wumpus

I don't think I've seen a paper with as much handwaving before. Presumably the "scalable Brayton units" could be powered by the NTR in some sort of closed figuration (presumably the radiation from the fuel), but this isn't covered at all, neither the amount of power needed by the ion systems for such things nor the power generated by the NTR (either firing propellant or not. Presumably they were mostly expected to work when not firing propellent and this isn't covered at all). Especially missing was any idea of the size needed for the "brayton cooling" bit: the ISS uses radiators roughly 1/10th the mass of the solar panels, but here (which presumably uses vastly more power than the ISS) such cooling is an afterthought. I still need to work out how many Pe kicks you can do between crossing the Van Allen belt and the burn beyond escape (presumably to Mars or the asteroid belt), but I suspect it is either one (a few km/s or so) or zero (it still does wonders in cutting down the thrust needed).

I'm sure I can build a payload to justify the ions (not the time to put it in place), but the NERV is pretty massive, so is less suitable for jutting to Mun/Minmus. On the other hand a NERV-based shuttle for use around Kerbin's SOI is quite useful. This is true even for ships that weren't intended for such duty. As long as they have a NERV engine, a docking port, and aren't erased they will do fine (you can do the same with Poodles, but it is harder to justify unless your launcher is a spaceplane).

This is certainly reasonably high for any travel inside the solar system, although you probably won't try any "fast Mars" trips (faster than Hohmann). Interstellar isn't going to happen with 3 (or even 4) digit Isp. I was told that the 800 Isp number was from the 1960s, and that materials science could provide better now (although I suspect that means either ejecting spent fuel or paying in cooling/dry mass so much to erase the Isp gains). Obviously you would want to turn waste heat into power, if only to avoid having to radiate it. Have you ever considered just how you would balance an ion system with a NTR? The concept seems completely insane (on the other hand, if you where using VASIMR you could at least scale up your power and use the same propellant) as the thrust of the ion would be completely in the noise of the NTR, while the Isp of the NTR would be such that if the ion was worth using, you would never use the NTR. Ions would only make sense if they were the most efficient means of transmitting energy (and thus heat) into the cosmos (I'd try LEDs first, or perhaps microwaves).

As far as I know, "brute force" is the only way this problem has ever been solved. There might be trivial cases where local maxima can be found and an optimal solution found, but each part will create a new function that still requires "brute forcing". Note that is still true after ignoring both gravity losses and aero losses. A brute force method that considers such possibilities may well be more efficient than an "optimal" one that doesn't. Ions and NERV are trivial to optimize. If in a vacuum and in at least a stable orbit (you don't require thrust to avoid falling into a gravity well) Ion>>NERV>>everything else (for mass/cost efficiency. Not remotely efficient for player time*). Consider mech jeb, kerbal alarm clock, and finally KOS before using these systems. In practice Ion powered ships are expected to spiral out (no Obereth) while NERV ships often use the Mangalyaan maneuver (often called "Pe kicking" in KSP) to use the Obereth effect with low TWR. The differences mean that these engines need more delta-v than a "subway map" might indicate (the NERV might be close, but you will always have to do your final burn of more delta-v than delta-vtotal needed - delta-vescape velocity (for you SOI). Drop tanks are unlikely to be added to this system as the obvious solution (for mass) is that all tanks are as small as possible, only two (or possibly one if you can afford to twist around and eject it off the top) tanks are used and dropped immediately when empty. Creating a structure that can utilize such a design is non-trivial. Slashy's answer is the best you will find in KSP. Also don't expect things to always neatly break into stages, although one favorite trick is to put drop tanks on top of solid boosters so that once they drop you have a full "1.5th stage". * ions may look "overpowered". Compared to reality, they are *underpowered* (the ISP is higher). The catch is that they have even less thrust in reality, which doesn't really matter as presumably NASA has somebody at JPL tasked with making sure it is still doing its thing [actually what I've heard it is more "somebody gets a few hours of time on the deep space network and has to resolve all possible issues in that narrow timeframe. Only steely eyed missilemen with deep experience need apply.]

A closed cycle reactor will have the same cooling system it used when operating after it is turned off, so that shouldn't be an issue. When a NTR (or any nuclear reactor) is "turned off' the nuclear fuel will still be reacting as some of the fuel will be turned into isotopes that are still emitting neutrons and powering the reaction. Simply "leaving it hot" is likely to cause a full meltdown*. Also I wonder at the idea of powering down a reactor to limit radiation. Normally I'd assume that lowering the output such the the reactor is "always on" would reduce the danger from radiation (assuming equal shielding), but in practice I'm less sure (ignoring strategies involving sequestering crew in highly shielded areas during a burn). I still think that cooling issues will drive a "always on" solution, cooling a reactor in space is non-trivial and the danger of coolant failure (abandon ship**) outweighs the danger of radiation. Propellant is a good word. I kept thinking "reaction mass" which also doesn't work in the context of a nuclear reactor. * KSP's "source of all information" describes this in a recent series: https://www.youtube.com/watch?v=pWWjbnAVFKA It might be the next video, but it does include how the "secondary reactions" work and why the reaction continues after the control rods are full down. ** more likely eject the reactor. This would leave you "dead in space", but at least have as much life support as possible and presumably a more comfortable life raft.

One of the huge advantages of nuclear thermal rockets is that they can do similar cooling tricks as chemical rockets: use the expelled mass for cooling before sending it into the "combustion chamber/reactor" for final heating. Of course, this leaves nasty cooldown issues, you either have to keep ejecting "fuel" (and killing your effective Isp) or somehow deal with cooling a reactor is still radiating plenty of heat/energy. I've suggested that a rather likely system involves ejecting all used fuel after each "burn". Obviously the existence of such a graphene system (or even just a peltier or thermocouple) is likely to be used to extract heat as radiators grow larger and larger. It isn't just the addition of power, just removing the heat is reason enough to do such a thing. Just don't expect such cooling to remotely compare to an open cycle system where transferring the heat to ejected mass is the whole idea.

Nuclear powered electric certainly makes sense for interstellar probes, but I'm not convinced that nuclear thermal power wouldn't be better (I'm not a fan of nuclear thermal power either, just that this has a lot of issues). One other thing to remember is that "breakeven" issues aren't as critical with thermal exhaust, fusion thermal reactors may have a place in space. The graphene idea seems to be designed more as an RTG replacement or any other nuclear power system that provides extremely low temperatures. I'm curious how pebble bed reactors might work in space, although I have even less understanding of the "shelf life" of the pebbles that need to be added and how long they can stay on board spacecraft before use (I'm imaging various pebbles with various radioactive levels stamped with different "use by dates" telling astronauts when to dump them in the core). There are a few reasons to use electrical methods of propulsion: 1. You need a ton of delta-v and are willing to wait a long time for the craft to produce it. In that case electrical methods are ready and have been used for at least a decade (Dawn carried 10km/s of ion power). 2. 800-low thousands of Isp aren't enough (i.e. for an interstellar voyage). Ion propulsion is already high (there isn't much reason to go higher in the solar system) and other methods go higher (liquid cesium is apparently doing well in the lab), and the likely case the emdrive fails, you can still produce "infinite" Isp by using photons as sources of momentum (you can produce arbitrarily high Isp by firing ions out of cyclotrons). Don't expect any efficiency from the last two suggestions, but don't forget that the black body radiation emitted from your radiators has momentum, radiating it behind you should make a big difference. 3. You find a way to scale up ion engines (I'm guessing something like shrinking them down onto a chip and then slapping down a billion of them. There are hard limits on the power of each engine, but nothing really limits the number you can use [note the chip example wasn't entirely serious. I think there are density limits as well]. VASIMR works well in the lab, so it is entirely possible that if you solved the problems in storing hydrogen you will be just as happy to use electricity generated by nuclear power to power VASIMR as you would simply heating the hydrogen and using it that way (nuclear thermal has lots of nasty issues, but I still suspect that using it to generate electricity has more). One last thing, I'd expect the power available from a nuclear thermal rocket to be so extreme that any power needed can be extracted from the waste heat. In this case graphene or peltiers (or even thermocouples) might be chosen entirely on reliability (or cost if funded by corporations). I would assume a situation similar to nuclear submarines with power being limited only by the size of the generators (actually it is even worse since the submarine has a heat sink and the spacecraft is limited to black body radiation and any energy used in thrust).

It certainly sounds like that. Note that 3000K steam should have an Isp similar to kerolox, but I can't imagine maintaining 3000K steam nor what you do as the pressure steadily drops. I can't imagine any steam-based design that can't be converted into a much more efficient pressure-based liquid rocket (although converting to bipropellant at least doubles the complexity but I'd hate to work with monopropellants). There was a company called escape dynamics that claimed to be working on laser based orbital launch designs (I can't imagine they employed enough people to do more than write proposals and make powerpoint slides). The idea was to heat up hydrogen (via an external laser) and push that way, considering the density of hydrogen it would likely make far more sense to launch with with a first fuel tank of water and then switch to hydrogen. Even though the water would likely have an Isp of ~300 (and hydrogen ~800) the density of the water would be so much higher to make a much more compact STTO craft (I'm also sure they didn't want to talk about such complexity until they are ready to commit to real designs). Another mention is that the *goal* is 1,800 feet, while simply flying to Pike's Peak and driving to the top will get you 5,500ft net elevation (Pike's Peak is 14,000 ft of elevation, but it starts nearly 9,000 ft up), although I'd expect you can see the "mile high" (~5,000 ft) plain. The whole project sounds like Jeb Kerman pitching a mission.

Note 1: While "The Martian" may be the most accurate SF this decade on the movie screen (a low bar I know), that doesn't mean that it is all that accurate (the dust storm was admitted to be forced). Any rotation has to keep the radiators pointing normal to the Sun, likewise you can assume that solar arrays will be pointing at the Sun (if using ions*) [note we can generally assume that this vehicle isn't going past Mars: forcing an "outer planets" ship would justify nuclear fuel, but the radiators still would take up a similar amount of space that the solar panels should have. Note 2: You certainly *can* place the collector between the mirrors and the Sun, but that leaves you with the radiators in front of the mirrors. Since they are going to be at right angles (roughly) to each other, it will certainly work. You still will require roughly similar amounts of mirror and radiator surface area, and all the radiators will be in front of the mirrors. Also assume that any material not absolutely flat (things holding the radiators in place, any heat pipes,. etc) will all be hit with the full force of the Sun. Not my first choice. * don't expect to use ions to move crewed voyages. PB666 has crunched the numbers in several threads and shows just how slowly any such craft has to go. I still have great hopes for ions, but not directly moving people.

As Regex says, you should be able to point it in arbitrary directions (this makes solar thermal more difficult). I wouldn't be too surprised if it is actually fixed to 90 degrees from the Sun, and only allow prograde, retrograde, normal and antinormal (and degrees in between), at least if solar thermal. This would greatly reduce the complexity of all the controls, but might require an additional form of thrust for radial in/out (possibly deliberately miss-aligning the mirrors (for minimal power) slapping a heat engine in the thermal chamber and using electric propulsion). It might have a limited ability to sweep fore and aft, but you certainly don't want the exhaust from the thermal rocket anywhere near the radiators.

Light itself exerts a force via momentum, which is likely what would be used to focus a mirror (perhaps of mylar) or angle a sail to exert a force in specific direction (I'm less sure about the sails, I suspect the light will be working against you). The catch is that with a mirror and electric propulsion, the efficiency of the electrical system more or less exerts an acceleration on the entire spacecraft (thus warping the mirrors). Some thoughts: Superconductors: There are two issues here. First is that high temperature superconductors tend to be ceramic which is extremely unlikely to be a useful material for high surface area - low mass structures. Rigidity is not your friend. The second is that even high temperature superconductors in the "shade" are likely to be heated by the radiators to non-cryogenic levels, so as PB666 says, the refridgeration system will be worse than the I**2R losses. Skin effect: skin effect is largely a function of frequency, which shouldn't be an issue for transmitting power between solar panels and spacecraft. I do wonder if multiple strands of tiny wire (which wouldn't be effected by the skin effect anyway) would transmit electricity better than a single thicker wire. The only time I've *ever* seen this done on Earth is for lighting protection: this can be done with a thin mesh of uninsulated wire (lighting will simply ignore any realistic insulation), so I might be missing something (it may also have to do with rounding and quality assumptions for wire gauge, I don't bother with where the amperage limits came from, I just use them.) Electrical connections need to be close to the cells. I have trouble following this. My vision for a highpower space solar array would be the smallest possible solar EV cells spaced as far as possible apart (mostly to give the radiators the room they need). Mylar mirrors would concentrate sunlight to the EV cells, and the arrays would transmit power in a daisy chain back to the spacecraft. Now that you mention it, a certain length of the wire will likely require insulation in order to avoid arcing and similarly require thicker copper to reduce heating. I wouldn't assume that the cooling isn't structural, expect anything that can do multiple duty to do multiple duty. I'd also expect radiators to be similar to the mylar mirrors, possibly with coatings that conduct heat along the surface or dye the thing black to radiate better. Still, the level of concentration will likely involve a heat pipe to transmit heat to the radiators at temperatures they can handle. I'd expect these (the piping used for the heatpipes) to drive the scale of the design, along with the temperature tolerance for the radiators. As far as "structural radiators" I would assume that solar cells would be held in place by 2 power lines, one hot (going out) heat pipe, and one cold (going in) heat pipe (expect some rare connections to include dampening). On the other hand this assumes that the mirrors all have adjustments allowing them to focus on the fixed cell array. It may be much easier to move the cells underneath the mirrors. Also expect the mirrors to be made like a Cassegrain telescope (a primary mirror collecting light and shining it on a secondary mirror, which then transmits the light through a hole in the center of the primary). This is to allow the radiators to be in the shade of the mirrors. Further expect the array to be placed in three dimensions so the radiators don't heat each other up. Hopefully this means the power lines can still hide in the shade (at a cost of being 40% or so longer thanks to following diagonals and such). To be honest, I suspect a large scale "solar thermal" system based on the Cassegrain idea would work better. No ideas on how you make the "combustion [energy transfer] chamber", that looks like a nasty problem. And yes, this is a decades out idea (permanent bases on Mars is likely to happen first). Most current designs that remotely resemble this type of thing have to unfold out of a fairing (and suffer all the "shake and bake" effects of a launch). This type of thing screams "assemble in space" and is nothing like the macroscale assembly of the ISS. It would take a massive load of research to switch to a "fragile, gossamer" spacecraft design (probably needed for efficient use of solar power. Or we could go nuclear, or stay on Earth).

One thing that the "cartoony" diagram gets right is that photon can be found in all the positions on the wave: this is fundamental to limits of lenses (it comes up more in microscopes than telescopes, but should also come up in cameras). Still, the photon shouldn't be thought of as moving from one bit of the wave to the next (even if it is a single photon): it will always have a velocity in the direction it is traveling (the beam, not the "wave"). There are similar problems with classic "atom" model that kids are exposed to. The electrons may be found in bands around the nucleus, and they may have angular momentum, but don't think of them as moving from positions around the atom to another. Electrons and photons don't do that. They simply act like quantum objects and are pretty weird.

I'll admit up front I hate gravity losses and the tyranny of the rocket equation. I threw together a python program to check how bad Saturn V fuel efficiency was for the first minute: 0 s : 1.54625223835 m/s : 1.54625223835 m (height) : 1.1577647422 =TWR 5 s : 10.0469603887 m/s : 34.2612803397 m (height) : 1.18409158743 =TWR 10 s : 19.8735115925 m/s : 113.433200768 m (height) : 1.21164360424 =TWR 15 s : 31.0884883467 m/s : 245.877244367 m (height) : 1.24050835371 =TWR 20 s : 43.7590114972 m/s : 438.735000052 m (height) : 1.27078194432 =TWR 25 s : 57.9571899464 m/s : 699.498434434 m (height) : 1.30257010107 =TWR 30 s : 73.76062748 m/s : 1036.03632806 m (height) : 1.33598939901 =TWR 35 s : 91.2529956488 m/s : 1456.62344005 m (height) : 1.37116869187 =TWR 40 s : 110.52468331 m/s : 1969.97276257 m (height) : 1.40825077228 =TWR 45 s : 131.67353548 m/s : 2585.2712853 m (height) : 1.4473943091 =TWR 50 s : 154.805696652 m/s : 3312.21976104 m (height) : 1.48877611686 =TWR 55 s : 180.036576818 m/s : 4161.07704799 m (height) : 1.53259382616 =TWR 60 s : 207.491962264 m/s : 5142.70970671 m (height) : 1.57906903985 =TWR Note that this ignores aero losses and assumes the spacecraft is traveling vertical and has full gravity losses (since 5km/s is ~mach .5 this seems reasonable). By 60 seconds (and ~200 m/s delta-v) it has burned 784 metric tons of fuel (it burned 65 tons just to clear the tower). The whole thing weighs just under 3000 tons. Let's forget about catapult launch and consider something already constructed: stratolaunch (no, it can't carry a falcon 9 much less a Saturn V. It is just an example of a non-ground launch). Two big features: the biggest (unless you *need* an inclination change) is that at 10km, atmospheric pressure should be 25% of sea level. This should move your Isp to much closer to Isp (vacuum) and allow for bell design much closer to vacuum (increasing it more). The other is about 450m/s in delta-v, as that is what it "costs" to get to 10km (you have to add any additional velocity (probably close to 200m/s [for mach .5]) via the pythagorean theorem as the "delta-v vectors" will be at right angles). [reality check for those lusting after that "450m/s". The Saturn V example should include an extra "313 m/s" due to altitude, which can be simply added to the 207m/s at the end (both are straight up). Also I'm pretty sure the Falcon 9 FT (don't know about the next one) should be pretty close to launching at ~1.5. It should be possible to add an extra 500m/s via simply adding fuel until you take off at TWR=1.15 Adding fuel until TWR gets close to zero is reasonable if launching from a pad, but redesigning your aircraft because you increased the mass of your rocket isn't going to happen]. So that's pretty big. But no plane will lift a Saturn V (and the reality check makes us less happy about planes anyway). So lets do what Jeb wants and real rocket scientists do when they have to: MOAR BOOSTERS!!! Same thing now with 4 SR-118 boosters (which wouldn't be possible since the Saturn V was dead in the 1970s and the SR-118 showed up in the 1980s. But the obvious solid booster (in the Thor) had far too long a burn time. 0 s : 3.67342251632 m/s : 3.67342251632 m (height) : 1.3748007873 =TWR 5 s : 23.110690987 m/s : 79.6301232657 m (height) : 1.41145410163 =TWR 10 s : 44.4025650675 m/s : 258.297313217 m (height) : 1.45011536423 =TWR 15 s : 67.6523604544 m/s : 549.25460682 m (height) : 1.49095422156 =TWR 20 s : 92.9722739953 m/s : 962.624449832 m (height) : 1.53415998455 =TWR 25 s : 120.484431702 m/s : 1509.11961067 m (height) : 1.57994456286 =TWR 30 s : 150.322096065 m/s : 2200.09637888 m (height) : 1.62854594076 =TWR 35 s : 182.63106263 m/s : 3047.61435481 m (height) : 1.68023231482 =TWR 40 s : 217.571282612 m/s : 4064.50388391 m (height) : 1.7353070455 =TWR 45 s : 255.318756904 m/s : 5264.44239817 m (height) : 1.79411461536 =TWR 50 s : 296.067757844 m/s : 6662.04118585 m (height) : 1.85704784147 =TWR 55 s : 340.033449274 m/s : 8272.94443327 m (height) : 1.92455666085 =TWR 60 s : 367.488834719 m/s : 10054.5614543 m (height) : 1.57906903985 =TWR So we add 200 tons of boosters to 3000 tons of rocket (and 784 tons of spent fuel) and get 160m/s more delta-v (and maybe another 100m/s of altitude delta-v)? Don't tell Tsiolkovsky (I'm sure the equation insists you get more). Actually all we are doing is helping get rid of those horrific gravity loses. Also doing such would certainly violate the warranty on your Saturn V (not just the sides having to bear the extra load from the pull of the boosters, but bearing the extra weight thanks to the extra thrust/acceleration). My guess was the engineers simply worked out roughly what they needed and then kept adding fuel till TWR nearly hit one, then added another F-1 engine (repeat until you have enough delta-v). Obviously they had a pretty good idea, but fine tuning simply included adding fuel. I assume that rockets that use rings of SRBs typically are rare heavy models of rockets that typically have much lighter duty. You certainly *can* get a rocket to work well this way, but more fuel is typically preferred. 367m/s may look small, but it certainly beats 200m/s for burning 784 tons of fuel. That's the tyranny of the rocket equation for you. It isn't so much that flinging a rocket off Everest at 824m/s (plenty of rockets burn half their fuel getting to mach 2), it is just building such a ramp is so ridiculously expensive that it is far, far cheaper to build rockets that are twice the size. My code in case you want to point out obvious bugs I missed: source for SR-118 data: http://www.spacelaunchreport.com/mintaur4.html much of the rest was pulled from wikis or less reliable media...

I would assume a centrifuge. I'd be curious if it is possible to have multiple "arms" spinning and have a negative pressure at the center (unequal heating?) to force equalibrium into different areas. Don't be surprised if the real answer is really, really weird. It might involve surface tension and carefully chosen substances as surfaces for liquids to creep along. Zero-g can get pretty weird at certain scales.

Because right now it is the only place to go? I find it amazingly optimistic that ISS will be functioning and/or intact by the time BFR launches.

I doubt it. The Germans used alcohol (a mix of ethyl alcohol and water, typically 75% alcohol/25% water, but 50%/50% also works) and liquid oxygen (this is "close" to the ISP of kerolox, and burns at about 1000K lower). Later ICBMs and rockets (both US and USSR) used hyrdrolox, but this had the issue of requiring fueling before launch. It was quite possible that an ICBM site could be destroyed before launch during a nuclear war. The US went with solid rockets for ICBMs and thus had the technology for boosters, while the USSR preferred hypergolics and even use this tech with the Proton. I don't think Russia has ever done significant work with solids (the Apollo program used hypergolics in a few places, and I think the shuttle RCS had some, but they typically don't carry much of that type of fuel). Just checking for another thread: looks like the Titan [2] missile used a solid lower stage and a hypergolic upper stage. I guess I shouldn't post about ICBMs...

I'm pretty sure you can use CNCs to carve from forged billets. The real problem would be re-forging your scraps into new ones (absolutely mandatory), I wouldn't be surprised if that made tool building impossible (along with the obvious additional wear on your CNC tools for dealing with extra strong stock). - I really need to read "Packing for Mars". I've enjoyed other Mary Roach works.

How many of these are sufficiently *expected* to fail that you would require spares shlepped from Earth? I'd expect Martians to break out the 3d printer* if a wrench broke (or you needed a specific "breaker bar" wrench). I'd look into some means of recycling batteries. Lead acid batteries might even get a resurgence if the chemical process of re-smelting lead and reconstructing HCl are within the chemical capacity of our Mars base (and Lithium ion and similar are not). Hydrogen fuel cells are also a no-brainer: assuming the catalyst will outlast Li-ion batteries (and other more exotic varieties from Earth), you wouldn't bother with batteries and go straight to fuel cells. While independence is a long way away, every tool should be looked at in a "can we repair/rebuild/remanufacture it on Mars? If not, can we replace it with something we can? * Obviously the 3d printer is typically a last-chance thing considering the mass of the printer and a presumably limited printing life. I'd suggest using CNC subtractive techniques any time you need real strength (assuming you didn't just weld up the breaker bar), but that assumes nearly "free" power to recycle the shavings into forged stock. The Moon (and inward) may be more likely to have enough sunlight for such "free" heat, while Mars gets a bit iffy (but I still expect a massive solar oven).

Lord of the Rings was "Seven Stars and Seven Crowns and One White Tree" (the seven stars are even more significant as presumably Palentir, a name already popular in the NSA). Possibly "Six stars of the Norther Cross, in mourning of their sister's loss..."

[this is agreement with PB666 and mostly directed at Matterbeam. Most of the efficiency issues appear to be optimizing irrelevant variables] To a zeroth order, all costs can be considered in grams (to LEO). Most of the discussion of the efficiency of solar panels boils down to one thing: how much mass do I have to lift to supply x amount of Watts or Joules (depending if usage is constant or bursty). If you need (or can use) more sunlight, you can almost certainly reflect more light via ultralight mirrors (probably mylar reflectors) [assuming you are staying away from "as hot as the Sun" limits], but that still has issues on how heavy the heatsink for your collector needs to be. The solar photovoltaic chart is outright strange. Cooling in space is difficult, things in sunlight get hot, and you are suggesting increasing such heating by orders of magnitude. Somehow I don't think max efficiency is worth dealing with the cooling cost of "the heat a thousand Suns" (I am a bit more interested if doing such on Earth is practical, although my last check implied that any lens was significantly more expensive than photovoltaic panels (mirrors may still work, and of course mass dominates in space).

I think I tried to send Jeb to Duna without the slightest clue how to set a Hohmann transfer. Jeb winds up in an highly elliptic orbit around Kerbol. There was absolutely no way then I could rescue him, and now it would take years/decades (to Jeb anyway). I think that was when I first restarted career (of course this was probably before careers were a thing, but I know I restarted after stranding Jeb this way).

Isn't this a standard procedure to detect the size of celestial bodies (comets, asteroids, and the like)? I seem to remember Scott Manley describing the procedure (for either our recent celestial visitor or perhaps New Horizon's new target). You basically measure how long they occlude the known stars behind them and work out the size of the object. This makes spacecraft a bit harder to stay "dark". While they might be hard to detect, the "background" is almost completely known.

I still don't expect crew. Blowing up a crew is the only way to cancel that thing, otherwise it will lumber on until Congressional districts change enough to make it unwanted. They could blow up an uncrewed vessel and simply increase the costs in the name of safety theater and the pork would continue, but blowing up a crew for no reason would look too bad.

Judging from my near-zero knowledge of high-bypass turbofans, I'm betting that the real engine is nearly all air intake as well. Most of that air bypasses the jet/turbine part and is either used as "propellered" by fans or for air augmentation (I'm not sure about the bypass cycle).

The original Post did include a case slightly different than what we've been talking about. There are two issues with using mods. 1. Enjoying a game differently than somebody else does. This will inevitably bring internet hate for "being wrong on the internet" and is what ".ignore" files were created. 2. Shared files to be used by others (this was OP's case). Here you should use mods as sparingly as possible. Because anyone who wants to use that file needs to install all the mods used by that file, regardless of how maintained they are or will be in the future, and how compatible with whatever mods a user might be using. This still doesn't justify the hate OP saw. 3. Challenges. I'm surprised that some of the more interesting challenges seem to have entries with arbitrary mods involved, but that shows how mod-centric KSP can be. I'd expect challenges to be either pure stock (for an even challenge) or possibly mod-specific ("baseline RO" would be an obvious one, but I'm not sure there is a "baseline RO"). 4. Shear spite thanks to buying the "wrong" (console) version and blaming everyone else for enjoying the game. A subset of #1, but I thought I'd throw it out (this mostly comes up in other well-modded games. Nothing like seeing Oblivion on a console and feeling sad for somebody stuck with the stock game (while KSP+mods is wildly superior to stock KSP, stock KSP is still great. Oblivion is practically broken in stock state and mods help save the amazing game underneath). I'd assume that procedural parts are a requirement for reducing partcount on a potato PC, but haven't tried it yet (I'm using an AMD Bulldozer-based system that has one of the most miserable single thread performance in recent memory. I'm not sure how much 1.2 helped, but I'll take anything I can get to ease the pain of the main thread). You can also include plenty of mods on a 4GB machine (you can add just as many mods as you could back when only 32 bit mode was available), but I'm less certain what happens with a 2GB (or less) machine.