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#200
by
Tass
on 29 Sep, 2013 20:15
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I wonder if the first stage ACS ran out of gas to overcome the torque of the turbopump because the flight duration was longer than the Grasshopper flights.
As was wondering on another thread what might have started the roll and what you suggest makes a lot of sense.
Again, M1D turbopump exhausts straight down, so it doesnt create any roll torque. And at any rate per Elon's twitter the spin up was cause by aerodynamic torque:
https://twitter.com/elonmusk/status/384407846349062144
The exhaust might not - but what about the pump itself? lot's of things spinning in there, right?
( please note - I don't say that it was the cause, just that it might be a factor. Elon certainly states that aero-induced forces where the main cause, instead of the pump torque. )
Conservation of angular momentum. If it aint leaving the rocket it has only a one time effect when starting, not a cumulative one.
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#201
by
Antares
on 29 Sep, 2013 20:19
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Ugh, viscosity. Learn some real physics.
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#202
by
cambrianera
on 29 Sep, 2013 20:26
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Ugh, viscosity. Learn some real physics.
Hmm, viscosity requires that the roll movement started sometime before relight, to be trasmitted to the propellant.
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#203
by
R7
on 29 Sep, 2013 20:31
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Did the first stage fly neatly backwards except for the roll, or did it wobble? How did engine exhaust(s) (main & TP) flow around rear end? Lots of unknowns to be revealed by telemetry and video. I hope the public version will show the second relight.
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#204
by
Antares
on 29 Sep, 2013 20:48
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Ugh, viscosity. Learn some real physics.
Hmm, viscosity requires that the roll movement started sometime before relight, to be trasmitted to the propellant.
Inside the turbopump.
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#205
by
sanman
on 29 Sep, 2013 20:52
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Sorry, if this has already been covered, but when is that SpaceX post-launch news conference? I keep surfing around the SpaceX site, and hope I haven't missed it.
Nextly, regarding the aero-torqued fuel -- would the stuff purely show torque/centrifugal motion, or would it likely be sloshing around too?
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#206
by
JBF
on 29 Sep, 2013 20:53
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Sorry, if this has already been covered, but when is that SpaceX post-launch news conference? I keep surfing around the SpaceX site, and hope I haven't missed it.
Nextly, regarding the aero-torqued fuel -- would the stuff purely show torque/centrifugal motion, or would it likely be sloshing around too?
It already happened, it was a teleconference.
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#207
by
cambrianera
on 29 Sep, 2013 20:54
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Ugh, viscosity. Learn some real physics.
Hmm, viscosity requires that the roll movement started sometime before relight, to be trasmitted to the propellant.
Inside the turbopump.
No, inside the tanks.
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#208
by
smoliarm
on 29 Sep, 2013 20:55
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Sorry, if this has already been covered, but when is that SpaceX post-launch news conference? I keep surfing around the SpaceX site, and hope I haven't missed it.
...
It's over, it was covered by Jeff Foust on twitter
https://twitter.com/jeff_foust
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#209
by
Antares
on 29 Sep, 2013 20:59
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Ugh, viscosity. Learn some real physics.
Hmm, viscosity requires that the roll movement started sometime before relight, to be trasmitted to the propellant.
Inside the turbopump.
No, inside the tanks.
That wasn't a question.
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#210
by
cambrianera
on 29 Sep, 2013 21:01
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Ugh, viscosity. Learn some real physics.
Hmm, viscosity requires that the roll movement started sometime before relight, to be trasmitted to the propellant.
Inside the turbopump.
No, inside the tanks.
That wasn't a question.
Only a inaccurately written statement then?
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#211
by
sanman
on 29 Sep, 2013 21:08
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It's over, it was covered by Jeff Foust on twitter
https://twitter.com/jeff_foust
Thanks for that
So Musk tweeted
Elon Musk @elonmusk 56m
Rocket booster relit twice (supersonic retro & landing), but spun up due to aero torque, so fuel centrifuged & we flamed out
Elon Musk @elonmusk 43m
Between this flight & Grasshopper tests, I think we now have all the pieces of the puzzle to bring the rocket back home.
What exactly is the solution to this? When the fuel centrifuged, how did that cause the flameout? Did it somehow interfere with the turbopump's ability to draw in fuel?
Is the best way to solve the problem by countering the aero-torque as it occurs? I'm assuming this refers to rotation around the booster's long axis. Or can you put up with the aero-torque and just implement some counter-measure at the turbopump side?
If you have to counter the aero-torque, then does this require some extra new thruster, or can the existing octoweb/center-engine be tweaked to stop the roll on the way down?
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#212
by
Jason1701
on 29 Sep, 2013 21:09
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It's over, it was covered by Jeff Foust on twitter
https://twitter.com/jeff_foust
Thanks for that
So Musk tweeted
Elon Musk @elonmusk 56m
Rocket booster relit twice (supersonic retro & landing), but spun up due to aero torque, so fuel centrifuged & we flamed out
Elon Musk @elonmusk 43m
Between this flight & Grasshopper tests, I think we now have all the pieces of the puzzle to bring the rocket back home.
What exactly is the solution to this? When the fuel centrifuged, how did that cause the flameout? Did it somehow interfere with the turbopump's ability to draw in fuel?
So is the best way to solve this by countering the aero-torque as it occurs? I'm assuming this refers to rotation around the booster's long axis. Or can you put up with the aero-torque and just implement some counter-measure at the turbopump side?
If you have to counter the aero-torque, then does this require some extra new thruster, or can the existing octoweb/center-rocket be tweaked to stop the roll on the way down?
The turbopump can only draw in fuel if the lines leading to it are filled with fuel, which is not the case if the fuel is centrifuging out to the walls of the tank.
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#213
by
clongton
on 29 Sep, 2013 21:13
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Centrifuging fuel/oxidizer tanks move propellant out of the sump at the bottom of the tank, causing the same condition as an empty tank, as far as the pumps are concerned. That's what "flame out" means: a running propellant turbo pump becomes starved for fuel and the engine dies.
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#214
by
Antares
on 29 Sep, 2013 21:15
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1) Propellants well settled. Single engine starts. Heavy rotor spinning several thousand RPM in one direction.
2) All ACS gas gone to overcome rolling torque due to viscous and rolling friction forces inside the single-shaft turbopump transmitting roll torque to the housing and therefore the entire vehicle.
3) Roll moment imparted to the vehicle draws propellant out of the sumps, up the walls. Engine starved.
I'm not getting paid enough to explain this.
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#215
by
sanman
on 29 Sep, 2013 21:18
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Thanks, gentlemen - somehow I pictured some kind of vortex forming from the spinning, sending an overdose of fuel to the turbopump. Oops - my bad.
So under the current "uncorrected" setup, is centrifuging pretty much guaranteed to happen? Like, could you somehow make it work for you? Could you just put some extra fuel lines on the outer edges where the fuel will centrifuge to, and then suck from there? Or is it better to try and stop the centrifugation?
Damn pesky degrees of freedom - leave one in there unnoticed, and it gets abused!
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#216
by
slavim
on 29 Sep, 2013 21:19
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There are viscous forces and rolling friction inside a turbopump that tend to spin whatever is holding it in the opposite direction.
If that was the case, they would've tested it with Grasshopper and found a solution for it.
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#217
by
aero
on 29 Sep, 2013 21:20
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well, the Kerbel solution is fins. Aerodynamic control surfaces.
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#218
by
clongton
on 29 Sep, 2013 21:21
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There are viscous forces and rolling friction inside a turbopump that tend to spin whatever is holding it in the opposite direction.
If that was the case, they would've tested it with Grasshopper and found a solution for it.
Grasshopper never experienced the kinds of aerodynamic loading that induced the spin.
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#219
by
LucR
on 29 Sep, 2013 21:21
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There are viscous forces and rolling friction inside a turbopump that tend to spin whatever is holding it in the opposite direction.
If that was the case, they would've tested it with Grasshopper and found a solution for it.
Grasshopper held much more fuel at this point (ballast) which might have countered or at least lowered the effect through pure mass inertia.
