Different staging techniques

[700NitroXpress]

So I wanted to know what types of staging techniques you guys use to get your craft into orbit or beyond. I have two right now that are personal favorites. There's asparagus with slack tank staging and air lifter to asparagus combo. The first image below is one of my original designs for a SSTO interplanetary rocket ship with a all in one lander attached to it. The staging was capable of getting the entire craft into orbit minus the solid fuel boosters without ejecting anything else. Then the entire craft could be refueled and sent to it's destination. However, I believe the TWR of this thing is relatively low and of course inefficient, but I've had this craft for a long time and haven't changed it until now.

This image is of my new asparagus lifter design that uses slack tanks that asparagus off of the main craft before getting to the core engines. Since the outer tanks are slack, I'm not loosing or maintaining my TWR, it's actually increasing at a linear rate as all of the slack tanks drop two by two. This means that I can power down the engines as I gain altitude and use less fuel to get an equalized TWR as when I launched. I think this saves fuel and you're not getting any deceleration at all when a tank runs out of fuel because there's no engine attached to it. This also helps the structural stability as it flies. This design has room for improvement, but it's not really necessary right now as the current lifter can get this 143 ton craft into orbit with half fuel to spare in the main tank at the end of the staging. Then I attach a engine configuration to the bottom to suit the crafts mission. The current craft can go to Moho and return to Kerban. It also went to Jool and made a successful landing on Lythe, but it is basically all out of fuel, however it was just the basic engine configuration with nothing on the lower docking port. It was a test flight.

Lastly there's my air lifter design. You can air lift a craft to about 22,000 meters, then fire the orbital engines at high altitude to achieve orbit. Shown here on my Duna Command Center below. I find this effective for lifting craft or stations into orbit with more than one main attachment point. I like using this whenever possible, but I do admit that it has some limitations on it's use and what kinds of craft can be fitted with it. But in some cases, this can be a very effective option to save on size if you're lifting oddly shaped craft or small craft into orbit that have multiple places to attach engines.

1. What do you guys think of these staging designs?

2. Do you have similar staging designs?

3. Share any staging techniques that you think are more effective or improvements to these (mainly the air lifter or the slack tank).

[celem]

Some cool designs you have there.

Firstly, yes I use asparagus heavily. Its a very efficient launch method, however I tend to have an engine on every tank that will drop, mainly to get it off the ground at kerbin. I tend not to use as much srb as you have there and drop some of my tanks on ascent. I have difficulties timing the srb seperations, if i have mainsails on all the tanks then my first LF tank drop comes before a large srb has burned, I can and do squeeze a few smaller srb's in for trickier payloads but it takes several launch runs to key the staging into the right order. Obviously the issue here is that you cant drop an empty tank if it has any kind of srb still running on it, it's TWR will rip past yours and so it tears up the side of the ship and causes problems. Neither do you want to wait out the srb, since you want rid of that empty tank (plus its mainsail)

I do like that you are able to srb the first design all the way to orbit, very efficient.

The air lifter is interesting. It seems to be carrying regular rocket engines so it is in effect a booster stage that then lets you launch from altitude. Highly efficient obviously, basically the same as an srb cluster that gets your launch craft high before igniting. The issue I have here is usually part count skyrocketing before I can get the lifter's TWR past 1 whilst carrying the rest of the gear. My solution to this is actually jet engines on my lifter. Since aircraft fuselage is very lightweight without oxidizer I build what amounts to a kerbin VTOL jet-skycrane. Deck the whole kit out in heavy air intakes and im usually able to get my launchers up around 15km with some serious eastward speed over ground. The main reason I started doing this was that it let me switch out some of my asparagus launch vehicle's rockets to aerospikes, which has led a couple of times to me having a considerable chunk of my mission's interplanetary dV still in the launcher stage after stable lko. Everytime this happens I redesign the mission profile, usually to something the payload is illfit for, but thats just me being stupid as a kerbal.

[Kasuha]

Asparagus staging is the most generic technique. You have a set of fuel tanks and an engine "below" each tank. When you stage, you drop an (empty) tank with an engine. Fuel lines pump fuel from lower stages to upper stages. By dropping fuel tanks you're getting rid of dead weight. By dropping engines you're modulating your thrust, which if designed properly allows you to ascend at full thrust without unnecessary losses to drag or time.

All other techniques are asparagus where you either don't put a fuel line between tanks (meaning you'll be carrying some empty fuel tank weight when you stage), don't put an engine below a tank (apply a "null engine"), or don't activate an engine (reducing your total thrust and thus TWR). That covers both onion staging and bamboo staging.

Staging using jet engines is just a sub-category of onion staging. You don't want to pump fuel from jet fuel tanks to rocket fuel tanks as you wouldn't have use for it there.

[SRV Ron]

An interplanetary design using both drop tanks and asparagus design. The asparagus launcher gets this into orbit and the drop tanks used by the LV-N for interplanetary burns.

Launcher;

Payload section;

[celem]

Staging using jet engines is just a sub-category of onion staging. You don't want to pump fuel from jet fuel tanks to rocket fuel tanks as you wouldn't have use for it there.

Yeah I learned that the hard way with my jetpowered lifter. If you fuel pump it across engine types then the ratios of LF to oxidizer get out of whack and you end up carrying around useless resources. You can use them within the jet engine stage obviously, but I find asparagus with jet engines to be inefficient, they wont give me altitude due to intakeAir anyway, its speed over ground I want from them, for which I want engine count really and therefore dont wanna drop any. Plus if the rig is carrying well over a hundred tonnes of launcher and payload then dropping jet engines is gonna really rapidly break my TWR

[Surefoot]

Using FAR, these methods are not really possible. Instead, regular stacks, procedural fairings..

[FuzzyLlama]

I like SRV Ron's design - asparagus stage the payload section for interplanetary voyages.

I have played with this a lot. But the best is to use vertical staging as well. If you take two fuel lines from your central lifter up to the first payload stages, you can burn your payload rockets all the way up. Then you have the option of using more efficient rockets with less thrust on your lifter, using less fuel, or whatever. Sometimes your payload tickets won't

[700NitroXpress]

An interplanetary design using both drop tanks and asparagus design. The asparagus launcher gets this into orbit and the drop tanks used by the LV-N for interplanetary burns.

Have you tried putting half of the fuel tanks of the launch stage on the outside as slack tanks and dropping that extra weight as the fuel drains out?

I like this design for an interplanetary probe or satellite.

[Geschosskopf]

I never do asparagus staging. I dislike asparagus; it tastes horrible and is a bit too far beyond realistic for my tastes. So, all I build is SSTO LOF lifters, although sometimes I need to add 2-4 SRBs for slightly overweight payloads.

The reason I do this is because I can't think of a single task in KSP (other than returning from Eve, and maybe not even that) that requires a mission payload weighing more 30-35 tons, including lander return fuel. And a transfer tug that can push such a payload anywhere in the system (except maybe Moho) doesn't weigh much more. So, my lifters are SSTOs capable of lifting about 40 tons by themselves and 45-50 tons with SRBs attached. Half carry payloads, half carry transfer tugs. Then I link these up in orbit into 2-part ships, which I send out in flotillas to the same destination in the same launch window.

[SRV Ron]

Have you tried putting half of the fuel tanks of the launch stage on the outside as slack tanks and dropping that extra weight as the fuel drains out?

I like this design for an interplanetary probe or satellite.

Usually, it is better to drop heavy engines with empty fuel and stay with a more even acceleration rather then risk compression failure from too much acceleration.

Here is one design that I will play with more by allowing the last asparagus stage to drop heavy engines so the remaining fuel can be used by the LV-N. Due to overheating, the LV-N is not used in the launch phase. It uses a booster ring for launch, then switches to a four place asparagus until orbit. Note how much fuel is left once orbit has been achieved. A small final stage is used to land the probe and is staged just prior to landing so thrusters alone control the final touchdown.

In orbit ready for interplanetary travel.

I have tested using stage-able engines. Fuel lines have to be run back to the engine from the center core stage. It does work.

[SpaceSphereOfDeath]

I put FL-400s on top of the rock-o-max SRBs

[SRV Ron]

Here is a asparagus payload design that works well. The drop tank LV-N, while giving much longer burn time, has nearly twice the delta V for the given weight of the engines. That is one case where the efficiency of the LV-N more then overcomes its inherent weight disadvantage. The launch stage is the same design.

Edited November 8, 2013 by SRV Ron

[700NitroXpress]

Usually, it is better to drop heavy engines with empty fuel and stay with a more even acceleration rather then risk compression failure from too much acceleration.

Very true, but here's the thing. If you choose to, you can throttle down as you drop the spent tanks. This allows you to maintain TWR while dropping the excess weight, without loosing the engines until the end. This also saves on fuel because the engines will use less fuel to maintain thrust as apposed to the other method. So if you throttle down as you stage slack tanks, you won't risk structural failure because you're manually maintaining the TWR and you're using less fuel to do so. Also there is that sudden deceleration jolt from engine flame out that can cause loss of velocity and potential structural failure if you have engines on all tanks.

Thoughts?

[700NitroXpress]

Here is a asparagus payload design that works well. The drop tank LV-N, while giving much longer burn time, has nearly twice the delta V for the given weight of the engines. That is one case where the efficiency of the LV-N more then overcomes its inherent weight disadvantage.

I love using tanks with these engines for inclination changes without burning fuel from the main tanks. Usually with heavily built rockets that are carrying a lander docked to them. They do have very good burn time for adjustment maneuvers.

[SRV Ron]

The updated LV-N core with the drop engines has been successfully flight tested. This design without the SRBs worked with sufficient fuel to justify the drop engines. Did the escape burn and still had lots of fuel left.

The 4 step modified asparagus design. Be advised, the staging is wrong. Refer to the orbit picture where the staging is correct.

Launch;

Orbit. The engines are dropped just before orbit and the LV-N used to finish circularizing.

Escape burn;

The SRB ring design as originally posted from 0.2101 built in 0.22

Launch, The SRBs reached over 5,000 meters at burnout.

In orbit, Note the extra fuel available, almost doubled.

The liquid fueled engines are most certainly needed for orbit, but, once achieved, the LV-N can do the work at over twice the efficiency.

Edited November 9, 2013 by SRV Ron
To warn of wrong staging in 1st design

[BrickedKeyboard]

Asparagus staging is the most generic technique. You have a set of fuel tanks and an engine "below" each tank. When you stage, you drop an (empty) tank with an engine. Fuel lines pump fuel from lower stages to upper stages. By dropping fuel tanks you're getting rid of dead weight. By dropping engines you're modulating your thrust, which if designed properly allows you to ascend at full thrust without unnecessary losses to drag or time.

All other techniques are asparagus where you either don't put a fuel line between tanks (meaning you'll be carrying some empty fuel tank weight when you stage), don't put an engine below a tank (apply a "null engine"), or don't activate an engine (reducing your total thrust and thus TWR). That covers both onion staging and bamboo staging.

Staging using jet engines is just a sub-category of onion staging. You don't want to pump fuel from jet fuel tanks to rocket fuel tanks as you wouldn't have use for it there.

Since fuel lines and struts have 0 mass, and you already have a decoupler attached to hold the jet engine onto your spacecraft, you could stick a rocket fuel tank on your jet engine booster and have it feeding fuel to a rocket stage. That way, when you stage separate, you drop off the empty tank.

Only tricky part is getting the size of the tank right.

[qm3ster]

Very true, but here's the thing. If you choose to, you can throttle down as you drop the spent tanks. This allows you to maintain TWR while dropping the excess weight, without loosing the engines until the end. This also saves on fuel because the engines will use less fuel to maintain thrust as opposed to the other method. So if you throttle down as you stage slack tanks, you won't risk structural failure because you're manually maintaining the TWR and you're using less fuel to do so. Also there is that sudden deceleration jolt from engine flame out that can cause loss of velocity and potential structural failure if you have engines on all tanks.

Thoughts?

You only need those extra engines if you are underspeed and have low TWR. In which case you wouldn't throttle. If you carry 3 engines and burn at 66% you will burn fuel at the same rate, and get the same thrust, but due to the higher mass have lower Fuel kg/dV efficiency, and TWR.

You should ideally never have to throttle down on ascent. If you are going too fast in atmosphere - take more payload. If you run out of fuel before orbit - take more fuel.

[Vanamonde]

Oopsie. This thread dates from a previous version of the game's aerodynamics system, and the discussions in it are no longer valid. The thread will be closed now to avoid confusing people.