When do you stage your rockets?

[Fourjays]

I've been pondering about doing my launches manually again (only thing I've really used MechJeb for) and was thinking about how to solve the problems that invariably end up causing me frustration (slow movement of huge rockets when attempting to target an inclination or circularize). Which in turn got me wondering, just when should I drop a rocket stage? When it is out of fuel? Or when it has served its designed purpose (i.e. getting to LKO)? I would guess the answer is a bit of both (I shouldn't have enough fuel remaining to worry about), but I then thought it would be interesting to find out what others do.

So, when do you stage your rockets?

[SalmonellaDingDong]

Out of fuel.

[Van Disaster]

I have pretty uncomplicated rocket designs - for a large rocket usually a main lifter stage with a payload attached, and a pair of radial tanks with some small propulsion. Radial tanks go when they're empty, and the payload is thrown out when it's where it's meant to be; hopefully there's enough fuel left to deorbit the lifter. Given my lifter gets to obscene TWR levels when it's low on fuel ( to the point where I worry about it breaking payloads ) I'm not inclined to make matters any more complicated, so any heavier loads would probably get bigger engines on the side tanks, and more fuel on the side tanks too.

I have been trying to drop stages while I'm still reasonably vertical but rotating the rocket so the outer stages are still horizontal when the turn starts makes that less necessary.

[oggylt]

when periapsis reaches 30km

[Francesco]

usually "out of fuel" and "it has served its purpose" tend to coincide.

[Flixxbeatz]

When the booster stage is out of fuel (primarily during launch). If in orbit, I'll just leave it intact for a while, until I've either decided to boost it to higher orbit or detach it already.

[SunJumper]

I usually engineer my rockets such that the first stage gets the rocket a decent way into the turn, the second does the orbital insertion, the third does the escape burn, and depending on the payload, the transfer burn, and the fourth usually does the rest.

If the payload is particularly big, the first gets to 10km, the second and third do the turn, and the third finishes the orbit, with the fourth doing the other operations.

[Felsmak]

That depends on the situation. If I'm feeling confident that the next stage will be able to complete its task on its own, I'll stage when the current stage has served its purpose. However, I always let the ground stage use up all of its fuel before I drop it. Just in case.

[Tw1]

While not so much of an issue at launch, as all your lifter's stages should all have a TWR of at least 1. Unless a problem happens, you might as well make us of all the fuel you've got.

When landing, it's a different story.

I fired of this transfer stage when landing on Moho because the hybrid ion engines did not have the thrust to stop me in time to land at the site I was aiming for.

(Duney just had to go out and have a look...)

Really, I should've started the burn earlier.

Any stage that will hinder the rest of the mission should be dropped. If not, keep it.

[ComradeGoat]

Quite often I keep my final Mainsail stage hanging around with the Mainsails deactivated to use as drop tanks for the LV-N stage, and also to give a "kick" out of LKO into my transfer orbits (with the Mainsails on), so I don't do have to do it over several orbits. I deliberately design my rockets so that they reach orbit with a bit of non-payload fuel left for precisely this reason.

Only issue is, as someone else said, using full thrust with those big engines on can be quite dangerous: 5G acceleration is often not appreciated!

This does have the disadvantage of leaving interplanetary space littered with debris acting as Kerbin crossing asteroids.

[Fendleton]

I tend to drop my final orbital-insertion stage while it still has fuel in it. It allows me to recover from a problem with spare fuel if I need to, and it means I can easily de-orbit the stage when it's ejected, rather than have it clog up LKO.

Alternatively, I use a single-stage+SRB-to-orbit design to lift lighter vehicles into circular orbits, which I then de-orbit in one piece and parachute back down to the KSC. Either way, I usually have fuel left in the tanks.

Of course, for some vehicles where I don't care about debris, I'll use all the fuel I can get so I can reach a destination. They're the oddity rather than the rule however.

[EndlessWaves]

It makes no sense to drop partially full stages, if you've still got fuel remaining then remove fuel tanks until you don't. It'll make the rest of your rocket lighter and more structurally solid.

The only exception is when you can't fit a small enough fuel tank, this is typically when using jet engines on a lightweight craft.

[Nimaci]

Only when that stage is spent/deployable and/or suborbital/deorbitable.

[Francesco]

a couple of tips on staging:

1. by designing side boosters so that they pack ~1500 m/s of delta-v, you can drop them off just before the start of a 10km gravity turn, enhancing the maneuverability of your ship

2. while circularizing a Low Kerbin Orbit, it takes only ~50 m/s more to raise the periapsis from 20 to 70 km.

on Kerbin, any object travelling below 23 km is deleted.

you can therefore watch your PE raise, stage as it reaches 20-22 km, and complete the orbit with the engines on your payload, without the need of de-orbiting the upper stage.

[drakesdoom]

I use KW for larger booster and my goal for a lifter is around 2000 delta v in solid booster lift stage, with 2500 delta v on a high thrust engine doing the LKO insertion. Not the most efficient I am sure but very reliable as the boosters are drooped around 10k before turn and the insertion stage is dropped at around 10km pe. Simple things do not break as much no matter how you look at it.

[RoboRay]

Drop a booster stage with Pe below 22km, if it's almost empty, to ensure it doesn't become spacejunk.

If you've got enough fuel left to reach orbit, hopefully you've also got a probe pod and battery on the booster so you can deorbit it with the left-over fuel after discarding it. It takes very little fuel to to this, as the booster will be very light with no payload and nearly empty fuel tank, and you only have to get the Pe below 22km.

Drop a transfer-stage on a course that impacts the destination world, so it also doesn't become spacejunk. Then, steer clear of the impact trajectory with your craft.

[Tw1]

I tend to complete orbit with my transfer stage, so I tend not to get debris around Kerbin.

[astocky]

I try to drop the stages either when they run out of fuel, or just before I get into a stable orbit (whatever happens first). I have not traveled successfully to the Mun yet, but I believe the plan is to deorbit the transfer stage so it crashes into the Mun as well. In case you can't tell, I am trying to do what I can to minimize the space debris.

[magnemoe]

Quite often I keep my final Mainsail stage hanging around with the Mainsails deactivated to use as drop tanks for the LV-N stage, and also to give a "kick" out of LKO into my transfer orbits (with the Mainsails on), so I don't do have to do it over several orbits. I deliberately design my rockets so that they reach orbit with a bit of non-payload fuel left for precisely this reason.

Only issue is, as someone else said, using full thrust with those big engines on can be quite dangerous: 5G acceleration is often not appreciated!

This does have the disadvantage of leaving interplanetary space littered with debris acting as Kerbin crossing asteroids.

I often do the same, but dependent on fuel left, if its just an fraction I tend to drop during circulating. Another option is to give the stage an small probe core and four small solar panels and drop it with 50 dV left. this is enough to deorbit it with an high AP who is typical for transfer stages.

If not transfer stages is usualy used for the deorbit burn.

[ComradeGoat]

I often do the same, but dependent on fuel left, if its just an fraction I tend to drop during circulating. Another option is to give the stage an small probe core and four small solar panels and drop it with 50 dV left. this is enough to deorbit it with an high AP who is typical for transfer stages.

If not transfer stages is usualy used for the deorbit burn.

If it's a long mission, to Jool or further, I'll refuel the penultimate stage in orbit and use it to resupply the station where I'm going (assuming there is one!). Fuel tanker + mission ship for the price of one!