If I ever make it back from Eve

[Reinhart Mk.1]

so im taking all the advice i've been given but it really is easier said than done, there comes to a certain point where it take every bit of focus and concentration i have to keep this thing where it needs to be without flipping. probably due to the lack of a nose cone on the center stage but honestly idk why you can put a heat shield on a nosecone, just seems like its unnecessarily unrealistic. maybe that's the frustration talking but YEAHHHH

[MassoudGL]

Did it once after three times of trying, with 5 Kerbals. First couple times I didn't make my heat shields symmetrical and it flipped on descent. Then I didn't realize that I didn't make enough TWR. But yeah, I launched from roughly 4km from "sea" level and had around 15k in dV. That was maybe 1 version ago.

REMEMBER that the atmospheric models got more realistic as versions passed, so if you're looking up pics of people's single stage to Eve and back vessels, they might be too old and not even come close to making it anymore.

It really is one of the hardest challenges in the game. You'll get it though.

Edited March 7, 2019 by MassoudGL

[herbal space program]

24 minutes ago, MassoudGL said:

Did it once after three times of trying, with 5 Kerbals. First couple times I didn't make my heat shields symmetrical and it flipped on descent. Then I didn't realize that I didn't make enough TWR. But yeah, I launched from roughly 4km from "sea" level and had around 15k in dV. That was maybe 1 version ago.

REMEMBER that the atmospheric models got more realistic as versions passed, so if you're looking up pics of people's single stage to Eve and back vessels, they might be too old and not even come close to making it anymore.

It really is one of the hardest challenges in the game. You'll get it though.

It's actually easier than it has ever been! Just take a look upthread for a bunch of examples....

[Reinhart Mk.1]

i honestly think its the nose cone and aerospikes, i cannot keep this thing stable at the point of gravity turn, sure it recovers but it defeats the purpose i think. landing my 40324230432043243243232432432423th lander now. can't wait to be done with this.

[herbal space program]

51 minutes ago, Reinhart Mk.1 said:

i honestly think its the nose cone and aerospikes, i cannot keep this thing stable at the point of gravity turn, sure it recovers but it defeats the purpose i think. landing my 40324230432043243243232432432423th lander now. can't wait to be done with this.

You are so close to making it! I looked at your video again, and there are really only a few small things standing in your way.  Other than the fact that you should be starting to turn sideways at 5 km rather than 30, your biggest problem is that as soon as you stage off your first set of side boosters, your TWR goes in the toilet, and then you're just bleeding yourself out on the altar of the gravity gods, trying to boost straight up with a TWR <1. Thinking it through, I totally concur with @Laie that the best way to remedy this is not by lighting up the next stage prematurely as I suggested before, but rather to make your whole bottom bundle into one stage, either by pulling off the hoses or enabling crossfeed on the decouplers. Alternately, I think you could do OK by just pulling out the hoses from your second pair of side stacks to the core stage. You could also add toggling the spikes on the next stage as a action group, to help you through that early phase of velocity loss. Apropos of that, one thing is for sure: no matter what you do, you never want to be slowing down at any point! Lastly, as to your flipping problem, that sort of instability is inherent to having all your thrust so far behind the CoM. To deal with it, you need to either stay closer to prograde the whole way, reducing the normal forces, or you need to put some fins as far behind the CoM of the flippy stage as you can. Either move will increase stability. Good luck!

Edited March 7, 2019 by herbal space program

[herbal space program]

14 hours ago, KerikBalm said:

#2- They don't act as a fulcrum, rather the high decoupler just pushes the top away. Any "fulcrum" effect that you see is an illusion due to momentum. The way the game works, that strut disappears instantly when the de-coupler fires. You can place the decoupler high, and then use autostrutting for the same effect, but less mass and drag.

So I did a little experiment around this, by placing 3 symmetrical side stages on a core tank , all with the decoupler mounted identically, well above the CoM of the side stage, and then placing a strut on each individually. These three struts were placed as low as possible,  as high as possible, or as close to the CoM of the side stage as I could estimate by eye.  Interestingly, when I staged these three decouplers off high up in Kerbin's atmosphere, where Aero forces are minor, all 3 side stacks behaved identically (not shown), so in a purely inertial situation I think @KerikBalm's assertion is true. However,  when I did the same test ascending from Eve at ~10km, where the aero forces are very strong, I saw the following:

 

You can see the different placement of the struts in the top picture, followed by how the two different stages behave in the instant after decoupling. Clearly there is a difference. I don't know if this has to do with the aero model getting updated differently from the inertial model or if it's about how the whole structure flexes with different strut placements, but clearly in this situation it's best to put a strut as far away from your high-mounted decoupler as you can.

[Reinhart Mk.1]

So I have new problem now, i accidentally staged the upper stages while landing and now when i go to actually stage them during takeoff they dont ignite... so either i have to leave them off or reactivate them one by one DURING the ascent... is there a way to undo this?

[Reinhart Mk.1]

I mean... i have a save where i can land again in the same spot but this makes everything way more difficult in the event that i found a great place to land but forgot to save...

[KerikBalm]

15 hours ago, herbal space program said:

2) You certainly don't disagree about placing the decoupler well above the COM of the side stack, do you? Let's not throw that baby out with the bathwater. On a highly dynamic rocket ascent like this, not doing that is deadly.

I do not disagree. You want the force to push the tips of the stack away from the core stack. By doing that, aeroforces will help separate them cleanly. If you have them at the base, then instead the base flares outward and aeroforces push the discarded stacks into the center stack... not good....

4 hours ago, herbal space program said:

Interestingly, when I staged these three decouplers off high up in Kerbin's atmosphere, where Aero forces are minor, all 3 side stacks behaved identically (not shown), so in a purely inertial situation I think @KerikBalm's assertion is true. However,  when I did the same test ascending from Eve at ~10km, where the aero forces are very strong,

...

You can see the different placement of the struts in the top picture, followed by how the two different stages behave in the instant after decoupling. Clearly there is a difference. I don't know if this has to do with the aero model getting updated differently from the inertial model or if it's about how the whole structure flexes with different strut placements, but clearly in this situation it's best to put a strut as far away from your high-mounted decoupler as you can.

#1) for best results, the staging should have been done in space, but very high in the atmosphere was good enough

#2) I think you are right about the flexing, but I think its not so much that you put the strut farthest from the decoupler, as it is that the strut should be closest to the engine.

When you have decouplers mounted very high, and no strut/autostrut, the force of the engine thrust will cause a lot more flexing (move leverage since the point of attachment is much farther away). When the engine is thrusting, it will splay the stage outward a bit. When the engine thrust stops (stage runs out of fuel) it will rebound and start to come inward from the stored mechanical thrust from when the engine was thrusting and splayed the stack outward. Even if you wait a moment between engine cut off and staging, there will still be some movement, waiting for the side stages to stop oscillating is waiting too long.

By placing a strut as close to the engine/source of thrust as possible, you minimize the flexing in the structure due to that thrust. Then its just the force of the decoupler pushing the tops of the stack outward, and aero forces/body lift then work to split the stacks away. Autostrutting the engine and fuel tanks above the engine typically work just as good for this, and don't increase part count, mass, or drag.

[Laie]

6 hours ago, Reinhart Mk.1 said:

so either i have to leave them off or reactivate them one by one DURING the ascent... is there a way to undo this? 

Depends on your stance towards mods.

In the stock game, your best solution is to revert to the last savegame before the staging accident.

Action Groups are a stock mechanism to toggle engines on and off, however, those can only be defined in SPH/VAB -- in other words, only before launch. But if you go looking for mods with "action group" in their names, I think there's at least once that will let you edit action groups in flight.

Action groups won't move your engines back to an "unstaged" condition, but at least it's a means to activate them all at once with a single press of a button.

Lastly, you can edit your savegame. I don't recommend it, but it is an option.

2 hours ago, KerikBalm said:

Autostrutting the engine and fuel tanks above the engine typically work just as good for this, and don't increase part count, mass, or drag.

Of the three, I find that only part count bothers me in ordinary gameplay. I don't think I've ever noticed the mass of struts outside of a low-mass challenge, and drag even less. Not even in the old days, when larger vessels often were 25% struts by part count. Autostruts has helped a lot in that regard. Of whatever amount I still add today, I only notice the benefits.

[KerikBalm]

In the old days, struts were massless and dragless.

[herbal space program]

For my own part recently, I've been trying to see how little of my dry mass I can stage off and still get to orbit, and this is the best I've done so far:

The whole 78-ton core stage gets to orbit from 4km, with only the two side stacks getting staged off. That represents a bit over 16 percent of the total starting mass and 70 percent of the dry mass of the vessel making orbit. I feel like that's a pretty good start but I can still do better. If not an actual SSTO, I think I can get pretty close to one this way....

[farmerben]

I did some tests with decouplers and struts by launching pods vertically  at the runway.  I have an exact measurement of altitude, which determines kinetic energy and momentum after full separation..  The F3 menu reports maximum speed and maximum G force, but these numbers could not have existed steadily for the .039s I estimate the decoupler force lasts.  

Conclusion attatching a lot of struts reduces the relative velocity of the stage, but the struts exert minimal torque on the part during the decoupling process.  However putting the center of a pod near the top or bottom of radial decoupler blows it away from the decoupler.

[TheFlyingKerman]

I have never lifted off from Eve before. So I gave it a try, cheating myself to Eve orbit and then land and then lift off. The most frustrating thing is I often land on the ocean or a slope. Otherwise I made it with my 3ro of 4th design.

At about 34t this is not the best design. Initially the rocket was designed to have asparagus staging but I found no cross feed better.

Good luck.

[GRS]

3 minutes ago, TheFlyingKerman said:

I have never lifted off from Eve before. So I gave it a try, cheating myself to Eve orbit and then land and then lift off. The most frustrating thing is I often land on the ocean or a slope. Otherwise I made it with my 3ro of 4th design.

At about 34t this is not the best design. Initially the rocket was designed to have asparagus staging but I found no cross feed better.

Good luck.

You need to get rid of that Truss Structure, it's killing Aerodynamics, great job if you know how to get rid of it and leave it in the ground (or destroy it).

[TheFlyingKerman]

Just now, GRS said:

You need to get rid of that Truss Structure, it's killing Aerodynamics, great job if you know how to get rid of it and leave it in the ground (or destroy it).

The fairing/truss is used to protect the craft during entry and is discarded at the moment lifting off.

[Superfluous J]

On 3/6/2019 at 7:07 AM, KerikBalm said:

What I've done for Kerbin launches is to have fins just slightly ahead of the CoM of the stage that gets discarded (which should be behind the CoM of the stage when its fueled), and at a slight (<5 degree AoA) angle so that aerodynamic forces pull the spent stages away... that or a combination with sepratrons.

You missed the word gloriously there. The way boosters glide away with those fins is majestic.

Edited March 8, 2019 by 5thHorseman
fixed a swypeo

[Reinhart Mk.1]

NAH NAH, enough of this. I'm just gonna straight up use SRB's with a ending terrier stage. My thought process seems sound but we'll see

[Foxster]

I think you are going to find the isp of SRBs just not good enough to get off the ground on Eve. 

One of the reasons for using either Vectors or Aerospikes is their high isp at ground level on Eve. SRBs though good enough on Kerbin just ain't gonna be up to it on Eve. 

I hope you prove me wrong. 

Edited March 8, 2019 by Foxster

[Reinhart Mk.1]

12 minutes ago, Foxster said:

I hope you prove me wrong. 

oh i most certainly will not but hey i've failed this entire time so i might as well (its a healthy number of rockets, not just two or anything)

also since i tried to look this up but im not too good with geography uhhhh, where is the tallest point on Eve? I think I know the general area but a screen shot would be nice

[herbal space program]

1 hour ago, Reinhart Mk.1 said:

oh i most certainly will not but hey i've failed this entire time so i might as well (its a healthy number of rockets, not just two or anything)

also since i tried to look this up but im not too good with geography uhhhh, where is the tallest point on Eve? I think I know the general area but a screen shot would be nice

I just want to reiterate that you definitely have the juice to make orbit with the rig you already have. You just need to stage and fly it a little differently.

[Reinhart Mk.1]

15 minutes ago, herbal space program said:

with the rig you already have

oh i already still have the save, just saw something on yt that was interesting. but either way it would make it ALOT easier to know where the tallest point on eve is

[FleshJeb]

12 minutes ago, Reinhart Mk.1 said:

oh i already still have the save, just saw something on yt that was interesting. but either way it would make it ALOT easier to know where the tallest point on eve is

http://ksp.deringenieur.net/ Turn on Points of Interest.

[Reinhart Mk.1]

4 minutes ago, FleshJeb said:

Turn on Points of Interest.

i just found this thank you! unfortunately im awful at reading flat maps like this but i have an idea now, thank you again

[herbal space program]

2 minutes ago, Reinhart Mk.1 said:

i just found this thank you! unfortunately im awful at reading flat maps like this but i have an idea now, thank you again

If you look upthread at the coordinates shown in the HyperEdit window on any of my recent flight posts, those are for a nice, flat spot at 4000 m, that is right next to the tallest peak. If you poke around a bit from there, I'm pretty sure you can find it fairly quickly.