Staging: Delay or "Fire in the Hole"?

[AdmiralSirJohn]

I'm just wondering how many of you, when staging a rocket, set the decouplers as separate stages or group them with the next engine, so that the engine fires as the decoupler releases (what NASA calls "Fire in the Hole")?

Personally, I prefer using the "Fire in the Hole" method.

[Xannari Ferrows]

I prefer having them separate, just for control reasons. Especially helpful in space.

[AdmiralSirJohn]

Good point. I've occasionally done that myself on rendezvous and docking launches.

[NathanKell]

There are considerable efficiency advantages to the "fire in the hole" method, and the disadvantages that come in real life aren't modeled in (stock) KSP.

[jkool702]

I use both - on my launching stages I tend to fire in the hole, but if the stage will be activated in space i tend to stage it separately.

[Rhomphaia]

Usually I go for Fire in the Hole on launch vehicles.

If I have an engine cluster covered with an inter-stage fairing then fire in the hole won't work.

[Signo]

"Fire in the hole" does not work properly if you need to decouple an interstage fairing too, you risk the "stowed engine" alert message. In this case I set up a "fairing in the hole" to make the engine activate properly.

Oh, well, ninja'd. Sorry guys, +1 Romphaia.

[StrandedonEarth]

I always rig for "Fire in the Hole!" and it has only burned me a couple of times, when I forget to kill throttle when I decide to stage off the burnt-out previous stage in orbit

[Orbital Vagabond]

I use both - on my launching stages I tend to fire in the hole, but if the stage will be activated in space i tend to stage it separately.

This is what I use. The fewer actions I have to take and fewer issues I have to attend to during launch, the better. I can focus on my trajectory that way. I also use fire in the whole for 2-stage landers. This way I can:

1- Deactivate the landing engine

2- Throttle to max

3- Press spacebar once

4- ???

5- Profit Orbit

In space, I take my time, so engines aren't activated after stages are dumped. In fact, I rarely activate anything via staging in orbit. I almost always right click.

[sumghai]

I configure the engines and decouplers on my vessels in the "Fire in the Hole" configuration, to keep my staging list as compact as possible. AFAIK, MechJeb's autostage allows you to specify a delay between pre- and post- staging, which apparently imparts a nice short delay between the decoupler jettison and the engine ignition.

[wumpus]

Vertical staging works fine (in KSP) for "fire in the hole". Once you branch out and have side-mounted boosters, you will find they will easily break things unless you *slowly* get free and then fire your rockets. Or you can go the Wackjob route and use fleas (or greater) as seperatrons and simply shove them out of the way.

[Ripper2900]

I usually think the opposite when dropping radial boosters. I want to get out of the way asap so the spent boosters don't hit my center stage. Going full throttle while separating spent radial booster does that. I usually also have a fin on those large boosters that "catches the wind" and helps them separate cleanly.

[ajburges]

Fire-in-the-Hole

Less stages means a shorter staging list. Even recoverable boosters are fine after I toast then.

Only my crazy TWR launchers could use coast time. They use radial boosters so the choice doesn't apply there.

[tater]

I have used delay with srb rockets in early career when I can tell that the twr is too high (drag the separation to a new stage after launch). I then can let it coast a little into thinner air.

[amorymeltzer]

I have used delay with srb rockets in early career when I can tell that the twr is too high (drag the separation to a new stage after launch). I then can let it coast a little into thinner air.

This. Depends on the rocket but in general:

1. Staging right after SRBs for the reason tater mentions

2. FitH throughout the atmosphere for efficiency/get the hell away from dangerous debris reasons

3. Staging in space because I like the control, especially when transitioning to a lander stage.

[Nothalogh]

I use both - on my launching stages I tend to fire in the hole, but if the stage will be activated in space i tend to stage it separately.

Yep, same here.

When fighting gravity and atmosphere at the same time every second counts

[Zyffyr]

As quite a few others have said already - FitH for my in-atmo staging and separated for in space.

[magnemoe]

Usually I go for Fire in the Hole on launch vehicles.

If I have an engine cluster covered with an inter-stage fairing then fire in the hole won't work.

Tue if satellite engine is covered by fairing you need to drop fairing and separate first.

[Juicy]

Generally FitH, though I do often conciously throttle down before seperating. Even if it's just because I want to see the change in speed from seperating, which is especially noticable when seperating the last stage before a tiny non-powered satellite.

[Broda]

Yep, same here.

When fighting gravity and atmosphere at the same time every second counts

+1 here.

However, I do sometimes rearrange staging while in space, i.e. in case I see I will need to ditch the stage mid-burn not to overshoot the node.

[Sharpy]

Both, depending on context. Sometimes, when separating radial stages I shut off the engine to let them clear the vicinity (one of my Asparagus launch stage subassemblies absolutely requires this: 3 outer stages fall just fine, then 3 inner come - 4th explodes on decoupling but it doesn't damage the main craft. 5th and 6th need to be separated at like 5% thrust.

I've also made a 2STO spaceplane (not really successful, though I need to try it with 1.0.3 aero) - the idea is the vessel is to be 100% recoverable: the separation is in almost-orbit, where the main "airplane" boosts to reach full orbit, then I switch to the launch stage for reentry. Anyway, the launch stage is a ring of jet boosters that go around the plane cockpit area, then a looong hull (mk2) that goes along the plane's bottom, and a big rocket engine on an MK2 to MK3 adapter so that center of thrust is flush with center of mass.

The process of separation looks really impressive as the airplane extricates itself from the ring of boosters, going in reverse on RCS and turning tail to a side to get past the hump on the back. Nope, bodywork doesn't come out unscratched.

[eddiew]

In atmosphere, FitH. The next engine kicking in gives a better chance of staying clear of the decoupled stage, even if you've managed to press the spacebar when there was still a little burn time left in it

If the current stage has burned out and the vessel is in vacuum, then separate, because there's no need to hurry.

[Sharpy]

I usually think the opposite when dropping radial boosters. I want to get out of the way asap so the spent boosters don't hit my center stage. Going full throttle while separating spent radial booster does that. I usually also have a fin on those large boosters that "catches the wind" and helps them separate cleanly.

The radial boosters *will* hit your center stage. But did you notice what's the unit of impact durability of components? m/s. If you go with your engines off, they will bounce off harmlessly. If you're going 20m/s relative to them when they bounce, things *will* explode.

The "untouchable" approach is difficult to execute. Accept that things will collide, bounce, scratch, just make sure they do it within allowable force, and things get much easier.

If you get better at that, you can accept controlled destruction of parts as an important aspect of the game.

I have a return/reentry vehicle with an mk3 passenger cabin, a cargo bay, a fuel tank just big enough to get back home, and a weak engine of good ISp. And *not enough parachutes* to slow it down to a safe landing speed.

The engine is the crumple zone. It explodes upon ground impact, producing just enough upward force to slow down the rest to a safe speed.

Damn the 1.0.3 new thermal model. Yesterday I was testing an abort sequence for my SSTO MK3, and couldn't get it right. The idea was to include a bunch of separatrons inside the cargo bay (just behind the cockpit) and make them fire into the walls. By destroying the cargo bay, the cockpit would get separated. OTOH yesterday I successfully made a cluster bomb. Lots and lots of separatrons on a liquid fuel fuselage, plus a strut with a couple separatrons aimed *into* the fuselage. As it explodes it frees the 100 or so separatrons attached to it, flying *roughly* in direction the thing was aimed.

Simply, an engine/solid fuel booster can change any part into a decoupler.

Edited June 24, 2015 by Sharpy

[Wallygator]

Too bad ullage motors have no place in stock KSP yet, as they would add another very interesting dimension to our staging events.

Not sure if there are any mods which mimic it...

[WeirdCulture]

Both. Fire in the hole at launch at the bottom stages, so i will not loose the continuous thrust, at higher stages i need more control.