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Stage Separation (Was: Hot-Staging)
by
sanman
on 21 Jun, 2017 16:50
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Is it possible for to use hot-staging in order for an upper stage to gain extra delta-V by effectively springboarding off the lower stage?
What are the limits to the extent of which this can be done? What are the considerations here?
Why doesn't everybody do it?
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#1
by
Jim
on 21 Jun, 2017 16:54
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Is it possible for to use hot-staging in order for an upper stage to gain extra delta-V by effectively springboarding off the lower stage?
What are the limits to the extent of which this can be done? What are the considerations here?
Why doesn't everybody do it?
It does not provide extra delta V and it has some obvious drawbacks, especially for reusable vehicles.
See Titan II staging.
And it is called fire in the hole staging
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#2
by
envy887
on 21 Jun, 2017 20:33
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The main problem is exhaust impingement. To get any "springboard" effect, the exhaust from the upper stage has to impinge twice: first on the booster, then again on the upper stage.
The biggest gain is actually from eliminating gravity losses during the few seconds of coast. But a few seconds of coast ahead of a 400 second upper stage burn isn't enough make up for the drawbacks.
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#3
by
whitelancer64
on 21 Jun, 2017 20:44
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The Soyuz family of rockets actually does this. The 3rd stage ignites while the sustainer (2nd) stage is still firing, that's why the rocket has an open trusswork instead of a solid interstage.
The Proton, too.
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#4
by
Space Ghost 1962
on 21 Jun, 2017 21:15
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Zenit too:
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#5
by
whitelancer64
on 21 Jun, 2017 21:27
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Interesting! The Long March family, as well.
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#6
by
Sam Ho
on 21 Jun, 2017 23:01
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The other benefit is that you may be able to avoid adding ullage motors for propellant settling, since the stage ignites while it is under acceleration.
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#7
by
ulm_atms
on 21 Jun, 2017 23:11
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The other benefit is that you may be able to avoid adding ullage motors for propellant settling, since the stage ignites while it is under acceleration.
I was of the thinking that this was the only reason. By starting up while the other stage is firing, all of the fuel is in the right place to keep from getting a gas pocket in the line.
Are there any other reasons? I just can't think of any.
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#8
by
envy887
on 22 Jun, 2017 00:40
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The other benefit is that you may be able to avoid adding ullage motors for propellant settling, since the stage ignites while it is under acceleration.
Doesn't help much on stages that need 3-axis RCS/ACS already, since they double as ullage thrusters.
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#9
by
Jim
on 22 Jun, 2017 01:06
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The other benefit is that you may be able to avoid adding ullage motors for propellant settling, since the stage ignites while it is under acceleration.
That is the main reason for the technique.
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#10
by
SWGlassPit
on 23 Jun, 2017 14:32
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The other benefit is that you may be able to avoid adding ullage motors for propellant settling, since the stage ignites while it is under acceleration.
Doesn't help much on stages that need 3-axis RCS/ACS already, since they double as ullage thrusters.
But it does eliminate the chicken-egg problem of ensuring that RCS/ullage thruster propellants are also settled.
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#11
by
Lars-J
on 23 Jun, 2017 15:41
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The other benefit is that you may be able to avoid adding ullage motors for propellant settling, since the stage ignites while it is under acceleration.
Doesn't help much on stages that need 3-axis RCS/ACS already, since they double as ullage thrusters.
But it does eliminate the chicken-egg problem of ensuring that RCS/ullage thruster propellants are also settled.
RCS/ullage systems are almost always pressure-fed, so is no such chicken and egg problem in this case.
Anyway, hot staging appears to be going out of favor in newer Chinese and Russian launch vehicles. And there is no other nation that fields a current hot stage launch vehicle as far as I know. (India perhaps?)
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#12
by
Jim
on 23 Jun, 2017 16:00
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But it does eliminate the chicken-egg problem of ensuring that RCS/ullage thruster propellants are also settled.
those have bladders
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#13
by
JAFO
on 23 Jun, 2017 19:45
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Let's not forget the ultimate Fire in the Hole staring, the N-1. Dan shame we never got to see if it would have worked.
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#14
by
Space Ghost 1962
on 23 Jun, 2017 20:48
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Let's not forget the ultimate Fire in the Hole staring, the N-1. Dan shame we never got to see if it would have worked.
Wrong - we did see that it (N1) didn't work. (Not for such staging.)
Could it have been made to work? Eventually.
(And note that the upper blok's (above the third stage) are enclosed, so not necessarily handled the same.)
The last stages have the flight computer/avionics/GNC. The sole benefit is for the lower stages to potentially be more mass/propulsion efficient as in less mass in the expendable LV. A two stage vehicle does not get a benefit, especially if the US restarts, as it needs RCS/GNC/ullage (also, it is less efficient due to propulsion start causing the vehicle's direction to wander and more loss (cosine) induced in recovering the inertial state of the vehicle).
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#15
by
JAFO
on 23 Jun, 2017 21:24
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Let's not forget the ultimate Fire in the Hole staring, the N-1. Dan shame we never got to see if it would have worked.
Wrong - we did see that it (N1) didn't work. (Not for such staging.)
Could it have been made to work? Eventually.
I was speaking more in general terms of the N1 FitH staging itself, not the success of the entire vehicle. That's a whole 'nother thread.
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#16
by
Arch Admiral
on 24 Jun, 2017 06:09
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The first design to use this technique was Titan I, and it is known that the Soviet ICBM design teams got a detailed data package on Titan I from a GRU informant working for Martin. It was incorporated into the R-9A with some other Titan technology and spread from there to many Soviet designs. Oddly, it never appeared in later US boosters. For instance Saturn V had at least a dozen small solid-fuel motors for separation and ullage, each of which could have exploded and killed a mission. This is the only area where N-1 actually looks good by comparison.
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#17
by
MP99
on 24 Jun, 2017 07:41
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ISTM that one disadvantage is that any impulse from startup through to separation is lost.
Cheers, Martin
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#18
by
sanman
on 24 Jun, 2017 13:03
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The main problem is exhaust impingement. To get any "springboard" effect, the exhaust from the upper stage has to impinge twice: first on the booster, then again on the upper stage.
But why isn't it possible to engineer a vigorous piston effect, above and beyond mere exhaust impingement? Like a gas piston, or a bullet launching from a gun barrel. The idea would be for the separating stages to push away from each other with the highest possible impulse. Do the newer methods, like the pusher-rod on Falcon 9, offer the highest possible impulse at separation?
If you're not flinging your lower stage backward with maximum possible force, then you're missing an opportunity for useful momentum transfer to benefit upper-stage Delta-V.
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#19
by
Jim
on 24 Jun, 2017 13:21
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The first design to use this technique was Titan I
Wrong. Titan I did not use fire in the hole staging. It had staging solid motors that separated the stages.
Hence, the rest of your post is in doubt. Also, the Russians flew upper stages on the R-7 before the first Titan I launch.