sevenperforce

Yes, balloon launch would work very well on Eve. Balloon habitats would work well, too...cloud cities, basically. On Venus as well. Not so much on Earth/Kerbin because atmospheric pressure is much lower. I think an RTG-powered helicopter first stage would work well on Eve.

You cannot "build up velocity on the way up" with nukes, or anything else, because drag is too high due to the thick atmosphere. Your proposal won't work for much the same reason that balloon-assisted launch on Earth is a bad idea. With a balloon-assisted launch, you release your orbital vehicle at high altitude, where it can use more efficient engines, but it is still releasing at essentially zero velocity. In contrast, if you lift it to the exact same altitude with a rocket stage, it is already moving at a fair percentage of orbital velocity. The latter will almost always outperform the former. On Eve, you can potentially take advantage of the thick atmosphere and a solar or nuclear-powered helicopter to get high enough to make a significant difference in engine efficiency. But it would be tough.

No, because LVNs have virtually no thrust at sea level on Eve. They are very pressure-dependent. What you could do is use something like a helicopter to get high in the atmosphere and then fire up rockets. But, critically, you are never, ever going to be able to get any significant fraction of orbital velocity in air-assisted flight on Eve. It just doesn't work.

Oh, it's simple. No trouble getting a space plane of 1-5 tonnes into Eve Orbit. You just take off the wings and landing gear, since they are dead weight that you don't need. Then you use drop tanks. With engines. We can call these drop tanks plus engines "stages". Then you just drop stages as you no longer need them.

Thanks, that was exactly what i wanted to know! The upgraded payload adapter they'll be building for FH will be theoretically able to take up to 65 tonnes or so, but that might be pushing the structural limits of the upper stage.

Hmm, let's see. There, Mach 5.8. No offense, but this is a prime example of an ill-thought-out challenge. There is nothing to work with here. It took all of 10 seconds to build this. If you want to make this a little more interesting, you could specify stuff. Like, "build a HTOL, single-stage, pure-airbreathing vehicle capable of exceeding Mach 3 in level, sustained flight and returning to the runway. Must carry at least 2 kerbals. Lowest takeoff mass wins." That would be interesting.

Apart from lift-induced drag, you have two areas of drag to contend with: pressure drag and form drag. There's not much you can do about form drag (basically, the friction over the skin of your vehicle), but you can do a little more about pressure drag. Pressure drag happens because you have high pressure at the front of your craft, pushing you backward, and low pressure behind your craft, pulling you backward. You can decrease the effects of high-pressure drag on your nose by using streamlined parts, like nose cones and shock intakes, which direct the air around the craft without letting its pressure rise as much. But low pressure at the back is tough, especially with engines like the Rapier that just have a big blunt end. The trick is to place two Rapiers at the back and then add two more Rapiers, flipped backward, attached to the rear node of the first pair of engines. Then rotate the Rapiers and offset them and build the rest of the craft from the rear forward. This tricks the aerodynamics engine into thinking that there is no low-pressure drag at all on the Rapiers. If you press F12 while flying, you can see the drag over the vehicle and you'll see that there is no red drag at all on the engines that are attached this way.

All vehicles have a "lift to drag" ratio. The L/D ratio says how much upward force the wings and body generate for a given amount of parasitic drag. For example, a glider with very long wings may have an L/D ratio of 50, meaning the upward lift produced by the wings is fifty times greater than the backward drag of air over the wings. In contrast, a Boeing 747 may have an L/D ratio of 17, meaning the upward lift produced by the wings is seventeen times greater than the drag on those wings. Importantly, the L/D ratio tells you how much engine thrust you need in order to maintain level flight at constant speed. A 747's engines need to produce 1/17th of its weight in thrust just to fight the drag produced by the wings. A high-performance fighter, like an F22, has a much lower L/D ratio and so its engines must be much more powerful (in proportion to its weight) to maintain cruise. But when you're talking about spaceplanes, things get messy. L/D ratio is dependent on air density, airspeed, and angle of attack. As you climb, the air gets thinner and your L/D ratio drops. As you accelerate, drag forces increase quadratically and your L/D ratio drops. If you pitch up, your wings become less efficient and your L/D ratio drops. So you need ridiculously powerful, ridiculously efficient engines to continue thrusting harder so you can counteract drag AND have enough thrust left over to continue accelerating into orbit. The RAPIER is good for this because it has good specific impulse at all speeds and its thrust skyrockets once you are high-supersonic, which is precisely where you need thrust the most. This is why spaceplanes won't work on Eve. The air is thick, so you can get a good L/D ratio at low speeds...but once you start accelerating and climbing, the quadratic increase in drag robs you of your L/D ratio and you need exponentially increasing thrust just to stay aloft, let alone continue accelerating. Meanwhile, airbreathing engines don't work on Eve, so you have no engines efficient enough to do the job. It just doesn't work. A glider would work very very well on Eve...but not for getting into orbit.

I know this is an old challenge but I think I'm going to go ahead and attempt it. I assume it is all right to bring crew in any pressurized modules; they don't HAVE to be in cockpits or command modules, right?

All the more to factor into the challenge!

@dundun92: If I may gently offer some advice... Just because people push back against your challenge, it doesn't mean your challenge is bad. I've had quite a few challenges that were shot down when people pointed out problems with my scoring systems. Rather than becoming offended, use it to make your challenge better. You might want to consider other elements than part count alone, like physical size, powerplant(s), dry weight, gross liftoff weight, endurance, armament capabilities, and the like. All those things can be compared to the actual plane. My entry earlier carried way, way too much fuel but if I had tried to replicate the real Mirage more closely it would have ended up handling a lot better because I would have given it weapons rather than fuel.

Most plants get their nitrogen from the soil, not from the air, so that's not the primary reason for needing nitrogen in the atmosphere. The primary reason for getting nitrogen into the atmosphere is to increase the atmospheric pressure above the Armstrong limit and decrease the partial pressure of CO2. Gaseous carbon dioxide is corrosive to exposed skin as well as equipment at high concentrations. The gross mass of the Martian atmosphere is 25 terratonnes, most of which is carbon dioxide.

Agreed. Ideally, you'd have the entire recovery module couple onto the existing (or the upgraded) payload adapter, with a second payload adapter mounted to the recovery module.

Anyway, here's my submission.

The outer mold line of the vehicle needs to remain the same during ascent, or the qualification is moot.

Depends on the mass of the recovery assembly. The MVac only masses 500 kg or so.

And the answer will be "uh, can't you tell?" I like the challenge but it either needs to be unscored, or scored differently.

Remember that whatever is used for recovery has to fit inside the payload fairing, with the possible exception of fold-flush grid fins.

I think there are some intermediate steps that could be useful. If we could get the atmospheric pressure above the Armstrong limit and find a Martian source of nitrogen, then it might become possible to grow plants on the exposed surface or walk around outside without a spacesuit (though an oxygen mask would still be required). Not full terraforming, but enough to make the expansion of existing colonies much easier.

Good grief.

All right, @Abastro, here's my entry. Not sure if I can manage the Laythe run, but I got the Duna run down. Four Rapiers and two nukes; the Rapiers use the node-attach-and-rotate trick to negate parasitic drag. The placement of the wing strakes helps keep CoM and CoL stable across a wide range of airspeeds and fuel loads. There are four bipropellant tanks; everything else is liquid tankage. The Rapiers are set to manual cycle-switching. I programmed action groups to switch the mode of the rapiers, turn the nukes on and off, and toggle the airbrakes. The canards on the nose rotate with the airbrakes to produce a shuttlecock for passive stabilization during high-speed descent. The ship takes off VTOL and immediately translates to forward flight for efficiency. At full fuel load, it needs to run the Rapiers in closed-cycle to get enough thrust to get off the ground. For maximum efficiency, it can lift off with only liquid fuel on board by using an assist from the nukes. The Verniers assist with stability during hovering flight. Taking off in open-cycle (partial fuel load): Using the action group to switch between open and closed cycle really helps with VTOL landings, since the reaction time of the Rapiers isn't very good in open cycle. I use the efficiency of open-cycle to get into position, and then use the quick throttleability of the closed-cycle engines to hover and land gently. Flying over to the SPH: Descending in open-cycle: Switching to closed-cycle for the fine landing burn: Landed! I think I could probably manage all the required landings in a single run. Taking off from the SPH (open-cycle mode): Jetting (literally) over to the VAB for another landing. Approach in open-cycle: Landing, closed-cycle: Landed! Taking off again! I'm almost out of oxidizer so I'll have to try and land on the bridge in open-cycle, which will be...challenging. Alllllmost... Made it! Lifting off again, just to prove I can: Going to refuel and head off to the island for that landing. This will prove I can transition from forward flight back to a hover. I nose over almost immediately so it is a lot of fun to just barely skim the ground. Having four Rapiers for a vehicle this small makes it VERY speedy, but since almost all my fuel is in lifting parts, I can also get great stability at low speeds. Lots of fun to fly. Keeping aero turned on during low-altitude flight helps prevent unintended lithobraking. This jet is almost impossible to stall. Easily supersonic. Lined up for my approach, cut thrust to zero. This is where I'd extend landing gear.......oh, wait. If I switch to closed-cycle temporarily with the throttle set to zero, it cuts the thrust on the Rapiers immediately, which is much better than waiting for the turbofan to spin down. Then it's just a gradual nose-up until vertical, careful not to stall, and I extend my airbrakes and canards. The canards really help with stability on descent. Back to open-cycle. Using closed-cycle to make some adjustments. Easy... Almost there! Made it! Airbrakes closed, open-cycle Rapiers throttled up, and we're off! As you can see in this image, the outer ailerons control roll while the inner ones control pitch. Blowing past Mach 1.25 easily. Back at KSC. Now, I'm supposed to fly UNDER the bridge, right? But wait, there's another helipad here! What's happening? Suddenly I find myself landing on it. Can't help it. Now to go fly under that bridge. Some horizontal translation... Sizing it up. Hmmm. I had originally planned to hover under the bridge, but I MIGHT just be a little too tall for that. Guess I'll have to do it the old-fashioned way! Taking off, dropping my nose... Dropping pretty fast here, just a few meters from dragging my canards. But I punched closed-cycle and made it through! Back to open-cycle and climbing fast! So, let's see: I've met conditions 1, 2, 4, 5, and 6. I've landed on the SPH, flown under the R&D bridge, and landed on the R&D bridge. So that's a 1.452x multiplier to my score, right there. Now for the endurance run! I topped up all my liquid fuel tanks and removed all my oxidizer for maximum efficiency...here goes! Letting the open-cycle Rapiers throttle up: Kicking on the nukes to help jump off the ground. Immediately nosed forward. Cut the nukes as soon as I had body lift. Now, the trick is going to be to see how low my fuel consumption can be in level, stable flight. I don't know if it will be more efficient to fly very low or very high...though 11 meters is probably not safe. 0.45 fuel units per second in a climb while gaining speed...that'll be the value to beat. The rarefied air at higher altitudes allows lower fuel consumption, though I don't know if I can hold altitude. Plus, as I fly for a bit longer, my fuel load will decrease and I'll be able to get away with lower fuel consumption. This was my lowest fuel consumption, though I couldn't hold altitude. Cutting it close over these hills! Haven't flown this far from KSC before...at least, not this low. Closest call so far! Starting to get dark and I can already tell I won't be able to circumnavigate, so I should probably just establish minimum fuel consumption in level flight and finish. With two thirds of my fuel gone, I'm much lighter, so I can maintain lift at higher altitudes at very low speeds. And here you have it! Level flight, no loss of speed, at 0.23 fuel units per second. Based on the above (and Rule 7), I calculate a total remaining flight time of 4,304 seconds, for a total projected flight duration of 2 hours and 47 minutes. Now, before I apply multipliers, I need to do one more thing... ...go to Duna! Full fuel load this time, using the Rapiers in closed-cycle to jump off the ground: Immediate transition to open-cycle. Going to nose up as rapidly as I can. The Rapiers are roaring at this point. Kicking on the nukes to help maintain acceleration and ram effect so the Rapiers don't lose thrust; trying to level out so I don't get too high too fast. I haven't flown many airbreathing spaceplanes before so I'm not quite sure about the right balance. Switched to closed cycle at a lower speed than I'd like, but oh well. Cut the Rapiers to conserve oxidizer and I'm powering up toward apogee. Orbital node set. Orbit achieved, with quite a bit of fuel remaining! Duna transfer node set. Completing Duna transfer burn. Some fine adjustments.... 31 km should be a good place for an intercept, I think. Inside Duna's SOI, I adjust to a good aerocapture altitude. Airbrakes extended and canards feathered. First re-entry heating. Heating wasn't nearly as bad as I'd anticipated, actually. Captured and ready to land! Kicking the nukes on to start slowing down: Since the nukes don't gimbal I had to turn the Rapiers back to closed-cycle to help straighten out, which burned through my oxidizer. Final landing approach! And I'm down! Didn't stay upright, but at least I managed to stay intact! So let's see here. I'll add the 1.5x multiplier for reaching orbit and the 3x multiplier for landing on Duna intact, which gives me a total score multiplier of 6.534, for a total score of 65,405 seconds.

Also, question -- what if I am able to circumnavigate Kerbin while remaining below 5 km, but that is not my longest timed run? For example, let's say I can stay aloft at 4500 meters at 200 m/s for long enough to circumnavigate, but I can stay aloft at 100 meters at 70 m/s for much longer? In the former case, I can circumnavigate; in the latter, I can't. Can I count the time from the lower-speed run even though I didn't circumnavigate on that particular trip?

Reverse thrust! Very, very nice.

There are already certain branches (threads?) of string theory which posit that gravity's low strength relative to the other forces is due to it "leaking" into other dimensions.

But brown dwarves are a very very different thing from white ones.