After a long time playing this game and playing around with different ways to land and return from Eve, I've finally done it. One launch (IE I can reset to pad still, yeah this was in normal-sandbox, it was also a first for me), 1890 parts at launch, over 23 megatons, and a guaranteed destroyed launchpad. I've uploaded the entire flight (what I captured in screenshots anyhow) to an imgur album, but I'll go over the highlights here with a few choice images.
This craft is as yet unnamed, so I'd love some good name suggestions for it.
I did use a pair of mods, though all of the parts involved were stock parts save for the mechjeb AR202. I found it necessary to use FSHangarExtender due to the size of this rocket: 98.6 meters high, 71m x 71m in the other two axes. FSHangarExtender simply allows me to zoom out much further, to be able to place the outer layers. This isn't strictly necessary as you can move the rocket to one edge, I'm pretty sure I had enough room for that, but it certainly does make it easier. Mechjeb I'm sure most of you are familiar with, for those of you that aren't, it adds a lot of functionality which I'll definitely take advantage of. I can (eventually, a lot of trial and error nodes sometimes) do all of the things I used mechjeb for. Interplanetary transfers are a pain but I know how to do em. But without mechjeb, I probably wouldn't have completed the mission- at 23 megatons this craft still had barely enough fuel at 2 points in the process, where hand planned burns would potentially have used up that fuel.
So first, the rocket in the hangar, with fancy MSpaint lines to show which tanks belong to which branch of the fourfold symmetry the tank belongs to, as well as the stats screen. FSHangarExtender saved my sanity.
The engineer's report is really something else, though I do have quite a few launch stability enhancers. Getting rockets this large past physics load-in is a task in and of itself. Each tank is primarily anchored to the one it is staging off, with 6 connections each to that one. There are two additional supports in either direction between tanks in the same ring, though those primarily support rows outside, as once that ring starts staging, the circle is broken and stability greatly decreases. I lost quite a bit of thrust to cosine still, but I did want my computer to be able to eventually process the launch, so I had to limit the amount of stability I could add via struts.
Still, it loads onto the pad. It needs time to settle down after physics load-in, time to stop the wobble, but after a few minutes because of framerate drop, it's stable.
This launch is exactly as ridiculous as it looks. And for what it's worth, goes mostly as planned. The mechjeb dV stat page really tells the tale of a brief yet agonizing climb which took more than an hour to process 5 minutes worth of launch, and actually reach orbit. Highlight reel of the launch with brief commentary, if you want the full story and full commentary, check the imgur album: First stage, cleanly away, but I'm barely off the pad. This is all according to plan, though my launchpad is toast. And yes, 5.2s to burn through 8 big 3.75m tanks. 15 minutes realtime, 36 seconds game time have elapsed, this is mid-stage so the max acceleration isn't accurate I don't think. But I've put on some real speed, and this is the final 2-tank stage. Tipping now, though late, at ~14km. 2 more 2nd ring and 3 more inner ring stages remain. Last ring booster away: about 45* tip right now, still svel+ alignment. It was at this point that I messed up.
The two mammoths which are further back along the ship are to be staged rapidly, less than 10 seconds to burn in each stage as they each have only a single tank to burn. There is a rhino located above each of them. I decided to switch to orbital alignment at this point, which nearly blew up the craft. One of the newly emptied tank+mammoth debris tagged one of the mammoths that was still burning and destroyed it. Luckily, the game was still moving at a snail's pace, so I could react quickly enough to save the launch.
I quickly shut off the engines and staged again, to blow off the crippled stage, before I resumed full thrust. I lost around 90 dV from this because I didn't get to use that stage, but that's much better than imbalanced burning and the pains which come with that. There was a slight fuel imbalance in the later asparagus stages, but it was apparently so little that I didn't have problems from misalignments during Eve entry. But now I'm into first rhino burn stage, which will last 1 minute 15 seconds, starts with 0.98 TWR (because of my elevation, live SLT for rhinos is now maxed), and has over 800 dV. I've made orbit.
End of first rhino stage, and I also get rid of the mammoths which I still had adding additional thrust. I don't need the thrust and can afford to shed the weight here.
As I said, I started tipping late: I'm well, well above the atmosphere during my main horizontal burn, which should be more like 50km.
But it's enough for me to be able to set up an orbit of 92/605, which I then circularize at apoapsis in order to warp at 100k. Here's what the craft looks like at that 600k circular orbit:
Just 8 fuel tanks outside of the Eve lander itself, which you can finally see. This is my biggest development here, which is really just asparagus staging taken to an extreme: There are 52 Vector engines, equivalent to 13 Mammoths, mounted on 2.5m to 4x1.25m quad stack adaptors. Each quad Vector is the same thrust as a Mammoth, 4,000 kN, and though it does weigh slightly more, it also has better atmospheric performance, which is ESSENTIAL to this process. The 2.5m form factor allowed me to more easily use 2.5m fuel tanks, which helped quite a bit with keeping the weight still manageable.
The big secret is that the lander has 3.55 TWR in Kerbin SOI vacuum. The hardware is not payload- the fuel on it is payload, but the hardware is VERY TWR positive. The ship seen above, with the 4x8 fuel tank only stage, is still 13 m/s/s of acceleration!! Pumping fuel into those engines from the ground means that I need fewer engines to be staged off later, which allows me a much larger craft. Lifting off is about maintaining sufficient TWR and angle for your current velocity- more thrust = more fuel hauling ability. The Eve lander itself is so net positive TWR that it can get the 4x8 stage off the ground alone, respectably even with 1.3 TWR.
The craft itself being forced to have so high a TWR in order to lift off Eve and combat the heavy atmosphere down near sea level, can lift a lot of its own fuel. Two additional 4x7 fuel tank + rhino stages, along with the mammoth on the first 7+rhino stage that I showed earlier, is enough to actually achieve orbit around kerbin from 35k and 300-400 m/s, as well as to transfer to Eve and slow down enough to achieve low eve orbit with minimal use of the fuel on the lander itself. The booster stages were just there to 1) fuel the lander and the other engines as they went, and 2) provide additional thrust to get those large tanks up to 35km+ from the pad. Each 3 tank + mammoth provides some net TWR bonus, but the 2 tank + mammoth as a booster stage provides a much higher TWR bonus. The 1 tank + mammoths were the last to be staged because of their position inside the rings, under the rhinos which would not have helped much at sea level anyhow, in order to keep TWR high at lower altitudes.
This is Asparagus staging taken to an extreme, really, with utilization (in design anyhow, I didn't fly it very well) of changing TWR levels appropriately throughout the staging.
The orbital stuff's pretty normal orbital transfers. I had a quick transit so I didn't actually pass through a plane node, so I didn't bother to plane change. I did do a fine tune burn to get a periapsis of 100km at Eve.
Deorbited a bit too hard I think, should've had less thrust at this point. The tale of this landing is a long and harrowing one best read in full, because highlights won't do it justice. This picture shows a critical error which almost cost me the mission, slowing down too quickly at too high of an altitude, causing me to plunge into the lower atmosphere too quickly, without enough fuel. There were other errors along the way before a last minute save at only 6km, with my drogue chutes destroyed, no fuel, and very little chance of aero effects braking me sufficiently for my parachutes to save me.
The fins! They can help!
Safe with parachutes only, using Eve's atmosphere for my benefit for once!
Quite a bit of time warp later, I've used the mining drills, converters, solar panels, radiators, and the engineer for a nice healthy bonus, to fill the fuel tanks up again for launch. Immediately after take off (for safety's sake) the fuel generation equipment and entry fins will be staged off.
Launch stage 2 is away cleanly but I'm still not going very fast, or very high, ~12km.
Tipping away now that my q-limit is dropping off
That'll do. Repacked my parachutes, pushed orbit up to over 600km circ, and made transfer. Still have some dV left. Guess I WILL match planes
Fine tune burn later, and I'm parked at 25km periapsis at kerbin, which is enough to capture and deorbit safely with only an ablator.
Safe by a ways, actually.
So it'll pull 5 g's or more for a while, between 20km and 35km or so it'll be pulling close to 5g's, but it'll shed off all that heat, and because I wasn't aimed at the ground, it'll still be a shallow enough entry that I'll slow down more than enough for parachutes.
And I'll land safely on kerbin again.
So yeah, this was the longest single mission I've run with the ability to reset to VAB at any point, at over 4 hours when I recovered my vessel. I gathered no science and didn't even leave the vessel lol, but I landed and took off. This is the eighth iteration of my eve lander that I've been working on in the same style for the past few weeks, and is certainly the largest, though I've attempted many times before with no real successes. A few in this recent sprint I did landed, but I did not have them set up right to actually take off from Eve again successfully, for a variety of reasons.
The biggest thing I'd change to make this work better, IE less mass/parts at launch, is to try to shave mass off the Eve lander itself. I just don't see how it's even possible to make fundamental changes to sufficiently lose mass.
Changing the last stage to a 16x ion cluster, instead of the LV-N's, leaves me with ~4500 dV, but at a third the thrust. It's also much, much lighter. The problem I see is that the vector engines are still necessary to this style in order to lift off Eve. It is possible to asparagus some 1.25m tanks with a single vector on the bottom, resulting in many more stages and no doubt a more efficient launch, but the number of parts would balloon quickly, especially if I were to attach separatrons to keep the stages close together. 1.25m asparagus is also simply not as strong as 2.5m, so for those reasons, I think the 2.5m tanks make launches much more feasible. Kerbin launches too, fixing the main 3 tanks to the Eve lander I used is much easier than a more awkward 1.25m setup.
This being said, even if I decrease the mass of the final return craft by changing to ion, the biggest problem is still the lower atmosphere. The LV-N stage brings my final stage weight to around 42 tons, where the ion cluster would be ~16t. But the *empty* mass of the stage immediately prior with 20 x 1.25m tanks and 4 vectors, the mass that's shed when the stage is empty, was over 18 tons, and carries 80 tons of fuel at its start. That's 98 tons, bringing the ion cluster's total weight at that point to around 114 tons, and the LV-N's to around 140T. This will give it a lot more thrust and dV, to be sure.
The problem with that is, that it doesn't make very much difference in what I *can* bring for the lower stages. I'm still likely going to strap on the same red booster stages. Tsiolkovsky's gets me a great return for the ion switch, *if* I can shed the rest of the mass. Switching to 1.25m tanks is problematic but possible, but if I use the same red booster stages, the final mass of the craft isn't going to change very much. I will have higher thrust (not by much, not enough to switch to 3x vectors instead of 4x, I don't think) and better fuel efficiency, but from my new experience with variations on Vector designs, and lifting off Eve, the vast majority of the fuel goes into the lower atmosphere, either into aero forces or into maintaining terminal for so long.
Eve takeoff needs a lot of thrust, for a long time, which needs a lot of fuel. I think the extremeness of this atmosphere problem does a number on the Tsiolkovsky gains you make from switching to ion cluster, to the point where viable liftoff configurations which will lift small payloads to low Eve orbit don't benefit much from the mass being 16T instead of 42T, despite Tsiolkovsky's law. I don't know how much fine tuning can go into making the Eve launch more efficient, as there is a long phase where 1.1 TWR is all that's required. Setting up a rocket to 1) have 1.1 TWR for that period, and 2) being able to quickly boost to that point prior to that, would be a way to potentially remove 4 or even 8 vector engines by switching to tristacks instead of quad, so it's possible that more weight could be shaved off there.
But the dry mass at landing was nearly 500 tons, wet mass 1.6 megatons. It's playing a game of inches when the scale is in miles. I probably could shave 50-100 tons off wet mass of the lander by tweaking things using that flight's data, but then I've got to get 1.5 megatons to low Eve orbit instead of 1.6. And with the amount of time it takes to launch this, as well as the complexity of reconstructing on any changes, I'm loathe to tweak designs as opposed to just constructing new. If I change the spacing on where the big 3 sets of tanks are, I have to redo almost every single fuel duct and strut, which means a lot get left behind and are extra parts doing nothing.
So yeah, hope you guys liked it, I know I had a lot of fun and even though I made some mistakes in flying it, the mistakes didn't kill me. I might make another attempt at it in the future if I can drop the part count, or find a better way to launch from Eve. Please let me know what you think, I'd love to get some fresh ideas on how to build these things!
