really talk about, but I suggest you do a bit of your own research. * I'm using PS5 as an example of improvements a lot more than SX because I've seen more officially published technical material from Sony. I don't want to even remotely imply that I'm drawing any sort of comparison between PS5 and SX capabilities.

It's a Unity game. There's zero reason not to release on PC and both generations of consoles at the same time. The XBox versions will probably even have the same SKU via XBox Smart Delivery. It's actually going to be easier to release proper next-gen builds than trying to push through the XBOne and PS4 versions via backwards compatibility. Game industry is currently experiencing almost no slow-down due to the pandemic. It's hard to insist definitively that this will continue to late 2021 and that the current trend in game sales will extend to consoles, but at the same time, there is currently no reason to suspect that next gen won't sell well. It looks like Sony finally figured out how to have their cake and eat it, and are shipping a console that still has familiar hardware and API to avoid pitfalls of PS3 release, while still providing plenty of amazing improvements that makes PS5 worth having. I'm sure you've heard about switch to an SSD, but I don't think you have any idea just how much of a difference that makes. It's nothing like installing SSD on your PC, because they've built the entire pipeline from SSD memory, to memory controllers, to hardware decoders, and into the chipset to completely streamline how data gets from SSD to RAM, and it's basically as fast as technologically possible right now. There are a few other improvements that are a bit technical to discuss, but will provide improvements to quality of gaming experience for both PS4 and PS5 era games running on PS5 with either zero or absolutely minimal effort from devs. Microsoft hasn't been quite as open about what they're putting into their console so far, from what I've seen published, but they are also making improvements across the board. They are also going with an SSD, but it's hard to say if they're quite as all in as Sony. What we do know is that with next generation hardware support for ray tracing becomes an established feature across all major platforms, which is huge in and of itself. Again, it's a little hard to say for sure yet how big RT will be based on officially published info, but my biggest takeaway from last-year's SIGGRAPH and how heavily ray tracing has been featured, even a little goes long way, so long as you have hardware support for it. You don't have to render every pixel on the screen with rays to get a much better looking scene. It's subtle, but once you start playing games that feature good GI and shadows using RT, it will be hard to go back, and both systems claim to be capable of it. It won't be long until game developers embrace this new tech and it will be a must-have for a lot of new games. This means sales for next gen consoles and RT-capable graphics cards. All in all, I think by late 2021 the install base for Series X and PS5 will be significant. They certainly won't come close to install base for current gen yet, but in terms of generated game sale revenue, they should start getting close. But kind of a moot point, like I said. Even if install base for SX and PS5 will be tiny, there's just no reason not to have a build for them. You can justify having less QA on it, and maybe not bothering to tune for better performance, but given that install bases will grow, and you can patch the games later to leverage the hardware better, it's best just to ship all of the versions on the same date.