Getting back from Eve?

[korda]

So I decided it is time to make mission to Eve that involves getting back. If what wiki states is correct I will need to build, send, and land lander that has almost 12km/s of delta V left after landing (and enough TWR to actually fly).

I've installed Kerbal Engineer Redux (I decided it is actually better to use it than to spend few hours trying to complete mission that is doomed to fail from the very start, didn't use it before) and started planning of lander. Few quick drafts showed that even simplest lander (by that I mean it's really stripped down from every decal I usually put) is very hard to design hard for me. 13 engines asparg-something-bored-to-google-it-every-time staging rocket barely reached 10km/s of total delta V and I'm not even sure if I will be able to put it into space to send it to Eve in the first place. Or how will I land it (my first tests showed that I need absurd amount of parachutes on Kerbin to land it without exploding. and 10km/s was without mass of parachutes).

Ideas I've got so far for my mission, I've put my questions in bold:

- build and send lander as separate mission, dock it with nuclear rocket that will send it to Eve and then dock it again after getting back to Eve orbit, scrap lander and get back home with nuclear rocket.

EDIT: that means that lander will only be needed to get from orbit around Eve to Eve and back to orbit around Eve. Please don't post this again as advice, that was my first idea for this mission anyway

- put some sort of landing engines high on lander, make them decouple. strap army of parachutes on them. high placement is supposed to help keeping correct end of rocket pointing space. How many chutes per tone of craft I will need on Eve to slow down to say, 5m/s? Are there ways to calculate this?

- land somewhere high, so I don't have to start from sea level. How much less of delta V I will need then? Does it even worth trying? Are there any easy (big and flat) high ground landing spots?

Any other advice is also welcome, of course also I'm not really interested in using mods that will make this much easier/different than while using stock parts (like turbojet engines for Eve, I don't know). Also don't show me your designs so I can feel at least tiny bit proud of making sth useful at least partially by myself

Edited July 1, 2013 by korda

[automcdonough]

Yeah, boil the return stage down to the bare minimum weight. Leaving the landing stage behind is a good strategy, you won't need those legs or chutes anymore. Might have empty tanks to lose too. If it's a manned mission you can re-pack chutes on the return craft.

If you must use nuke engine then don't do more than one, they have horrible TWR. Return craft should be like just one of those and a fuel tank, the rest of the tanks and lifter engines you can eject on the way up. Often I end up with such a small return craft that nuke isn't worth it's weight, can get by with the .5t engine instead. If the d/v is a little lower but still good enough for return trip then consider it because it'll be easier to lift without the extra 2T of weight.

[Geschosskopf]

Another option is to use the Hooligan Labs balloons. These apparently work very well on Eve (the download comes with an example ship). Anyway, the balloons get you up pretty high without you ever having to burn the engines, so that saves on the amount of delta-V the lander needs to get back up.

[korda]

Yeah, boil the return stage down to the bare minimum weight. Leaving the landing stage behind is a good strategy, you won't need those legs or chutes anymore. Might have empty tanks to lose too. If it's a manned mission you can re-pack chutes on the return craft.

If you must use nuke engine then don't do more than one, they have horrible TWR. Return craft should be like just one of those and a fuel tank, the rest of the tanks and lifter engines you can eject on the way up. Often I end up with such a small return craft that nuke isn't worth it's weight, can get by with the .5t engine instead. If the d/v is a little lower but still good enough for return trip then consider it because it'll be easier to lift without the extra 2T of weight.

Problem here is mass of lander. Not sure what minimal mass I can get on it while actually putting normal command pod and some stuff like ladders or lights. So far it seems that it will weight at least few dozens of tons. Getting that (without using its fuel) to Eve orbit with only one small engine would probably end up being extremely boring (those burn times). So I'm using 2.5m nuclear engine from one of mods. It weights more than 9t but gives 240kN of thrust (still it has similar TWR to stock nuclear engine). I've also have separate lander for kerbin, but it's really simple - 2.5 probe core, hitchhiker, ladder, legs and chutes. I've put it in-line in my nuclear rocket using two decouplers. I plan to start reentry with whole rocket then decouple Kerbin lander. But that isn't important in fact. I've already landed here and there and got back. What is challenge for me is getting back to orbit... from Eve.

[Johnno]

Parachute calculator: http://ksp.freeiz.com/

As for altitude, you can visually determine it somewhat, the darker the ground the higher it is..

And high altitudes on Eve help but I can't give you exact numbers. As far as I remember from mentions in other threads you can save a couple thousand in dV.

[korda]

Another option is to use the Hooligan Labs balloons. These apparently work very well on Eve (the download comes with an example ship). Anyway, the balloons get you up pretty high without you ever having to burn the engines, so that saves on the amount of delta-V the lander needs to get back up.

Yeah, seen some stuff on spaceport, even tried some. (but not sure if it was this mod or other similar). but as I said "I'm not really interested in using mods that will make this much easier/different than while using stock parts". I'm treating this as some sort of a challenge.

[korda]

As far as I remember from mentions in other threads you can save a couple thousand in dV.

Well, that would be really good (this last 2-3 thousands of delta V are actually my biggest design problem).

[allmappedout]

Landing high is the single biggest benefit you can use to get back from Eve. From 10km/s+ dV at 0m, you get it down to a 'reasonable' 6.5-7km/s dV (if I remember) from a higher mountain (about 4500m elevation). The issue is hitting that plateau with any degree of accuracy...

[Bekiekutmoar]

Never attempted a return-mission from Eve before but I'm going to try it soon. I've already fabricated a Asparagus-style lander with a mass of 71.54 tonnes and its supposed to land on highlands (at least 4000 meters above molten lead-level). It has to pick up 2 Kerbals.

[Hovis]

An alternative plan might be to have a second craft remain in orbit around Eve and have that either dock with the lander to bring it home, or have it collect the Kerbals.

[foamyesque]

An Eve Orbit Rendezvous profile will make your life immensely easier. Much less fuel you need to haul up from the surface. Stick a nuke engine with a docking port, probe brain, RCS tank, -8 tank, and a nuke engine in orbit before you descend, then dock your pod to it once you come back up.

[korda]

An alternative plan might be to have a second craft remain in orbit around Eve and have that either dock with the lander to bring it home, or have it collect the Kerbals.

An Eve Orbit Rendezvous profile will make your life immensely easier. Much less fuel you need to haul up from the surface. Stick a nuke engine with a docking port, probe brain, RCS tank, -8 tank, and a nuke engine in orbit before you descend, then dock your pod to it once you come back up.

Well I've already stated that this is my plan. Sorry if I didn't made that clear already. I'll edit my post to make it more clear.

[Fabri91]

I'd also move all the rendezvous equipment to the transfer stage awaiting in Eve orbit, letting the ascent stage be the passive vehicle during docking, in order to save weight by not having to carry the RCS system to the surface and back. You could also leave out the docking port and trasfer the crew via EVA. Every gram counts on Eve.

[tavert]

See kerbalmaps.com for elevation maps. Aim for the highest mountains at around 6400 meters altitude and you can reduce the delta-V requirement to around 8500 m/s, depending on your TWR.

Also don't forget about SRB's, they work quite well in the first stage of Eve ascent. <deleted link to my example, nevermind> With a pod, I've made an Eve ascent vehicle under 40 tons. Going any lighter will likely require Kerbals in seats or on ladders.

You don't need all that many chutes. The atmosphere is so thick that terminal velocity is very low. Depending on your desired landing speed, mass, landing altitude, engine Isp, etc it can be more mass-efficient (though more stressful) to do a powered landing, or a semi-powered with both chutes and engines. numerobis has some good Python scripts to optimize semi-powered landings here https://github.com/numerobis/KSP-scripts

Edited July 1, 2013 by tavert

[korda]

I'd also move all the rendezvous equipment to the transfer stage awaiting in Eve orbit, letting the ascent stage be the passive vehicle during docking, in order to save weight by not having to carry the RCS system to the surface and back. You could also leave out the docking port and trasfer the crew via EVA. Every gram counts on Eve.

I was even thinking about using KAS to dock it, since I will use quantum struts anyway.

Since I'm not actually building it as one ship (Lander and Transfer Stage will meet at Kerbin orbit) I actually need some way to dock them before flight to Eve. I guess I can always slap decoupler and then docking port.

BTW, my PC wouldn't like lifter needed to put both parts of mission as one to orbit, so this isn't probably an option

[AndreyATGB]

I did it like this. I'd HIHGLY suggest KAS surface refuelling. Don't even think of docking ports, they'll make you question your mentality.

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[korda]

So I managed to put my 180t lander in space, I needed to use some of it's fuel so I will have to refuel it, and then build and send transfer ship. How much delta V I will need for transfer from LKO?

[capi3101]

1,030 m/s will get you from an 80 km LKO to an Eve intercept. IIRC, a 55k periap will put you in orbit (I'd quicksave before making the attempt just in case my memory is bad). Lower than that and you're going in.

[AndreyATGB]

For transfer theoretically it's around 1100. I'd have at least 500 more though, for mid course corrections and what not. You're gonna want all the fuel available on the surface.

1,030 m/s will get you from an 80 km LKO to an Eve intercept. IIRC, a 55k periap will put you in orbit (I'd quicksave before making the attempt just in case my memory is bad). Lower than that and you're going in.

For me under 63000m it'll go in for a landing. Depending on velocity, I'd aim for 63.5-64.

[korda]

Well I designed tug that has 4000 delta V with 200t cargo and TWR (relative to Kerbin) around 0.2, I guess that will work.

[automcdonough]

so i'm trying this.. pretty tough! my 12kdv "lander" is like 300T. I don't think it'll make it there.. gotta find a better way.

[automcdonough]

so just strapping a chair to a rocket i think i can get it under 70t. this is a tough one. :/

[numerobis]

Nao had a rocket that could make it in about 45t from the tallest peaks. I think I remember it being as follows (I'm unsure about the very top of the rocket):

LV-909, 3x 24-77s, 4x aerospikes, 2x RT-10 (the medium SRB), and 6+8+8+2+1 tonnes of fuel. It used the Mk1 capsule, which was the lightest at the time. For decouplers, use a cube strut and a probe-sized stackable decoupler, a total of 15kg, rather than the 25kg radial decoupler. Use the landing gear (the wheel you'd use for a plane); it can handle 10-15m/s landing, and it's massless despite claims to the contrary.

First stage: Light all the engines. Turn off the 24-77s as soon as you hit terminal velocity, then turn off the LV-909 when you exceed a TWR of 2.0, then throttle back the aerospikes. First stage drops the RT-10 remnants and the emptied tanks for the first 6t of fuel.

Second stage and third stages: 8t fuel each. Turn all the engines back on. Toggle the 24-77s on for the beginning of the stage until you've burned a quarter of the fuel, then turn them off again. Dump a pair of aerospikes and the emptied tanks for 8t of fuel at the end of both stages.

Fourth stage: all engines (the LV-909 and the 24-77s) on for the first quarter, then just the LV-909. Dump the LV-909 and 2t tanks.

Fifth stage: the three 24-77s at full throttle.

With practice, apparently you can get this to orbit; I was always ending up a few tens of m/s short.

In the latest release of the game, you have the small lander can to save you 200kg on the final stage; that should make it easy to take a configuration like this one to orbit.

Hanging Kerbals off ladders, the record was around 35 tonnes, but I don't clearly recall how it went.

[capi3101]

Well I designed tug that has 4000 delta V with 200t cargo and TWR (relative to Kerbin) around 0.2, I guess that will work.

So...7 LV-Ns then?

4,000 oughta get you there and back, no problem. And shoot for 64k; I'd bet good money AndreyATGB's memory is better than mine. Still might want to quicksave as soon as you hit Eve's SOI.

[automcdonough]

Thanks for the tip nub, I'll try it.

also, check this out:

If you watch the craft Scott Manly uses, it's built for closer to 1.5 TWR (I had figured 1.7 min) and his ascent from the high plateau to 200k orbit only burned 7600dv of fuel. These numbers are MUCH easier to deal with, all my landers lost any sense of feasibility as they passed the 10kdv mark.