wafflemoder

No worries there. Here's a "basic" rundown of what a water propelled AM Gas Core SSTO could look like. My assumptions: 16000 m/s of dV. Upright landing, change height to length if sideways landing is desired (doesn't make any real difference) 8 meter diameter rocket, height determined by tankage volume. Additional 8 meters in height from engines, and 25 meters in height from payload bay. 100t payload + 10t for misc structural and avionics. Water: 0.8 kg/L in tankage. Tankage mass is 5% the propellant mass. (95.3% propellant) Antiprotons: 0.01 kg/L in tankage. Tankage mass is 10000% the fuel mass. (1% fuel) Water:Antiproton mass ratio = 1,000,000:1 (used at a rate of 10,000,000:1, allowing for 10 water refuelings before additional antimatter is required) Vacuum ISP = 2400s, sea level ISP = 1600s. Engine vacuum TWR = 6. Engine sea level TWR = 4. Minimum allowable surface TWR: 1.4 Calculated values: (masses calculated after payload mass fraction is known) Combined reaction mass (water+antiprotons): ~0.8kg/L in tankage. Tank mass is 5.1% the reaction mass. (95.1% reaction mass) Gross mass/dry loaded mass: 1.9731 = 835.4 t Tankage mass/dry loaded mass: 0.0496 = 21 t Engine mass/dry loaded mass: 0.6906 = 292.4 t Payload mass/dry loaded mass: 0.2362. = 100 t Misc structural mass: 0.0236 = 10 t Dry empty mass: = 323.4 t Water propellant mass = 412 t Antiproton fuel mass = ~0.41 kg Total vacuum (sea level) thrust: 17.21 (11.47) MN Total height: 43.3 meters dV (no payload): 19340 m/s (no payload) Vacuum (Sea level) TWR: 2.39 (1.59) Time to fill by US fire hydrant (500-1500 gal/min): 1.2 to 3.6 hours Time to fill by average garden hose (17 gal/min): 4.44 days For comparison, Starship (just the upper stage) has a 9 meter diameter, is 50 meters tall, and weighs ~1420 tons fully fueled with payload.

In terms of shuttle craft, there should be a lot of options available (I'm assuming shuttles are non-FTL craft primarily for ferrying small crews or payloads to and from planets and moons with various masses and atmospheres) With how large your ships are, you could probably get away with having a few types of shuttles for various purposes and/or of various sizes. If the technology is available, you could have smart ships that reconfigure themselves for a specific task. Shuttle craft probably wouldn't be needed (but nice to have) for more developed worlds with extensive orbital infrastructure in place, or smaller moons like those of saturn and uranus (excluding titan), where gravity and dV are minimal. Main categories I can think of are moon-mars sized (atmosphere is negligible), earth-superearth sized (low pressure), and earth-superearth sized (high pressure). ...and now I want to design a family of shuttle vehicles for an assortment of planetary environments of 5-10 crew/20t payload (space shuttle like) and 25-50 crew/100t payload (starship like) Any prefered propulsion system for shuttle craft.

As none of them are chemical based, pretty much any fluid propellant can be used, with the exceptions of nuclear saltwater rockets and fusion augmented antimatter. Internal plumbing would have to be tailored to a certain propellant though (no jury rigging an H2O fueled craft to use O2, or at least not easily). The propellant used would affect the ISP and engine power with higher molar mass particles generally giving lower thrust and ISP. Some propellant processing will be required though, to remove any materials that could cause blockages in the plumbing where temperatures aren't 5000+ Kelvin. Salts, metals, and carbon soot would be the biggest offenders, remaining solid while the more volatile components are evaporated. Some propellants may also chemically react with the engine itself, oxidizing, corroding or otherwise jeopardizing the integrity of the engine. Halogens and Chalcogens like bromine, oxygen, sulfur, chlorine and especially fluorine should be avoided because of this. For this reason propellants would still need to be processed (often quite heavily), but could be sped up significantly by the shear power available from these spacecraft (The mainsail's description of being able to power a small nation isn't that far off the mark). Resource extraction would still take some time though, especially for larger craft. Distilled water would probably be your go to for exploration vessels in locations without the infrastructure in place to refuel with hydrogen. More civilized areas would probably stick with hydrogen though. Some of the more favorable and abundant propellants (ordered roughly by efficiency): H2, He, NH3, H2O, Ne, N2, O2?, Ar, CO2?

It is quite probable that there are additional planets in the system. Here's my somewhat lengthy, but hopefully comprehensive summary on what types of worlds could be where in the system based on our current understanding of planetary science. For reference, these are the two types of planetary orbits in multiplanetary systems. S-type orbits go around a singular star, and P-type orbits go around multiple stars. There are four main regions where planets could reside in the Alpha Cen. + Proxima Cen. ternary system: S-type orbits around Proxima (C), S-type orbits around A, S-type orbits around B, and P-type orbits around both A and B, but not Proxima. Planets around Proxima (Alpha Cen C): There are currently two planets known to orbit Proxima: proxima b, and proxima c. Based on recent measurements of the inclination of c, the two planets likely mass 2.1 and 12 Earth masses respectively. As current detection limits are fairly low, and planets have already been found here, it is quite probable that there are additional bodies in the system. Planets around Alpha Cen A: It's certainly possible for there to be planets around A, but there are some complications. Alpha Cen A and B are separated by 17.6 AU on average (varying between 11.2 and 35.6 AU). While planets orbiting up to 2.8 AU away would be stable, it is unclear if planets could have formed in this region. Several planets have been found around single stars in multistar systems, but few as close together as Alpha Cen A and B. OGLE-2013-BLG-0341L B is currently the record holder for tightest binary with an S-type planet, and is separated from its companion by somewhere between 11 and 17 AU. This is very similar to Alpha Cen, but the stars in the OGLE-2013-BLG-0341L system are both red dwarfs, where planets would form much closer in, so its still unclear if planets could have formed around Alpha Cen A. There is some evidence for dust around A and/or B, so its certainly possible that planets could exist there. Planets around Alpha Cen B: A very similar case to A, certainly possible, but the situation is made complicated by the AB binary pair. Unlike A, there is an unconfirmed exoplanet around Alpha Cen B. Bc, if confirmed, would be a lava world about the same size as Earth. Alpha Cen Bb was found to be cause by data artefacts in 2015, and so is extremely unlikely to be present. With unconfirmed planets and possible dust, it is possible that one or more planets could be present. Planets in P-type orbits around both Alpha Cen A and B: This is possible, but less likely than planets around either A or B. There are numerous binary systems with planets in P-type orbits, but none have been found in systems with stars as far apart as Alpha Cen A and B. The current record holder is FW Tauri AB b, orbiting stars separated by 11 AU, which is only two-thirds the average separation in Alpha Cen. It is also unclear if FW Tauri AB b is a high mass planet, brown dwarf, or low mass star. Even if no planets were able to form in P-type orbits around A and B, it is possible that some worlds were flung out from A or B into orbit around the pair. Cool Info, but what do I actually think? I'd guess there are few more planets orbiting proxima. I'd also guess that there are a several planets in S-type orbits around A and B, but wouldn't be too surprised if this wasn't the case. I'd guess there aren't any planets larger than Earth orbiting A and B in a P-type orbit, but wouldn't be shocked if one was found eventually. I would however guess that there are several circumbinary dwarf planets around the pair. Hope this helps give ideas and clears up more confusion than it causes.

Now that have a slightly better handle on what your aiming for, here's a shortlist of what might work in your setting for planetary operations, and my best guess of performance and what they might look like. The Nuclear (Fission) Options: Liquid Core Fission Rocket (Open Cycle): Very good TWR, but lower ISP. Liquid fissiles mix with and heat hydrogen propellant. Most fissiles are kept within the reactor, but some can escape, possibly bad for occupied worlds. ISP of 1000-2000s, engine TWR of 8~50. Bright translucent white exhaust. No residual smoke or steam trail. Gas Core Fission Rocket (Open Cycle): Similar to Liquid cores, but fissiles heated to a gas for increased efficiency. Fissiles escape more easily than liquid cores, possibly bad for occupied worlds. ISP of 3000-7000s, engine TWR of 5~20. Bright translucent blue exhaust, with subtle hints of magenta from hydrogen plasma. No residual smoke or steam trail. Gas Core Fission Rocket (Closed Cycle): Similar to above, but fissiles and hydrogen are kept separate, at the cost of added complexity and reduced performance. Not intrinsically bad for occupied worlds. ISP of 1500-3000s, engine TWR of 2~15. Bright translucent blue-white exhaust. No residual smoke or steam trail. Salt Water Nuclear Rocket (Very Open Cycle): Liquid Fallout, very very bad for inhabited worlds. ISP of 4000-10000+, TWR of 10~40?. Very bright translucent blue exhaust, with hints of magenta from hydrogen plasma. Residual trail of white-light grey steamy clouds. External Fission and Fission/Fusion Pulse systems are a poor choice for planetary use for reasons already discussed, so wouldn't be a fit for the setting imo. Fusion isn't well suited for planetary use either. ICF and MIF systems suffer similar problems to other pulsed propulsion systems, but with lower TWRs in favor of much higher ISPs. MCF systems have very poor TWRs but fantastic ISP. You can thrust augment a Fusion drive with "afterburners" (injecting additional propellant to increase thrust at the expense of fuel economy), but this results in worse performances than fission thermal rockets. Antimatter Options: (probably the better choice for an FTL capable society) Liquid Core AM Thermal: Cleaner than fission, antimatter annihilates before it can escape, but some x-rays can be emitted. Pretty safe. ISP of 1500-2500s, engine TWR of 10-40. Bright blue-white exhaust Gas Core AM Thermal: Uses more antimatter than liquids. Emits some x-rays and gamma, but otherwise fairly safe. ISP 4000-10000s, TWR 3-10. Bright blue-indigo? exhaust. No trail Fusion augmented AM Gas Core: Using deuterium in addition to hydrogen. Less antimatter is needed and x-ray emissions are reduced. Safe. ISP 3000-7000, TWR 3-10. Bright blue-indigo? exhaust. No trail Any higher power antimatter systems aren't well geared for planetary use, and put out significant amounts of x-rays and gamma. As for how you could handle your FTL Plotdrive™, Project Rho has a page for designing FTL in fiction which might be a useful resource.

Oh yeah, that completely slipped my mind . Still beam cores might run into in efficiency issues with energy conversion with less reaction mass that can absorb the gamma (another reason why AM thermal is pretty good). AM thermal is a really good propulsion system, especially where high TWR is required and when antimatter is hard to come by. Just figured with the large amounts proposed in the OP that you might as well use it (that amount would also be ideal for a plasma core). Speaking of, just some math on the power requirements to produce 1 ton of antimatter every two months at various tech levels. Basically a swarm of specialized factories inside mercury's orbit should be able to crank it out no problem, just not today. At current efficiencies. (1E-13 %) Pretty ridiculous: 1.7E28 W, 9E14x Global power output, 44x Output of the Sun. Specialized facilities a billion times more efficient (0.0001%) Pretty reasonable for an advanced civ: 1.7E19 W, 900000x Global power output, 0.000004x Output of Sun. Pair production from black hole hawking radiation (~30%) Easily doable, assuming you can make and maintain the 5-10 Mt black holes: 5.7E13 W, 1100x Global power output. Max efficiency from Andreev Reflection in quark nuggets (~85%) Trivial, quark nuggets not included: 2E13 W, 380x Global power output.

That's totally understandable. You can probably further justify whatever propulsion system you choose to use, even ones that are very obviously obsolete or problematic, with legal nonsense. I could totally see a megacorp or the like copyrighting the idea of fusion or antimatter drives, forcing unaffiliated parties into using orion drives instead.

If you're looking for theoretically plausible options, than magnetic monopole catalyzed nucleon conversion, or Q-ball antimatter mirrors are really good options. Essentially monopoles can force protons and neutrons to decay into pions and positrons, which can further decay into muons, neutrinos, and gamma rays. The end result is nearly identical to matter-antimatter annihilation. What makes 'conversion' systems better than antimatter is that magnetic monopoles are not consumed in the reaction, so as long as propellant is available (which can be anything from hydrogen to literal dirt) the drive can operate indefinitely, without additional monopoles being required. You could also make a monopole conversion ramjet, a more feasible variant of the bussard fusion ramjet, which uses monopoles to convert interstellar or interplanetary gas directly into energy, giving you essentially unlimited range and top speeds of very high fractions (30-80%) of lightspeed. In addition to this, the magnetic monopoles are far easier to store than antimatter and you would need to store less of it. Magnetic monopoles only convert matter (at reasonable rates) in high temperature conditions, allowing for it to be stored bound to regular matter. These could be used in any applications antimatter could, with only slightly reduced performance for far safer and more manageable fuels. One of the best resources for information on Magnetic monopole propulsion is The Orion's Arm Universe Project, which is a very realistic sci-fi setting. Q-balls can also be used for effective propulsion, in more ways than one. Q-balls are a hypothetical particles (?) and dark matter candidate than can "reflect" any matter it comes into contact with into antimatter for zero energy (in fact the Q-ball actually gains energy but we'll get to that). This allows for Q-balls to be used in a 'mirror' converting some fraction of a crafts propellant into antimatter for propulsion. This is really convenient as it also allows for you to both work around antimatter storage and allow it to be trivially created in situ from any materials. Much like the magnetic monopoles mentioned earlier, this can be used as a ramscoop to allow for (nearly) unlimited range. As mentioned, Q-balls actually gain energy when converting matter into antimatter. Apparently they draw it from the quantum vacuum (not entirely sure myself). A single Q-ball can convert ~8000 tons of matter to antimatter before becoming fully charged (unable to convert any more matter), gaining ~31 grams of mass in the process. The real kicker is that these charged q-balls, despite only massing 31 grams, actually have 8000 tons of mass-energy, meaning that they can store 260 million times more energy per kilogram than antimatter. Now there probably isn't a way to harness this energy, but if there was, it would allow for ridiculously efficient craft. Again, Orion's Arm also has a fair deal of information regarding "Q-Mirrors" and "Q-Batteries", though there are also several scientific papers floating around about the interesting properties of Q-balls.

I had pointed out in my previous post that both antimatter's specific energy and energy density are only comparable to fission when factoring in storage and energy liberation. It's quite probably that this may improve with time, but so may fission and fusion technologies. Furthermore, fusion can very handily beat antimatter in terms of energy density (per volume, not mass), as Ultra Dense Deuterium can have a density of 130 kg/cm^3, which is more than enough to make up for the lower specific energy of fusion compared to antimatter. Both specific energy and energy density are important to have, with certain applications valuing one over the other. While heat engines are certainly the efficient and one of the simplest ways of harnessing energy, they are not very mass efficient, so if trying to minimize the mass of your antimatter fuel cell, alternative methods of energy extraction are preferred. Magnetohydrodynamic generators, while slightly less efficient, are far lighter and more compact than a heat engine (which is why they are often proposed for fission, fusion, and antimatter bimodal power generation on spacecraft instead of more traditional brayton cycle heat engines. Considering this discussion is about general uses for antimatter, not specifically in rocketry, discussing the storage efficiency of the antimatter batteries previously brought up in the original post seems like a fairly reasonable tree to bark up. Additionally, we don't have battery powered rockets for the same reason we don't have fission powered phones, it doesn't have the desired properties for the application with our current level of technology. Gamma rays are pretty useful in heat engines and antimatter thermal rockets, but not in MHD generators. This is because MHD generators work with charged particles (which photons are not). Similarly in more advanced antimatter beam-core/pion-core rockets, only charged pions can be magnetically directed as exhaust. These charged pions eventually decay into neutrinos and muons (which decay into more neutrinos), which can lead to some losses via scattering. Neutral pions and gamma ray photons, not having an electric charge, cannot not be redirected as exhaust and heat up the rocket, facilitating the use of an ungodly amount of radiators.

I've only ever seen Orion figures above 10000s when using thermonuclear hydrogen bombs, which do get really efficient with size. Pure fission weapons are pretty terrible, which is why they were quickly superseded by thermonuclear weapons. Looking through some of the papers on Mini-Mag Orion, they seem to top off at 25000s using Curium 245 as the fissile material, with values around half that for plutonium and uranium based charges. The 482 ks value for NSWR probably represents the theoretical maximum, in much the same way H-bomb orion can have a theoretical maximum ISP of 100 ks.

Nuclear saltwater rockets can actually be made much smaller than orion drives, as like minmags they are not limited to the minimum size of self contained explosives. Regarding specific impulses: Pure fission Orion can have isps between 1800-4500s, Thermonuclear Orion can push this up to 7500-12000s, MinMag Orion can do 9500-16000s, NSWRs can do 4000-8000s (though I've also seen values of 67000s and 482000s)

Antimatter is absolutely terrible for energy storage. Currently antimatter requires ~1,000,000,000,000,000 times more energy to make than is stored in it. While matter-antimatter annihilation is 100% efficient, you'll only be able to get about 70% of the energy from it at most, as much of it is released in gamma rays which creates significant amounts of waste heat. This is to say that of the energy you put in, you only get 0.00000000000007% of it back. Compare this to a common battery, from which you get 80% of what you put in back out. Even with perfectly efficient antimatter production, so only the 70% energy retrieval is considered, batteries still beat out antimatter. To make things worse, any device capable of liberating energy from antimatter in a controlled manner would need to be fairly big, and certainly not compact enough for any real applications. A lack of miniaturization is what doomed the "atomic future" of the 50s, and antimatter will likely suffer a similar fate. In terms of energy density (usable energy per volume) and specific energy (usable energy per mass), fission probably beats out antimatter, when storage vessels are factored in. Something to point out, there is very little point to creating antimatter atoms larger than helium or lithium. With any conceived methods of producing or harvesting antimatter, you're only going to be getting single antiprotons and antineutrons out of it. While you could in theory get energy from "anti-fusing" it up to iron, this is a barely plausible idea for regular matter, and even more lucrative for antimatter. The density of the antimatter itself does very little to impact the density of it when stored electromagnetically, and electromagnetic antimatter storage does not require ferromagnetic antimatter (that might even hinder storage attempts). If the density of antimatter is a factor, you could probably settle with anti-lithium, which should be a solid metal like in standard conditions like its matter counterpart. Most systems that would use antimatter also function better with lighter antimatter particles, especially in rocketry.

In terms of surface to orbit applications, nuclear saltwater is probably the best you can get for a self contained launch system. It has better performance than orion (traditional, thermonuclear, or min-mag), operates under continuous thrust (to vastly reduce structural and aerodynamic loads), and would have far simpler plumbing. Of course vacuum cable maglevs of various sorts (launch loops, orbital rings, startrams, etc) would be far superior options, but it seems non-rocket launch methods don't count for whatever reason.

Yes, solar power is arguably worse in Antarctica than on Mars, but all other forms of power gen are superior (especially wind). Regarding legalities, Mars and other celestial bodies also have their fair share of international treaties limiting how they can be utilized. Currently these are not enforced, but I imagine the situation will change once someone is in a position to actually profit from it.

Mars is basically a worse antarctica, and antarctica is basically empty. The cases for science, tourism, and industry are all basically the same for antarctica and mars, with resource claims being equally difficult. Antarctica is more accessible (being on earth), and is far more habitable than Mars, and has been occupied for around a century, and yet it still has only a temporary population of only a few thousand. As much as I hate to say it, not much will happen on Mars even with cheap transportation.

External pulse propulsion systems like orion, medusa, minmag orion, or even epstein-like fusion or antimatter systems aren't very feasible for usage in atmospheric or low orbital flight. The first issue is that they can't be used on the surface, as the shock wave reflecting off the launch pad would shred the craft. This is already an issue with larger vehicles like the shuttle, and would be far worse with pulse systems. Medusa can get around this, as it launches explosive ahead of itself, but it will have ridiculously stupid amounts of drag and be aerodynamically unstable, as it's basically launching while keeping a parachute in front of your craft. Having an external pulse propulsion system as a second stage could also potentially get around this issue, as continuous pulse systems like conventional rockets would be less catastrophic. Using an orion drive or other external pulse drive in the upper atmosphere and low orbit also has its fair share of problems. Each blast would result in a large EMP, knocking out power in a significant area. Detoning nuclear and antimatter weapons in orbit can also create artificial radiation belts, with isn't exactly desirable. External pulse propulsion is certainly good in space (though there are certainly better options), but don't even think that they can be used anywhere near a planet.

For RCS, like most forms of propulsion, the molar mass of the exhaust gases has a very important role in determining specific impulse. Generally speaking, gasses with lower molar masses will give greater specific impulses when used as a reaction mass. CO2 has a molar mass of 44 g/mol, compared to O2 (32g/mol), N2 (28g/mol), H2O, (18g/mol), and H2 (4g/mol). Considering that O2 and/or N2 would be far more abundant than CO2 in crewed vehicles, using CO2 instead of straight air would not only be more difficult, but would also be less effective and have a much more limited supply. If power is abundant, than it may be feasible to electrolyze the CO2 into CO and O2, and use them as a bipropellant mixture. This is actually one of the proposed ISRU pathways for a mars mission, because CO2 is so abundant on Mars (24 terratons in the atmosphere, twice that in the polar ice caps, and many times more in carbonate minerals in the regolith)

Current surface pressure maglevs are rather useless for spaceflight, but evacuated vacuum maglevs can reach similar speeds to cannons without worrying about overpressure (though under pressure becomes a problem). StarTram is a good example of how maglev can be effectively used for near term space launches, and Launch loops are a good example of more mid term space launches. If you're looking for lightweight support and/or need impossibly strong materials, then active support and/or buoyancy is the way to go.

You're probably thinking of specific energy, which is very high in nuclear devices. In terms of specific impulse, the explosive casing can limit final velocities, and much of the energy is wasted from cosine losses, as only a fraction of the explosion actually hits the pusher plate. There was a proposal to launch the nuclear bombs ahead of the craft and use a large sail structure to use around half of the explosion called Medusa, which could achieve specific impulses of 50000 to 100000

There are several problems with launching ultra heavy payloads into orbit. The bigest issue is that your launch method needs to be extrodinarily energy efficient to avoid major collateral damage from the waste heat alone. External pulsed propulsion like Orion, Minmag, or Epstine-like torchdrives are the only drives capable of lifting such a behemoth and waste a lot of energy, with 50-80% of the energy being wasted in cosine losses alone. For a 100 kt craft, 50% efficient engine, 8 minute continuous burn of 10 km/s to orbit. 10^16 Joules of energy is needed (equivalent to 2.4 Mt of TNT or 100 hiroshima bombs), half of which is waste heat, with a power of 1.33 PW (100 x primary global energy consumption). Regardless of whether or not such a vehicle launches directly from the surface or not, it will leave a nuclear fireball behind it and likely knock out all electronics on the hemisphere it launches from. It will also probably supercharge the van-allen belts, which isn't a good thing. This is where Orbital rings excel over any rocket. An orbital ring can only lift a modest 1 kt (only a small freight train) at a time per each of the hundreds of cables connecting it to the ground. As an orbital ring is stationary relative to the surface, and lifting can be done by electric motors, much less energy is needed to get payload to space. A 100 kt payload send to 200 km over 100 trips would only need 10^14 joules , which is a lot less, but still a lot. The real kicker is that less than 5% of the energy would be waste heat, and instead of this energy being released in intentionally uncontained nuclear explosions over a matter a minutes, it would be as friction in the motors which could be dissipated as non-ionizing energy directionally into space over several hours. This only gets the vehicle into space, and not orbit though. This is where the orbital ring also excels. An orbital ring is well... a ring encompassing the entire planet, this makes it the perfect place to magnetically accelerate a craft in the natural vacuum of space up to orbital or even escape velocities, again with negligible amounts of waste heat that can be safely dissipated. You could even have a series of orbital rings at increasing heights, different inclinations and eccentricities, or around other planets, to receive the craft and send it to its next destination. Orbital rings also have the added bonus of being incredibly good for intraplanetary (earth based) transportation, being able to between any two points on earth in an hour for the price of a train ticket, and unlike starship, could link directly to city centres or rural areas (no supersonic booms, or launch pads, only a train terminal) The real question is why launch from Earth at all. Even star trek builds their large ships in space, with only shuttles for surface-orbit transportation. In this case, the orbital ring is still superior. Take up the pieces individually (or from the moon) and construct in on the ring itself. As far as interplanetary and interstellar travel, beamed plasma propulsion (like Magbeam) or laser propulsion are the way to go. No on board propellant would be needed to achieve speeds between 10% and 50% of c, several times faster than what bussard fusion ramjets could do if proton-proton chain fusion wasn't a distant pipedream. This is more than fast enough to warrant hyper-responsive point defence systems to track, ionize, and deflect specks of dust hundreds of kilometers ahead of the craft in a matter of milliseconds to avoid becoming a relativistic scrap heap. The main difference between laser and plasma propulsion is that plasma can provide greater acceleration for less energy, but would need a supply of particles to fling at craft and has a more limited range. Even the "vast unknowns" of what-would-have-already-been-extensively-studied-by-orbital-mega-telescope-arrays-with-enough-resolution-to-identify-life-and-civilizations-decades-prior-to-any-vessels-arriving-there-space could be accessed, as both methods can be used to brake at distant stars. Beamed laser propulsion requires a light sail on the craft, which can slow the craft down for a stars light pressure. Beamed plasma propulsion requires a plasma sail, which can be used a magnetic brake to stop just about anywhere. All of this can be achieved without any developments in material sciences, fission, or fusion (apart from the sun), and without irradiating half the planet with every launch. As of yet theoretical developments like gamma-ray lasing, magnetic monopole catalyzed nucleon decay, Q-ball based on demand free matter-antimatter conversion, Q-ball vacuum batteries, and subluminal alcubierre warp drives would be a major game changer. Even more so in the unlikely situation where the universe is broken enough for superluminal travel to actually be possible, and the lack of causality that results from that. Regarding hard scifi propulsion systems, space infrastructure, and future developments, the Orion's Arm Universe Project, Atomic Rockets, and Isaac Arthur youtube channel are all great places to look into this stuff more.

Some people want green, some people want orange. The obvious solution is alternating bands of green and orange ... or yellow

It all depends on how you define "best", "spaceship", and "now". Best could mean the most cost effect way of achieving a desired goal (either per unit cost, cycle cost, operational cost, or development cost). Best can also mean having the largest payload fraction, the smallest fuel fraction, lowest environmental impact, highest throughput (payload mass per day), most scientific versatility, or simply the largest. Spaceship also has various possible interpretations. It could be a vehicle for surface to orbit transport, orbital transport, interplanetary transport, or a lander. It could be used strictly for cargo, crew, fuel, or perform some other function like scientific research, or ISRU, or industrial manufacturing. Now is also a surprisingly flexible term in terms of spaceflight. It could limit things to existing craft, those currently in development, those that could be made with existing facilities. Anything beyond that would require significant R&D time, even just with preexisting space proven technologies, and is too far removed to be considered "now". Despite that, some might still consider craft made with flight proven technologies, or with technologies that have been demonstrated on a smaller scale as "now". In terms of surface to orbit vehicles: As far as today today: the Long March Family of rockets probably has the highest throughput to both LEO and GEO, the Delta IV M+(4,2) has the highest payload fraction, Falcon heavy has the highest LEO capacity, and either Falcon Heavy or Delta IV Heavy has the highest GTO capacity (depending on who you believe). And either Atlas V 431 or Falcon Heavy has the best price per kilogram to LEO (again, depending on who you believe) In terms of what is being developed: New Glen, Vulcan, Starship, or the Long March family will have the highest throughput (its hard to say at this point), Vulcan will have the best payload fraction, either SLS Block 2 or Long March 9 will have the highest LEO and GTO capacity (depending on if the block 2 uses the pyrios boosters, and if the Long March 9's upper stage is hydrolox), and either Vulcan ACES, New Glen, or Starship will have the best price per kilogram to LEO (depending on pricing and market forces) As to what we can do with flight proven technologies, not much better. Most demoed propulsion systems have been for deep space, and have little use in surface to orbit transport. Maglevs as currently demonstrated can't provide enough velocity to warrant use for non spaceplanes, as they can only provide near horizontal velocity and reorienting a rocket for vertical flight could cause massive aerodynamic loads. In anycase, there are issues with large loads for current maglev systems (which is why they aren't used for freight) which would exclude their use in spaceflight for everything but smallsat launches. For demonstrated, but not flight proven technologies; a superheavy chemical rocket like the original ITS will still have the highest LEO and GTO capacity, a laser thermal rocket would have the highest payload fraction and cost per kilogram, an airbreathing spaceplane TSTO would probably have the most throughput. Orion was never demoed with nuclear weapons, and was also deemed unfit as a first stage (sound reverberations from the first explosion would shred the craft). Nerva has a stupid low TWR and specific power. The Timberwind NTRs were never demoed, and their values were likely exaggerated to garner additional funding (not that that helped in the end). Minmag Orion testing was inconclusive, used non-fissile materials, and may be incompatible with maglevs from magnetic interference. If development and deployment time is ignored for "Now", as long as the technology has been demonstrated, than dynamic orbital rings are the best. They can be made with current materials (no nanotubes, graphene, room temp superconductors, fusion or anything like that), only need power (which they could easily make on sight with solar), can take several megatons to orbit per day, kilotons per trip, and all for a few cents per kilo. Hope this helps.

There are a lot of different ways of measuring how good a launch vehicle is. You can do it financially (unit cost, development cost, operational cost); by rocket performance (payload fraction, fuel usage, specific impulse, specific engine power, energy efficiency); or by time (time from contract to orbit, integration time, vehicle production time, facility production time, vehicle turnaround time, facility turnaround time, throughput) How good a vehicle is also highly depends on what you are trying to accomplish (LEO, GTO, Moon, Mars) and how developed your technologies and infrastructures are. Currently, there are no fully reusable launch vehicles, SSTOs, air-breathing spaceplanes, nuclear thermal rockets, or high powered ion thrusters. Thus today, partially reusable rockets seem to have the best cost per kg. But expendable rockets have superior throughput and payload fractions, owing to simpler vehicles and only needing ideal weather at the launch location. If all feasible future technologies are allowed, then a dynamically supported orbital ring is the best surface to orbit transport, as they can take thousands of kilotons up per day at a few cents per kilogram. For anything in between, it really depends on what we develop first. In the near term, full reusability will join the competition with partial reusable and expendable rockets. As refurb costs go down and numbers of flights increase, reusable vehicles will out compete expendables. Precooled jet engines, such as those on Skylon, will start competition between reusable rockets and space plane TSTOs. Technologies like air-augmented rockets, pulse detonation engines, and dual ramjet-scramjets would continue to fuel competition. While SSTOs would be possible at this point, they wouldn't be practical until the development of laser thermal launch vehicles. These would take over the small sat market, but rockets and spaceplanes would continue to dominate for larger launches. This would continue until the skyhooks capable of lifting several dozen tons are put in orbit, at which point chemical rockets will be put out of the running, and only spaceplanes and LTLVs remain. Air breathing laser craft, if developed, would quickly rise over the other two, as it wouldn't require an onboard propellant. An airbreathing nuclear TSTO spaceplane is certainly better than existing technologies, but will probably be made obsolete before they are ever developed.

There seems to be four separate discussions going on: Kerbin vs Earth, Kerbol System or Solar System Regardless of scaling, do we want to launch from Kerbin or Earth? As mentioned previously, this is Kerbal Space Program. I'm pretty sure everyone is well aware that we are getting the kerbol system no matter what, but the question remains if we will also get the solar system. With multiple star systems already in the game, and an abundance of height maps and textures of real solar system bodies, adding our solar system into KSP2 would take surprisingly little effort. Regarding planetary realism, what's realistic doesn't have to be real. No binary planets have ever been found (unless you count Earth-Moon, or Pluto-Charon, or the countless binary asteroids in our solar system), but they are still realistic. Limiting KSP2 to what's physically possible doesn't do much to hamper planetary creativity. A real planet around PSR J1719-1438 is either a white dwarf star that was eroded away into an ultradense diamond world, or a lump of strange quark matter born in the collision of two still hypothetical quark stars. Adding our solar system may even help drive the diversity of the Kerbol system, as it would no longer be bound to being a slightly weird solar system analog, and could do its own thing better. I honestly don't care one way or the other if the solar system gets added. If it does great, if it doesn't there will be mods. As for why RSS Earth looks like butts, it's a marvelous combination of dark oversaturated textures, and false expectations. Oceans and Forested areas tend to look too dark in images from space. I'm not sure why that is, but when used in something like RSS, it doesn't look great. Reefs and tropical waters stand out like sore thumbs, because they do, and also the rest of the ocean is too dark. Gameplay Balance From a Scaled Up System Simply scaling up or down the kerbol or solar system doesn't really affect difficulty all that much. You need more or less dV, and things take more or less time. Both of these problems can be fairly trivially solved even by less experienced players. This burn or transfer is taking too long, use timewarp. Not enough deltaV, add more rocket. Making a big rocket isn't any more difficult than making a small rocket, especially with parts for various sizes of rocket. A big tank and engine is more capable than a small tank and engine, without using any more parts. For an upscaled system, you need only make the rocket bigger, without also increasing the payload. That being said, I do not think it should be upscaled for everyone, and it probably won't be anyways. We already know that for better or worse, stock scale is a thing. That being the case, if people are advocating for a larger scale, why have just one? Adding a difficulty setting to rescale the system would be a great way to let people to play the game how they want to. Rebalancing parts to match a larger or smaller scale isn't an issue. As I've mentioned previously, SMURFF does a great job at this, and even allows you to change how much it tweaks. If something like SMURFF was added, it would give an additional level of difficulty customization not found in KSP1, especially when alongside a rescale factor. In KSP1, you can't make sandbox easier or harder, but with part rebalance and planet rescaling, you can. Gameplay Balance From Added Mechanics Most of the difficulty in RSS/RO/RP isn't from the added scale. Its things like limited ignitions, ullage, fuel types, life support, and non-magical reaction wheels most of all. Some of these things *cough* ignition limits *cough* are even exaggerated in RO for difficulties sake. While these features *may* add realism, KSP is first and foremost a game. Realism, difficulty, and entertainment are fully independent of one another, as much as having a real scale earth does not mean having ullage and ignition limits. Reaction wheels are overpowered in KSP not because the devs don't know anything about irl reaction wheels, but because it keeps the game easy and entertaining for beginners. It would be neat if life support was added as an optional thing, especially with the colonies. Every else is meh at best. Gameplay Balance From Progression KSP1 can be challenging for some players, and a large part of this is a lack of guidance. KSP1 lacks any real tutorial, and just throws new players into literal actual rocket science with nothing but a few hard to find in-game help resources. This situation has improved slightly with each new release. Maneuver nodes, Offset tools, KSPedia (someone has to have used it by now), and in game delta V and TWR readouts have made things easier, but only for those that already know where to find them and how to use them. Yes there are many tutorials and walkthroughs available online, but how many people have given up on the game before finding them? Missions might be close to a tutorial, if they weren't dlc. You might say that career mode is a tutorial, but that definitely is not the case. Science isn't explained at all, early parts make achieving orbit harder than it should be, maneuver nodes can't be used until you progress far enough, funding can be an issue for less experienced players, and contracts can be misleading and/or block progress. If KSP2 has a proper tutorial and better ingame documentation (people who use the wiki, forums, subreddit, or youtube make up only a fraction of the playerbase), I am confident that everyone would be able to at least make it to orbit. Getting to orbit is the most fundamental thing in KSP, and teaching new players how to do this should not be made harder by limiting them to 1950s era rocket tech. Future technologies may actually help to aid in this, providing an easy way to get to orbit in a tutorial, while allowing for chemical propulsion to be made for difficult for actual career.

So first and foremost, I am not advocating for RSS to be included. I have played with RSS before and am of the opinion that a full 1:1 scale solar system would put off players for similar reasons to those in the original post. HOWEVER, I also do not believe that the stock scale kerbol system is the answer either, or at least that it shouldn't be the only answer. Regarding Gameplay and Balance KSP2 seems to be adding an assortment of futuristic technologies. This may render the "RSS is too hard" or "RSS takes too long" arguments completely invalid. Fusion, fission, metal hydrogen, or whatever else they put in may make achieving orbit trivial even at RSS scales. Furthermore, some advanced technologies, and even some technologies present in KSP1, can't be fully implemented or appreciated without a larger scale. This is most apparent with spaceplanes. One of the biggest problems with the stock scale is that, while orbital velocities are ~30% IRL, jet engine speeds are not reduced. This means most of the current/near future jet engine technologies like precooled jet engines, pulse detonation engines, and ramjets will need to be nerfed. In fact, the RAPIER (a precooled jet engine) is already nerfed both in its jet and rocket modes, and is arguably still overpowered for KSP1. More advanced scramjets, shcramjets, or liquid air cycle engines would be far too overpowered to be added as anything but a glorified reskin. A modest mach 10 from a scramjet would be enough to get you on a flyby of Eve if done correctly, and a mach 14 shcramjet could get you to Jool or Eeloo. If stock scales are retained, none of these technologies would work in KSP2. Rocket powered SSTOs also have problems with the stock scale. Because of the small scales, you can make pretty much anything into an SSTO, sometimes by accident. This is most prominent in early career saves, where it is often difficult to make your 1 or 2 kerbal crew launches anything but an SSTO with a detachable capsule. Of course, part of the reason for this is to make it easier for beginner players to progress. Some wiggle room is nice, but that can already be afforded by adding an extra stage (or boosters, players love boosters). That isn't to say that difficulty is good. As with all things, there's a balance. Global Part Rebalancing: The 'Easy' Way Out If RSS is integrated, parts would indeed need to be rebalanced, but I strongly disagree on how difficult this would be. Rebalancing every part, is actually easier than just rebalancing some, as you can just modify everything at once. A lot of stock parts are a lot heavier than they should be, specifically so they are balanced for such a small system. Even something as simple as halving the dry mass of every part goes a long way. Your fuel fraction basically doubles, which gives craft either double or an extra 2000-2400 m/s dV, for low and high initial fuel fractions respectively. This really helps with RSS and basically negates the added difficulty of intermediate scales (more on that later). SMURFF is a wonderful example of how this can be and has already been achieved for a stock game and modded parts, all without adding new parts or custom tweaking individual parts by hand. 2x, 3.2x, 6.4x, or 10x Kerbal System, Half or Quarter RSS, and Other Scaling Options The problem of RSS being to difficult and stock being too easy has been around for as long as RSS. Since then, there has been a cornucopia of scales between stock and RSS, for both the kerbol system and the solar system. The orbital velocities for 2x and 3.2x scale are 1000 and 2000 m/s higher than stock respectively, and launch & orbit times are about 1.3 and 1.6 times longer. This is in a similar ballpark to differences from aerodynamic drag or launch profile. Sigma Dimensions allows for custom scaling, and in my opinion should be how KSP2 handles things. Allowing the player to set the scale in game as a difficulty option would make the most people happy. If I'm remembering correctly, I believe that planet rescaling was actually demoed in KSP2 in real time, but I might be wrong. There is also nothing saying that Kerbin has to be the same size and mass as Earth in a RSS or kerbal equivalent. The dV requirements for Kerbin is actually extremely similar to Mars, so having a slightly downsized kerbal system in an RSS setting (~6.4x size, but realistic densities) is also an option. From a planetary science perspective, this would even help explain some of the odd planetary properties of the kerbol system, like the large size of moons, the low (relative) density of Jool, the temperature and color of Kerbol, and the lack of a crushing atmosphere on Eve.