Eve landing 1.9.1

[O5-7]

Hello this is my first KSP forums post. I have been having trouble lifting off on Eve for my career mode project. I've tried a few things like making my craft more aerodynamic, but it still has difficulties in Eve's thick atmosphere. I am using a Rhino engine on my craft, and the lander has a mass of around 47 tons in total. What do I do?!?

[Vanamonde]

Everybody has trouble lifting off of Eve. I myself have yet to recover anything from Eve surface, despite playing the game on and off for years. Even so, 47 tons sounds quite large for an Eve ascent vehicle. Are you sure you need all of that? 

[Space Nerd]

Rhino engine is more rated for vacuum operation, so it probably won't work very well on Eve, try to change that to a cluster of vectors or aerospikes, or just use a mammoth engine (which is just a cluster of 4 vectors).

[Superfluous J]

I 2nd Aerospikes or Vectors. Make sure your lander has at least 8000 (preferably 9000) m/s of dV in vacuum listed in the VAB and at least the first 5000 (the more the better) of that is with the Aerospikes/Vectors.

Then land as high and as flat as you can, burn straight up to 20-25km, and then start a pretty aggressive gravity turn to space.

Then retry that a dozen times or so until you don't make a tiny mistake that ruins your chances of orbit.

To show all of this as succinctly as possible, here's a link to me lifting off of Eve with closed caption commentary.

https://youtu.be/5mHtUfd3U4g?t=500

(except turning aggressively but smoothly to space at 20km. that was too hard so I just went straight up)

Edited April 25, 2020 by Superfluous J

[hendrack]

If you're on PC and don't regard this as cheating, you can build an ascent module with those engines:

 

[OhioBob]

@O5-7, others have already given you some sage advice, but here's some more...

The atmospheric pressure at Eve sea level is 5 times what it is on Kerbin.  High atmospheric pressure destroys the performance of rocket engines.  Engines always work best in a vacuum and get progressively worse as the ambient pressure goes up.  There are two strategies you can employ to make getting off of Eve possible:  (1) take off from a location where the atmospheric pressure is lower, and/or (2) use the engines that are best suited for the higher pressures.

While the sea level pressure on Eve is 5 atm, it decreases with altitude.  So the higher the terrain from which you take off, the lower the air pressure and the less of a performance hit you're going to take in regard to your engines.  This also means you'll have lower drag losses, reducing the amount of delta-v it requires to attain orbit.  It might be hard to find a nice flat spot to land on at Eve's higher elevations, but if you can, every kilometer rise in elevation decreases the air pressure about 9%.  For instance, if you can find a landing spot at an elevation of about 2500 m, you'll only have to deal with an atmospheric pressure of 4 atm instead of 5.

Rocket engines come in all types.  Some are designed specifically for use in a vacuum, while others are designed for use at higher atmospheric pressures.  In real life this difference is attained by varying the expansion ratio of the nozzle.  In KSP we see the difference in the engine specifications.  The "sea level" optimized engines that we have in KSP are designed for use on Kerbin, where the sea level pressure is 1 atm.  None of them are optimized for use on Eve where the air pressure can reach 5 atm (except arguably the Dart [aerospike]).  This means that when on Eve we must make do with engines that are not designed for the conditions and produce quite poor performance.  There are only a handful of engines in KSP that gives enough performance at 5 atm  to make them even worth considering.  One of the ways we can judge how well a particular engine will perform is by looking at its specific impulse.  Here are the best options available to us, with the specific impulse listed for pressures of 5, 4 and 3 atm.

Specific Impulse (seconds)
Engine	5 atm	4 atm	3 atm
Thud	140	174	209
Mainsail	148	184	220
Twinboar	148	184	218
Vector	193	220	246
Dart	230	242	251

Far and away the best performing engines are the Vector and the Dart, as others have already said.  Unfortunately these are very expensive engines that don't come until very late in the tech tree.  (Of course if you're not playing career that doesn't really matter.)  You can make do with the other engines if necessary, but you can see there's a big performance hit.  I wouldn't even consider any other engines not listed as their performance is just too low.

My mod Eve Optimized Engines provides variants of several stock engines by adapting them specifically for use in the high ambient pressures found on Eve.  This is justified by presuming the nozzle expansion ratios are modified to better match the operating environment.  Some players consider it cheating, but it is based on real science and engineering practices.  I consider it selecting the right tool for the job.
 

Edited April 25, 2020 by OhioBob

[HansonKerman]

On 4/24/2020 at 2:14 PM, O5-7 said:

47 tons

why? I don’t see why it’d need to be that big. Some very very strong engines are needed, apparently 12k, so use strong engines like Mammoths, Vectors, and Darts (on the outside), but make sure it isn’t amazingly heavy. Are you sending a probe or a Kerballed mission? My advice (not firsthand, just theory) is: make it light. Have decouplers for any unnecessary stuff on ascent: fins, empty tanks, ladders, parachute modules, anything. It won’t matter on descent. Make it lightweight, with powerful engines like mammoths, darts, vectors, and maybe a cluster (Darts will probably need to be in clusters). Can you send a pic of the lander?

[OhioBob]

One word of warning about the Dart... it has no thrust vectoring.  Just keep that in mind when designing your lifter.  You may need to make other accommodations for steering, like control surfaces, RCS, or strong reaction wheels.

[KerikBalm]

Most of my Eve lifters meant for ascent from sea level, pre breaking ground +rotors, use 2 vectors and an aerospike core.

Aerospikes have better Isp overall, but at certain altitudes, the vector beats them.

Also, Isp is one thing, but so is TWR, and when drag is a problem, you also should consider thrust to cross section. The vector beats the dart handily in both those areas. So I like to use them, but the aerospike can perform OK the whole ascent, so I use it on the core with cross feeding.

The Rhino is a great upper engine for many uses, but getting off eve isnt one of them.

[Mephisto81]

Eve is hard.

Here is a rather simple Eve ascent vehicle meant for players new to the difficulties of getting to orbit from Eve.
Maybe it can give you some ideas for your own builds.

https://kerbalx.com/Mephisto/Simple-Eve-Ascent-Vehicle

The lander is massively overengineered . If flown properly, you can reach orbit with over 2,200 m/s dv left. This is intentional to provide generous margins for beginners.

On the profile, there are several other Eve landers as well, some with propeller stages, some more conventional. Basically any craft with something purple in the background.
The lightest one is about 11.5t and has a propeller stage, an aerospike, a terrier and a spark stage.
https://kerbalx.com/Mephisto
https://kerbalx.com/Mephisto/XE-02-Stingray-Eve-Lander-115t

Some thoughts on Eve landers and ascent vehicles:

Copy crafts
Don't hesitate to copy a functional design. By rebuilding it, you will gain insight into the workings. Even if it is from watching youtube videos or downloading craft from KerbalX.
Kergarin and Bradley Whistance have some really nice designs on Youtube, Foxxster has some nice builds here on the forum as well.

https://www.youtube.com/channel/UCPFuJDY-mn-DZxykUydyN9g

https://www.youtube.com/user/nEvermore930

Gravity, atmosphere and drag
Others have already laid out the basic dv requirements (8,000 m/s dV is a good start) and the impact of atmospheric density on rocket performance. A dense atmosphere basically limits your engine choices to Vector and aerospikes for the lower stage. For upper stages ignited above 35km, Terriers and sparks are useful.
Drag is another issue. Always check the drag of your craft by displaying the aerodynamic forces (shows coloured lines during flight). Especially with the dense atmosphere and high friction, you will lose more dV than on Kerbin to this.
Try to use the smalles diameter possible for your rocket and built it in a streamlined way.
Discard landing gear, parachutes, or anything else you don't need for your ascent immediately after lauch. This will save you weight and drag.

Ascent profile
You best watch lots of youtube videos and take notes, at which height crafts are starting to turn, which engines they use, which velocity they have at a certain height and and how they throttle to prevent overheating.

Build backwards
Might be obvious, but don't bother with bring your craft to Eve and attempt atmospheric entry before you can take off.
1. Build a functional ascent vehicle. Test it thoroughly. Hyper Edit is your friend.
2. Make it capable of Eve landings. The simples method is to add two inflatable heatshields, one at the front, one at the back. Bunch of parachutes and landing gears.
3. Find a means to get your craft to low Eve orbit. Build the rocket or spaceplane at last, because the layout depends on mass and size of your lander.

Have fun and good luck!
 

Edited May 1, 2020 by Mephisto81
Added words. Words are good.

[O5-7]

Thanks for all the advice! I am redesigning the rocket from the ground up. I promise that the lander will only be 10-15 tons this time ! I will use a stock propeller for the asent and then dart engine for circularization, escape, and deorbit into kerbin!