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Ullage, retro, and upper stage ACS Q&A
by
just-nick
on 14 Feb, 2009 21:56
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Reading through the Saturn V manual, I'm struck by the careful attention paid to the very complex systems for retrothrust on expended stages, ullage control on upper stages, and attitude control on the S-IVB.
Now obviously physics hasn't changed a lot since then, but I don't hear as much about these systems on contemporary launchers (Delta II, Delta IV, Atlas V, Ariane V, Falcon, and all the other usual suspects). Can anyone share what sort of systems and configurations are used for these functions on the newer boosters? Thruster sizes, configurations, arrangements, etc. Are these systems considered less important -- just because we are more confident (and the Saturns were so overbuilt) with separation and propellant control? What kind of Delta-V requirements does a typical upper stage with an extended coast require?
Thanks,
--Nick
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#1
by
Jim
on 14 Feb, 2009 22:36
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Atlas V uses retro rockets and Delta Iv uses push off springs to achieve separation. Both use settling thrusters/jets that basically fire constantly during coast for prop management. This keeps the liquids stable and keep them away from the pressure relief valves.
Ullage rockets are seldom used
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#2
by
Fequalsma
on 15 Feb, 2009 02:52
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Which Saturn V manual are you referring to?
F=ma
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#3
by
just-nick
on 15 Feb, 2009 04:54
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#4
by
TrueGrit
on 16 Feb, 2009 03:33
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Every rocket must have and does have both separation systems, liquid level control systems, and coast steering systems. Each of these systems are fairly well developed by now. And are considered ancillary systems and as such not very well detailed in the marketing material.
That's not to say propellant management during coast is not considered critical. There also quite a lot of thermal management requirements that must be incorporated into the integrated sequences. But since a lot of these details are considered proprietary there will be little information publically available.
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#5
by
Lee Jay
on 16 Feb, 2009 03:40
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Atlas V uses retro rockets and Delta Iv uses push off springs to achieve separation. Both use settling thrusters/jets that basically fire constantly during coast for prop management. This keeps the liquids stable and keep them away from the pressure relief valves.
Ullage rockets are seldom used
Okay, I just have to ask. What is the difference between a settling thruster and an ullage rocket?
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#6
by
Antares
on 16 Feb, 2009 04:20
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Ullage rockets fire once and are expended. The settling thrusters are actually part of the ACS and are pitch or yaw motors when not fired in balance.
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#7
by
TrueGrit
on 16 Feb, 2009 04:25
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Nothing but a name thing... Comparing SIV-B to Delta and Centuar they all use the same pitch/yaw/roll control thrusters to provide axial thrust prior to engine start to force the propellant liquid to settle at the bottom of the tank prior to engine start. SII had single shot solids to due the same, but that's because it didn't have either spaceflight control thrusters or the need to restart.
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#8
by
Fequalsma
on 16 Feb, 2009 12:35
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#9
by
Jim
on 16 Feb, 2009 13:00
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Nothing but a name thing... Comparing SIV-B to Delta and Centuar they all use the same pitch/yaw/roll control thrusters to provide axial thrust prior to engine start to force the propellant liquid to settle at the bottom of the tank prior to engine start. SII had single shot solids to due the same, but that's because it didn't have either spaceflight control thrusters or the need to restart.
A little clarification. Saturn V S-IVB had ullage motors and axial thrusters. Saturn IB S-IVB had only ullage motors
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#10
by
just-nick
on 16 Feb, 2009 14:29
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Thanks everyone.
So I can understand why the Saturn IB version of the S-IVB ditched the aft-firing APS thrusters -- no need to reignite, no need to worry about propellant management after the initial burn.
But I also noticed that the S-II went from eight...to four...to none in number of ullage rockets.
The latest generation of upper stages seem to use comparatively tiny thrusters to settle propellants -- which I can understand after a long coast when things have had a chance to reach a steady state condition -- but right after the acceleration of stage one the sudden deceleration from residual atmospheric drag, jolting of springs and pyros, and with just a few little monopropellant puffers, it surprises me that all the fluids are where they need to be.
Are there other tricks?
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#11
by
just-nick
on 16 Feb, 2009 14:30
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Atlas V uses retro rockets and Delta Iv uses push off springs to achieve separation. Both use settling thrusters/jets that basically fire constantly during coast for prop management. This keeps the liquids stable and keep them away from the pressure relief valves.
What thrust levels are we talking? Over a long coast, wouldn't the propellant expenditure add up to something pretty significant? Or is this where propulsive venting thrusters come into play?
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#12
by
kevin-rf
on 16 Feb, 2009 15:16
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The latest generation of upper stages seem to use comparatively tiny thrusters to settle propellants -- which I can understand after a long coast when things have had a chance to reach a steady state condition -- but right after the acceleration of stage one the sudden deceleration from residual atmospheric drag, jolting of springs and pyros, and with just a few little monopropellant puffers, it surprises me that all the fluids are where they need to be.
Are there other tricks?
Full tank? Bubble is at the top of the tank at seperation and doesn't have time to work it's way south?
I thought the trick with centuar was there is enough LH boil off (Vents through the nozzle) during coast to keep the propellants settled good enough.
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#13
by
TrueGrit
on 16 Feb, 2009 16:30
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I believe all cryo stages use primarily propulsive vents during coast to manage propellant.
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#14
by
Jim
on 16 Feb, 2009 16:45
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Atlas and Delta use hydrazine thrusters. They try not to vent during coast
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#15
by
TrueGrit
on 16 Feb, 2009 17:23
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Got to disagree with you on that... While I'm not very familar with Centaur I know that DCSS vents both LO2 and LH2 during coast from propellenat conditioning. The LO2 vents thru a non-propulsive vent, but the LH2 vents thru a propulsive vent.
From DIV Planner's Guide: "Propellants are managed during coast by directing hydrogen boil-off through aft-facing thrusters to provide settling thrust, and by the use of the ACS, as required."
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#16
by
Jim
on 16 Feb, 2009 17:51
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Got to disagree with you on that... While I'm not very familar with Centaur I know that DCSS vents both LO2 and LH2 during coast from propellenat conditioning. The LO2 vents thru a non-propulsive vent, but the LH2 vents thru a propulsive vent.
From DIV Planner's Guide: "Propellants are managed during coast by directing hydrogen boil-off through aft-facing thrusters to provide settling thrust, and by the use of the ACS, as required."
I said they try not to vent vs that they don't vent
They have found that more use of the ACS is required because there isn't enough H2 for settling, since they are trying to minimize the need for venting, since it reduces performance.
Watch the next Atlas or Delta IV flight and you will see that the aft jets are almost on continuously. The display of the simulated upperstage in flight accurately portrays the thruster firings
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#17
by
just-nick
on 18 Feb, 2009 16:35
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Thanks.
Here's an interesting paper that I found that relates to the D-IV and slosh management.
http://sloshcentral.bbbeard.org/Refs/DeltaIVLaunchVehicle_PulseSettlingFinalPaper.pdfA big realization for me has been the idea that "continuous venting" isn't REALLY continuous. It is just a matter of capturing a little settling power out of the venting that you've got to do anyway.
On another note -- how is the Ariane's ACS and settling system put together? Didn't the Ariane IV's 4th stage use a GH2 system? I assume that's not at tank pressure (super low isp) so how's that work, then? And what about the ECA and ECB?
Thanks,
--N
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#18
by
Jim
on 18 Feb, 2009 16:51
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#19
by
Nick L.
on 19 Feb, 2009 23:18
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Thanks.
Here's an interesting paper that I found that relates to the D-IV and slosh management.
http://sloshcentral.bbbeard.org/Refs/DeltaIVLaunchVehicle_PulseSettlingFinalPaper.pdf
A big realization for me has been the idea that "continuous venting" isn't REALLY continuous. It is just a matter of capturing a little settling power out of the venting that you've got to do anyway.
On another note -- how is the Ariane's ACS and settling system put together? Didn't the Ariane IV's 4th stage use a GH2 system? I assume that's not at tank pressure (super low isp) so how's that work, then? And what about the ECA and ECB?
Thanks,
--N
WRT Ariane, I have heard reference to "cold gas thrusters" during their webcasts so I assume it is vented propellant on the ECA versions. I don't know about the others (and I don't want to go too far off topic...
)
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#20
by
Antares
on 21 Feb, 2009 16:15
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Cold gas usually refers to GN2. This would be as opposed to a biprop hypergol system or to a monoprop hydrazine system with a catalyst bed that causes exothermic decomposition.
BTW, this is a pretty good thread for the Q&A section. Anyone mind if I flag it for relocation over there? (or a mod can do it without me flagging it)
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#21
by
just-nick
on 21 Feb, 2009 23:40
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WRT Ariane, I have heard reference to "cold gas thrusters" during their webcasts so I assume it is vented propellant on the ECA versions. I don't know about the others (and I don't want to go too far off topic... )
I found this in the Ariane V user's manual - the reference to 4 GH2 thrusters for roll and four clusters of three GH2 thrusters does imply they are using vented propellant. Though the reference to O2 jets for longitudinal boost seems weird.
From what Jim says, though, the loss of propellant if you intentionally vent for RCS functions has a bigger cost (mass) than bringing along a monoprop system. There is an offhand reference in some documentation on the Vinci development that implies some sort of heat exchanger attached to the propellant vent system. Perhaps warming the vented gas to further pressurize it so you get some meaningful isp out of it?
Anyone know?
--N
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#22
by
just-nick
on 21 Feb, 2009 23:40
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BTW, this is a pretty good thread for the Q&A section. Anyone mind if I flag it for relocation over there? (or a mod can do it without me flagging it)
Sounds great to me. Wasn't sure where to start it and it has now taken on an international flavor anyway.
--Nick
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#23
by
Archibald
on 02 Dec, 2010 07:13
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A question for all experts here...
After the CSM-LM got away from the S-IVB, the spent stage ullage motors fired for a last time to move the large rocket body out of the way (either in heliocentric orbit or on a collision course to the Moon)
Does anybody know how much delta-V did the solid-fuel ullage motor provided to the S-IVB ?
thanks in advance...
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#24
by
madscientist197
on 02 Dec, 2010 08:22
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Surely it would have been venting of propellent from the upper stage?
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#25
by
Jim
on 02 Dec, 2010 10:12
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A question for all experts here...
After the CSM-LM got away from the S-IVB, the spent stage ullage motors fired for a last time to move the large rocket body out of the way (either in heliocentric orbit or on a collision course to the Moon)
Does anybody know how much delta-V did the solid-fuel ullage motor provided to the S-IVB ?
It was venting of the propellants through the J-2 that provided the delta V
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#26
by
Danderman
on 11 Jan, 2011 19:24
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During the 1980s, the Delta II upper (second) stage was uprated to some 10,000 lbs (heritage from the Apollo LM). The question is why the stage was wasn't uprated to the Apollo service module's 22,000 lbs, since the Delta II 2nd stage seemed puny compared with the first stage?
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#27
by
Jim
on 11 Jan, 2011 23:01
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During the 1980s, the Delta II upper (second) stage was uprated to some 10,000 lbs (heritage from the Apollo LM). The question is why the stage was uprated to the Apollo service module's 22,000 lbs, since the Delta II 2nd stage seemed puny compared with the first stage?
The thrust for the Aerojet AJ10-118K Transtage derived engine was 10Klb, TRW TR -201 LM derived engine was 9,850 lb.
The SM engine is a different branch of the AJ-10 family -138.
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#28
by
Danderman
on 04 Mar, 2011 15:42
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This not entirely On Topic, but I don't see a place for this type of question: when I look for Pegasus or Taurus stage masses, what is generally given is the motor mass. For example, Pegasus stage is an Orion 38 stage, so what is listed is the Orion 38 mass as given by ATK, but not the avionics ring, payload adapter, separation systems, ACS cold gas system, etc.
Is there a source of information for OSC vehicles that gives actual stage masses, and not the masses of motors as provided by ATK?
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#29
by
Boost
on 04 Mar, 2018 14:34
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Does anyone know why the Saturn-1B AS-209, displayed at the KSCVC Rocket Garden, has no ullage motors ?
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#30
by
Boost
on 04 Mar, 2018 17:24
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To be more precise, is it by design on the booster or did this model have those ullage engines some time in the past and had it removed for some reason ?
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#31
by
Jim
on 04 Mar, 2018 20:26
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To be more precise, is it by design on the booster or did this model have those ullage engines some time in the past and had it removed for some reason ?
It would have never had them. They are mounted just before going to the pad or at the pad, depending on the pad.
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#32
by
Boost
on 04 Mar, 2018 21:15
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Thank you. Any reason for this unusual process ?
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#33
by
Jim
on 05 Mar, 2018 02:06
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It is a standard process. They are solid motors. There are safety considerations.
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