Eve ascent and engine ISP/Thrust numbers

[Kelderek]

I've started to do some testing and planning for an Eve ascent mission and I'm really amazed at how poorly all of the stock engines perform at low altitudes on Eve.

First of all, it looks like the "ASL" numbers listed on each engine for thrust and ISP (which are meant to be sea level on Kerbin) correspond to roughly 10.6 km altitude on Eve. At 223m altitude on Eve every stock engine I looked at had an ISP below 200 with the "mammoth" engine topping the list at 198.3 ISP. Some engines were abysmal though like the "swivel" at only 64.6 ISP and 40.4 kN thrust. The SRBs were the worst with ISP numbers in the 30s and 40s and thrust numbers that are only 25% as good as when at sea level on Kerbin. Even the "aerospike" engine (189.5 ISP, 100.3 kN thrust) seems like a poor choice.

All of this seems to point towards needing a really huge ascent vessel with a lot of "mammoth" engines to get you up the first 20-30km. The downside is that landing something that big or even flying it there from Kerbin will be all that much harder, plus you need for all that size to be aerodynamic if you want to control it at all. We may only need 7500 m/s DV +/- to get to orbit on Eve now, but getting that much DV seems to take a bigger rocket in 1.0.x than having a 12km/s rocket did in 0.90.

Does this mesh with what you guys have found so far with Eve ascents in 1.0 or am I just doing something very wrong here?

P.S. I wrote down a lot of numbers on paper for ISP and thrust when I did my testing at 223m and 900m altitudes on Eve and I could post them her if you guys think it would be useful.

[Xannari Ferrows]

It doesn't always have to be a huge rocket. You can use a plane with long-burning engines, or an ion glider. Using natural lift will save on TWR hassle, and ion gliding gets rid of atmospheric worries. The new fuel cells can be an exemplary source of power.

Of course, if you do find liquid engine solutions, it would be great to hear from a professional, such as yourself.

[Teilnehmer]

P.S. I wrote down a lot of numbers on paper for ISP and thrust when I did my testing at 223m and 900m altitudes on Eve and I could post them her if you guys think it would be useful.

I did the same. Here are my figures for Isp and thrust at 2, 3, 4, and 5 atm.

Meithan’s engine chart can also be used. It’s great!

Does this mesh with what you guys have found so far with Eve ascents in 1.0 or am I just doing something very wrong here?

I haven’t completed the Eve Return mission yet, but my calculations and tests show basically the same.

TwinBoar, Mainsail, and Aerospikes are good enough though.

or an ion glider

Unfortunately, no. In 1.0.2, the ion engine doesn’t work at all at Eve’s pressure levels.

Here’s my empirical Isp graph for the ion engine at different pressure values.

If using wings, the aerospikes seem the engines of choice.

Edited June 11, 2015 by Teilnehmer

[Xannari Ferrows]

Really? It still does for me. Then again this thing is an atrocity that really shouldn't have even been able to take off...

EDIT: Oh, I see why. Normally the engine's thrust get's knocked down to accommodate the loss of Isp. I wonder why mine doesn't do this?

Edited June 11, 2015 by Xannari Ferrows

[Signo]

We may only need 7500 m/s DV +/- to get to orbit on Eve now, but getting that much DV seems to take a bigger rocket in 1.0.x than having a 12km/s rocket did in 0.90

I quoted just this sentence but I completely agree with you.

I ended up with a bigger rocket in 1.02 compared to 0.90, so I added the ISRU to save on the total fuel weight. I "borrowed" Mesklin's ascent vehicle and I added my descent/drilling module, dual seater rover, transfer stage and booster.

Do not bother the gigantors and the oversized useless drilling system, the picture refers to my first succesful landing there in 1.02 and at the time I was not aware solars do not work there.

My current design has got less drills and more RTGs and cells.

[Foxster]

Or you can do it pretty light like this...

That's five Mainsails, dropping down to one, then a Reliant and finally four Sparks. Landed nearly empty. Easily makes orbit from sea level with 1000dV spare.

If you don't mind hauling a bit more mass to Eve or refuelling at, say, Gilly then you can skip the mining stuff. Just add some smallish drop tanks in their place and use that fuel for de-orbit and final landing braking, dropping those tanks along with the landing gear right after lift off from Eve.

Edited June 11, 2015 by Foxster

[soulsource]

If one doesn't care about the sciency aspect of sending various engines to Eve to test them under "real" conditions, the stage information window of the VOID mod can display sea level performance data for any planet (dV, TWR,...) in the VAB, so figuring the I_sp for engines on Eve should be a trivial task with this mod (as dV is proportional to I_sp -> build a small rocket, take vacuum I_sp, divide by vacuum dV, multiply by Eve sea level dV, profit).

As I neither have aerospikes, nor the NASA engines unlocked, my choice for the bottom stage is the Mainsail. I haven't tested my lander design yet, it's still on its way to Eve...

[Signo]

I tried a 4 legged config similar to yours but I experienced some bouncing issues during a little bit harder than usual landings. Moreover I wanted to have at least 2 bays close to the terrain level, one for the rover and the other one with a pod to allow for an almost ladderless ship. I kept the extra ISRU as a ballast cause I did not want to stretch it too much in the sense of height putting just one ISRU at the bottom. The landing footprint is already pretty small for such a tall lander.

Mainsails may experience hard times to lift you off the sea level if you fail to go supersonic as soon as possible, meanwhile if they are your second stage and you already reached 10000m they are wonderful. After 35000m you can safely go with anything with a TWR of 1 or even slightly less.

Do you launch it full or empty? Did you test it on Eve yet?