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wafflemoder

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  1. Something I realize I didn't actually talk about was the origin and orbital situation of Minmus. Whether its ceramic, ice, or as I envisioned it tar, it's clear that Minmus has a different composition to Kerbin and Mun. As such capture seems to be required. Its orbit then would likely have a higher inclination, though its placement is probably fine. It's possible that Minmus may have caused some instability in the early Kerbin system, but I'm honestly not sure to what extent with how massive Mun is.
  2. It's complicated. Duna and Laythe are the only obvious cases of increased cratering, however the craters on are clearly from different sources. Duna has many relatively small craters, which would indeed be suggestive of sustained impacts late into the systems history. However in contrast to this, Laythe has far larger impact features more reminiscent of lunar maria. In order for these to be geologically recent, it requires objects large enough to cause these impacts to still be abundant and frequently encountering not only Laythe but at least the entire Joolian system if not Kerbol as a whole. The lack of these massive craters on other young surfaces like Vall would seem to contradict this.
  3. Not sure I would've gone that far, but I do think much greater liberties could have been taken. I would not be surprised if in the future we do see new objects added to the Kerbol system, but likely any new objects are being saved along with the other systems.
  4. DISCLAIMER: This IS NOT a suggestion, request, or complaint. I DO NOT believe that hyper realism is somehow "superior" to the more loose approach KSP and its sequel have taken, and am in fact quite fond of the planetary systems of both KSP1 and KSP2. I am merely using the familiar Kerbol system to talk about planetary science, both for my own amusement and hopefully yours too. The Kerbol system in KSP1 is a setting filled with novel fantastical worlds, but others are hard to tell apart at a glance (particularly Mun, Ike, Dres, and even Tylo to an extent). KSP2 sought to not only bring unique character to these worlds, but also improve the realism of what was previously established, all while making as few modifications to the system's recognizability as possible. This endeavor is not something to be overlooked, and the results are very admirable. However at the same time, I'm a worldbuilder, one who particularly focuses on realistic planetology and has far too much free time. And having had time to stew over KSP2 over the last week and a bit, I want to share my unique perspective on the Kerbol system and what changes I feel could have been done better, as well as what choices I would have made were scientific feasibly my only concern. Kerbol: Carrying over from KSP1, its much larger than what you'd expect for a solar analog. The reason for this is so that it matches the apparent size of Mun in Kerbin's skies for eclipses. However, imo I don't think Kerbol being smaller would take away from this in any way. Additionally, Kerbol is also much redder than a solar analog, looking about 2000-2500 K (for comparison the sun is 5775 K). The lensflare is significantly whiter, looking to be around 4500-5000 K. Moho: Moho obviously draws inspiration from Mercury. The brownish color appears to be rust, however this would likely require an atmosphere to maintain the high oxidation state over geologic timescales. It is also a notable departure from Mercury's ironically iron poor crust and mantle (fun fact), but more than doable. Eve: In the original KSP, Eve's oceans were comprised of "explodium", which presumably is some form of volatile hydrocarbon based fuel. KSP2 reimagines these liquid bodies as molten sulfur instead, and I am very pleased with this. Molten sulfur is an often overlooked fluid on Earth, occasionally occurring as "blue lava" in terrestrial environments and in volcanic pools at the seafloor. However, while sulfur is a very common element in terrestrial worlds, getting enough of it to form deep oceans is practically impossible even with extremely extensive volcanism. Even then, you'd likely require greater sulfur abundances, which would likely reduce density due to iron sulfide in the core. This is in stark contrast to the high density we see with Eve, with an inferred core mass fraction similar to Mercury. Additionally, this does not provide a particularly satisfying explanation for the relatively thin atmosphere of Eve as sulfur cannot sequester CO2 back into the mantle like water. So unfortunately as much as I love the idea of molten sulfur, I think long chain hydrocarbon like parrafin or asphalts would have been better options. A hydrocarbon ocean also lines up very neatly with other observations, as the more reducing conditions would discourage CO2 formation, instead favoring CO, C2H2, CH4, and H2 like in titan's atmosphere. Additionally Mercury's crust is actually quite carbon rich (with graphite making up a few percent of it by weight) so assuming similar processes on Eve would give a large body of reducing carbon to work with. Now as for why Eve is purple, maybe its some retinal based phytoplankton in the atmosphere? Not the best, but still far better than the iodine or fullerene explanations. Gilly: Not much to be said. It's a lovable little potato. Kerbin: I could probably go down a rabbit hole about climate models and tectonics and all sorts of things. But honestly even with realism in mind it serves its purpose as an Earth analog well enough. Mun: I could not have asked for a better interpretation geographically, though offsetting the mare from the near side may conflict with some models for the lunar surface dichotomy. A part of me wishes it wasn't such a perfect moon analog, as it lost what little unique character it had left, but I suppose its larger size and closer proximity will have to do. Minmus: Oh boy, I can certainly see why the dev team struggled to figure this thing out, and tbh I'm stumpted myself. Glass is a good step up from ice, but just creates new problems. Naturally occurring glasses do not make glistenning flat fields, they make jagged boulders which only when sheared reveal their reflective shine. Those of you familiar with Minecraft may recognize obsidian as one of the most popular volcanic glasses, but there are others. Unfortunately most require shock cooling in the presence of water to form, which needless to say is difficult to explain on Minmus. That being said, I gotta give the dev team massive credits for finding something that at least could resemble Minmus. Still, what could Minmus be instead? My best guess would be to once again turn to hydrocarbons, a forming comet long since devoid of water, with only dark organic material and rock. over geologic timescales the tar would be fluid enough to relax into flat almost "lakes". Duna: Obviously Duna is Mars. We all know this, but it actually misses the mark in a major way. This version of Duna is plastered in craters, which while interesting, doesn't line up with the geologic processes we expect to be occurring there. Like Mars, Duna should be tectonically active, especially with Ike for tidal heating. Volcanism and other tectonic processes can do great work in erasing craters from the surface. Also unlike Mars, Duna has a rather respectable atmosphere, and the aeolian erosion should further help to smooth over craters. But speaking of the atmosphere, another unexpected facit of Duna may emerge: precipitation. The atmosphere of Mars is rather thin, and so temperature variation across latitudes is high. As a result, the poles act as very effective cold traps for water ice, keeping the rest of the planet dry. Duna's much thicker atmosphere reduces the strength of these cold traps, as evidenced by the atmosphere itself (Mars' atmosphere is actually limited by the vapor pressure of CO2 at the poles. So because Duna has a thicker CO2 atmosphere, we can infer much higher polar temperatures of >170 K compared to Mars' 140 K). While not much, this does allow for more moisture in the air and cloud formation, which will inevitably come down. This means we can expect snow covered regions extending past the polar ice caps, particularly in lowlying regions and craters. Mars actually does have a few snow-filled craters like Korolev, which are astoundingly beautiful. However in addition to snow there is likely also rain, as Duna's higher pressure can keep water a liquid, and thicker CO2 atmosphere should enable reasonably warm summers. While I don't like the idea of actual lakes or seas for Duna, I do think riverine terrain could be featured much more strongly to imply seasonal melts and drainage paths. Ike: I appreciate the effort that went into diversifying Ike from the other grey worlds, with extinct volcanism being a distinct feature. However, with that being said I really don't feel this was executed very well. The current volcanoes are mentioned as being extinct, which means active resurfacing is no longer taking place. As such, we should still expect significant cratering (at least more than Duna) on Ike. Additionally while stratovolcanoes are a neat touch, more expansive flat volcanoes and basaltic lava fields would be more accurate, as our own moon also has a history of volcanism. If activity does continue to the modern day, one might also expect some discoloration around the volcanic regions, like a very desaturated and far less extreme version of Io. It’s also possible that there could be some discoloration through surface oxidation, either from material delivered from Duna or native oxidation via a trace volcanic atmosphere (ie less than what KSP defines as vacuum) which is also similar to what is present on Io, though the low temperatures there freeze most of it out. Dres: First off, love the rings. And the equatorial bulge does suggest a complex history with past rings long since lost, as obviously the present rings cannot have fallen to the surface and still be present. However, I think the Iapetus inspiration went a bit too far with the two-tone design. The reason for this is quite simple, it doesn't work for Dres. For this we must take a brisk detour to see why Iapetus looks the way it does. TL;DR, dark dust from Phoebe coats the leading hemispheres of all the major Saturnian moons, and because Iapetus has the longest days its the only one that got hot enough for a feedback loop of bright ice sublimating leaving darker organics causing more sublimation etc. Now, Dres doesn't have any way to preferentially deposit dark material on it, and even if it did, being much further in its already hot enough for this feedback loop to occur over the entire surface (which is why Ceres is actually very dark). So unfortunately this just cant work here. However, cryovolcanism can create bright spots on the surface (like Ceres), and brighter ring material can at least lighten the equatorial region, so not all is lost. Jool: Jool is still just a big green gas giant. Why is it so green? honestly aliens putting paint in isn't the worst option. Plants can be green, but to completely cover a gas giant in such a brilliant shade requires an exceptionally large biomass. Chlorine enrichment is also a non-starter, since you really can't enrich gas giants without some absurd tomfoolery or enriching other stuff as well to make it a moot point, chlorine isn't even that green, and it would form chlorides and sink below the visible cloud deck. As for Jool's moons, one might be familiar with the fact that Jool's moons are extremely unstable if actually simulated. This is for two reasons, one: they are in a laplace resonance, which is pretty trick to actually keep stabilizing, and two: they're just SO DARN MASSIVE. For comparison, Jool is 80 times more massive than Kerbin, comparable to what Saturn is to Earth. Tylo is 80% the mass the Kerbin, compared to Titan being just 2% the mass of Earth. And Jool has two other moons nearly as large. If I were splitting hairs, I'd probably do some combination of making the moons less massive, making Jool more massive, and opting for a less troublesome resonance chain and greater separations. But that is quite a departure form the architecture of KSP1, so its understandable why they didn't. Laythe: Keeping Laythe's oceans liquid is a challenge. It'd be trivial to just add enough hydrogen or methane, but oxygen puts a cap on how abundant those can be. CO2 freezes out of the upper atmosphere; nitrogen oxides break down too quickly; natural antifreeze mixtures can’t get cold enough; tectonic heating, while great for interiors, does nothing for surface temp. The only real option is to turn to CFCs, potent and long-lived GHGs which can also handle low temps and oxygen, but you'd have to rely on biology. The oceans would probably end up with some hydrochloric acid in it and both them and the atmosphere may turn slightly green from chlorine. Regarding its terrain, Laythe’s only terrain seems to be crater rims, which really doesn’t line up with the thick atmosphere, and active geology. As presently depicted, Laythe should have terrain far more similar to Kerbin, albeit heavily inundated, with a higher focus on volcanic island chains. Laythe's terrain is also pretty monotone, and some color variation would be nice with dark basaltic volcanoes and lighter shores. Also because greenhouse heating is responsible for Laythe's clement temperatures, you shouldn't expect any latitudinal temperature variations, and so the poles would be no colder than the equator and thus iceless. Vall: While I love the dichotomy between its hemispheres, the explanation for it is troublesome. Unless Jool was far hotter (either through a young age or very high mass), its radiation cannot be the cause for this disparity. Jool’s gravitation influence will however produce increased tectonic activity at the poles as well as the leading and trailing points (as seen with Enceladus, Dione, Miranda, and potentially even Titan)vbut there really aren’t any signs of activity on Vall at all beyond the single crack revealing the subsurface ocean (or more likely a liquid inclusion in the icy crust above it), so more signs that this world is indeed active would be good. It’s also lso worth noting that Vall is far less dense than either Laythe or Tylo, suggesting a higher water mass fraction. We also see this in Jupiter’s outer moons, but unlike them, Vall is sandwiched between two more rocky worlds. Were Vall swapped with Tylo, it would fit better compositionally, but this would create its own problems. Tylo: I love the new Ganymede-inspired direction of Tylo, and think its perfect fit. My only real issue with Tylo is its higher density compared to Vall. As previously mentioned this could be resolved by swapping the two, but that would also mean Tylo would be more active than Vall. Alternatively reducing the density of Tylo and/or increasing the density of Vall would be the simpler option. Bop: Bop is an interesting case. I like its irregular appearance and love the massive crater. But at the same time, being more massive than both Minmus and Pol, small rounded worlds, one would expect Bop to be similarly shaped. I think the easiest solution would just be to swap the sizes and masses of Bop and Pol. Pol: It clearly draws inspiration from Io, with a volcanic and sulfur covered surface. Unfortunately this conflicts with its distant orbit, where tidal heating is pretty negligible. Pol is mentioned to have a high radiation environment, which if the result of very extreme radioisotope enrichment might be able to resolve this contention, however that would necessitate an interstellar origin of Pol, which is disfavored by its low inclination orbit of Jool and synchronous rotation. This explanation would fit better if instead Pol were not tidally locked to Jool and orbited at a greater distance and much higher inclination (30-70° / 110-160°) Alternatively, Pol could be moved to a more circular orbit interior to Laythe where tidal heating would be sufficient to drive volcanism. Its high radiation environment would then be the result of its volcanism producing a plasma torus around Jool. Eeloo: I have my doubts that Eeloo would be active enough to produce its observed features (bright surface and large ravines) with its relatively small size and in the absence of any companions. Its lack of a nitrogen atmosphere is also a bit troubling, as it suggests processing within a circumplanetary disk to reset its volatile composition. One possible interpretation from this is that Eeloo is an ejected moon of Jool, though I am unsure of the feasibility of it entering a 2:3 orbital resonance after this. This would also suggest a much more chaotic history of the Joolean system, making orbital resonances between its moons unlikely. Additionally, Eeloo would become inactive after its ejection so a darker and non-reflective surface would be expected. So what’s my overall take on things? I like it. There is a clear attention to detail that has been put into making the objects more realistic while preserving the existing content and diversifying the system. I feel greater realism could have been achieved if greater departures were taken, which I feel I’ve adequately illustrated. But realism was not the sole goal of the development team, and it’s extremely important to keep that in mind. Again, I am not claiming that realism is somehow better. A lot of people couldn’t care less if the world they land on is realistic or not, and that is certainly a respectable opinion that I too have on occasion. Fantastical environments can give rise to unique gameplay challenges that pure realism often cannot. Does it really matter if Tylo’s probably too big and dense? Of course not. It’s a fun challenge to go to and without its size and gravity that would be diminished. Heck, this entire time I’ve been glossing over the scale of the Kerbol system. Obviously its smaller than irl, which results in all sorts of weird densities, but it makes launching easier and more approachable. However at the same time, when realism can add to a world to make it more unique, I can’t help but feel it’s a missed opportunity.
  5. yeah. with procedural wings I was kindof hoping we'd get other procedural parts. even if it was just one of each size profile. kindof expected this tbh
  6. I'm excited to see how the new parts can be used aesthetically
  7. If basically any part of the pod fails, it doesn't matter if the parachute works or not, you will die before you can come down, if not on the way up. And you can absolutely pin-point what part in the pod is responsible for the failure, that's part of what telemetry is for. Even for a dumb chasis (which a pod very much is not) it is still larger and hence requires more material and a larger workforce to construct, and so should cost more.
  8. Yeah. As much I would like a total overhaul of the entire game balance, that is a lot of work. Part cost should be one of the easiest to rebalance since its basically self contained, which is why I focused on it.
  9. Its not the actual cost of the vehicles, and this is arguably just to not hinder new career mode players. The prices of parts are weird in relation to each other. That is true, but that also applies to every other part in KSP, not just engines. Relative pricing should still hold if all parts are manufactured at equal rates. The engines in cars and aircraft are good examples of this in action, as both are very much mass produced and engines still make up a large fraction of the total cost. The actual material costs should be minimal in comparison to the manufacturing process. Rolling cone shapes also isn't that much harder than a cylinder. You'll need a new form, but that goes for tank diamters as well, so itsn't likely to increase the cost that much. Yes, parachutes would be expensive to certify. But the same goes for a command pod, which is also larger and much more complicated. Not really, and that's kind of the point. You'd expect the price of your vehicle to be more than a passing thought in a gamemode about paying for your rockets, both for the players and the developers, but that isn't really the case right now.
  10. Part cost isn't something that is normally brought up with regards to balance or realism. Part cost is only important in Career, and even in career, it isn't really that big of a concern, so its understandable why it isn't brought up that much. Still, it is very much a part of the game that should be looked at, as there is a lot that can be improved upon. Before diving into KSP costs, it's good to look at the costs of components in real launch vehicles. Now, pricing launch vehicles is surprisingly difficult, but fortunately just relative costs for parts is all we need for now. For the planned Vulcan launch vehicle, it is estimated that the engines and related components are around 65% of the cost of the first stage. For the Falcon-9, propellants only make up around 0.3% of the costs of the launch vehicle. Now of course, we need to keep in mind that these values might not be accurate for all launch vehicles, especially things that are not conventional rockets, but hopefully its good enough to give a rough idea. From this, it seems engines are the most expensive part of the launch vehicle, and particularly the first stage, with fuel being only a minor contribution. Looking at the first stages of various stock and dlc vehicles, engines only comprise around 15-55% of the first stage cost, lower than what one might expect. Fuel costs are much higher than expected, between 5-30% of the first stage. These two departures from realism could be resolved by simply reducing the cost of liquid fuel, oxidizer, and probably also monopropellant for good measure. In fact, liquid fuel is currently 4.4 times as expensive as oxidizer (0.8 funds/unit vs 0.182 funds/unit), so even just reducing liquid fuel and possibly also monopropellant would work (monopropellant has a cost of 1.2 funds/unit). Now you may have noticed that those price fractions varied a lot, and the reason for that is aerodynamic parts, with control surfaces in particular. As a point of comparison, the smallest and cheapest control surface is the Elevon 4 (the small one), which has a steep cost of 400 funds. This is more than a LV-909 Terrier (390 funds), and two-thirds the price of a Mk1 Command Pod (600 funds). Now, Elevon 4 costs the exact same as an Elevon 1 (the normal one), so its really only tied for cheapest control surface, but that should show that something is wrong with these prices. The Elevon 5 (slanted one) is more expensive than the Elevon 3 (large triangle one), despite giving less lift and being unlocked in the same tech node. The AV-R8 winglet costs more than the Tail fin, despite the Tail fin giving more lift and deflection, and being unlocked in a tech node of the same price. Now, these are not the only oddly high prices with regards to aerodynamic parts. Wings are slightly less expensive than control surfaces, but not by much. The AV-T1 in particularly is especially crippling, costing a whopping 500 funds for a small wingless. This is 5 times the cost of similarly sized wings unlocked not soon afterwards, so they are clearly a rip off. Now, the probably-too-high costs of some of these wings can be excused by the fact that they are capable of withstanding reentry heat, not something most aviation wings need to handle, which can be seen with the cheaper but less capable FAT-455 series of parts. Nosecones, especially the smaller ones, are also probably a bit to costly, with costs approaching those of engines in the same size. Moving to structural parts, for the most part they are rather inexpensive, which would be expected, but there are some oddities. The Structural Fuselage actually costs more than the Mk1 Liquid Fuel Fuselage its based on (when empty), despite it presumably being far easier to manufacture without an integrated fuel tank. The size adapters are also pretty costly, being around as expensive as nosecones. The multicouplers have some odd prices too. The 1.25m tri and quad couplers are both more expensive than their 2.5m counterparts, with the TVR-2160C Quad-Coupler costing 2000 funds, compared to the TVR-400L Quad-Adapter costing just 800 funds. There are more examples of oddly high/low prices. Mk16 parachutes are nearly as expensive as the Mk1 command pod, radiators cost close to or more than the ISRU parts they are designed to cool, J-90 Goliaths are less than twice the price of the J-33 Wheesly while having a built in air intake and side mount, the Clamp-O-Tron Jr. being over twice as expensive as the regular Clamp-O-Tron, the list goes on. Hopefully this is enough to clearly show that prices need some revisions, if not a total overhaul. It would nice if this would be done in KSP, but knowing this community, I'm sure people would much rather the time be spent on something more exciting.
  11. Two things I noticed about the FX-2 and FX-3 fusion reactors that may not be the intended behavior: 1) D-He3 mode consumes 10 times as much fuel as D-D mode, but only puts out twice as much power. 2) Assuming I did the math correct, the specific energy of the D-D and D-He3 fuel cycles are less than that of enriched uranium in the NFE reactors. For this, I used a two part formula. One for finding the energy per unit of fuel (generated power/ fuel use), and the other for converting in game units to kg (mass/units) - The NFE reactors give fuel specific energies between approximately 78 to 131 GJ/kg, varying between the reactors (which interestingly gives electrical efficiencies of around 3-5% for 3.5% enriched uranium) - In D-D fusion mode, the FX2 and FX3 have fuel specific energies of 23 and 28 GJ/kg respectively, between a third and fifth that of NFE reactors. Interestingly though there is still a use case for the D-D reactors despite their lower specific power (not counting radiators) and fuel specific energies than the NFE reactors, and that is that their fuel is comparatively inexpensive. - In D-He3 mode, the FX2 and FX3 have lower fuel specific energies of just 7.3 and 9.1 GJ/kg, although the high specific power makes them useful either way. Hope this helps
  12. A relevant method for reducing thrust without throttling down http://www.projectrho.com/public_html/rocket/realdesigns.php#id--Basic_Solid_Core_NTR--Cascade_Vanes This design was considered for use in solid core nuclear rockets, but some magnetic equivalent might be feasible for more energenic propulsion systems.
  13. You can get the same effect by using the moon itself as a gravity tractor for earth. This simplifies the design, and saves both the tides and venus. A large solar laser could be used to push the moon, or even the earth itself, further simplifying things and allowing for much faster timescales.
  14. A relevant video by Isaac Arthur on the logistics of moving planets Hope this helps.
  15. Well yes, but actually no. Like all things, it's complicated. So first off, my one and only defence what you were watching. We can do a pretty good job correcting for observation bias, as its something scientists know about going into things, and they have to work around it on a regular basis. When correcting for the planets we know we can't observe, and using the planets we can see to gauge their likelihood, we still find that most exoplanets are larger than Earth. That being said, there are still a lot of assumptions and misconceptions that can be unpacked here. Most of the exoplanets we've found were found by the kepler spacecraft, which was geared towards looking at K, G, and F type stars. These only make up 20-30% of all main sequence stars. The remainder is almost exclusively M type red dwarf stars. So we still lack a good census of what planets are like around these smaller, more abundant stars, which the TESS spacecraft and JWST will hopefully address as time goes on. From what we do know, it seems that planet mass may be loosely correlated with star mass. So worlds around these smaller stars will generally tend to smaller. In a further miscommunication, there is actually a frustrating amount of ambiguity in the compositions of exoplanets (even those with well defined densities). This is most apparent with mini-neptunes, which could either be rocky worlds with an extended hydrogen atmosphere, or water rich ocean worlds with little or no hydrogen. For smaller planets below about 1.5 Earth radii, where hydrogen is almost certainly not present, their compositions are slightly easier to pinpoint. As we don't know for certain how much iron an exoplanet has, or how much of that iron is oxidized, there is a lot of room for volatiles like water and carbon dioxide to sneak into a "rocky" planet's composition. In the small fraction of rocky planets with known and well constrained densities, most can allow for anywhere from 0 to 10% of their mass in water (for comparison, only 0.02% of Earth's mass is water). This doesn't seem bad, until you realize that an earth mass planet (or larger) only needs to be ~1% water for it to have a global ocean with a seafloor covered in high pressure ices, which would remove the rock-water interface which is thought to be a key requirement for abiogenesis. Also these ocean worlds have much smaller habitable zones, quickly going from frozen iceball to boiling steamhouse, much like the faucets in most buildings. What makes things worse, is that larger rocky worlds may also be unsuited for life. Planets larger than 2.5 earth masses will likely lack tectonic plates, and possibly magnetic fields as well. While neither are strictly required for life to develop (Earth's magnetic field and plate tectonics likely started after life developed), they are very very nice things to have for a developing biosphere. The thick atmospheres these worlds will have will likely make up for the lack of a magnetic field for surface life, and the larger masses of these planets will prevent atmospheric escape in the habitable zone. Hope this helps.
  16. Fusion rockets are in fact easier to achieve than fusion power. This is because a fusion power plant needs to break even, making more energy than it uses. On the other hand, while a self sustaining fusion rocket would be very good to have, especially one that could be tapped for power, they aren't necessary. There are some designs for fusion rockets that use a fission reactor to provide power for their operation.
  17. Well yes, but actually no. You could, but it wouldn't be an ion thruster anymore. Ion thrusters specifically use electricity to energize their propellant, rather than through heating by use of fusion or antimatter. In principle, you could use an ion engine powered by a fusion reactor and antimatter fuel cell, but it would be better in almost every circumstance to just heat a propellant through fusion or antimatter instead. Thermal propulsion would be lighter, simpler, and would give higher performance. The only downside is that these thermal systems wouldn't be able to change throttle as quickly (needing to heat up an entire reactor versus using ultracapacitors to regulate power) This might make fusion/antimatter electric propulsion feasible for RCS, but not for a main drive.
  18. Realistically, any form of space elevator, space tower/space fountain, launch loop, or orbital ring will be more environmentally friendly in the long run as no propellants are needed, and all components are multi use. But, its nonsensical to say that any of these methods are "propellants". The original question was about the most eco-friendly propellant, not the most eco-friendly surface to orbit transportation system, or even the most eco-friendly rocket design. These are all complex and intertwined questions for sure, and the question is framed in such a way that some pollution will be unavoidable from the production of the launch vehicle and the propellants. It is even fair to assume that a "nuclear space faring civilization" is one that uses nuclear propulsion (either in part or exclusively), which may make any chemical propellants considered irrelevant if that is the case. Based on all of this, and trying to pool everything together, here are 4 answers previously suggested that could be valid answers. LH2 would be the cleanest nuclear propellant, if only the impact of the launch itself is considered. H2O (water) would be the cleanest nuclear propellant if the impact of propellant production is considered, with minimal effort to produce. It remains a possibility for LH2 to be cleaner than water if there are significant advances in how its produced, but currently this is not the case. Hydrolox would be the cleanest chemical propellant, ignoring the impact of propellant production. Either methalox or hydrolox would be the cleanest chemical propellant if the impact of propellant production is included. As methane is more naturally abundant than hydrogen, and hydrogen typically being produced from methane or water, methalox may be cleaner overall. But this also depends on how these technologies would develop.
  19. First off, if a civilization's goal is to preserve the environment, monetary cost will be a non-issue. And biogas isn't even cheaper than minning, thats why we still mine. Secondly, Biogas is biologically produced methane and methanol, as are all fossil fuels. What makes biofuels "cleaner" than petroleum fuels isn't that they're a different chemical, its that biofuels are made from the carbon already in our atmosphere, rather than carbon which has been stored in the ground for hundreds of millions of years. Burning biofuels simply returns the CO2 that was used to make it back into the atmosphere, whereas burning natural gas adds more in. Third, the Kværner process is another way of turning methane into hydrogen. The difference is the waste product. Steam reforming creates ten times as much CO2 as it does hydrogen. The Kværner process produces no CO2 as a waste product, and so less greenhouse gasses. The kværner process instead creates carbon dust, which can be stored and removed from the carbon cycle. When taken as a whole: CO2 is taken from the air by plants to produce biomass. Some of this biomass is burnt, generating power and turning it back into CO2. The rest is put through the kværner process (using the power generated from before) and converted into hydrogen and carbon. The carbon is not returned to the air, so there is an overall net decrease in atmospheric CO2.
  20. Which is why I suggested running it off of a biogas powerplant rather than natural gas. Also its abilty to sequester carbon in elemental can reduce, or even give it a negative carbon footprint. Interestingly, the Kværner process is very similar (and possibly identical) to what happens in a nuclear rocket when you use methane as a propellant, only the carbon soot builds up in the engine, which can cause blockages or affect the neutron moderation in the reactor, and isn't desirable in that situation.
  21. Introducing the Kværner process, which converts natural gas or biogas directly into nearly pure carbon and hydrogen. A carbon neutral biogas powered and biogas fueled system could be implemented relatively easily by any eco-conscious future civilization if so inclined. As a bonus, the carbon could be used in ceramics, composites, or high strength carbon allotropes like carbon nanotubes and graphene. So technically it would be a carbon sink, rather than simply carbon neutral. Much more broadly speaking, an eco-conscious space fairing future civilization could migrate all power, manufacturing, and living space off of Earth to preserve its environment. As I mentioned previously, though in a less serious way, you can't pollute an environment that isn't there. Because of this, any environmental impact caused by the manufacturing of any of the rocket's systems (fuel, structure, power, electronics) could be disregarded entirely.
  22. The best solution I could see is having space-based FTL capable superships with a fleet of surface-to-orbit shuttles and a few interplanetary shuttles. These supership would have to be constructed in orbit or on a small moon or asteroid, mass hundreds of kilotons to over a gigaton, and be up to several kilometers long. This lines up well with what you were originally looking for in terms of size (or many times larger) but be limited to space. They would be able to land on the smallest rounded objects like Ceres, but anything larger would be a one way trip down and cause significant damage to the ship and surface. The largest of these ships might even carry small space elevators (one megaton for a 100,000 km long carbon tube 5 cm wide) and 'lay anchor' to planets and moons from stationary orbit or their L1 point. As they can FTL between planets, their conventional propulsion should be optimized to facilitate quick travel within a planet's SOI. As both thrust and isp are important for high speed transit, a system that can vary between speed and efficiency would be desirable. Fortunately most AM and Fusion systems can facilitate multiple "gears", so this won't be an issue. This would also allow for the supership to travel interplanetary on conventional engines in a pinch. I'd go with an AM pion-beam core that gives 0.01 gee of acceleration and 3,000,000s ISP with a 1:10 AM:H2 fuel mix at high gear and 0.15 gee, 200,000s ISP, and a 1:2,250 AM:H2 fuel mix at low gear. This would on a continuous burn on low gear (high accel), go from LEO to the moon in ~10 hours using 54km/s dV, from ganymede to callisto (max sep) in a day with 130km/s dV, or Earth to Mars (min sep) in a week with 686 km/s dV (probably not enough fuel for this on low gear, but you get the picture) Depending on the limitations of their FTL drive, they could do a lot of work within a planets SOI on FTL alone.
  23. Can't polute an environment that isn't there anymore Forehead On a more serious note, you need to consider not just the propellant itself, but what the exhaust products will be, how they can react to the air, and how the air responds to the intense localized heating of an engine. Regardless of the propellant, if it's hot enough, some of the surrounding air will be converted into the nitrogen oxides NO2, NO, and N2O, which are all powerful greenhouse gasses (N2O is ~15x worse than methane and 300 times worse than CO2) and are toxic. As these are also created by natural biological and geophysical processes, they aren't too big of an issue, and there really isn't anything that can be down about this while still using a rocket powered launch vehicle anyways. Kerlox, Methalox, and Hydrolox all produce water as an exhaust product, with kerolox and methalox also producing some CO and CO2. Carbon monoxide is only ~0.6 times as potent of a GHG than carbon dioxide, but is toxic. Water is only ~0.4 times as potent of a GHG as CO2 (but contributes the majority of Earth's greenhouse heating because of its atmospheric abundance) and its clouds are reflective to create a small cooling effect, so is pretty mundane. Some unburnt RP1, or methane could be problematic though. Alumilox (Aluminium + LOX) doesn't produce water or CO2, but does produce a fine Alumina dust that could potentially be harmful. Solids, Hybrids, and Hypergolics are all less efficient than the big three cryo fuels, and will produce more toxic fumes to various extents. Fluorine or Beryllium based fuels can get higher isps than hydrolox, and even rivaling some nuclear rockets, but both are pretty nasty substances to work with and would be quite bad for the environment. As for nuclear propellants: H2 is probably the most environmentally friendly; maximizing ISP while exhausting a gas with negligible GHG contributions (on par with O2). Some hydrogen may react with nitrogen and/or oxygen in the air to produce water and ammonia, which are greenhouse gasses, though in only small amounts. Water, as mentioned is one of the cleaner GHGs. Ammonia however, while very short lived (breaking down in a few hours or days), is nearly as potent a GHG as methane, and is pretty smelly. It is naturally produced by many organisms though, so can be tolerated by the environment to a degree. Helium could also be a good nuclear propellant, though there are issues with supply. Methane is a non-starter for a nuclear propellant, dissociating into H2 and soot in the reactor, which could be problematic for the reactor, or be exhuasted out and enter the atmosphere, neither of which are very good. Ammonia is probably a better option. Although is has a slightly lower ISP than methane does, it breaks down into inert N2 and H2, which will also be handled by the reactor better. Solid core reactors aren't hot enough to cause water to dissociate, but higher power liquid, colloid, droplet, vapor, gas, and plasma cores would be. The O2, H2, and H2O exhausted by such a rocket are non-problematic. Bipropellant mixtures like Hydrolox can also be used in nuclear rockets, but give lower ISPs in favor of higher TWRs. This may be useful in less developed NTRs, where TWR can be rather lacking. More advanced designs can get high enough TWRs and ISPs to be useful without bipropellants. As for what type of nuclear thermal rocket, it depends. A closed cycle is best, as no nuclear fuel can escape, but has reduced performance over open cycles, making them more difficult. Hotter engines also get better performance, but are also harder to contain. Solid cores don't get hot enough to take a performance hit from a closed cycle (other than TWR), so these types kind of blend together, especially since solid fissile materials can't be exhausted out unless something Really Bad happens. Liquid, Colloid, and Droplet cores get hot enough for open cycles to be problematic, but not hot enough for closed cycles to be much better than a simpler solid core. Vapor and Gas cores do get hot enough where closed cycles start to significantly out performing solid cores, but there are issues designing close cycles with current material science (especially the hotter gas cores). Plasma core are simply too hot to contain in any meaningful way, and despite magnetic confinement being a plausible option, it could still allow for some fissile losses during operation. All nuclear rockets have to worry about the potential environmental impact of a failure occurring, which would be significantly worse than the failure of any chemical rocket. When operating as intended would have a lower impact. For comparison of closed cycle options (assuming H2 as the propellant. Keep in mind that any other propellant would give worse performance): Solid core NTR: ISP 800-1200 s, TWR 0.8-40 Vapor core NTR: ISP 1100-2000 s, TWR 0.5-10 Gas core NTR: ISP 1300-2800 s, TWR 2-15
  24. A ship like that would probably be able to refuel from water ice and hydrates. This would allow it refuel basically anywhere. The only locations in our solar system such a vessel wouldn't be able to refuel from would be Venus, Jupiter, Saturn, Uranus, Neptune, and possibly Io. Nearly all outer solar system bodies (with the exception of Io, and possibly some minor bodies) have thick crusts of icy material. Main belt objects like Ceres and Vesta have hydrate minerals at the surface, where water can be cooked out of them fairly easily. Mars has considerable amounts of ice under much of its surface, as well as hydrated minerals. Mercury and the Moon only have water ice in polar craters, and I don't believe they have any hydrated minerals. The ship would still be limited by its antimatter reserves, but it could dedicate a fraction of its payload volume to more antimatter. With the amount of antimatter present on this ship, (about a pound), the storage efficiency has a negligible impact on the overall craft specifications. Even so, the antimatter containment unit is 100 times more massive than the antimatter itself, while this is slightly optimistic for magnetic storage, it isn't something unattainable with the efficiencies of storing more than a few thousand atoms at a time. You could alternatively have antihelium stored inside fullerenes, for a tankage fraction of ~200:1, which is in the same ballpark as what is being used. Magnetic levitation of antihydrogen ices might be able to approach tankage fractions of 1:1 or lower, but I decided against using it from the potential danger of a single centralized antimatter container.
  25. Yeah, antimatter is kind of insane, and thats with using less efficient water as a propellant. This craft could probably only get 100t payloads off of worlds less than 2 Earth masses with thin earthlike atmospheres, which should cover most "Earthlike" planets. On smaller worlds however, its payload capacity skyrockets. Quick table of parameters for the same vehicle for different world sizes. (limiting vehicle parameter in bold) World Mars Ganymede Pluto Ceres Required dV (km/s) 4 2 1 0.3 Gravity (gee) 0.38 0.15 0.06 0.03 Low Orbit Payload (t) 1460 4800 8760 27100 TWR (local) 1.4 1.68 2.05 1.4 Vessel dV (km/s) 4.9 2 1 0.35
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