-
Ullage, retro, and upper stage ACS Q&A
by
just-nick
on 14 Feb, 2009 21:56
-
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
-
#1
by
Jim
on 14 Feb, 2009 22:36
-
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
-
#2
by
Fequalsma
on 15 Feb, 2009 02:52
-
Which Saturn V manual are you referring to?
F=ma
-
#3
by
just-nick
on 15 Feb, 2009 04:54
-
-
#4
by
TrueGrit
on 16 Feb, 2009 03:33
-
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.
-
#5
by
Lee Jay
on 16 Feb, 2009 03:40
-
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?
-
#6
by
Antares
on 16 Feb, 2009 04:20
-
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.
-
#7
by
TrueGrit
on 16 Feb, 2009 04:25
-
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.
-
#8
by
Fequalsma
on 16 Feb, 2009 12:35
-
-
#9
by
Jim
on 16 Feb, 2009 13:00
-
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
-
#10
by
just-nick
on 16 Feb, 2009 14:29
-
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?
-
#11
by
just-nick
on 16 Feb, 2009 14:30
-
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?
-
#12
by
kevin-rf
on 16 Feb, 2009 15:16
-
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.
-
#13
by
TrueGrit
on 16 Feb, 2009 16:30
-
I believe all cryo stages use primarily propulsive vents during coast to manage propellant.
-
#14
by
Jim
on 16 Feb, 2009 16:45
-
Atlas and Delta use hydrazine thrusters. They try not to vent during coast
-
#15
by
TrueGrit
on 16 Feb, 2009 17:23
-
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."
-
#16
by
Jim
on 16 Feb, 2009 17:51
-
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
-
#17
by
just-nick
on 18 Feb, 2009 16:35
-
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
-
#18
by
Jim
on 18 Feb, 2009 16:51
-
-
#19
by
Nick L.
on 19 Feb, 2009 23:18
-
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...
)
)