Let's talk staging efficiency.

[Colonel_Panic]

A lot of really great info and discussion in this thread! thanks!

So it sounds like a bigger core stage and smaller outer stages is the best thing for an ascent profile, maybe solid boosters for the start.

I haven't had a problem with losing engines or tanks due to poor staging unless I'm doing something wrong. I guess some people like to pack their asparagus stages all together (and, as the namesake implies, this is probably common practice) but I always try to keep to a 6-sided radial pattern, very rarely needing more than one 'shell' of stages. When it comes to the big tanks and mainsails, separation motors are useful for keeping them away from your core engines.

Where I start running into issues with lifter efficiency is when I'm dealing with really big payloads... for example the single-launch round-trip Eve lander. I can get about 6k of delta-v 'for free' with really simple staging, but after that you rapidly start approaching diminishing returns. After around 9k delta v, I can only gain maybe 200 delta v at most per additional asparagus stage. Then stuff starts to become a mess of 'tagged-on' boosters to try and get that extra oomph, and I'm wondering if there's a better approach to net me higher delta-v for ascent and escape, and save me the trouble.

Generally speaking I never stage off tanks without engines on ascent, but I do in orbit, preferring to keep one engine or engine cluster for all maneuvers in space, and just ditching fuel tanks as I go, though I've considered setting up staging that would allow me to ditch engines as well with the final few stages of tanks, since I wouldn't need the extra thrust anymore of, say, 3-4 LV-Ns once my fuel weight is mostly gone, and especially if I'm parking it in orbit for use as a return transfer vehicle, since when I come back from the surface the remaining payload will be much lighter.

Right now I have an Eve lander and return vehicle, which should theoretically do the job (haven't actually completed that mission yet) at under 1000 tons on the pad. But I figure I can, with sufficiently optimized staging in the later parts of the mission, do much more with much less, because every inefficiency is compounded sevenfold by the time you've pushed that capsule into orbit and transferred the second time. I'll let you know what I figure out.

EDIT:

my ultimate goal here is to make a lifter for a single manned capsule that can achieve 8000-12000 delta-v for an atmospheric ascent from Eve with under 50-80 tons of weight respectively. If I can hit the 50 ton mark, the transfer vehicle required to get it there and subsequently the lifter to get it off Kerbin will be dramatically reduced.

Edited May 14, 2013 by Colonel_Panic

[Temstar]

my ultimate goal here is to make a lifter for a single manned capsule that can achieve 8000-12000 delta-v for an atmospheric ascent from Eve with under 50-80 tons of weight respectively. If I can hit the 50 ton mark, the transfer vehicle required to get it there and subsequently the lifter to get it off Kerbin will be dramatically reduced.

What you could do is to have the ship probed controlled and pilot hang onto ladder on the way up. Leave the capsule on the return vehicle waiting in orbit.

Or wait till 0.20 for seats.

[Colonel_Panic]

What you could do is to have the ship probed controlled and pilot hang onto ladder on the way up. Leave the capsule on the return vehicle waiting in orbit.

Or wait till 0.20 for seats.

Lol, that's officially the cheapest idea I've ever heard for this... I like it.

That said, I'd rather do this right I do leave my return vehicle with engines and fuel probed in orbit though, so all I have to do is reach orbit with the capsule and a docking port, then re-attach to the return vehicle and burn home. Saves the weight of carrying a nuclear engine and a small tank's worth of fuel down to the surface and back up again.

[Nao]

@Colonel_Panic

To my knowledge The lowest mass of a ship with a pod that was managed to get off the surface of eve was ~44t stock. There was a Smallest Eve Ascent Vehicle (SEAV) challenge on the forums if you want to get some ideas. But that was from the highest possible location on Eve.

I would say 100-130ton for a lander would be more realistic number if you want to make a full mission (more redundancy and realism) and maybe even land near oceans.

I don't want to spoil much but if you want i can share a lot of tricks on Eve operations.

[birrhan]

I would say 100-130ton for a lander would be more realistic number if you want to make a full mission (more redundancy and realism) and maybe even land near oceans.

I don't want to spoil much but if you want i can share a lot of tricks on Eve operations.

Go on....

Seriously, not to derail the discussion, but I am very curious about attempts to get a 3 person craft to Eve's surface and back. Most trips are 1 Kerbal trips. I've been trying to use Engineer to predict dv on Eve, and the best I can do about 180 tons at 8000 dv or so. Is there a link for that?

[Temstar]

Go on....

Seriously, not to derail the discussion, but I am very curious about attempts to get a 3 person craft to Eve's surface and back. Most trips are 1 Kerbal trips. I've been trying to use Engineer to predict dv on Eve, and the best I can do about 180 tons at 8000 dv or so. Is there a link for that?

The trick is no command pod - the Kerbals ride the rocket back to orbit while clinging onto ladders.

If my memory was correct the smallest stock SERV was somewhere around 17 tons and could return two crew back if landed on a 6.5km mountain top. It used combined normal asparagus staging and an ingenious "vertical asparagus staging" method where the core of the rocket itself was 4 stages but used the small orange radial engine and so was capable of firing all four stage engines at the same time. Each stage in the core was a 200L tank and had a fuel line that pumped fuel to the stage above it around the stack decoupler. It had around 7500m/s of delta-V.

[numerobis]

8km/s will not quite get you off the highest peak. Nao was managing with about 8600, but I couldn't quite make it with the same craft (one of these pilots is better than the other...)

[Temstar]

8km/s will not quite get you off the highest peak. Nao was managing with about 8600, but I couldn't quite make it with the same craft (one of these pilots is better than the other...)

No I'm pretty sure 7.5km/s is enough. I could get off with a bit over 9km/s from as low as an altitude of 4.7km.

[Colonel_Panic]

@Colonel_Panic

To my knowledge The lowest mass of a ship with a pod that was managed to get off the surface of eve was ~44t stock. There was a Smallest Eve Ascent Vehicle (SEAV) challenge on the forums if you want to get some ideas. But that was from the highest possible location on Eve.

I would say 100-130ton for a lander would be more realistic number if you want to make a full mission (more redundancy and realism) and maybe even land near oceans.

I don't want to spoil much but if you want i can share a lot of tricks on Eve operations.

I actually have a 140 ton lander in Eve orbit right now waiting to find a good place to put her down... whether she'll make it back up again though is anybody's guess. The ascent vehicle is only about 90 tons and carries 8300 atmospheric delta-v. It may depend a lot on how efficiently I staged the ascent, how well I do my gravity turn, and how well I pick and peg my landing spot, but I have only 100dv left to deorbit it before I dig too far into my landing deceleration tanks, so I need to be right on the money from a fairly long range. Like trying to drop a pickle into a barrel from 100,000m.

Edited May 16, 2013 by Colonel_Panic

[birrhan]

The trick is no command pod - the Kerbals ride the rocket back to orbit while clinging onto ladders.

If my memory was correct the smallest stock SERV was somewhere around 17 tons and could return two crew back if landed on a 6.5km mountain top. It used combined normal asparagus staging and an ingenious "vertical asparagus staging" method where the core of the rocket itself was 4 stages but used the small orange radial engine and so was capable of firing all four stage engines at the same time. Each stage in the core was a 200L tank and had a fuel line that pumped fuel to the stage above it around the stack decoupler. It had around 7500m/s of delta-V.

So I'm trying just that, and the fuel doesn't register between stages. No transfer is possible:

Incidentally, pictures of all these rigs would help IMMEASURABLY.

[Colonel_Panic]

might try connecting to the decoupler, not a truss.

[rakutenshi]

Not 100% sure but I think if you flip it around, with the truss on the source stage instead of the destination it might work.. alternately I've used the white hardpoints in similar circumstances, but sadly I'll tell you right now that design won't work, pendulum/tractor rockets in KSP will flip over and crash every time without a gimballing engine at the bottom

[Temstar]

Incidentally, pictures of all these rigs would help IMMEASURABLY.

Check out that delta-V

[birrhan]

Check out that delta-V

Indeed. but it's UGLY.

All kidding aside, I really want to put the command pod down. A "down and back". Like this one (that exploited the terrain going to 11000 m):

Also, how in the seven hells are you getting the fuel lines around the decoupler? For me, it always wants to connect to the decoupler.

[chiefsheep]

Also, how in the seven hells are you getting the fuel lines around the decoupler? For me, it always wants to connect to the decoupler.

One way I have found that works is to bolt one of the smallest fuel tanks (the Oscar-B I think) at each join and run a fuel line from the lower fuel tank into the Oscar, and then from the Oscar into the one above. Allows for routing around the decoupler.

[Temstar]

Also, how in the seven hells are you getting the fuel lines around the decoupler? For me, it always wants to connect to the decoupler.

Don't know, it just works for me:

Maybe the 200L tank is special?

[Colonel_Panic]

One way I have found that works is to bolt one of the smallest fuel tanks (the Oscar-B I think) at each join and run a fuel line from the lower fuel tank into the Oscar, and then from the Oscar into the one above. Allows for routing around the decoupler.

^This is the way I do vertical stack fuel routing, and a few other tricks (like routing around parts that are in the way between two tanks, or tanks and docking ports.)

That said, the game does treat the decoupler as a valid 'to' part for fuel transfer. If you connect a fuel line to a tank, and then the other end to a decoupler, it will provide that fuel to whatever the decoupler is attached to. Going up a stack rather than down though may be a bit more complicated because the decoupler is technically connected to the engine and not the tank above.