How to Get Off of Eve

[Ekku Zakku]

Bear in mind, this is all purely theoretical (as in, I haven't tested it); however, it should work for those of you who are trying to return from Eve, yet can't get out of its thick atmosphere and overcome its gravity.

The idea is, to save as much thrust and energy (I guess Delta-V?) as possible while lifting off from Eve. You might have 20 SRBs strapped to the side of your interplanetary craft, and you think, "surely, this will get me off of Eve". Not so fast though! Do you really want to fire all of those off at once just to get dragged down by the thick atmosphere? The faster you try to go through thick atmosphere, the more it'll just slow you down. You're wasting your Delta-V by trying to gain as much speed as possible early on. Now, how to actually do it!

Instead of firing all 20 SRBs at once, you should instead fire a few; enough to lift you off the ground and accelerate you a little bit, but not waste all of your thrust at once. Ok, now you're thinking: "but I have all this extra weight that's dragging me down now, surely that's not efficient at all"! Nope, not true. Take, for example, this simple craft here I use to get into low Kerbin orbit:

[spoiler=]

(Keep in mind, I'm not using the upper stage at all in the tests I ran. Let's just call it our "interplanetary return stage" analog.)

Firing all of the SRBs and the main engine at once (max acceleration mode) results in a straight-up Apoapsis of ONLY 48.8 km. The same craft only firing the SRBs and waiting to fire the main engine until after the SRBs are spent (yes, the engine is just dead weight while the SRBs are firing), can reach 112.7 km straight up, quite an improvement! Finally, in my last test, I only fired two of the four SRBs at once, then ejected them and fired the remaining two, and once those went, the main engine; this resulted in a whopping 148 km straight up! Even though it's slower off the launch pad, and slower when the main engine finally fires, it's at a higher altitude and a thinner atmosphere when it fires, and thus doesn't have to fight nearly as much atmosphere or gravity.

Thus, my final conclusion, is that in order to get off of Eve with a craft that can even remotely get into Kerbin orbit, you will need to slowly but surely use your rocket's energy and wait until you're at a higher altitude to expend most of your fuel, and thus should be able to get into low Eve orbit to either return home, or wait for a rescue craft. Thanks for reading!

[robsr3v3ng3]

This is sound advice. If you used mechjeb's autopilot for launching you'll have noticed that when you get it to auto throttle it will actually restrict your velocity sometimes, this is because it picks the most efficient speed, i.e. reduces the amount of drag as much as possible while not spending so long in higher gravity. Not sure about values for the new planets, but on Kerbin it's best to stay under 250m/s in the bottom 8kms or so and then only go full throttle when you're over 25km.

[Nadrek]

Purely from observation, I think Mechjeb perhaps tries to lower your thrust whenever your drag losses exceed your gravity losses; i.e. don't lose more to drag than you do to gravity.

Some other forum users have stated that Mechjeb ascent autopilot defaults are not the most efficient way to get to Kerbin orbit, however. I have yet to do serious testing.

As far as the OP goes, yes, balancing increased drag vs. more staging is critical. For those who prefer LFE's to SRB's, make sure your fuel always goes from outer (i.e. early dropped, higher number) stages to inner (i.e. late dropped, lower number) stages.