Northstar1989

Actually not. The rocket part of a ramrocket generates Thrust even when stationary. The rocket exhaust ignites the fuel-air mixture in the mixing chamber, so you get some (stationary Thrust from the ramjet part of this mutt of a rocket and a ramjet... (even with the scram-rocket version, the rocket itself will produce Thrust up until you reach the supersonic speeds necessary for the Scramjet part to ignite. And, this can be combined: for instance the proposed RBCC cycle is an all-in-one Ducted Rocket, Ramrocket, and Scramrocket...) The KSP ramjets actually perform much like ramrockets would IRL (substantial stationary Thrust, higher Thrust at speed) except that their ISP is much too high for a ramrocket, and they don't consume Oxidizer as a ramrocket would. A similar, related concept is a turboramjet- which uses a small rocket to pull in additional air and sustain combustion in a ramjet even beyond speeds/altitudes where a ramjet would normally be capable of operation. The rocket is placed a bit differently in such a design, though, and is much smaller relative to the ramjet. The bigger problem is that it's nuclear, and hence radiation is going to be a real concern. You probably wouldn't want to activate the reactor on the ground anyways (indeed not until you were already at a fairly high altitude). This would thus be an engine for the speed-run of a spaceplane, or the second (seperable/decoupling) stage of a two-stage spaceplane. You don't need to ignite all engines on the ground in a SSTO spaceplane. Indeed many proposed designs don't (having rockets you don't use until altitude, plus maybe briefly at takeoff), or use multi--mode engines which switch operations in flight (RBCC has *THREE* modes, for instance: Ducted Rocket, Ramrocket, and Scramjet). Re-read what I wrote (with the clarification here). Any type of ramrocket design usually behaves as a Ducted Rocket at low speeds. Ducted ("air augmented") Rockets produce Thrust and ISP slightly better than a rocket at first, increasing to the 700-800 second range by about Mach 3-4 (but a ramrocket will see ignition of the ramjet in the mixing zone long before this point...) Two-Stage Spaceplanes are entirely feasible: with the upper stage spaceplane that actually achieves orbit riding piggyback on a larger spaceplane (technically only a plane, but to really get the most out of this it needs to be a much, much, much larger, faster, and more efficient plane than something like a 747) that then flies back to the runway independently. This allows the upper stage to only be equipped with engines that work well at high speeds/altitudes, such as the nuclear ramrocket I refer to here (a CONVENTIONAL ramrocket doesn't actually need the booster to get off the ground: as the rockets within the ramrocket usually produce enough Thrust acting as air-augmented rockets without complete combustion yet occurring in the mixing chamber to reach speeds where the ramjets will operate efficiently. And I repeat myself: the primary rocket produces a sufficiently hot/fast exhaust stream for the ramjet to start producing a little Thrust even on the runway...) A diagram would be helpful, and maybe I'll produce one if you still don't understand. But this is a textual illustration of how both ramrockets and some designs of ducted rocket work: Primary Rocket --> Mixing Chamber --> Nozzle - The mixing chamber is where the 'primary' rocket exhaust is mixed with air. In a ramrocket, the rocket simply operates fuel-rich, and the mixing chamber is designed to encourage/allow for combustion of the air with the fuel-rich rocket exhaust. But this ramjet combustion is not NECESSARY for the rocket to produce a fairly large Thrust through the Air-Augmentation and nozzle on its own (indeed most Thrust comes from the primary rocket EVEN WHEN the ramjet is operating...) - The primary function of the mixing-chamber is to provide extra Working Mass for the rocket. This roughly doubles the Thrust if you mix the rocket exhaust in a 3:1 ratio with air and no ramjet combustion occurs, for instance. The ramjet combustion is actually a minor optimization to the design (typically providing around 10-20% extra Thrust in a conventional ramrocket design: although Nuclear ones would benefit more sue to their anemic base-Thrust levels)- ramjets don't produce that much Thrust at reasonable sizes in real life, unlike in KSP. - The Nozzle, is s nozzle. You can use a typical bell nozzle, or opt for an Aerospike. Aerospikes should work very, very well here as ducted rocket exhaust is much cooler than in a conventional rocket (although you also have less unburnt fuel from the turbopump available for Regenerative Cooling) and the nozzle needs to be larger to accommodate the high Mass Flow Rate from all the extra Working Mass from the atmosphere (larger rockets are, paradoxically, EASIER to keep cool: due to effects resulting from the Square-Cube Law, which reduce the relative surface area exposed to hot gasses... I *highly* recommend the Everyday Astronaut article on Aerospike Nozzles for more detail on precisely why...) A HTHL spaceplane is a FULLY reusable spacecraft. Earth isn't Kerbin. You have to reach incredibly high speeds in the atmosphere (by Mach 4 or 5 your plane is already catching fire magnificently: orbital velocity on Earth is around Mach 20, I believe) to have any chance of reaching orbit with a spaceplane, due to the much larger radius of Earth. A ramrocket isn't even designed for speeds that high. We're talking a propulsion system that operates best between about Mach 2-5 (ramrockets have a much wider performance window than ramjets, as the rocket exhaust stabilizes ramjet combustion at low speeds or pressures), and operates mostly as a ducted rocket (with lower ISP) from stationary to about Mach 2 (although, as said, you still see a *little* combustion in the mixing chamber even at takeoff). Its Thrust never drops to zero- or any less than the Thrust/ISP of the primary rocket. This differs from the conventional (HydroLOX primary rocket) design in that the rocket is nuclear. Once again, this means less Thrust (but higher ISP due to lighter exhaust gasses) when operating as a ducted rocket, but much, much more Hydrogen in the mixing chamber potentially subject to combustion (meaning instead of adding 10-20% Thrust, you might add 40-50% or more with a sufficiently large mixing chamber...) Normally a ramjet would "choke" on this much Hydrogen in one place: but the nuclear reactor superheats the Hydrogen to a much higher temperature than compressive heating would normally pre-heat the intake air of a ramjet to, and as a result the ramjet should able to operate at much higher Mass Flow Rates across a much wider performance envelope... (even so, the need to dilute the Hydrogen a bit is why the mixing chamber should be designed larger than for a ducted rocket...)

So, in looking at Air-Augmented ("ducted") rockets recently, and considering nuclear propulsion, this idea came to mind (I think I've read about it before- will post links for background when I have time) Basically, it combines the features of a nuclear thermal rocket (aka. 'NERVA' aa the most famous example) or a nuclear thermal turbojet, with a ramrocket (itself the hybrid of a Ramjet and an Air-Augmented Rocket). So, it looks something like this: air enters into intakes (and probably then a pre-cooler passing some heat to Liquid Hydrogen as a heat-sink: ala. "SABRE" intakes in real life) and enters a mixing chamber. Separately, Liquid Hydrogen is passed over a nuclear reactor's heat-exchanger, just like in NERVA or any similar design. The exhaust from the nuclear heat-exchanger then enters a mixing-chamber with the intake air, exactly like how any ducted rocket works (basically, ducted rockets mix the exhaust from a Combustion Chamber with intake air BEFORE ejecting it through a rocket nozzle- this is all there need be to such a design... If the air is pre-cooled first, heat management becomes easier and you can use more heat-resistant materials or a lightweight heat-vulnerable Aerospike Nozzle, without them melting, but this is not usually done...) However because there is Oxygen in the intake air, and the nuclear reactor exhaust is superheated Hydrogen, there is the possibility for Ramjet-style combustion. This is how a ramrocket normally works (the ONLY difference here is that instead of Hydrogen-rich combustion products from a conventional rocket combustion chamber entering the mixing/ secondary combustion chamber, you have 100% Hydrogen from a nuclear reactor's heat exchanger entering it instead...) This Hydrogen is afforded the opportunity to combust (this is also why you want pre-coolers: to allow compression and cooling of the intake airflow by Compressors to speeds/temperatures usable for a Ramjet even in very high speed/altitude flight), and you get additional energy from this Ramjet-style combustion, which gets you extra Thrust after you pass the exhaust through a rocket nozzle as with any ramrocket... Basically, it's a nuclear thermal turbojet, but with the addition of an integral ramjet for extra Thrust and higher Exhaust Velocity (which also means the whole thing is useful at higher speeds than a normal nuclear turbojet). The secondary combustion/mixing chamber could even be designed as a Scramjet: although that creates problems with no longer having any static thrust on the runway... (due to having low TWR, very high Effective ISP, and being optimal for high-speed atmospheric use: this is best used on a horizontal-takeoff spaceplane...) Other notables: - The airflow would be possible to close off at the point of the intake, or possibly also downstream, allowing for operation as a pure (but very heavy) nuclear thermal rocket once you leave the performance envelope for airbreathing propulsion. Thos is similar to the Rocket-Based Combined Cycle ("RBCC"- basically a ducted rocket, ramrocket, and closed-cycle rocket all in one...) propulsion system, except that the initial heat source is a nuclear reactor rather than a primary rocket combustion chamber. - This works best with lighter/more powerful next-gen nuclear reactors, like Molten Salt Reactors (not coincidentally, previous investigation into nuclear thermal turbojets looked at using MSR's for the reactor componemt...) - Nuclear Reactors with TODAY's tech actually eject COLDER exhaust than a rocket combustion chamber. The reason for their high ISP is due to using a pure exhaust of nothing but Hydrogen... This means that, if you further diluted this already-lower heat with colder-still atmospheric air, you would have exhaust temperatures very usable for an Aerospike Nozzle: these nozzles normally having tendency to melt without a lot of extra weight for heat-managenent.

A while ago there was this excellent discussion on air intakes and drag in KSP: This is still an important topic (would be even more so if the dev's could give us some larger airbreathing/jet engines, so spaceplanes are actually useful without massive engine-spam!) and I wanted to continue to draw attention to the idea, discuss it, and see if anything has changed. Also, there were some nuances to Right's graph (re-posted below for convenience) that I don't think really got any proper discussion- and couldn't be discussed there now without nero'ing a very old thread... Note, for instance, the shape of the Shock Cone Intake performance curve (or lack thereof). I think many players sub-optimally assumed the most efficient Spaceplane ascents involve keeping all your engines lit throughout your entire ascent. However I have increasingly found this is NOT the case-especially with the 2 stage spaceplane designs I have been experimenting with lately (a smaller Spaceplane optimized for high-altitude, high-speed operation rides piggyback atop a larger plane that breaks off. Awesome in Sandbox/Science, but requires a mod like Flight Manager for Reusable Stages so you can fly the lower stage back to actually be useful in Career...) Often it is better to have some engines- particularly Ramjet engines- you only ignite at higher altitudes and speeds, keeping your demand for IntakeAir (and Thrust production) relatively flat as you ascend... (this is even MORE true with modded parts like the Air-Augmented rockets from, I think, Mk2 Expansion: which, realistically for a ducted rocket, perform better at high speeds not only in terms of Thrust, but ISP...) If you have engines you only ignite at high altitude+speed (or simply don't throttle all the way up until you reach high speed/altitude due to heating issues, aerodynamic stability- particularly with dynamically unstable designs that become less stable at higher speeds, or not having your wings rip off due to aero forces in FAR!) then the Shock Intake curve suddenly looks a lot more appealing: note these curves are for constant altitude- the Shock curve ends up being flattened (in terms of rate of IntakeAir production) by reduced air density at higher altitude... Other things notable: - The Divertless Radial Supersonic Intakes appear to have the smallest performance-drop of any intake other than the Shock Intakes between Mach 3 and higher speeds (the slope of their curve is much more gradual, even controlling for their lower peak), making them often the second-best choice for high-speed planes (as well as great for fine-tuning *precisely* how much intake you have, so you don't have any more than needed...) - Engine Pre-coolers have, surprisingly (and unrealistically, given the whole POINT of using them in real life would be high speed+altitude performance) a steeper curve relative to the amplitude of their peak than the Adjustable Ramp Intake (aka the stock RAM-effect intakes). This makes them more poorly suited for high speed/altitude operations, at least as intakes (again, this is unrealistic- and the dev's ought to rebalance these to make them more useful). That being said, form-drag (from frontal cross-section mainly) becomes much more punishing at higher speeds, at least in FAR, so they actually do work well at high speed planes- but for all the wrong reasons (in real life, Pre-Coolers aren't even intakes at all, but allow you to cool/compress airflow before it reaches the engines so they "think" they're actually operating at lower speeds/altitudes. This would be easily simulated in KSP by simply having them decrease the airflow speed and altitude any engines they are connected too "see"- and indeed this is EXACTLY how they used to or still do work in KSP-Interstellar, which included special code to make pre-coolers work realistically: at least in older versions for sure...) In real life, they would produce a lot of intake Drag (as you slow the airflow more) and provide no direct intake functionality- yet be CRITICAL for a horizontal-takeoff spaceplane ascent... - On the topic of pre-coolers, again: there has been some mention that they are highly heat-conductive (wicking heat away from engines), yet this is somehow a BAD thing (as it causes them to absorb more heat from the atmosphere). It seems to me most players don't understand the Stock heat conduction system well, or how to use this properly. The best parts to attach pre-coolers to (on the other side of the engine) are large, heavy parts with a lot of cross-sectional area (so these parts in turn can pass the heat they absorb from the pre-coolers to other parts). This is entirely because the Stock heat model assumes an entire part is all at a constant temperature, to make the calculations manageable. Anyways, this makes good parts to attach Pre-Coolers to things like the long Mk2-Mk1 adapter, the Mk2 Bicoupler, the flat (rear) end of Mk3 parts, or especially large cross-section mod parts with inline 1.25 meter nodes (like the "Stail" to 2.5 meter adapter with shoulders in OPT Aerospace, or the Mk4 Adapters in Mk4 Expansion...) The parts they are attached to should, ideally, in turn be attached to even larger parts (like a Mk2-3 adapter in front of a Mk2 Bicoupler). The key is to wick heat away from the pre-coolers as quickly as possible so they can wick more heat away from the engines in turn. Not that engine overheating is THAT big of a problem in Stock (except for with the NERVA nuclear rockets- a part intake air precoolers would be USELESS for in real life, unless you were air-augmenting them... Or modded nuclear turbojets, like those in Mk2 Expansion- where at least the use of pre-coolers is realistic) - The Small Circular Intake has a relatively flat curve that LOOKS like it would be well-suited to high-speed operations: but in reality they tend to explode at high speeds, as they have terrible heat-tolerances...

They are, if you assume 1 EC=1kW. However 1 EC does far, far more than 1 kW could ever do in reality in an ion thruster- and far less than it would do in terms of powering probe cores. For the game scale/balance they're right on the nose, though. KSP-Interstellar has next-gen reactors which are amazingly more efficient for space use, though, and are ALSO true to real-life science. The difference is, the past tried/true tech represented in NearFuture is outdated and EXTREMELY marginal for space use (ironic given the name "NearFUTURE"- it's all nearPAST), whereas Interstellar has the kind of next-gen (ACTUAL future) tech that will probably take humans to Jupiter and such... (Mars is entirely doable with conventional rocketry: aka SpaceX) You can prolong the reactor life a lot more if you turn down the power levels. At lower power levels they produce less EC, but consume fuel more slowly. You can also reprocess fuel (turning a % of it back into usable fuel), and can swap in fresh (possibly reprocessed) fuel with an engineer while the reactor is powered down... You get longer mission life for a launch mass with a single reactor and regular fuel swaps than you can with multiple reactors... The way most players use batteries doesn't make much sense: they'd often be better off just loading on more (LARGER! This is a thread about larger parts after all: and we need larger panels than the Gigantor!) solar panels and setting the throttle to whatever the panels can sustain, while they go off and do something else for a bit (or use a mod allowing thrust while in higher time-warps).

First of all, 30 kW of thermal power gets you 5-9 kW of electricity at a reasonable (16-30%) conversion efficiency. This requires extra mass though (Stirling Pistons are much less efficient: hence why that design was only 1-2% efficient). Nuclear reactors DON'T scale linearly- their power output scales exponentially (the power per kg of fuel squares, if I recall) with the fuel mass- which also increases as a percentage of the reactor mass the bigger you go. So a 1 ton reactor might produce 400 kW of thermal power instead of the 103 kW you'd get for a linear scale-up. And since you'd be able to fit in a proper generator at that scale, within your mass budget (the 290 kg included the Stirling Pistons in its mass budget as well), you'd get 80-120 kW of electrical power from it: 160-240x that of the tiny reactor with Stirling Pistons! Pulsed Fusion is a niche purpose: and nobody disputes that would rely on capacitors. But most uses of power: such as an ion thruster, require constant power output. You can supply more power for a long burn with nuclear power than you can with batteries/capacitors plus solar. RTG's *are* a nuclear power source: just an incredibly inefficient one. They supply a lot less power per kg per second than proper reactors.

The smallest nuclear "reactor" and generator (one that uses Stirling Pistons) is about 600 kg- NearFuture actually hits the nose right on the head with this one (although, at KSP scale, maybe it should only be 300-odd kg instead). Yeah, no. Anything that uses 1000 kg of batteries is horribly unrealistic- at that point any space agency would just build a nuclear reactor (the Russians actually launched a few small space-capable nuclear reactors to Low Earth Orbit many decades ago...) or add more solar panels (depending on how far the probe was going from the sun...) Nuclear reactors in space have been done before. One of them (Kosmos 954) even crashed in northern Canada and caused a minor diplomatic incident: https://en.m.wikipedia.org/wiki/Kosmos_954

I'll keep this a brief introduction (because it's late here) and then maybe add to this post later... Having recently been reading up more about Aerospike Rockets, including coming across this superb article by The Everyday Astronaut: https://everydayastronaut.com/aerospikes/ I got to thinking about ways that Aerospikes could be made more useful (and potentially, gain a really solid edge over normal rockets- I think an accurate conclusion is that, on their own, Aerospikes are just a *little bit* better than normal rockets for atmospheric stages, but not really worth the extra R&D effort if their additional usefulness can't be demonstrated more convincingly...) One technology that is also, similarly, is just a *little* better in atmosphere, but not really worth the effort to fully develop right now, are air-augmented rockets (aka "Ducted Rockets", aka "Ejector Rockets/Nozzles" or "Rocket Engine Nozzle Ejector (RENE)" and related to "Ejector Ramjets" and multi-cycle applications like "Rocket-Based Combined Cycle (RBCC)" engines...) https://en.m.wikipedia.org/wiki/Air-augmented_rocket Now, one technology (Ducted Rockets) occurs entirely UPSTREAM of the rocket nozzle, whereas the other technology (Aerospikes) is a nozzle design- and doesn't have any particularly requirements upstream of the nozzle, other than an unusual (toroidal-shaped for Toroidal/Plug Aerospikes like the J-2T, a bunch of small rockets with seoarate combustion chambers and normally-shaped throats in a line for Linear Aerospikes like the XRS-2200/RS-2200) throat design in some cases, which is one of the sources of the heat issues that aerospikes have. By the way, here is some more background in the XRS-2200 in case it helps. Please note that, once again, the linear aerospike is s NOZZLE design- there are no special requirements for the many small combustion chambers that line the aerospike: http://heroicrelics.org/info/aerospikes/xrs-rs-2200.html So, I got to thinking, what if an air-augmented rocket (of the design type where you have a rocket combustion chamber empty into a mixing chamber with ducted air, then the mixed gases are ejected through a typical rocket throat and into the nozzle...) were combined with an aerospike nozzle instead of the usual bell-nozzle? I'm not just suggesting combining these two technologies for the heck of it: one of the MAIN problems with aerospikes is managing heat transferred to the throat and nozzle of the rocket from the exhaust-gases. Air-augmented rockets have cooler exhaust gases. Let me repeat this: air-augmented rockets eject a cooler exhaust gas mixture than do conventional rockets. Because the gases from the rocket combustion-chamber are mixed (diluted) with cooler air from an air intake system- which may be hot due to compressive-heating, but not NEARLY as hot as the gases of a rocket combustion chamber normally are- you get an exhaust gas mixture that isn't nearly as hot as you normally encounter for a rocket of similar Thrust. (Air-augmented rockets eject a larger mass of gases more slowly, with much of the mass coming from the atmosphere rather than the combustion chamber. Thus the exhaust is both cooler and slower-moving, but the EFFECTIVE ISP is *HIGHER* as you burn less fuel to get a given Thrust...) Since Aerospike Nozzles struggle with heat issues, ejecting a larger volume of cooler and slower-moving gases would be desirable- ESPECIALLY as Aerospikes become easier to keep cool at larger sizes (note that the size of a nozzle is based on the Mass Flow Rate, so air-augmented rockets normally have larger nozzles) due to scaling-effects from the Square-Cube Law (please see the Everyday Astronaut article and associated content for more on why larger rocket engines are easier to keep cool...) Aerospike Nozzles increase the nozzle-efficiency at higher ambient pressures of a rocket of most any type- meaning you get more Thrust at seal level (higher Sea Level ISP), while they ALSO have superb vacuum ISP (unlike s sea-level optimized bell nozzle: which they tend to outperform even at sea level in terms of ISP: usually by at least 20-30%). The usual drawbacks of aerospikes are issues with overheating that lead to the design of a heavier nozzle (even though an Aerospike is THEORETICALLY lighter-weight than a bell nozzle, you need so much extra mass for dealing with the heat issues they have that your TWR for the engine ends up being lower...) and added design cost/expense as Aerospikes are currently not at full tech readiness for use. In real-life, I'm also not aware of any issues stacking them (like in KSP) since it's not the actual nozzle itself that supports the weight in a stack arrangement- although as Aerospikes are prinarily atmospheric engines it's unclear why you'd ever want to stack them anyways... BUT, the bottom line is that if you combine aeeospike nozzles with Ducted Rockets, you might have fewer heating issues (due to the cooler exhaust), as well as better TWR due to not needing to invest so much mass in solving heat issues, and better ISP than either approach alone... Some details/math: - Ducted Rockets improve Thrust in proportion to the mix-ratio of combustion products and air. For instance, in a 3:1 mix you get, to a first approximation, a doubling of Thrust and Effective ISP (4 times as much exhaust mass, moving a little over half as quickly: due to E = 1/2 M V^2 and the same amount of energy being spread among 4x the mass. Note that this ignores 2 compounding factors: combustion of some of the residual fuel from a fuel-rich primary rocket combustion chamber, which adds a little additional energy, and change in the molecular mixture of the exhaust gases: which slightly decreases nozzle performance vs. a pure HydroLox rocket...) A 8:1 mix triples Thrust/ Effective ISP. - At the same time EFFECTIVE ISP increases (due to getting more Thrust for your fuel use), *actual* ISP based on Exhaust Velocity decreases: due to having slower-moving exhaust. The lower Exhaust Velocity (and pressure) means you don't need (and won't benefit from) as much expansion of your exhaust gases to reach ambient pressure, however, and ideal nozzle length/size is shorter/smaller for the Mass Flow Rate through the nozzle (though higher for the amount of fuel being combusted, as Mass Flow Rate through the nozzle is now many times higher). Large nozzles, low Expansion Ratios, basically. - Aerospikes can very easily achieve some rather impressive expansion-ratios, as they ALWAYS (both at sea-level and in vacuum) expand the exhaust stream to very near the ambient pressure, if large enough (at least, they do better at this than bell-nozzles, particularly at high ambient pressures...) But the more you expand your exhaust, the larger the spike/plug/wedge you need, and the more heating issues you have to deal with: so the lower need for expanding the exhaust of a Ducted Rocket (due to lower exhaust pressures/temperatures leaving the throat of the mixing chamber) is actually *particularly* beneficial for an Aerospike Nozzle, as it saves mass, and Aerospikes struggle with their TWR due to high mass... (lower expansion ratio required --> less nozzle mass needed) - Aerospike nozzles obtain higher ISP and Thrust, but lower TWR, than bell-nozzles (if your ISP and Thrust go up 20% vs. a bell-nozzle, your engine mass might rise 50% with an Aerospike rather than bell-nozzle, for instance...) - Most of the added mass is to deal with heat issues. To reiterate, Aerospikes are theoretically lighter than bell-nozzles, were heat not an issue. - Ducted Rockets also have low TWR's but high Thrust and ISP (TWR as little as 20% of a conventional rocket with similar Thrust, according to Wikipedia... But this is un-cited, and I think the author misunderstood: 5-6x the mass is NOT 20% the TWR if you double your Thrust as well, only about 32-40%...) This "short" prompt has gotten way out of hand, so let me wrap up my idea... Aerospikes increase both Thrust and ISP for the rocket chambers above them by a PERCENT, vs. a bell-nozzle. Keep this in mind... Ducted Rockets have higher base Thrust and lower true (exhaust velocity) ISP than conventional rockets, but higher Effective ISP, while mixing with air (once/if they switch to closed-cycle mode as they ascend to thinner air, which some designs such as RBCC are capable of, they perform similarly to a conventional rocket, but with a lot of extra weight...) When you combine an Aerospike and a Ducted Rocket, you should get an even higher Effective ISP (and less low true ISP) than before at high ambient pressures. For example, if you have 720 seconds Effective ISP at sea level with a HydroLox Ducted Rocket (a perfectly achievable number: you can more than double Effective ISP, and for instance get well into the 500's seconds with SOLID ROCKET BOOSTERS that have been air-augmented...) and you swap the bell-nozzle for an Aerospike- which augments ISP and Thrust at least 20-30%, you should get about 720*1.25= 900 seconds Effective ISP at sea-level with an air-augmented Aerospike rocket (note that TRUE ISP, based on Exhaust Velocity, was only about 180 seconds with a bell-nozzle, and 225 seconds with an Aerospike: but 75% of your working mass comes from the atmosphere, and so Effective ISP is 4x higher...) UNLIKE most airbreathing jets (except SABRE), this is easily a dual-cycle design: you can swap to closed-cycle mode and lose half your ISP at any time... (some Air-Augmented rocket designs are designed to allow you to preserve Thrust by increasing the rate of fuel-consumption proportionally, however...) The Effective ISP in-atmosphere is extremely impressive, and no less than a "normal" Aerospike outside the atmosphere (the RS-2200 was supposed to be capable of achieving 437 seconds on HydroLox, for instance... Not a great deal worse than the Space Shuttle Main Engines, at 451 seconds...) TWR is the main bogey of air-augmented rockets and Aerospikes both. But it's even lower for Ducted Rockets (probably about 30-40% of comparable higher-ISP conventional rockets with a good ducted rocket design, I'd guess around 25:1 - 30:1) than it is for Aerospikes (about 80-90% that of a comparable rocket is likely, once you consider that the RS-2200 was likely over-optimistic in its TWR: which would have exceeded the Space Shuttle Main Engines, at 83:1 vs. 73:1...) The mass penalty for an Aerospike Nozzle would likely decrease with a Ducted Rocket, due to having fewer heat issues. But even if it didn't, increasing that Thrust and ISP 20-30% would still only come at a fixed mass-penalty, attached to a much heavier (ducted) rocket engine. So TWR would fall very little (for a BIG, 20-30% increase in sea-level ISP), and might actually improve for the rocket as a whole (with the benefit of cooler exhaust-gases), by switching to an Aerospike nozzle... This is in sharp contrast to with a normal rocket: where Aerospikes impose a HEAVY (20% or so) penalty to TWR... For instance, let's say you have a standard 1 ton, 1000 kN sea-level Thrust rocket (TWR about 100:1, I will treat g at 10 m/s instead of 9.8 for easier math, as it won't affect the conclusions), 320 seconds ISP. If you make it ducted (air-augmented), mass might increase to 6 tons. Thrust to 2000 kN. TWR has now dropped from 100:1 to 33:1. ISP is now 640 seconds. Now, if you add an Aerospike to that normal (1000 kN) rocket, Thrust might've increased to 1200 kN, but mass to 1.5 tons (TWR now 80:1). ISP at sea-level from 320 to 384 seconds. To add an Aerospike to the ducted rocket, however, would add 2 tons to the mass instead of 500 kg, due to having 4x the Mass Flow Rate (4x the nozzle size), if heat issues were no way alleviated by the cooler exhaust gases, or scaling-benefits (because larger rockets have fewer cooling-issues with their nozzles, up to a certain point, Aerospikes experience less of a mass-penalty relative to Mass Flow Rate as you scale them up...) and you had the same mixture of exhaust-gases. However that last one is a bad assumption we CAN'T make here: the gases of the atmosphere (average MW about 29) are substantially heavier than the gases of a HydroLOX engine (mostly H2O, MW 18). So much so, that even though the Mass Flow Rate is 4x higher, the VOLUME of exhaust gases only increases about 150%, and the nozzle-size needs only go up proportionally. So, 1.25 tons is a more appropriate mass-penalty (nozzle is 250% as large as with the standard rocket, where mass-penalty was 500 kg) even WITHOUT any benefit from larger engine size or cooler exhaust-gases. If the Aerospike adds 20% to Thrust and Effective ISP due to higher nozzle-efficiency, like before, you would get 2400 kN Thrust, 768 sec ISP (192 seconds TRUE ISP, based on Exhaust Velocity). If mass went up 1.25 tons (worst-case scenario for the Aerospike) and sea-level Thrust/ISP only 20% (conservative end of the 20-30% range) you now have a 7.25 ton rocket, and TWR of 33.1 :1 (only *slightly* worse than 33.3 :1, before). However these are Worst-Case numbers (only a 20% increase in Thrust and ISP, no scaling-benefits, and no benefit at all from cooler exhaust gases). If Thrust and ISP increase 30% (to 2600 kN and 832 sec Effective, with true ISP of 208 seconds) then TWR is now 35.86 :1, HIGHER than before. If the mass-penalty is even a little less than before (due to scaling benefits or the cooler exhaust gases) then the TWR improves further. In short, an Aerospike Nozzle, Air-Augmented Rocket should have better ISP, and quite likely higher TWR, than a normal Air-Augmented Rocket. It should ease some of the design challenges of an Aerospike (mainly, these have to with heat-management, which should be helped both by cooler exhaust and larger nozzle size) and has the same intended uses (to improve atmospheric Effective ISP on a rocket) and so I do expect the two technologies would be complementary- each eases the other's challenges, at least slightly (Aerospikes suffer from heat-related issues due to having more surface area in contact with fuel, Ducted Rockets from low TWR...) Finally, an honorable mention of the uses of these technologies in spaceplanes- which accumulate a lot of speed (important for Ducted Rockets, which obtain higher ISP at higher speeds: presumably due to some effect of the increased mass or speed of the intake air) and spend a lot of time in the atmosphere, but still ascend beyond it: precisely the sort of ascent Aerospikes work best for (not to mention the reduced penalty for high engine mass on a spaceplane: which can reach orbit with overall vessel TWR less than 1 at takeoff, due to relying on Lift/Drag ratio for the initial takeoff, climb, and run for speed...) The high performance enabled by these technologies, and much greater simplicity than proper jet engines (despite using air for working-mass, Ducted Rockets don't burn it: and thus don't face issues with combustion instability at high speeds, as their primary rocket combustion chamber operates entirely like a rocket...)

Ehh, I bet it woul've been doable.

@JadeOfMaarso, I love all the time you put into this mod, and hope you continue to make it better- here's a couple things I noticed that need some tweaking along those lines... - The J Fuselage parts (those are the more modern ones vs the 'Stail' line, you said, right?) lack a J Fuselage to 2.5 meter adapter with 1.25 meter shoulders, like the Stail parts have. Heck, they lack any adapter to 2.5 meter diameter at all (extremely useful for some purposes...) - The ISP's on the linear aerospike engines appear to be far too high for Stock KSP. They appear to be based on real-life ISP's for HydroLox. Fine values for a Real Fuels config. But their ISP (330-430 seconds as I look at it in the editor this moment!) exceeds that for any vacuum-optimized chemical rocket engine in the Stock game: including the Wolfhound! (380 seconds ISP in vacuum). I suggest an ISP range of 335 to 385 seconds (rather than the 330-430 we have now) for these engines, based on what aerospikes are supposed to do (great sea-level ISP while still also obtaining vacuum ISP comparable to vac optimized engines- in exchange for higher cost and complexity) as well as some actual numbers on their efficiency (339-439 for the XRS-2200, vs. 366-452 for the SSME: the RS-25- both use HydroLox rather than Kerosene, and the SSME's had some of the highest vac ISP of any rocket engine ever used...) In short, the sea-level ISP is mostly fine (they are supposed to burn 25-30% less fuel than a comparable bell nozzle for the same sea-level Thrust: i.e. 25-42% higher sea level ISP!), but the vacuum ISP needs a MAJOR nerf (they are currently more than 13% more efficient than the best conventional vacuum engine in the game!) As they stand, the linear aerospikes are far too good in vacuum- which makes no sense when their intended benefit is in-atmosphere (although they also have *VERY* high TWR for a vacuum engine of such high ISP in real life...) Their Thrust, although considerable, could use some buffing- but their mass is too low. These engines are 2.5 the cross-sectional area of a Mainsail, yet have slightly less Thrust and only similar mass (their Thrust and mass should BOTH be raised: both are too low...) TLDR: I recommend increasing both the Thrust and Mass of the linear aerospikes (this will make them more powerful overall, and bring them more in line with Stock parts of similar cross-sectional area- **as well as reduce the need for part-spam**) but the Mass by more (TWR is currently too high for an aerospike: though nerfing their TWR won't hurt spaceplanes much). Decrease vacuum ISP by a LOT (45 sec)- which currently exceeds dedicated vacuum engines like the Wolfhound by a very large margin. Buff sea-level ISP slightly (5-10 sec). Also, in rease part-cost (should be just over double what it is now) Overall this is a nerf, due to the large drop in vacuum ISP and increase in cost/mass: but the increases to Thrust and sea-level ISP will at least make them better for their intended/realistic purpose...

Hope this is going well! Still eagerly watching and waiting to see what such a talented modder as yourself can do with this!

Awesome! I hope this goes well, and isn't too much work for you! While we're on the topic of larger parts, I also really, really would like to see larger Lifting Body fuselages in Stock (when you don't have FAR, you get Body Lift by giving fuselage parts a Wing module to generate Lift- much like the Mk2 fuselage parts have already...) Because as cool as the Mk2 fuselage is, it just doesn't meet the Demand for launching larger/bulkier payloads: and the Mk3 fuselage is Shuttle-like, NOT a Lifting Body, and is optimized for vertical rather than lifting ascents... Meanwhile, not many of the mods for this are satisfactory- I've found Nertea's Mk4 parts to be entirely too heavy, expensive, and unwieldy for what they do, with the Mk4 RCS pods having particularly unjustifiable part-costs, often each RCS port part cost measuring in the THOUSANDS (Nertea is one of those modders that likes to sucker-punch his Career players with excessive part dry-masses and part-costs on his fuselages and engines while you aren't looking...) @JadeOfMaaryour OPT fuselages are fascinating, even if many of them are too heavy for their form/function (I suggest looking to the "Stail"parts for better part cost and mass-balancing: although I'll try and get some of my own suggestions to you eventually...) But problems like the still-unresolved 1 km spawn bug with, some of the Type J fuselages I think you said (which are also the more "modern" versions of the Stail- which I mostly use instead due to their more reasonable part-masses and costs: the latter of which are relevant as I sometimes use them on orbital stages or reusable boosters for their handy side-mounted 1.25 meter nodes, great for attaching smaller engines or docking ports for crew capsules to a 2.5 meter vacuum stack, and cross-sections midway between the 2.5 meter and 3.75 meter diameters...) illustrates *precisely* why we need larger Stock fuselages- ideally SQUAD would just pay you to work with them in making versions of your existing larger Lifting Bodies stock- rather than just mods. Mods tend to be wracked by bugs: and modders often feel (in my opinion, a bit unjustifiably: projects are meant to be revised and carried forward) a bit guilty at revising earlier modders' work, even just to fix those bugs (like bugs with the recoil system in my Mass Driver mod, or in OPT's 1 km spawn bug), or even at just forking and updating/maintaining antiquated mods without permission (even when the license they are under *specifically* allows redistribution without permission: as it did for my Mass Driver mod- although many modders do opt for *certain* more restrictive licenses I won't name by default, just because they are popular, and they don't bother to investigate alternatives...) and the modders have been absent from the forums for months or years... (as I mostly had before finally returning and asking somebody to take over my mod- which was itself a fork and rebalance of some parts with permission from the even more outdated Stanford Torus Mod...)

To simplify things probably. Or maybe I am misremembering- and this feature was never made a part of the mod in the first place (and I am remembering testing revised ISP curves for different propellants in-atmosphere: as they end up with very different exhaust pressures for the same Thermal Power..) But do me a favor, alright: actually test this for yourself by pad-testing a variety of different thermal rockets (both nuclear thermal and microwave thermal) with different ThernalPower ratings but the SAME core temperatures, and different Thermal Nozzle sizes in relation to the reactors, and post Imgur albums of the rocket nozzle and reactor/thermal receiver context (right-click) menus during static thrusting on the pad here, so all of us can see, and can critique whether it's working properly. Posting images of the same combinations in orbit (just cheat-menu them there, or Hyperedit if you use it) will also help verify if the atmospheric Thrust/ISP's don't drop as much as expected, or drop too much... If the ISP/Thrust numbers aren't what would be expected for reactors/nozzles of those size and fuel types, I can advise FreeThinker on what numbers would be more realistic to incorporate into the mod (or at least point him towards some resources) and you might get your ISP curves after all, if they weren't already there! Regards, Northstar

They do. That was what I was just describing. Atmospheric ISP is a function of both the type of propellant being used, and the throttle/power levels. In real life, ISP does *NOT* remain constant as you throttle down, like it does in KSP (decreased exhaust pressure leads to a worse ratio between exhaust pressure and ambient pressure: decreasing ISP). ISP curves, as they exist in KSP, bear little resemblance to real life. They bore even less in the past-m: where ISP changed but Thrust remained constant with different ambient pressures in earlier versions of KSP... Interstellar was ahead of the curve, by setting Thrust and ISP to vary together at a constant Mass Flow Rate, like they do in real life. Throttle/Power also affects ISP, though, and this was reflected in Interstellar better than it was in Stock... The ISP you get varies based on which nozzle you choose. I don't know if you noticed this before, but (unless this was changed) you used to get better ISP when using nozzle sizes smaller than the reactor size when you were thrusting in the atmosphere with a relatively weak engine (due to not over-expanding the exhaust stream). There was talk about adding more customization of nozzle sizes/shapes, but ultimately that was never realized...

The beauty of plasma thrusters is their atmospheric ISP actually increases with higher power output. This is because the Exhaust Pressure goes up and up the more Mass Flow Rate you push through them, and there is less compression of the exhaust stream. The most critical number is that the exhaust pressure at least equals Ambient Pressure- otherwise in real life there would be invasion of the nozzle area with outside gases, shockwave formation, and collapse of the exhaust stream: with resultant massive loss of Thrust and ISP. Thermal rocket nozzles used to do the same thing in KSP-Interstellar Extended: this was most noticeable with Microwave Thermal Rickets back in the day- as they had some of the lowest exhaust pressures in the mod at very low power levels: but this could be increased drastically with the same design by adding additional ground-stations transmitting power nearby.. I still remember viewing the Thrust and ISP of a launch clamped thermal rocket, with different numbers of ground stations nearby active/inactivated (each station was basically just a big old Molten Salt Reactor with a Microwave Transceiver/Transmitter) to test that this feature was working properly, and the Thrust/ISP levels were right... It worked back then- I assume it still does now (though I have a feeling not many users of this mod concern themselves with mastering Microwave Beamed Power now: being in such a rush to make it to Antimatter Power and other advanced rocketry). Back then there WERE no reliable, reasonably bug-free mods to go to other star systems though. Now there are- and players are eager to climb the tech tree and visit the stars: or at least I hope that's whst's going on... As for the ducts: it's up to FreeThinker in the end, but I think a lot more research would be needed into actual engineering documents on nuclear reactors and what's at least theoretically possible with their heat management first. I will say this, though: it becomes about 100x more realistic if you're willing to suffer a large (like 50%) drop in the "reactor temperature" the nozzles see, due to using a coolant to carry the heat instead of somehow managing it with superheated gasses through long ducts directly. Which means much lower ISP, lower energy efficiency, but actually somewhat better Thrust output for the amount of power consumed... Also, the max temperature this could transmit would be pretty much s hard ceiling based on tech level, not going up no matter how advanced the reactor became... Fans aren't that draggy, though. You hide them in a cargo bay until needed, only opening the bay doors (exposing them to Drag) when it's time to fire them. And the Banshee fans come in inlinevstack-mounted versions that fit right into a Mk2 fuselage: although it does seem to glitch out when quicksaving/loading. Still, you can run a mindboggling number of electric fans off a single nuclear reactor... P.S. There are some KSP players who will complain about anything, and are eternal pessimists. My point was that some of them scoff at the idea of pre-coolers even working, or being useful: in fact I got into several bitter disagreements about this in the Science Labs subforum back in the day... (this is before BAE and Reaction Systems finished quietly working on the SABRE precooler and started testing/demonstrating it to prove it to the world...)

Some of these are already built into base game, to the point there's no removing them without heavy modding on the scale of Realism Overhaul: but KSP-Interstellar didn't create these issues in the first place. No reason to add more unrealistic nonsense to the mod by adding a part that is, frankly, near-impossible in the real world, and harder than much of what is already in the mod. It used to be (correct me if this has changed) that reactors could transfer thermal power to stack-aligned thermal nozzles up to 2 parts away, allowing them to "skip" a single part (or letting you put a reactor on the internal stack node of a cargo bay or fairing, with a nozzle on the rear side). This was considered a bit of a departure from realism in itself: as sometimes this could lead to thermal power crossing a single very long part to reach its destination with no added mass required. But at least this was only a single part, with likely no substantial flexing between the two. The required equipment would likely involve a very large, heavily-insulated duct: something a lot larger than a mere "pipe", to have sufficient structural strength and insulation to transfer the heat of a reactor (or the superheated gasses) and significant distance, and be able to bend their trajectory. Magnetic confinement would also be required for thermal levels much over those of a Molten Salt Reactor: so it would be even harder to pipe your heat from fusion/antimatter reactors... I don't think you would find this of much use in a VTOL engine, even if it were added...

Not *quite*. The microwave beam spreads out as it travels from the transceiver (this effect is worsened by atmosphere in between, as is reflected in the mod) and the larger the transceiver cross-sectional plane *normal to the beam vector*, the larger a % of this power can be captured despite this spread. If a spaceplane rolls, the cross-section on this plane changes (the Mk2 profile has a smaller cross-section when sliced in a Saggital Plane, than when sliced in a Coronal Plane, to borrow terms from animal anatomy and apply them to the anatomy of spaceplanes...) This is basic science/math. I didn't need you to tell me how it works: I already know this for a *fact*, having done much of the research for the original rebalancing of many KSP-I Extended parts with FreeThinker, and read too many articles on Microwave Beamed Power to count... But what I DON'T know is if the radial asymmetry of the Mk2 transceiver (not around back when I worked on the mod) is correctly accounted for in receiver effectiveness...

I was able to replicate this recently- in fact TWICE. I don't have any contract packs installed. It's definitely a bug with the way the mod handles save integration. Loading up a quicksave from AFTER launch, of the main vessel, and then using the menu "Revert to Launch" actually saved me this problem the 2nd time around. Also occasionally still getting penalties for killing Kerbals when the main stage spins out of control, explodes, and crashes my crew modules into other parts due to not being controlled while replaying a side-booster separation much earlier in the flight (the main vessel in my main save already safely made orbit!) The ascent looked a lot like a Falcon Heavy cire+booster recovery, but with crewed payload. This seems to only be a problem when I get the "vessel nearby" text on the other separated side-booster while flying one back (I'm.pretty sure, though not 100% confident). It doesn't seem to occur if there's just one stage separated at a time... Also, I've been playing around with air-launches a lot lately, and saw someone earlier asked a while back about using FMRS to air-launch a rocket on Eve, essentially... I know this is kinda old questionsl, but may still be relevant for many people: often (this is a really old but very useful feature in FMRS: dating back many versions- so I'm not sure it's gotten all the maintenance it could) you can fix this by quickly pressing "[" or "]" to switch vessels immediately after (the mod gives like, 5 seconds) the stage separation. This changes which vessel is assigned as the main vessel, if you then continue flying the seperated vessel. In a case like that, the airlaunch plane needs to be the one that appears in the menu, while the orbital rocket is the "main vessel". The mod hasn't figured out how to integrate vessels in orbit into a save if they're not the main vessel (YET, at least... This really SHOULD be changed...) so the only way you can save other stages that seperate and fly all the way to orbit is to land them somewhere, eventually... Also, @linuxgurugamer what happens if we make a stage separate on a daughter vessel AFTER it separates from the main vessel? This could be useful in certain contexts: but I'm afraid of what might happen if I try it...

Also, @FreeThinker, do the precoolers still work on a variety of airbreathing engines (not just thermal turbojets) to improve their high-speed, high-altitude performance (as they realistically should: pre-coolong airflow allows the compressors to bring it down to lower speeds and higher pressures without melting themselves in the process!) like I think I remember: or was this functionality stripped from later versions of KSP-Interstellar Extended for some reason? (A reason such as the whining "realism- it can't be done!" crowd: who are really just a bunch of pessimists who don't even attempt to understand cutting-edge science or what ACTUAL reality entails: i.e. the SABRE pre-cooler was recently PROVEN to work in a hypersonic wind tunnel, and the basic concept of precooling an airflow so you can operate airbreathing engines more effectively at higher speeds/altitudes is sound with regards to basic physics... The engine doesn't "know" it's in a fast-moving, high-altitude plane if all it sees is air compressed and slowed down to subsonic speeds and sea level pressures, for instance...)

Oh. I haven't played with Interstellar in a while, and am just now about to get back into it in my current Career Mode game, having finally advanced through much of the Community Tech Tree- thanks in large part to Covid-19 and finals being over... (on my 2nd of 3 Master's in a dual-degree!) Does the receiver account for the roll-angle of the spaceplane relative to the vector of the ground station, as it should? (i.e. if you are flying directly overhead, and roll to a 90 degree angle, the Mk2 receiver *should* receive a lot less power, for instance. Or if you mount the receiver at a 90 degree angle to the normal axis, it should be far less effective for ground stations directly below: but more effective for those off to the side...) As for heat-pipes from a reactor: that is just ASKING for trouble and an engine-failure, as well as being far harder to realize in real life than you imagine. Nuclear Thermal Turbo/Ramjets work because the air passes DIRECTLY over a heat-exchanger surface on the surface of the reactor: likely to be made of extremely heat-resistant materials like Quartz, Silicon Carbide, etc.- materials NOT at all flexible or amenable to being used to construct a heat pipe likely to undergo significant structural stresses. Not to mention the insulation mass-requirements would be high. Also, the mass requirements of such heat-pipes would scale very non-linearly with increasing amounts of thermal energy transferred (small pipes transferring small amounts of heat would actually be least efficient, whereas larger pipes would have a better ratio of mass to power transferred: although still very poor, and heavy) You're much better off just using some kind of electric lifting fan (such as the Banshee from either Mk2 Expansion or OPT Spaceplane Parts, I don't recall which) for VTOL: which would actually probably be more energy-efficient in real life, as it takes 4 times the energy to get 2x the Thrust when you double exhaust-velocity (and electric fans have VERY low exhaust velocity. The downside is you lose Thrust more quickly with increasing speed: but VTOL is almost always done from a standstill anyways...) If you REALLY want a VTOL using some kind of rocket/thruster, stick small reactors on rotatron parts: so both reactor and thermal turbojet/rocket nozzle move together (having flexible/stretchable air or fuel-ducts that can accommodate this rotation is at least feasible in real-life) OR use a plasma thruster powered by a huge reactor (will reduce fuel-use for VTOL on non-atmospheric planets, but INCREDIBLY energy-inefficient) OR just place a few small fixed-orientation reactor+nozzles inside cargo bays facing down, so they can VTOL when the bay doors are opened...

Intriguing. I'm not sure I understand all that about PAWs and modularity, though? Also, in a different topic: do you happen to know if the airbreathing engines in this mod work with KSP-Interstellar precoolers? Last I worked on helping develop, or played with, Interstellar (which was admittedly quite a while ago: real life and game updates got me away from such a complex-but-awesome mod that most players fail to understand is actually HEAVILY based on real science and more realistic than Stock in many cases...) it added code to the Stock precoolers, and precoolers from mods, using ModuleManager, that allowed them to do what they would in real life: cool the airflow and effectively allow it to be compressed further than normal, to internal speeds/pressures (inside the duct systems and entering the engine) much lower and higher, respectively, than what compressors cpuld ever achieve without them. Effectively, this meant that when the precoolers were activated (a right-click/ action group command was added to turn them on/off) the intakes they were attached to passed "slower" and "lower altitude" (higher pressure) air along to their engines: shifting the velocity and altitude-curves to the right (so engines could produce peak Thrust at higher speed/altitude, and would flame-out at higher speed/altitude as well...) This is extremely realistic, actually- and why the British government is jumping on adding SABRE-derived precoolers to their under-development supersonic jet fighters/bombers, now that the precoolers have been demonstrated to work effectively in a hypersonic wind-tunnel to the same parameters they were expected to. In space terms, this would mean you could use airbreatgers up to higher speeds and altitudes, increasing the potential viability of spaceplanes and very high-altitude airlaunch systems... Anyhow, I was wondering if it is possible to combine something like a OPT Turboramjet with the KSP-Interstellar precooler code, and have it improve airbreathing performance, like I hope (and as it realistically should). This might also be a way to make the mod more "balanced" and silence some of your critics- rather than have the most advanced engines in OPT work up to such high speeds and altitudes, nerf their performance somewhat: but bundle the Interstellar pre-cooler code with the mod so players can obtain the original performance by throwing on some pre-cooler parts (the code would work with stock pre-coolers, and any pre-coolers of your own design if you made sure the code recognizes them as pre-coolers and knows how powerful they should be...) A note on pre-coolers, though: if I remember correctly, they can be VERY electricity-hungry (power is used to pump coolant fluids around, to the abstracted coolant system present in KSP-Interstellar and the various radiators and convective heat-exchangers especially) and they might require the WasteHeat code and associated radiators from Interstellar as well. These pre-coolers were not the hydrogen-cinsuming designs of a SABRE, but assumed the use of active radiators powered by nuclear reactors or Microwave Beamed Power converted directly into electricity instead... (I do think there was talk of letting them consume cryogenic fuels as a heat-sink to reduce EC usage, though. Not sure if it was ever realized...) This is pretty complicated now that I think of it, though. Maybe it would be best just to include KSP-I compatibility patches (if they're necessary for the engines to work with pre-coolers) or make a hand-wavy reference to "integrated precoolers" and increase the mass and Center of Mass offset (forward, away from the rear-facing engine mounts where most of the mass of KSP airbreathing engines is unrealistically concentrated) to represent precooler parts not actually represented, instead?

In essence, yes. They emit more kW/MW of heat the hotter they get. Which is realistic, and as-intended: deployable radiators (one of the parts I helped theory craft and balance for this mod based on real-life data back in the day: the radiators inherited by Extended from the original KSP Interstellar were a bit underpowered and unrealistic...) in the mod and in real life rely MOSTLY on Black Body Radiation to emit heat: which increases with the *4th power* of temperature- 2x the temp gets you 16x the radiation of heat as photons (mostly Infrared, but can enter visible wavelengths when white-hot). This is a big part of the reason radiators with higher maximum temperature have higher maximum cooling (we even added upgrade-nodes in the tech tree to increase their maximum temoeratures back in the day: as well as emissivity coefficients- with some modern materials actually already SURPASSING a coefficient of 1 in real-life due to clever use of materials science and nanotechnology... I had a big part in bringing this science into the basis for the mod, as I felt it important to get radiators right... Didn't hurt that my slightly-younger brother had an interest in becoming an engineer working on materials science/nanotech for defense+aerospace tech at the time, either...) Radiators actively pump coolant fluids into themselves, to suck heat into themselves from the rest of the craft and cool it back off before recirculating it- coolant systems are one of the many abstractions we decided to not elaborate on in Interstellar Extended, back in the day: which is a shame, as open-cycle coolant systems that vaporize and emit water as superheated steam would be very useful for certain applications, such as hypersonic jets, cooling reactors near water supplies like in real life, dealing with heat during peak re-entry heating, and cooling of aeroshells used for Mass Drivers... (shoutout: some awesome modders have taken over my Netherdyne Mass Driver mod for me, and are releasing an updated version for 1.9.x with some bugfixes and code-cleanup, although sone players say the OLDER version actually still works on 1.9.x even though my thread doesn't say so: due to lack of thorough testing before a "release" in my part, and some overdue code-cleanup and recompiling I didn't have the time/skills for, that probably makes the old version run a bit slower/worse with heavier computer load on newer versions of KSP...) The deployable radiators *DO* engage in a certain non-trivial amount of Convection, though, due to their massive surface area, even they aren't optimized for ir- as would be true in real life... (unless this was stripped from more recent versions of Interstellar, for some odd reason) The flat radiator panels, if they're still in the mod, used to do a respectable job of cooling spaceplanes in-flight or in re-entry (just like the Stock flat panels still do: I use them to help prevent wing overheats in re-entry, actually...)

@FreeThinker I've been playing around with Mk2 Expansion lately, and it gave me an idea... What if we could have some Thermal Rockets and Thermal Turbojets in Mk2 form-factor? After all, the original source of the idea for the Microwave Beamed Power in the mod was probably the plans of the New Space startup Escape Dynamics (which, sadly, eventually went under), which basically seems to have planned on using a lifting-body spaceplane with a form similar to the Mk2 fuselage (with minimal, highly-swept wings), stuffed to the brim with Liquid Hydrogen, in order to provide more absorptive area for the microwave thermal receivers vs. a cylindrical fuselage (the entire bottom of the spaceplane was basically one giant Microwave Thermal Receiver, if I recall...) This also provides more Lift, and better aerodynamics, for a lifting-ascent: which they seemed to have opted for as it: (1) Allowed for the spaceplane to spiral upwards over the Microwave Transmitter site for a while as it gained altitude (to reduce transmission distances), and then set up a run for speed and altitude starting up-range of the transmitters once they got as far as they could in a constant spiral (again, the goal seemed to be to reduce distances so the Thermal Receiver got as much focused power, and time to reach orbit, as possible with just one or two beamed power array hround stations...) (2) A lifting-ascent allowed the spaceplane to reach orbit with less Thrust than a comparable-payload rocket: which was critical as the most expensive component of the entire system was the beamed-power ground station transceiver arrays (with costs scaling proportional to how much power they had to aim towards the spacecraft...) All of this translates fairly well to KSP-I, actually: which is part of the reason I discussed it here (all of these ideas work in KSP. Even the increased receiver-area of the lifting-body form factor: if you use a Mk2 Bicoupler to put two 1.25 meter thermal receivers on the bottom of your spaceplane right now...) It really would be nice to see some Mk2 form-factor parts in KSP-I (especially the Microwave Beamed Power systems: which are one of the first really powerful KSP-I launch systems you reach in the Community Tech Tree...) Given how much there is to add there, especially with more aerodynamic parts and the Microwave Beamed Power system needing a little love, maybe it would be best to split KSP-Interstellar into a bundle of related mods, much like NearFuture does? Would make things more manageable for players: instead of one colossal mod, they could pick-and-choosr different mods in the pack with self-explanatory names: i.e. one for atmospheric parts, including Thermal Turbojets; one for ISRU and resource systems including the Propulsive Fluid Accumulators; one for Microwave Beamed Power; one for the nuclear reactors- which players might want on their own just for electricity generation; one for the plasma thrusters and other related electric propulsion systens; one for the really advanced nuclear propulsion systems; and one for the Warp Drive itself. Of course, all of these are complementary- and it might be best to keep a centralized wiki/documentation (only split into sub-sections for each mod, so players can find what they're looking for). Just an idea, anyways. Might also make it easier to branch/fork off some parts of the mod to different authors too, so you can focus better on the remaining parts. Might be a terrible idea too: if it doesn't work well for your authorship style. Whatever works for you FreeThinker: this continues to become an ever more impressive mod, that amazes me every day: and I'm glad of any part I had in helping you develop it (I think my username is even still found on the authors of a few configs I helped tweak years back, no?), and also importantly: giving you ideas along the way...

I'm a bit confused: why do these parts eve exist? RCS and SAS are two competing control systems. What's more, they optimize to different placement... RCS is best placed as far from the CoM of a vessel as possible for rotation-control, to increase their lever-arm and increase the torque produced for a given RCS force (increasing effectiveness and reducing Monoprop consumption for a given turn-rate/torque. Although with really large, unstable designs, you're better off just using a proper rocket-engine removed from Main Throttle for rotation control...) The Monoprop tanks, meanwhile, are best placed centrally to reduce CoM shift. SAS, on the other hand, is best placed close to the Center of Mass of a spacecraft- to reduce wobble and "spaghettifying" of long, thin spacecraft/planes- although in a plane, there's also justification for putting it more towards the nose, as it will weaken the fuselage structure less there. And the more SAS you have, the less RCS you need. Generally the only reason you might want RCS in the same place you'd put SAS is for translation-control: and even then you're usually better off with a set of RCS thrusters far from the CoM, precisely-balanced for translation (thrust-vector for the RCS must pass through CoM) to do this: as then they can also double as rotation-control the rest of the time... I suppose there's a marginal use for this in reducing part-count, and SAS systems placed towards the nose on unmanned spaceplanes with large Canards (cockpits are too heavy to have an SAS module between them and the main wings- it will cause the fuselage to flex too much. Canards provide some Lift to the nose, helping reduce the weight that must he supported by the fuselage all the way to the main wing...) and FAR installed and providing body-lift from the fuselage to reduce flexing further... Which are basically all I ever build (as unmanned, canard-using spaceplanes are basically the most efficient designs possible in FAR with regards to fuel-usage: especially as Center of Lift shifts backwards in FAR with increasing mach speed- making forward swept Canards very efficient for keeping the nose up), now that I think of it- and I'm very limited on part-counts my CPU can support- so maybe I shouldn't be complaining...

Any chance someone can explain the logic behind the New Glenn legs parts to me? The legs don't seem to want to attach to any part besides the specialized base, and the specialized base, despite being cylindrical, REFUSES to attach in stack mode- only attaching in surface attach mode (and quite poorly at that: often half clipped into the base of the rocket, which can create Kraken problems as well as being very draggy in FAR...)

I don't play Realism Overhaul. Nor would it make much sense for me to- as I currently play on Stock scale (partly as a function of the slow FPS and limited part-counts my computer can support: hence why I want to install an updated Procedural Parts- to shrink my part catalog and reduce Part Count on my craft!) I'm not looking for a rebalanced fork meant for RO- I'm looking to use the stock mass ratios and such (because realistic ones are incredibly OP'd when it's less than 4 km/s vacuum Delta-V to LKO, even with a SpaceX style ascent and booster recovery. ..)