How do rocket stage seperate in real life?

[Hyrogen]

I know that in Kerbal Space Program, we use seperators and decouplers to seperate empty stages, do launch vehicles uses them in real life? If so, what do they call them?

[NFUN]

Yes. Pyrotechnic fasteners (explosive bolts) are often used.

[peachoftree]

I know that decouplers are a real thing and called that IRL, but I'm not sure if real rockets use a sepratron-like system.

[Gaarst]

I'm pretty sure that real rockets do use "separatrons" for side boosters, and I know they use solid fueled retro-rockets between stages to push them away from the rocket after deocupling (at least Saturn V did).

You could probably find examples if you searched a bit, but I'm too lazy yo do it right now

[monstah]

and I know they use solid fueled retro-rockets between stages to push them away from the rocket after deocupling

Oh, by the way, I use those in KSP, too. Great for cheaply deorbiting circularization stages!

[NathanKell]

The interstage uses explosive bolts, yes. You usually also have retros on the lower stage, and ullage motors on the upper (unless you're hot-staging / doing fire-in-the-hole staging).

[Gaarst]

Oh, by the way, I use those in KSP, too. Great for cheaply deorbiting circularization stages!

I use Fleas boosters placed in "V" for decoupling my largest rocket stages (usually 7.5m from SpaceY Expanded). It just looks awesome !

(Will get a screenshot if I remember to ^^)

[Alshain]

The space shuttle SRB's did and their exhaust directly impacted the main tank and caused scorch marks without destroying it. (hint NathanKell )

[regex]

The space shuttle SRB's did and their exhaust directly impacted the main tank and caused scorch marks without destroying it. (hint NathanKell )

Do you see how slowly those boosters separate? You can mimic that in KSP by reducing the fuel load in your Seperatrons. They will then produce a much shorter, and thus less damaging when pointed at other tanks, burn. In this way, a semblance of realism can be preserved while also giving players a range of options to choose from.

[Mat2ch]

Hey, there's a whole Wikipedia article about this: https://en.wikipedia.org/wiki/Pyrotechnic_fastener

Also some fairings use springs to separate from the rocket.

[Alshain]

Do you see how slowly those boosters separate? You can mimic that in KSP by reducing the fuel load in your Seperatrons. They will then produce a much shorter, and thus less damaging when pointed at other tanks, burn. In this way, a semblance of realism can be preserved while also giving players a range of options to choose from.

If that works, somehow I doubt it. Damage is pretty instant in this game unless 1.0.5 is making a much bigger change than described. We'll see I guess.

[Hcube]

Do you see how slowly those boosters separate? You can mimic that in KSP by reducing the fuel load in your Seperatrons. They will then produce a much shorter, and thus less damaging when pointed at other tanks, burn. In this way, a semblance of realism can be preserved while also giving players a range of options to choose from.

... Are you aware that this is in slow-motion ? While it's true that SRBs used to separate slower than KSP boosters do, it's by far not this slow ! Just watch a real time video by a camera fixed on the SRB and you'll see how fast it is

Edited October 17, 2015 by Hcube

[Gaarst]

I guess the main issue with slow separation in KSP is the SRBs behaviour: at separation, the shuttle's SRBs had very low thrust, so they kinda stayed at the shuttle's level while slowly drifting off; in KSP, boosters go from 100% to 0% in an instant. So the booster will most likely "fall" behind the rocket and hit its bottom if it doesn't get away from the rocket fast enough.

[Corw]

I guess the main issue with slow separation in KSP is the SRBs behaviour: at separation, the shuttle's SRBs had very low thrust, so they kinda stayed at the shuttle's level while slowly drifting off; in KSP, boosters go from 100% to 0% in an instant. So the booster will most likely "fall" behind the rocket and hit its bottom if it doesn't get away from the rocket fast enough.

If you are losing your main stage engines to boosters, you are placing both your decouplers and sepatrons wrong.

[Alshain]

If you are losing your main stage engines to boosters, you are placing both your decouplers and sepatrons wrong.

You haven't kept up with the devnotes. In 1.0.5 they are going to be more damaging if the plume impacts an object and according to NathanKell you have to "aim them carefully". Not only is that unrealistic as evidenced by the video but it isn't something not easy to do in the editor. Simply using sepatrons to separate boosters mounted on a TT-38K will have the plume impacting the main tank, if that plume is going to now destroy the tank, sepatrons will be severely limited in use. Because damage in the game is instant, unless that has changed too, the moment the plume touches, it will be destroyed.

Edited October 16, 2015 by Alshain

[Vanamonde]

Since this question is about real rocketry rather than the game, the thread has been moved to Science Labs.

[InsaneDruid]

I'm pretty sure that real rockets do use "separatrons" for side boosters, and I know they use solid fueled retro-rockets between stages to push them away from the rocket after deocupling (at least Saturn V did).

You could probably find examples if you searched a bit, but I'm too lazy yo do it right now

Especially russian designs act a bit different. For example the sojus boosters are more or lest just "slotted" in the central stage so that they can fall off. The straps that connect them to the central stage are cut, the remaining thrust tilts the boosters so that their lower end swings out, and then the nose of the boosters are pushed away from the core by venting oxidizer. Also russian designs often don't use ullage motors but use an open truss-like interstage. That way the next stage fires when the lower one is still active, followed by MECO and separation. You find this design on the Sojus, the Proton (first/second stage with large truss interstage and also second/third stages where the vernier engines of s3 fire before separation and their exhaust gases flow through little openings in the interstage), the N1, the Zenit..

[regex]

If that works, somehow I doubt it. Damage is pretty instant in this game unless 1.0.5 is making a much bigger change than described. We'll see I guess.

Heat is not instantaneous, and that will be the source of damage from exhaust. If you exhaust for a shorter time, less heat will be applied.

... Are you award that this is in slow-motion ? While it's true that SRBs used to separate slower than KSP boosters do, it's by far not this slow ! Just watch a real time video by a camera fixed on the SRB and you'll see how fast it is

Even so, the burn time on those separation motors is probably very small. What you're seeing is likely just residuals. It's also worth nothing that those separators are not pointed directly at the tank; it is being scorched by indirect exhaust.

Milliseconds after SRB separation, 16 solid-fueled separation motors, four in the forward section of each SRB and four in the aft skirt of each SRB, are fired for just over one second to help carry the SRB's away from the rest of the Space Shuttle. Each of the separation motors can produce a thrust of about 22,000 pounds.

Bottom line: Don't point your separatrons directly at the core, or reduce their fuel to enough for clearance. No problems.

[Shrike99]

Just like to add that SpaceX uses Pneumatic separation, rather than Pyrotechnics.

This is a different, interesting approach, that is focused on re-usability, but more complicated and heavy iirc.

[YNM]

Slightly related question : does the engine fairing supports all the weight above it ? Or the engines ? Or some other specialized structural parts ? I mean, if it's really the fairing, wow then Saturn V second stage engine fairing or any other more than 2 stage rockets must be very sturdy...

[InsaneDruid]

The engines aren't involved in connecting the stages and its the interstage that bears the load. (Unlike in KSP where you attach the decoupler to the engine). Here is an image of the interstage truss structure of a russian N1 moon rocket, now converted to a shelter (along with a part of a fairing as roof). But not only the instagestage carries the load of acceleratin the upper stages, its the skin of the tanks, too. Sometimes, if they are too week, the tanks are pressurized to keep them stiff and from collapsing, sometime even from their own weight.

Its also notworthy that IRL normally you won't normally find the centered, rather punktual attachment points used in KSP. You always want to distribute the force outwards onto the skin of the rocket using cones or cone-shaped structure. So there are no wobbly rockets in real rocketery. For example, take the donut-shaped droptank of the breeze-m upperstage. It surrounds the core of the breeze. The rocket itself (third stage o the proton) connects to the lower, outer side of the droptank. The core attaches to it on the top, inner side. To avoid shearing the tank there are conic load-bearing structures in the tank, connecting the inner, upper wall to the lower outer wall and thus guiding the forces. You can see them in this image, its the diagonal lines on the left part of the image, inside the donut shaped tank structure. (Left of the arrow from "additional tank structure").

The speltra and syltra payload adapters for ariane 5 are also good examples.

[Nibb31]

Slightly related question : does the engine fairing supports all the weight above it ? Or the engines ? Or some other specialized structural parts ? I mean, if it's really the fairing, wow then Saturn V second stage engine fairing or any other more than 2 stage rockets must be very sturdy...

On the Saturn V, the SLA (Saturn LM Adapter, the shroud around the LEM) supported the entire weight of the CSM throughout launch. The CSM was attached to the top of the SLA panels (with pyro bolts). The LM was attached to the base of the SLA. The early versions were hinged, so that the panels would stay attached to the S-IVB. However, during Apollo 7, they became concerned that the panels might become an obstacle for the docking and extraction of the LM, so they switched to spring loaded detachable panels. After the panels were jettisonned and the CSM was detached, the CSM docked with the LM and another set of pyros separated the LM from the base of the SLA.

Other than pyro bolts, Apollo also used guillotines. These were basically heavy pyro-powered blades that would cut through the wires and sever the wiring and plumbing between modules. There were guillotines between the LM and the S-IVB, between the CM and the SM, and between the LM ascent and descent module. Without the guillotines, the separation would fail, causing a catastrophic failure.

Edited October 17, 2015 by Nibb31

[magnemoe]

If that works, somehow I doubt it. Damage is pretty instant in this game unless 1.0.5 is making a much bigger change than described. We'll see I guess.

In KSP the only place seperators are dangerous is then the part is already overheating, the 1x2 engine adn tank combination tend to run very hot and is in danger for this, LV-N after long burns too however this will only happen i deep space so you can power down an rotate the ship to drop tanks.

Did not know about the changes in separation behavior. Tend to use two angled anyway. We should have some smaller ant like cold gas seperatrons to, the current ones are overkill for most uses, you only need the full power for huge designs.

Note that this can be used to our benefit. Put seperatror on core stage, use it to blow up the booster to avoid any seperation problems

Edited October 17, 2015 by magnemoe

[Hcube]

Just like to add that SpaceX uses Pneumatic separation, rather than Pyrotechnics.

This is a different, interesting approach, that is focused on re-usability, but more complicated and heavy iirc.

But it has never failed them yet (as far as i know), and they have launched quite a number of rockets, so that looks somehow safe...

[Corw]

You haven't kept up with the devnotes. In 1.0.5 they are going to be more damaging if the plume impacts an object and according to NathanKell you have to "aim them carefully". Not only is that unrealistic as evidenced by the video but it isn't something not easy to do in the editor. Simply using sepatrons to separate boosters mounted on a TT-38K will have the plume impacting the main tank, if that plume is going to now destroy the tank, sepatrons will be severely limited in use. Because damage in the game is instant, unless that has changed too, the moment the plume touches, it will be destroyed.

I was talking about seps in current version.