NERVAfan

IIRC it's just barely possible for the Earth to be pushed into an unsurvivable 'runaway greenhouse' state given its insolation. I doubt there is enough fossil fuel in the world to get us there. I can see us ending up in an Eocene/warmer parts of the Mesozoic type scenario with no permanent ice cover - 'hothouse earth' - but that is survivable. Ecologically disastrous, yes, and tragic on a human level too -- agricultural regions would shift enormously, sea levels would rise and flood coastal cities*, much of the human population would have to move, especially bad in the poorer nations which have less spare resources to relocate people and feed them. We should make huge efforts to avoid it -- but the planet won't actually cook or turn into Venus. EDIT: Humanity will survive, civilization will survive. *I can't see seawalls working if the East Antarctic ice cap melts with its ~60 meters of sea level rise, but that would take ages given its gigantic thermal inertia. If it somehow did happen, we'd have to remove CO2 from the atmosphere with 'carbon capture and storage' technologies, use things like iron fertilization of the oceans to try to trap more CO2 biologically, and even try the crazier things like injecting sulfur dioxide into the upper atmosphere to darken the skies and cool the planet (this is mostly why huge volcanoes like Krakatoa and Tambora cool the world, the ash mostly falls out quicker, it's sulfur aerosols in clouds that do most of it). Of course that has the side effects of acid rain and more, but if the world was going to cook... This is not true. The ONLY reason our current agriculture is at all 'unsustainable' is because of its use of fossil fuels; if we switched to renewable energy we'd be entirely OK food-wise. The US farm subsidies etc. actually mean we farm very inefficiently. I would be surprised if current technology couldn't grow enough food for 20 billion people (note that China is a net exporter of food, is the same land area as the US, and is probably worse farmland on average -- I would expect US at max efficiency to be able to feed several billion people minimum). And technology will continue to improve. The Sahara desert was mostly grassland until ~7000 years ago, we could probably change it back (probably even without too many ecological ramifications; 7000 years isn't much time for evolution, the species should be able to survive in a wetter environment). And we are just entering the age of genetic engineering; I don't think crops 10x as efficient in calories/acre/year are at all unlikely in 50-100 years... possibly much sooner if we stop being paranoid about GMO crops. (As for that, even corn is completely un-natural; most people wouldn't recognize the wild ancestor, teosinte, as being corn -- it looks more like some ugly wheat/weed hybrid. And there is all kinds of crazy hybridization and genome-switching in nature, there's a grass in North America that has octets of chromosomes instead of pairs -- octets composed of 4 separate pairs, from 4 separate ancestral species -- it's a four-way hybrid. Bacteria swap plasmids all the time. And even "transgenic" organisms, DNA transfer between wildly distantly related organisms, exist in nature. A sea slug, Elysia chlorotica, has incorporated DNA from the algae it eats into itself. The bacterium, Agrobacterium tumefaciens, used in genetic engineering naturally inserts its DNA into plants. ) -- Overpopulation is pretty much a myth; Malthus was simply wrong - a technological society's ability to feed itself will grow faster than population. Especially since birthrates are crashing in the developed world; below replacement in most developed nations. We will actually have economic problems as a smaller working-age group has to support a huge retired group.

Ah, I'm glad to know this, I've been putting ladders on both sides of my Mun landers....

Sure, but it still lets you have more stars and planets. Well, there is actually a debated report of a sizzling planet (3.4 day year) around Alpha Centauri B. It hasn't been confirmed yet by other astronomers, and some have tried to find it and not been able to, so maybe not... In any case, there have been models/studies saying that planets are stable in that system as long as they are close enough to one of the two main stars (Proxima hardly counts as it's so far away, like a fifth of a light year). Earthlike orbits are supposed to be stable, and there is actually a project looking for them (FINDS Exo-Earths, run by Debra Fischer... the Planetary Society has been raising money for it), but it's currently taking a hiatus to improve equipment and because A and B stars are now too close together and are interfering with the observations. http://www.planetary.org/blogs/bruce-betts/20140401-update-on-the-search-for-planets.html (Planetary Society blog update on the project from just a week ago where they talk about the hiatus, and not being able to find the reported really close planet) We already have fission rockets (nuclear thermal), that's what the LV-N is. Fission rockets are great compared to chemical rockets, and some hypothetical/more advanced types, like gas-core, could do significantly better than the solid-core NTR that the LV-N represents, but it's still only a few thousand seconds Isp, and that's not enough for interstellar. I am always a fan of Orion drives, but even they are slow over interstellar distances. Workable as a generation ship (or maybe with future advances in anti-aging/life-extension), but only then. I think they are supposed to max out at something like 3%-5% light speed, even for highly advanced versions, which would mean about 85-150 years to Alpha Centauri, even scaled down at 10:1 that's ten or fifteen years... at 100,000x time warp 10 years compresses to about 53 minutes, assuming my math is right. That's long... but hmm, not as bad as I expected, and if they could add 500,000x or 1,000,000x warp (maybe once you get beyond a certain distance from Kerbol, interstellar-only or something), you could drop it much further. But the real problem is ... ....this. Really long non-time-warped burn times. I think compressing distances much more by creating a multiple star system (or just say Kerbol is in a really close star cluster, but at the kind of distances I think make sense, they'd probably be gravitationally bound anyway) is a better option. Plus, I'm not sure if the game could handle a really large number of stars and planets. KSP planets are not Spore planets, which were tiny (and probably had randomly generated surfaces too, though I'm not 100% sure). As awesome as a whole cluster or even galaxy would be, I think 2-3 stars and 10-20 planets would be a very full system. And a minor nit-pick... Actually, I think disease would be very unlikely to be a problem. Assuming you are careful (quarantine before boarding) there will be very little disease, because once they're embarked... there's no one outside the small population to catch anything from, and the generation ship is tiny compared to Earth so there will be vastly fewer opportunities for diseases to jump from animals to humans. (Especially if you are careful to bring healthy animals...)

Sure, but that would be like 10 parts instead of 1. As someone playing KSP on a not enormously new laptop, I like the part-count-reducing effects of ARM a lot. EDIT: I'm fine with it existing as an option of course, the standalone engine would be cool. I just really do like the clusters.

That's "the size of Texas" or slightly larger than Kerbin (assuming they mean a diameter equal to the distance across Texas), even Kerbal-scaled down it would be the size of Dres... so in a sense, we already have one. Right now, we have celestial bodies that are "on-rails" and can't be moved no matter how much thrust you apply, and asteroids which can be moved. There would need to be a "demarcation line" size, somewhere between Gilly and a class E asteroid, where the two categories meet... presumably at whatever size it isn't practical to move them. I'd imagine that size would be wherever the acceleration applied by a couple of the biggest engines at max thrust would be small enough to fall in the game's "noise"... I don't know what that would be, though. Probably significantly less than 1km, as a wild guess.

I like the idea. Latitude/longitude and elevations too, though maybe only after mapping (elevations anyway).

And the 5x speed means 25x kinetic energy, so yeah, significantly less dangerous than Chelyabinsk even without the weird-physics deletion of them. Also, I believe KSP asteroids are quite low density, and IIRC those tend to airburst more than iron-nickel ones (is that correct)? So yeah, I think they would mostly not be much of a problem.

I don't actually mind the increased thrust, as such... it lets you do the same stuff faster, and from that perspective it's a good thing. But it's a step away from the fix I would like: thrust-during-timewarp, low-thrust ion engines. Well, I didn't think that was the case, they worked fine for me... for niche applications, yes, but they're niche anyway since LV-Ns can get you everywhere in the scaled-down Kerbol system. There's not much point in having ion engines in the game, given that scaled down system and the availability of LV-Ns, unless you get to use the different kinds of trajectories real ion engines use. But it can, it's been done in mods (Orbit Manipulator Series and -- I think -- KSP Interstellar's solar sails). Exactly. Not only is the time warp thrust engine more interesting, the current ion engine is kind of out of line with the other engines. The KSP solar system is scaled down, but the physics is all pretty much realistic allowing for simplifications (except the atmospheric drag model which I hope is still a placeholder). The planets may be "too small", but their surface gravity is still right for their mass and radius, etc. The rockets mostly work like real-world rockets ... simplified, of course (only one kind of liquid fuel), and they're too heavy because of the scaled down system, but things are pretty close to right. And then you have the ion engine way off by itself in totally-unrealistic-land. It shouldn't even be called an ion engine. (The old ion engine had this problem too, though. Again, my only real complaint is that the change seems to make us less likely to get a real ion engine.)

We could just give the Sun a small binary companion (red dwarf maybe) with its own planetary system. It could have its own enormous SOI within the Sun's SOI. If we get a second gas giant at maybe 1.5 or 2x Jool's distance from the Sun, then I'd suggest putting the second star at maybe 5-10x Jool's distance. It could have some 'weirder' and/or 'hard mode' planets like a planet in an orbit inclined 90 degrees to the rest of the system, a super-Eve with even denser atmosphere, a planet in an ultra close orbit to the star...

I think it can do even better than that -- Earth to Enceladus, IIRC.

Yeah, but on a mission to Eeloo it may add up... A good point, though, in that KSP's solar system is scaled down so there will be less time for an ion engine to work on a Kerbin-Jool trip than an Earth-Jupiter one. Still, .01 (10 N) or .002 (2 N) or whatever is way more than the thrust of real-world ion engines (Dawn's are 90 millinewtons http://dawn.jpl.nasa.gov/mission/ion_prop.asp) so that should balance out the shorter mission time. Something like Dawn, according to my limited understanding, flies a totally different kind of trajectory, thrusting most of the time, than a chemical rocket which makes short burns at the most efficient points and coasts the vast majority of the time.

I don't think it's even vaguely comparable realism-wise, though. The NTRs work more or less like NTRs; their thrust-to-weight isn't THAT great (about 6 to 1). I think the atmospheric Isp was lowered to make liquid fuel engines more competitive, but still... they more or less act like they should. The ion engine doesn't act anything at all like a real ion engine. It didn't even before 0.23.5, really, the ability to land on bigger bodies with it just makes it more blatant now. A real ion engine in KSP would be a thrust-during-timewarp thing. There's not even much point calling this thing an ion engine because it's nothing like one... it's more like a VASIMR, and even then, it has way too low power requirements for thrust. EDIT: Yeah, exactly.

I don;t understand why not? Do you mean it would overheat? I thought the problems with ground-launch NTRs were low TWR and nuclear-phobia. What nuclear waste? A solid core NTR like the NERVA does not emit radioactive materials, it emits plain hydrogen (or water or whatever, but that gives you less Isp) that is merely heated by the nuclear reactor (thus "nuclear thermal"). If radioactive stuff is coming out the exhaust something is very seriously wrong (that's how I unerstand it anyway). EDIT: apparently erosion of the reactor elements can cause this problem. But again it's a problem -- an NTR is NOT supposed to do this! I've heard of a gas-core NTR that would emit uranium, as would an Orion drive or nuclear-salt-water-rocket (a Robert Zubrin concept which is basically an Orion without the pusher plate and with a continuous nuclear explosion rather than a series of nuclear bombs). But not a NERVA style NTR. EDIT: here's a pretty in-depth description of different NTR types. (The person who wrote this posts here as nyrath) http://www.projectrho.com/public_html/rocket/enginelist.php#ntrsolidcore

I think the main point of the M55 is if you have a rocket that is a bit too heavy for a single Mainsail (or the bigger engine, now) but doesn't need a full 3 mainsails. It saves part-count over putting in extra side tanks with "in-line" engines or using the smaller radial engine (24-77?). At least that's the only time I've ever used it. Maybe it's also for heavy landers?

Yeah, I just thought it would make sense to have it 'packaged' with the mod as none of the stock engines are really low-thrust/long-burning enough to make full use of thrust-during-timewarp (especially with the 0.23.5 increase in ion engine thrust).

The ISS is in the upper atmosphere (thermosphere) AND in space. The main definition of space is above 100km, but for some purposes (US astronaut wings) 50 miles (80km). These are fairly arbitrary and rounded numbers. The 100km is supposed to be an approximation/rounded version of the Karman line where an aircraft would have to travel at orbital speed to support itself by aerodynamic lift. I don't know the source of the 50 miles, beyond being a round number. But both are also decent approximations of the top of the mesosphere/beginning of the thermosphere and also of the "turbopause" where the atmosphere stops having a pretty constant composition and stratifies out. http://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line http://en.wikipedia.org/wiki/Turbopause http://en.wikipedia.org/wiki/Thermosphere The thermosphere is incredibly thin, but at about 500km (or higher) it thins out to the exosphere, which isn't really a "gas" at all but a bunch of molecules that hardly ever collide with each other (don't behave as a gas). The exosphere then thins out to the interplanetary medium...

Yeah, the existence of drop tanks (the Shuttle ET was one -- though not with its own engine like a KSP asparagus-stage) and crossfeed (the Falcon Heavy is planned to use it) isn't inherently unrealistic. I think the point is that the 'classic' KSP 7 core asparagus rockets would in real life have too many parts (pumps etc.) likely to fail to be at all reliable, not that real world physics actually prohibits it from working... there'd probably be some drag penalty, yes, but according to my (limited) understanding the bigger the rocket the less it cares about drag (assuming the same shape).

Yeah, that's definitely over-built. You shouldn't have 4 gigantor panels on the thing. 6 of the smaller unfolding panels instead, that's enough to run 1 ion engine at full thrust (or was before 0.23.5 anyway). EDIT: Not that it's "wrong" as such... but that's why the burns are so absurdly long. Pre 0.23.5 ion engines reward building really light. They were totally worth using before, for sun-diving and Kerbol escape. Beyond those niche roles, there's really no point in them anyway even at 2 kN thrust, since kerbol system dV requirements are so low that you don't NEED better Isp than NTR engines for interplanetary transfers, and they don't work for Eve/Tylo/Kerbin ascents.

But ant engines are liquid fuel engines, totally different. Spamming shouldn't work because the TWR of the engine itself should be too low to land on any significant body, and in that case, adding more doesn't help.

Source, please? The only calculation on the subject I've heard of is Dyson's from the original Orion project era and that was 0.1 - 1 person per launch. And I think what they used back then would have been some version of the LNT model, even though not the current one... Also true. It doesn't really make biological sense that it should be linear at low doses, few things are, and radiation is a part of the natural environment we evolved in so having no defenses at all agianst it is also questionable. Now I'm not sure I'm ready to say that low doses have no effect at all (they may well not - but we don't know yet). I have heard that people living in higher background radiation areas do not have higher cancer rates, but I don't know that for sure...

I doubt it needs to be even close to that big. Biosphere 2 probably would have worked just fine if it was designed better (some serious design issues there)... EDIT: Of course their CO2 levels varying so much would have been better with more air volume relative to plants, I think, but I think they could have supported the people with way less plants if they hadn't tried to replicate all those Earth ecosystems. Design it like a farm (with air as a crop) not like a mini-copy of Earth, which doesn't really work on that scale.

The biggest problem I think is EMPs in low space frying satellites for really nasty effects on communications -- don't know if the bombs are big enough for this though (I know the "Starfish Prime" test caused lots of satellite failures, but it was 1.4 megatons).

Speaking of ions, could you add an ion engine with way less thrust so we can use it with x100, x1000 or x10000 time warp and have it actually act like an ion engine? Thrust of .01 or less maybe?

Yeah, the way it SHOULD work is allowing ion engines to work in on-rails time warp. There's a mod for that (Orbit Manipulator Series), and I think KSP Interstellar has solar sails that work in on-rails time warp too. Then drop the thrust to like .01, and then you can use it at 100x time warp and the burn takes 80% of the (real, player's) time it would with a 0.23.5 2kN max-4x-warp ion engine. In terms of dV alone, no, but it DOES change where you can go in terms of being able to land with ions on more bodies.