Aegolius13

I think Matt Lowne would launch a giant SSTO powered only by Thuds, put the entire station inside a cargo bay, and fly it to Eeloo and back for good measure. But your way is good too.

A more reasonable engine for rough economic times, the Poodle Kestrel engine doubles as a BBQ when at low power.

I'm fine with some simple parts of this sort. We know from the extendable landing legs that the Kerbals have some experience making things that move. Just wish they could adapt the technology a little more broadly. Of course, this is the same species that invented like 6 different kinds of rocket engines before the rung ladder...

I believe the Bobcat beats in it terms of pure thrust. My take is that prior to the 1.6 rebalance, the Skiff was a bit of an awkward tweener engine (not optimized for sea-level or vacuum) that was redeemed mostly by its ridiculous TWR. After the rebalance, it's lost that advantage, and is not really spectacular at anything -- it's a jack of all trades, master of none. It's kinda decent as a core stage when combined with higher-thrust radial boosters, since it has serviceable sea-level ISP and pretty good vacuum ISP. I've also had some luck surrounding it with a ring of Reliants or Kodiaks, which can be turned off or staged off, Atlas style, when no longer needed. I tend to think of it as a slightly bigger and better Swivel.

If you're not familiar with the underlying.. thing... https://en.wikipedia.org/wiki/Nyan_Cat

Interesting idea. My experience has been that if your ship is too pointy, you won't slow down enough by the time you hit the really thick atmosphere, and things will get crazy hot. But doing this, with an inflated heat shield at the BACK of the ship, could be a great way to maintain stability. Of course, there's also the issue of covering up all the stuff in front. And since an uninflated heat shield only covers a 2.5m cross -section, if you never inflate it, you might be better off with the regular 2.5 heat shield. I imagine it's draggier, plus it can probably dissipate more heat through ablation.

I'm gonna go out on a limb and say the SLS's transition from the core stage (4 RS-25 / SSMEs giving over 80,000 kN thrust) to the second stage (one RL10 giving ~100 kN of thrust) is not quite the ideal ratio.

Manley's on it, including a KSP version.

Your assessment is correct. Crossfeed is bidirectional, so outer engines will continue to draw from inner tanks until you take action. To get the automatic shutoff but still allow for crossfeed, you need to use fuel lines (or possibly a mod). See also:

Anyone know why it's taking so darn long to get perigee up to lunar level, especially when the Falcon 9 is putting it into a pretty elliptical orbit to start with? Is it just low enough TWR that it has to do a bunch of periapsis kicks?

Those must be from mods - they're not stock experiments.

I guess it depends in part on what other engines you're using. I.e., if you're using Rapiers, my personal opinion is that it's never going to be worth it to put a Swivel or Reliant onboard. Yeah, the vacuum ISP is a tiny bit higher, but it comes at a very significant mass and drag penalty. Whereas if you have a Rapier anyway for jet mode, its rocket function is effectively free. As a general rule, the further your mission is going, the more important vacuum delta-v will be. If you need so much vacuum delta-v that you need an upgrade over the Rapier in rocket mode, the best answer is probably a nuke. If you're using a lower-ceiling jet engine like the Whiplash or Panther, then yeah, rockets will have more of a use-case. But even then, keep in mind that you're likely not lighting up the rockets until you're well over 10km in altitude. At that point, you can essentially disregard the sea-level performance figures and just look at vacuum. Given that, the Reliant is a pretty bad fit, since it has poor vacuum ISP and no gimbal to help with attitude control. The Swivel is a little better, but still not ideal for this role. You might also take a look at more vacuum-oriented engines: the Terrier, Poodle and (if you have Making History) the Cheetah, Wolfhound or Skiff. As mentioned above, by the time you turn them on, these "vacuum" engines should already beat the sea-level engines on performance. The Spark can work nicely on small planes, and I guess the Skipper is a possibility as well, though I would think the Poodle would have adequate thrust most of the time if you're going 2.5m. The Vector could work if you need a ton of thrust on a 1.25m stack, but its vacuum ISP is not ideal. I'd suggest using fewer, but bigger engines over a lot of small engines. E.g., a Poodle mounted to the back of a 2.5m fuselage might work better than 4 Terriers on 1.25m nacelles. The jet engines might have to go on nacelles, but you don't really have an option with those since they're all 1.25m anyway.

If you can post a picture, that would help to diagnose the issue. But in general, space shuttles in this game are really, really hard. The main reason is the center of thrust does not go through the center of mass. I.e.. you've got a heavy external tank sitting out to the side, which makes the craft want to tip in that direction. To deal with this, as with the real-life space shuttle, the engines have to angle so that they point through the center of mass. But making things worse, the center of mass changes as the SRBs burn out and the external tank loses fuel and gets lighter. I'm not aware of any easy fix to this issue; it just takes a lot of very careful tweaking part placement and the like. Another problem is that the space shuttle analog parts are not balanced correctly, so it's very hard to make a 1-for-one copy. The Kickbacks are way too weak compared to the shuttle SRBS, and the Vector engines are way too powerful compared to the SSMEs. But Vectors are quite helpful due to their very wide gimbal range, so a common solution is to use less than 3. The issue about rolling to the side is a bit more of a mystery -- if all the parts are symmetrical that theoretically should not happen. It could just be a result of your control surfaces and engines trying to deal with the unbalanced torque, or you could have some actual asymmetry.

Of course, even if a toss-up on delta-v, there are other differences to keep in mind. The extra thrust for the Wolfhound usually counts in its favor. On the other hand, a Wolfhound stage would have more total mass, which would decrease the delta-v obtained from earlier stages (though the difference here is quite minor).

Re: the possible subsequent Eve flyby, you'll likely run into the same problem where Eve is not in the right phase angle when you hit its orbit. One option to deal with this is to: Burn from Duna such that your perhelion matches Eve's orbit (i.e., your orbit is tangent to its orbit). Set a maneuver node at perhelion, which will likely be in deep space if the phase angles don't match. Set up a retrograde burn to bring your aphelion in. But mess around with the size of the burn until, on your next pass (or two), Eve is in the right place. This is similar to a regular vessel rendezvous, and to the the "node" method to get to Moho. Of course, you lose some Oberth efficiency on the retrograde burn to bring aphelion down, but it's not that big of a deal, and you can use really low TWR engines. I suppose you could use the same approach to get back to Kerbin, but this will likely take more in-game time. (Since Eve revolves faster, it'll be in the right place sooner).