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#180
by
simonbp
on 29 Sep, 2013 18:57
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As designed, they were. I meant when they did the "OMS Assist" and ignited the OMS during ascent.
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#181
by
mlindner
on 29 Sep, 2013 19:27
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Musk: rolling "centrifuged" propellant, shut down engine early. Did recover "portions" of 1st stage after splashdown. #falcon9
First I've ever heard of centrifuged propellant causing a shutdown. This has probably happened before somewhere though, does anyone know?
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#182
by
ugordan
on 29 Sep, 2013 19:28
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Jeff Foust @jeff_foust 44s
Musk: attempted relight of upper stage, encountered anomaly. Understand what it is and will fix before next flight. #falcon9
Re-light is a must for the SES flight. Wonder if this will delay it.
Or cause a switch to Thaicom first, depending on how risk-averse SES is? Is that even an option or is Thaicom also predicated on successful demontration of a relight?
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#183
by
HMXHMX
on 29 Sep, 2013 19:29
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Musk: rolling "centrifuged" propellant, shut down engine early. Did recover "portions" of 1st stage after splashdown. #falcon9
First I've ever heard of centrifuged propellant causing a shutdown. This has probably happened before somewhere though, does anyone know?
Probably means the tank sump was uncovered and the engine was breathing fumes. He tweeted that the stage was rolling since ACS control authority was inadequate.
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#184
by
R7
on 29 Sep, 2013 19:38
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First I've ever heard of centrifuged propellant causing a shutdown. This has probably happened before somewhere though, does anyone know?
Falcon 1 flight 2 comes to mind.
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#185
by
mlindner
on 29 Sep, 2013 19:40
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Jeff Foust @jeff_foust now
Musk: will next attempt recovery on 4th F9 v1.1 launch, of CRS-3. That vehicle may also have landing legs. #falcon9
Well now, THATS interesting... So CRS-3 is definitely volume limited, and they're going to test landing legs right on orbit? I guess they're assuming grasshopper 2 will be flying before CRS-3?
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#186
by
ugordan
on 29 Sep, 2013 19:41
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First I've ever heard of centrifuged propellant causing a shutdown. This has probably happened before somewhere though, does anyone know?
Falcon 1 flight 2 comes to mind.
I always wondered if the roll on the maiden F9 2nd stage was the culprit that prevented a restart, using up all ACS gas just to try and kill the roll.
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#187
by
Jarnis
on 29 Sep, 2013 19:42
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Too bad the 1st stage recovery failed. This also probably means we don't get to see a video of it as SpaceX probably doesn't want to show off failures
...even if it had to get pretty low before things went bad - as I understand it, center engine burn happens only at the very last moment, which would mean that it stayed intact and upright almost all the way down.
Here's hoping things go better with CRS-3 (supposed to be the next recovery attempt)
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#188
by
ugordan
on 29 Sep, 2013 19:49
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#189
by
Jarnis
on 29 Sep, 2013 19:51
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#190
by
Antares
on 29 Sep, 2013 19:56
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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.
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#191
by
rst
on 29 Sep, 2013 20:01
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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.
IIRC, Grasshopper carries ballast to keep the thrust-to-weight ratio in a range where it can hover. That's also likely to reduce roll. (If the ballast takes the form of extra fuel, that may also help keep things stable in the tanks.)
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#192
by
sublimemarsupial
on 29 Sep, 2013 20:02
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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.
Merlin 1D turbopump exhausts straight down, so no roll torque from it. Merlin 1C turbopump exhaust was angled to null out torque caused by the flow swirling due to the tube wall nozzle design - M1D doesn't have that problem.
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#193
by
ugordan
on 29 Sep, 2013 20:02
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I'm speculating it was aerodynamic forces that imparted the roll and the ACS used up all the juice again, failing to null it. The stage isn't completely left-right mirror symmetrical so it could be susceptible to spin-up even if coming straight down.
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#194
by
douglas100
on 29 Sep, 2013 20:05
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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.
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#195
by
cambrianera
on 29 Sep, 2013 20:07
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I'm speculating it was aerodynamic forces that imparted the roll and the ACS used up all the juice again, failing to null it. The stage isn't completely left-right mirror symmetrical so it could be susceptible to spin-up even if coming straight down.
Agreed.
Moreover to transmit the rotational motion to the fluid inside the roll must last some time (it's not immediate).
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#196
by
ugordan
on 29 Sep, 2013 20:08
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#197
by
sublimemarsupial
on 29 Sep, 2013 20:10
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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
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#198
by
Silmfeanor
on 29 Sep, 2013 20:12
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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. )
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#199
by
Antares
on 29 Sep, 2013 20:15
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Yeah, it doesn't require exhaust. A turbopump spins, and conservation of momentum makes the thing it's attached to spin the other direction. Aero rolling moment of a symmetric vehicle is tiny.
