camacju

Yes, that's the basic idea. For a bit more complex of an explanation: The craft consists of four "stages." The first stage is powered by two small DLC rotors with a maximum size motor (you can probably get away with a smaller motor, saving mass and cost), each with eight basic fins rotated 20 degrees. Basic fins are great for an Eve helicopter because while they don't have a good top speed, they have much more wing area per mass and per fund than DLC propeller blades, and they don't fall off a cliff once their velocity passes Mach 1, meaning they can spin faster and generate more lift in the thin air. Additionally, centripetal force will pull the basic fins outward when the rotors spin up, meaning I can package the helicopter more conveniently and have it expand later. The ceiling of the helicopter stage is probably somewhere around 36 kilometers, but I found that detaching it at 35 kilometers is sufficient to get to orbit. It's powered by solar panels because it needs to ascend for a long time, and would require too much battery mass. The solar panels double as landing gear. The second stage is powered by three Twitch engines, two Ant, and one Spider. It has a couple clipped Donut tanks and a Dumpling tank. This stage is also very aerodynamic due to the fairing, so it takes a steep ascent in order to leave Eve's atmosphere. It's still able to pick up a good amount of horizontal speed, however. For the third stage, the Twitch engines and fairing are dropped, as well as all the drained fuel tanks and reaction wheel. I guess this is a stage and a half? No electrical systems whatsoever mean that the third stage must be controlled entirely through gimbal of the Spider engine, but I need more thrust than just the Spider, hence the Ant engines which have better vacuum efficiency. This stage is sufficient to get the kerbal almost to orbit. The final stage makes use of the kerbal's EVA pack to finish circularizing the orbit and rendezvous with the return vehicle.

Not only is it kerballed, it's a significantly older version of what I ended up doing. Here's the most recent version of the lander: 4378 funds, 1779 kg, not including kerbal. This can bring a kerbal from Eve sea level to low Eve orbit with about half of a jetpack remaining. This implies further room for both mass and cost reduction but I don't want to do that. I actually abandoned the "lowest cost to Eve" mission in order to do a "lowest mass to Eve" mission. Turns out, a low cost Eve ascent vehicle tends to also be quite low mass. I got the total mass at launch down to 7.5 tons, which I believe is a record (that is, for missions that don't abuse aerodynamic bugs). Here's the video I made about the minimal Eve mission:

I would... except you've already got a great time! 16 minutes is faster than what a jet-only craft can do, and I don't really want to mess with rockets for this challenge

Launch 1: Duna advance team, return module 65492 funds in VAB Duna transfer. The transfer stage is also the Duna return stage, and takes the Duna return module along with the forward operating base. The base is lonely. Let's hope it gets some company soon. An interior view. The four dunatians are having a fun time. Bonus: My provisional design for a Duna ascent vehicle.

Here's the rocket I'm going to be using: The lower stage is a Clydesdale and the upper stage is a Wolfhound plus three of the 1/8 length 2.5 meter fuel tank. It can bring 40 tons of payload to orbit while expending 11015 funds of fuel. Both stages are fully reusable. In practice I'll use a slightly higher fuel load and a slightly lower payload mass for some extra margin, but I don't expect the cost of any payloads to be over 80000 funds.

If your craft is properly drag optimised, 55 tons per Nerv should not be too much to get into orbit, even with zero Rapier closed cycle. I've gotten the best results with 3 Rapiers and 2 Nervs for a 110 ton craft, so doubling it would give 6 Rapiers and 4 Nervs for a 220 ton craft.

Looks fun! Are we allowed to use a recoverable SRB plane for this? It'll probably be the best option for efficiently putting stuff in orbit.

usually it's a good idea to post your own completion of the challenge, just so everyone else knows it's possible

Oh nice! Basically all you need to ensure is that both sides of the fairing are fully occluded, but it seems you don't have enough parts to do so. I'm not sure which part gets the best occlusion area per weight and cost however.

The other side was occluded by a bunch of random parts. I used the decoupler, both spark engines, and an octagonal strut, all attached to the interstage nodes. Also, the reason you have lower drag is because I have a higher AoA in my screenshot at 60 m/s. Note that I have lower drag at main engine cutoff, when I am going both faster and lower. This is because I'm using a root fairing body in the craft. If you do this you could probably save more mass and cost.

Fuel flow also causes a lot of lag. In fact, if engines are running, the fuel flow calculation is the largest cause of lag. Stratzenblitz made a good video about this.

I've got a video that would be pretty good for this challenge. First lap: 9805 delta-v in LKO Laythe outbound route: Kerbin-Mun-Mun-Minmus-Mun-Kerbin-Mun-Eve-Kerbin-Eve-Kerbin-Laythe-Tylo-Laythe Laythe return route: Laythe-Tylo-Laythe-Laythe-Kerbin 7503 delta-v on Kerbin surface Delta-v used: 2302 m/s Second lap: 6190 delta-v in LKO Laythe outbound route: Kerbin-Mun-Mun-Mun-Kerbin-Mun-Kerbin-Mun-Eve-Kerbin-Eve-Kerbin-Laythe Laythe return route: Laythe-Tylo-Laythe-Laythe-Kerbin-Eve-Kerbin 3878 delta-v on Kerbin surface Delta-v used: 2312 m/s Third lap: (Less efficient because I had fuel to spare) 2611 delta-v in LKO Laythe outbound route: Kerbin-Mun-Mun-[DSM]-Mun-Kerbin-Mun-Eve-Kerbin-Mun-Eve-Kerbin-Kerbin-Tylo-Laythe-Tylo-Laythe Laythe return route: Laythe-Tylo-[DSM]-Tylo-Kerbin 134 delta-v on Kerbin surface Delta-v used: 2477 m/s Edit: Oops I didn't see the requirement for crew. But that seems like a pretty arbitrary requirement, as the necessary delta-v doesn't depend on payload. All I'd need to do is scale the craft up in order to be able to do this same mission, or replace some of the fuel with cargo.

Okay, here's my submission. I didn't tick all the score objectives as I was going for a small and light craft. Craft in VAB. One Vector, two Nervs. You can see the three landing legs and the three RCS ports. Also the mild part clipping. Breaking Ground hydraulics are used to deploy the tank Landed I believe my score is: 200 for completion 30 for landing legs 15 for ladder 10 for RCS placement 30 for only using nuke for Mun landing 60 for tank Total: 345 points

How are you getting 48% payload fraction? I don't think you can even get close to 48%. With a properly drag optimised rocket you can get into low Kerbin orbit for 2800 m/s, and sometimes even lower if TWR is sufficiently high. Suppose delta-v is 2800 m/s = g * isp * ln(mass ratio). Vector isp goes from 295 to 315 and with a properly drag optimized rocket you'll be mainly burning lower in the atmosphere so we can assume isp of about 305 on average. This means mass ratio = e^(2800 / 9.81 / 305) = 2.549, so your craft's mass in orbit can be at most 0.392 of your mass on the ground. This means 0.608 of your mass must be liquid fuel and oxidizer for just the ascent. LFO tanks have a mass ratio of 9:1 which means that 0.684 of your craft must be LFO tanks, which leaves 0.316 of your rocket to be payload, fairing, engines, control systems, crew, etc. I've found that a Vector surface TWR of 1.5 is close to optimal for rocket SSTO craft. A Vector has 93.6 tons of thrust at sea level, which means a rocket mass of 62.4 tons. This would imply that the rocket has 42.68 tons of rocket fuel tanks and 19.72 tons of other stuff. Subtract four tons for the Vector engine and you get 15.72 tons of usable payload. This would imply payload fraction of 25.2%. Note that this figure is calculated based on an extremely low delta-v ascent as well as zero mass for a fairing, fins, or anything else you may need. In reality, payload fraction will probably be even less than 25%. The good news is that 25% is probably enough to do a Mun mission and return on nuclear engines, but fitting in all the extras might be difficult...

Single cubesat launch, 2380 funds, fully reusable (except for the fairing shell). In VAB. Two spark engines, a bit of fuel, 2380 funds. I use the FL-T100 because it has better drag occlusion properties than just spamming Baguette tanks. Is this beneficial? I don't know. But it makes flying this craft a lot easier.

From AeroGUI you can see that static pressure is 809 Pascals. Since Eve gravity is higher than Kerbin gravity, it's likely that the min pressure is even lower on Kerbin. I haven't actually tested this assembly on Kerbin though. It's even simpler than that, I place a static angle on the fins and keep the RPM limiter on 100% the entire ascent. By the way, here is the altitude this same craft reaches with a useful payload. This upper stage rocket can actually bring a kerbal all the way into Eve orbit with most of his jetpack to spare.

For once I actually have some Eve-related expertise that may help with this. It turns out that the tiny basic fins actually make quite good propeller blades. I recently did an ultra low mass Eve mission where the Eve lander uses a propeller to ascend out of the thick part of the atmosphere. A ducted fan prop could only get me to 22 km, while a basic fin prop (weighing less than the ducted fan) was actually able to climb all the way to 35.1 km. The same propeller with no extra payload can go even further.

Newest version of Eve lander. It's actually been pretty fun iterating the design further and further on this. 2889 kg, 7249 funds. I could probably save some more mass (and/or cost) by switching out the elevon 1 for elevon 4 (if the reduced control authority works), reworking the landing gear to use batteries or the elevons instead of the structural plates, and swapping a spider engine for an ant engine on the third stage.

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Working on an Eve return mission, here's a design of an Eve lander I had a couple iterations ago. Should be able to cut cost down a few hundred more funds

Maybe you could divide the challenge into three categories: Manned sample return, unmanned sample return, unmanned science transmission

ooh, this is interesting. I've been wanting to do something like this for a while now.

A couple days ago, not today, but: I took an unrefueled single stage plane from Kerbin to Laythe back to Kerbin, three times in a row.

This is a mission I have been thinking about for a long time, but I haven't gotten around to actually flying it until recently. Flying from Kerbin's surface to Laythe's surface and back three times is at the very edge of what a liquid fuel only SSTO craft can accomplish. Consequently, this is the first mission I've flown that required close to optimal piloting, and a lot of quicksaves and reloads. I use no ISRU, no docking or refueling, no part detachment shenanigans. This is a purist single stage craft that I fly as far as it can go. I don't use ion engines either, because I don't like ions - they're a hassle to work with. If I were to use ions, I might possibly be able to do a fourth landing, but I'm not willing to try it. Note that the Laythe Star is not quite at the peak performance of a liquid fuel craft. I've had better performance with three Rapiers and two Nervs for a 105 ton plane. However, the part count means that landings and takeoffs have to be done at quite a low frame rate, and vacuum TWR will be lower, requiring more periapsis kicks. In other words, it would be a lot less fun to fly, and the plane as-is can pull off the mission. Stats of the mission: The craft is composed of a Rapier and a Nerv, as well as six strakes, which I've arranged into a star shape purely for aesthetics purposes. Almost all of the rest of its 39 ton mass is Mk0 fuel tanks. In this mission, I perform 49 gravity assists, which is more than I've ever done before in a single mission. The bodies used were: Mun x15, Kerbin x13, Eve x7, Tylo x7, Laythe x6, Minmus x1. The Minmus assist was to prove that a Kerbin-Mun-Mun-Minmus-Mun-Kerbin-Mun-Eve route was viable in a real mission rather than just a proof of concept. All gravity assists and burns over 1 m/s are shown in the video.

If you thought the last SSTO mission had a lot of gravity assists... The 'Laythe Star' has enough range to go from Kerbin's surface, to Laythe's surface, and back to Kerbin ... three times in a row without refueling. To do so, however, requires many, many gravity assists.