Aegolius13

Side note - you COULD operate the lander as desired if you have one of the command pods with the "remote control" ability, and the requisite pilot count, in the "carrier" vessel. That lets you bypass the need to get the signal back to Kerbin. https://wiki.kerbalspaceprogram.com/wiki/Probe_Control_Point

When the Kerbal returns to a pod, you should be able to right-click the pod and select "review stored data." Then you can transmit it, delete it, etc.

I'm a little confused about the mission profile - does it land on the Mun and just go back to Mun orbit to refuel? Or does it come back to Kerbin? If you're only going down from Mun orbit and back, you don't need a lot of range so convenience may play a role as well as efficiency. For an ordinary-sized lander, the Terrier is usually a good all-round choice. As mentioned above, they're short so you don't need a ton of landing leg and can stay close to the ground. If one doesn't provide enough thrust, you can always cluster several. Sparks can serve a similar purpose the same thing for smaller landers, and again you can use more than one if you want a little more thrust. Poodles are good for larger craft or higher gravity, but are probably overkill on the Mun for anything short of mining ship. If you have Making History, the Cub is a nice lander engine. Best thrust and ISP of any of the radials. Only catch is they only gimbal in one axis each, but reaction wheels usually suffice for attitude control. Nuclear engines can be useful for big mining rigs and the like, but for a typical lander, I think it'd be more trouble than it's worth to accommodate their height.

I've never really understood the purpose of this restriction. I get not being able to create a new node. But deleting an existing one doesn't really give you an advantage; it's just nice to reduce the clutter.

First step is making sure your SSTO can make it to orbit at all. Once you've accomplished that, make sure you've disabled your Rapiers. If the nuclear engines are the only ones active, the delta-v readouts from either stock or KER should take into account the ISP of the nukes in calculating your available delta-v. If you want the maximum range possible, it will likely mean a plane that just barely has enough thrust on nuclear propulsion to make orbit, so as @bewing says it can be a very fussy process. When I was building a single-stage-to-laythe and back, I did this kind of iterative test over and over and over. Make a tweak to plane (fuel, engines, aerodynamics, etc.). See if it can make it to orbit. If it can't, tweak again to address the problem. If it can, note available delta-v in orbit. Then make more tweaks for possible range improvements (more LF, less oxidizer, fewer engines, etc.), and lather, rinse, repeat. Note, however, that if you want to land somewhere and return, you may need to use additional engines to get the necessary thrust. Rapiers in jet mode work great on Laythe; but anywhere else of course you'd have to rely on some form of rocket power. So that may add add a complication to getting a simple available delta-v number. I used some cheaty hyperedit testing to figure out approximately what my plane would consume landing on Laythe and getting back to orbit.

I don't think what you're looking for is possible without mods. One option would be to use HyperEdit, which lets you land a craft at a specified latitutde/longitude. If you plunk down your launchpad at an exact coordinate, and then plunk down your rocket on top of that (setting a bit higher altitude for setdown), that might put the rocket in the right place. Or it might all blow up. Amusing either way in my book. There's a mod for extraplanetary launchpads called... Extraplanetary Launchpads. I haven't used it so not familiar with it; dunno if it lets you add pads on Kerbin as well. Sounds like KSP2 will have something closer to this feature with the colony system.

Having a high TWR at the start is not necessarily a bad thing in and of itself. For the first few seconds after liftoff, when you're going too slow for aerodynamics to matter and you're losing a large portion of your thrust to fighting gravity, you want all the TWR you can get. Things can get out of hand later in the launch, but if you start to accelerate way too fast, that can be solved by throttling down. The reason people advise something in the 1.4ish range is more about efficiency. If you're familiar with the Rocket Equation, it tells you that rockets get delta-v (and hence range) but having a lot of fuel mass and very little mass of anything else, including engine mass. If you have a very high TWR, it means (1) you're missing out on the opportunity to add fuel, and extend that stage's range, without hurting your performance, and/or (2) you're using a bigger engine than necessary, and thus carrying more dry mass than you really need. Thus it's generally not advisable to switch engines just to get a low TWR. If a less powerful engine fits the profile better, then by all means switch. But if the alternative engine is worse for the task at hand, no need to switch just to lower your TWR. The Swivel and Reliant are interesting case studies . The Reliant has more thrust, less weight, and higher sea-level ISP. The Swivel's advantages are gimbal and better vacuum ISP. If you have another means of attitude control, like fins, I find the Reliant is better suited for boosters due to its sheer thrust, while the Swivel can make more sense for a core stage. But the ideal layout can vary from mission to mission. Which is a really, really long way of saying that if you want to maximize range, using Reliants and adding fuel until TWR falls into the sweet spot is probably the better call. But if your rocket has enough range with Swivels, that's perfectly fine too.

Been said above, but putting everything from the Ants in a fairing should solve your aero worries. This will also let you lose the nosecone, and not have to worry about blowing up science instruments or anything. I actually like the Soviet capsules for certain things. Since they come with a built-in decoupler and heatshield, it's a decent tradeoff for the needed reaction wheel. Plus, for some reason, the abator burns off incredibly slowly, so you can cut down the amount to save some more weight. And, OP mentioned, they're nice for cramming many Kerbals into a small volume. And I often use a fairing even with the conical capsules anyway, if I have a draggy spacecraft, low-temp-tolerance instruments, etc.

Not aware of a direct way to do this, but you can always use the cheat menu (alt-f12) to complete the contract.

I mean that the "hot preburner exhaust" is itself a mixture of the CO2 / H20 formed by preburner combustion, and the remainder of the 90% of the methane/oxygen flowing through each respective pump. The "mixing" (probably a poor choice of words by me) occurs at the point of combustion in the preburner - I didn't mean a separate stream of propellant was being added later. What I was trying to say was that in full-flow staged combustion, the propellant entering the combustion chamber would presumably be cooler than whichever propellant was being routed through the turbo in a single-turbo staged combustion engine, since in FFSC all of the propellant is available to absorb some of the preburner heat. (Hence the similar exhaust temperatures you cite). Whereas in an SSME for example, the fuel-rich gas entering the combustion chamber would be pretty hot, and the oxygen would be pretty cold. But anyway, your numbers on exhaust temperature were what I was looking for.

I think we're saying the same thing, me not very artfully. "Extra" was supposed to mean the majority of the fuel / oxidizer that passes through but doesn't get burned in the respective preburner. Which, presumably, would mix with the hot preburner exhaust such that the mixture is not very hot by the time it reaches the combustion chamber.

Thanks. Makes sense they'd have to also light the preburners. Guess this is one of the (probably many) reasons FFSC is tricky enough no one's flown one before. Not that this is probably ever going to happen, but the Hopper success makes me wonder -- if, hypothetically, SpaceX decided to make an expendable version of SH and a simplified Raptor-based second stage, how much more time / money would that take? Seems like we more or less know Raptor works, assuming (1) that orange flame was not a major problem, (2) the interaction of multiple of Raptors won't pose new problems, N-1 style, and (3) they can air-start the upper stage. Making structures and tanks out of steel seems almost trivial based on what's happened to date. The big challenges remaining with the official program seem like propulsive landing and heat shielding, but those wouldn't apply to a hypothetical expendable system. As far as cost, I think Everyday Astronaut estimated that Raptors cost $2 million each, with the price hopefully coming down due to mass manufacture. The steel stuff is very cheap per Elon. The fuel is very cheap. So even if you threw the whole thing away, a simplified version of the whole thing should cost, maybe, one or two hundred million dollars? The nub of my question is, as you might expect, how much more would SpaceX have to do to have a working rocket that matches or beats SLS in performance at a far lower cost? (Putting aside political issues, of course). Final thought - in the spirit of Bridenstein Kerballing Orion on top of Falcon Heavy, if you were able to put an RL10 or BE-3 powered third stage on top of this hypothetical rocket, that seems like an awful lot of delta-v for something like Europa Clipper.

The ignition issue with Starhopper on Monday got me wondering - how does ignition on a preburner vs. combustion chamber work? Do they separately ignite them both? In a certain order? I would have thought that in a closed-cycle engine, if the preburner was going, the hot exhaust might be able to light the main chamber without a separate ignition source. Though perhaps not in a FFSC design where the exhausts are getting mixed in with all the extra fuel/oxidizer, and presumably getting cooled substantially.

Whoops. So it does. Was thinking that was some kind of stage/ total thing.

The engineer's report says your rocket has 255 parts. That seems like some kind of glitch. You might want to try removing parts and putting them back on until you see that number normalize. I've had quite a bit of trouble with the symmetry on those bi/tri-couplers, where it stacks multiple instances of the same part in each of the nodes. So I'd suspect that first and foremost. Otherwise, I agree with everything @5thHorseman said, though I tend to like my initial TWR more in the 1.4 to 1.6 range. But since SRBs increase more than LF engines in TWR as they burn out, starting a bit lower with an SRB stage might be prudent. Another thing to consider is using Swivels on the second stage. As mentioned, you have more than enough TWR, so the hit from the Swivels isn't much. And they would likely provide better overall specific impulse - their sea level ISP is lower, but by the time the SRBs burn out, they may have closed the gap, and will continue to do so as you climb. Plus, the engine gimbal should help with your roll issue (two or more gimbal engines can control roll). If you downsize to 2-way symmetry and need to add back some rocket, it looks like you could add some more fuel to that second stage.