How to survive Eve Atmospheric descent in 1.1.2

[gilflo]

Hello

This is my Eve ascender for 2 kerbals. It is perfectly balanced and can reach a 100kms orbit with 200-300 DV left.

My problem is the descent through Eve Atmosphere.  Here the big vernors the are supposed to help to maintain retrograde on descent are perfectly balanced  (no side effect) but between 70 and 50 kms the lander will unavoidably get upside down and explode. Whatever is my entry speed, wherever i put my vernors, at the top to get more efficiency for example, issue is the same. Not using any vernors or RCS mopropellant engines will give same result....

Whatever is the shield, same result. Here it is the inflatable shield and I built a more curved shield with 5m and 3.75m ablation shields pieces, but it won't work anymore....

Any suggestion? 

Edited May 26, 2016 by gilflo

[Snark]

It's way too tall and skinny for stability, without some sort of help from aero surfaces.  The deceleration g-force you get with that big heatshield is so large that there's basically nothing you can do with vernors or reaction wheels that are going to help.

There are essentially just two ways to solve that problem.

One way, which is probably not an option for you, is to adjust the mass distribution so that the CoM of the craft is as close to the heat shield as possible, i.e. very low.  I say "probably not an option" because that would mean making it very short and squat (which would be a Bad Thing on Eve, where you need to be tall and skinny for aerodynamics during ascent), and also you'd need to engineer it to keep the mass down at the bottom of the rocket (which would be good for aero stability on descent, but very bad for ascent).

Another way would be to add some sort of aero stabiity, which ought to be doable.  Attach fins or airbrakes to the top of the rocket during descent.  As long as they're in the "shadow" of the heat shield, they won't get fried... but they will still get aero forces and that can help maintain stability.

Of course, that will be a problem on ascent, since then your fins/whatever will be on the wrong end of the rocket.  There are a couple of ways to deal with that.  One would be to mount them on decouplers so that you blow them off once you're done with the heat shield.  But the way that I like to do it is to put the heat shield on the top of the rocket, and enter prograde rather than retrograde.  That way, my fins go on the bottom of the rocket, which helps stability both for descent and for ascent.

[bewing]

What is your typical Ap and Pe when you enter the atmosphere? Or is this a direct aerocapture?

[gilflo]

It's not a direct entry, it's an entry from a 110kms orbit

I tried the prograde entry with the shield on top, not good.

Finally i tried a tower of small vernors on the very top of the ship around 2 tanks and it works pretty well until 25 kms where temperature is no more a factor.

Then, tanks and vernors are ejected, shield is ejected. 7 stages of 8 vernors all around the tank! works pretty well.

The only flyable shield is the one i built with the 5m ablators shields, the inflatable one is not flyable with this method or on the top. So it's more weight on take off from Kerbin.

Here is the ship, 163 T on landing, something like 138 on take off

 

 

Edited May 26, 2016 by gilflo

[Foxster]

Really, as Snark said, air brakes are your friend here. 

Stick a bunch on the top with your 'chutes. Probably about 8 in total for your craft. Deploy them before re-entry and you should be good to go. Throw them away along with your 'chutes before ascent. 

[gilflo]

Well, I add 8 speed brakes on top and it helped keeping retrograde until 20 kms, so I won 5 kms more on retrograde, but anyway vernors are mandatory during the hot part of descent, but maybe i can lower the number of vernor engines, i had to try

Thank's

[Snark]

The other thing you can do that will help you is to get your overall ship mass down.

Eve ascent is a bonebreaker of an engineering challenge.  It's arguably the hardest engineering challenge in the game; brute force alone doesn't work (though you need plenty of that!)-- you have to really understand what you're doing and tweak your ship's design just so.

138 tons on takeoff isn't terrible-- it's clear you've already put a lot of design thought into this.  But it's not too hard to get an Eve ascent lander that's around half of that on takeoff.

If you can cut your mass in half, that will make atmospheric entry a lot kinder.

The typical design I've seen folks use for an Eve ascent vehicle in the 60-80 ton range is something similar to this:

• top stage is a pod, 2-ton LFO tank, and Terrier
• under that is a stack of two of the tall, skinny 4-ton LFO tanks, with a Vector underneath
• put six radial boosters around that, asparagus-style, each of which is also a stack of two 4-ton tanks with a Vector

...and then various clever arrangements of landing legs, struts, parachutes, batteries, yadda yadda, but that's the gist of it.  Lots of variations, of course, but it's remarkable how many different folks I've seen end up with something pretty similar to that.

[gilflo]

I have a 100T lander for 1 kerbal, this one is for 2 kerbals, so the pod is 1.8T. I aim a 102-105 kms orbit with 300Dv left, so there's a little bit more weight. Yes Eve is challenging and 1T more to lift is many more tons underneath.....

i tried the Vector engine, but i found the Ratite from SpaceY much more efficient on Eve.

I landed  a much heavier ship on Eve: a plane ( mix of plane and rocket) allowing to explore Eve after landing and allowing to leave Eve by launching its rocket from 14km to reach orbit!

a real challenge! The rocket part of the plane is still to heavy and I'll use the improvement i made on this Evelander to design the next plane to Eve. Just waiting update from adjustable landing gear mod because actual wheels are not usable

 

[Snark]

2 hours ago, gilflo said:

i tried the Vector engine, but i found the Ratite from SpaceY much more efficient on Eve.

Ah, if you're using SpaceY, then some options get a little simpler.  There's a handy 5m heat shield that allows you to stack a pretty good Eve lander on top of it; that's enough elbow room for a 1.25m central stack, 1.25m radial asparagus boosters mounted to radial decouplers, and the nice big SpaceY landing legs mounted on those.  I've done an Eve lander on that, works great.