camacju

And then it gets even more fun! The current low mass Eve/Tylo records are super beatable if you've been keeping track of the tech being developed in the ksp optimization community. Probably at least 500kg savings over both the current Eve and Tylo records. One such optimization is to use a completely unguided upper stage. For Eve, the stage can be made aerodynamically stable, and for Tylo, it can be lined up on the ground before lighting the engine and decoupling. None of the current low mass records use this.

I think the various low mass challenges would also be good for this. Each season a different planet/moon?

There's some fuel margin in the solution I gave, which should allow some time for one of the planes to slow down in flight and enable refueling on the ground.

If you can control planes at the same time and refuel the planes on the ground, a possible method would be as follows (I'm assuming this is approximately your intended restrictions). Jeb, Bill, and Bob take off at the same time and fly 1/8 of the way around Kerbin. At this point they're all at 3/4 fuel. Bob transfers 1/4 of a fuel tank to both Jeb and Bill, bringing them both to full fuel, and has 1/4 of a tank remaining for the trip home. Bob turns around and can fly back to KSC, landing on fumes. He refuels his plane and prepares to take off again. Jeb and Bill fly 1/6 of the way around Kerbin. At this point they're both at 2/3 fuel, and approximately 29% of the distance around Kerbin. Bill transfers 1/3 of a fuel tank to Jeb, bringing him to full fuel, and has 1/3 of a tank remaining for the trip home. This isn't enough, but he begins flying back toward KSC. Bob takes off for the second time with a full load of fuel, and meets Bill 1/8 of the way around Kerbin, where he's just run out of fuel. Bob transfers 1/4 of a tank to Bill, and they both have enough fuel to get home (with Bob landing with 1/4 of a tank, so theoretically Bill could have flown further before returning, but I didn't want to calculate the exact optimum). Meanwhile, Jeb is flying still. He can reach 75% of the way around Kerbin with some fuel margin remaining. When Jeb reaches the halfway point, Bill and Bob take off for the second and third time respectively with full fuel tanks, heading the opposite direction. 5/6 of the way around Kerbin (1/6 from the refueler's perspective), Bob refuels Bill and returns to KSC. 3/4 of the way around Kerbin, Jeb's fuel tank is running low, and Bill has 5/6 of a tank remaining. He transfers half of it to Jeb and turns around to head back toward KSC. Bob takes off for the fourth time heading westward with a full load of fuel. 7/8 of the way around Kerbin, Bob refuels Jeb and Bill. All three touch down at KSC. There's actually a bit of wiggle room in both the outbound and return trips because the refueler's return trip doesn't need to keep three planes fueled, only two. So this general scheme would work for a planet slightly larger than Kerbin. Anyone want to calculate the maximum range? Generalizing this problem to more planes, I suspect the maximum range goes to infinity, since I feel like it would grow as the sum of 1/n (so approximately O(log(n))) where n is the number of planes. I actually did something similar to this a couple years ago when I took the Aeris 4A stock craft to Laythe and back! But I was able to use low Kerbin orbit as a staging area, so I didn't need to mess with simultaneous control.

Youtube cinematics?

A fourth reasonable explanation is bad photoshop. Why else would they refuse to provide the actual footage? (Also, where would they even get it in the first place? If there were really a coverup, that footage wouldn't be released anyway.)

Bill pulls out his standard issue laser welder and wonders why they never read the cargo manifest before?

I completely forgot to post this here! A collaboration between myself and @Ultimate Steve, trying to build and fly the lowest mass stock+DLC grand tour possible. While we didn't quite hit that goal, as there is still quite a bit of mass to be saved, we did take a lot of mass off the previous record.

1.447 ton to Moho by JeDoesStuff

You can also change the vessel type to Debris or DroppedPart and pick it up that way

Here's a challenge for exactly this. People have gone way beyond just one lap of Kerbin. Here's another for flying all the way around Earth. This took me 59 hours but luckily I could put on time warp and let autopilot fly while I did something else in the background.

Eve in 4 tons. 3996 kg without pilot or cargo, 4061 kg by this thread's rules. @Alpaca Z The central trick of this mission is the use of a ladder to effectively ignore a kerbal's mass and drag. By the rules of this thread as they are now, this should be legal, but an official ruling on this specific trick would be nice.

What are the rules for drag reduction techniques? It's possible to SSTO on Jupiter with stock parts and all the aero tricks in the book, but I don't think it fits with what you're thinking.

The issue was that it wasn't a simple grand tour. Even something like designing the structure connecting the landers to the main craft was a puzzle that required several days, and we still didn't get the optimal end point as we stopped on something that would be relatively user friendly.

At the core it's really similar to the low mass Jool 5 that I already did, I guess it's up to you to decide where it fits better (you're the challenge manager after all) but please remember to also credit Ultimate Steve (: about that... There's actually a fair amount of improvement in the mission. Once we got it below 8 tons the primary focus was to preserve our sanity while flying it. We possibly could have gotten it below 7 tons but this already took nine months and I'm unsure if the maximally optimized version would ever be finished.