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#320
by
AncientU
on 30 Sep, 2013 14:54
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Agreed, some aero baffles integrated into the bottom panels.
Sounds good and involves no additional drag on the way up.
This theory requires that the additional spin came up only when the stage was falling already at a relatively low speed. So SpaceX should know.
Maybe a crazy idea, but could gimbaling all eight outer engines in the direction of rotation produce preferential vortex shedding that opposes rotation?
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#321
by
malu5531
on 30 Sep, 2013 15:02
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Maybe a crazy idea, but could gimbaling all eight outer engines in the direction of rotation produce preferential vortex shedding that opposes rotation?
I see your crazy idea and raise you another one; how about venting GOX in addition to gimbaling? Would it be possible to let some LOX expand in each combustion chamber without fuel, not using the turbopumps, and exit through the nozzle as GOX? (a "hack")
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#322
by
Lars_J
on 30 Sep, 2013 15:06
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It depends on how cold the gas is and how moist the air is. If they just using LN2 for the propellant, the exhaust could be plenty cold enough to precipitate ice crystals an produce a little cloud.
But at that altitude - stage sep - it has already left the atmosphere. (For all intents and purposes)
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#323
by
AJW
on 30 Sep, 2013 15:39
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I have a possible explanation for the roll experienced by the first stage the way down. When the vehicle is subsonic, the air impinging on the bottom of the stage must escape sideway to return in the airstream.
The passage between nozzles is partially obstructed by the fuel lines, carrying fuel to the nozzle; this way air is forced to have a swirling motion, causing roll.
In pic 1 is clearly visible the fuel pipe, pic 2 is a reminder of the relative positions of the engines, finally the sketch explain the movement of air.
When the stage is still supersonic, the shock wave from the nozzles should shield the bottom minimizing this effect.
In that case I would think just cheap aero "baffles" oriented to redirect half of the air flow the other direction could entirely eliminate the torque... if that's the cause after all.
It would be interesting to know if the proposed spin direction matches the actual direction experienced. Secondly, while they do not plan to try another soft landing on the next two flights, is there anything that they can test during those flights that might lead to or verify a solution to the spin?
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#324
by
guckyfan
on 30 Sep, 2013 16:13
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Maybe a crazy idea, but could gimbaling all eight outer engines in the direction of rotation produce preferential vortex shedding that opposes rotation?
Assuming the reason of the spin is really down there and maybe even if not it sounds not crazy at all to me but like a very reasonable method, even with the possibility of active steering adapting the gimballing to the airspeed.
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#325
by
AnimatorRob
on 30 Sep, 2013 16:27
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Have we seen this video yet?
Thanks for posting! Mighty interesting stuff going on after stage separation....
Great video, here's my take:
There is a really large plume right at the end of the video from what seems to be the first stage. Possibly the Merlins re-lighting?
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#326
by
meekGee
on 30 Sep, 2013 16:29
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I have a possible explanation for the roll experienced by the first stage the way down. When the vehicle is subsonic, the air impinging on the bottom of the stage must escape sideway to return in the airstream.
The passage between nozzles is partially obstructed by the fuel lines, carrying fuel to the nozzle; this way air is forced to have a swirling motion, causing roll.
In pic 1 is clearly visible the fuel pipe, pic 2 is a reminder of the relative positions of the engines, finally the sketch explain the movement of air.
When the stage is still supersonic, the shock wave from the nozzles should shield the bottom minimizing this effect.
I like that. Burt Rutan would hook up an octaweb to a truck (on a rotary shaft!) and go cruising around the runway
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#327
by
Danderman
on 30 Sep, 2013 16:30
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Remember, whatever Elon says about time frames for recovery and re-use of the first stage - triple it.
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#328
by
Lars_J
on 30 Sep, 2013 16:33
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Remember, whatever Elon says about time frames for recovery and re-use of the first stage - triple it.
And your data-points would be...? Remember that this recover attempt came far earlier that most of us outside observers would have anticipated.
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#329
by
kevin-rf
on 30 Sep, 2013 16:34
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Remember, whatever Elon says about time frames for recovery and re-use of the first stage - triple it.
Since he said the second stage relight issue should delay SES-8 by two weeks, does that mean add six weeks, so instead of late October/early Novemeber, early December instead?
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#330
by
cambrianera
on 30 Sep, 2013 16:35
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I have a possible explanation for the roll experienced by the first stage the way down. When the vehicle is subsonic, the air impinging on the bottom of the stage must escape sideway to return in the airstream.
The passage between nozzles is partially obstructed by the fuel lines, carrying fuel to the nozzle; this way air is forced to have a swirling motion, causing roll.
In pic 1 is clearly visible the fuel pipe, pic 2 is a reminder of the relative positions of the engines, finally the sketch explain the movement of air.
When the stage is still supersonic, the shock wave from the nozzles should shield the bottom minimizing this effect.
I like that. Burt Rutan would hook up an octaweb to a truck (on a rotary shaft!) and go cruising around the runway
That is, you can mount an octaweb on a shaft and test it in:
1) wind tunnel.
2) moving bench.
The second being more cool....
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#331
by
cambrianera
on 30 Sep, 2013 16:38
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Maybe a crazy idea, but could gimbaling all eight outer engines in the direction of rotation produce preferential vortex shedding that opposes rotation?
I see your crazy idea and raise you another one; how about venting GOX in addition to gimbaling? Would it be possible to let some LOX expand in each combustion chamber without fuel, not using the turbopumps, and exit through the nozzle as GOX? (a "hack")
This adds another layer of complexity; hydraulic power without turbopump spinning.
Doubtful....
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#332
by
corrodedNut
on 30 Sep, 2013 16:41
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Have we seen this video yet?
Thanks for posting! Mighty interesting stuff going on after stage separation....
Great video, here's my take:
There is a really large plume right at the end of the video from what seems to be the first stage. Possibly the Merlins re-lighting?
Or the 1st stage tanks venting.
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#333
by
Norm38
on 30 Sep, 2013 17:00
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^^^ Why would the 1st stage tanks vent before re-entry? Don't they need pressurization for strength and rigidity? And the tanks just got done emptying, they shouldn't be overpressurized.
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#334
by
Jim
on 30 Sep, 2013 17:15
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^^^ Why would the 1st stage tanks vent before re-entry? Don't they need pressurization for strength and rigidity? And the tanks just got done emptying, they shouldn't be overpressurized.
Because the residual LOX (and the LOX for relights) is still boiling off and pressure is increasing in the tanks.
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#335
by
dcporter
on 30 Sep, 2013 17:21
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^^^ Why would the 1st stage tanks vent before re-entry? Don't they need pressurization for strength and rigidity? And the tanks just got done emptying, they shouldn't be overpressurized.
Because the residual LOX (and the LOX for relights) is still boiling off and pressure is increasing in the tanks.
Do we have a firm consensus at this point re: whether the awesome-looking spurts were boring GOX venting or awesome ACS firings of some sort?
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#336
by
ugordan
on 30 Sep, 2013 17:28
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Do we have a firm consensus at this point re: whether the awesome-looking spurts were boring GOX venting or awesome ACS firings of some sort?
My 2c is that
* the rapid, short puffs were definitely ACS of some sort - either He/N2 or GOX-powered.
* the couple of radial puffs might be tank pressure relief vents - the puff duration looks about right to me.
* the diffuse plume that's present the whole time and slowly fading might be due to engine purge/chilldown for restart
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#337
by
Mader Levap
on 30 Sep, 2013 17:39
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Remember, whatever Elon says about time frames for recovery and re-use of the first stage - triple it.
And your data-points would be...?
While this "triple" remark was pulled out of nether regions...
Remember that this recover attempt came far earlier that most of us outside observers would have anticipated.
... it is indeed very advisable to be sceptic about schedule announced by SpaceX for anything. For example, this very flight was originally supposed to fly in 2008 on F1. Here is your data point. Want more?
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#338
by
Lee Jay
on 30 Sep, 2013 17:48
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Remember, whatever Elon says about time frames for recovery and re-use of the first stage - triple it.
And your data-points would be...? Remember that this recover attempt came far earlier that most of us outside observers would have anticipated.
http://www.nasaspaceflight.com/2009/01/musk-ambition-spacex-aim-for-fully-reusable-falcon-9/"With Falcon I’s fourth launch, the first stage got cooked, so we’re going to beef up the Thermal Protection System (TPS). By flight six we think it’s highly likely we’ll recover the first stage, and when we get it back we’ll see what survived through re-entry, and what got fried, and carry on with the process." -- Elon Musk
That was January 2009.
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#339
by
Lars_J
on 30 Sep, 2013 17:50
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While this "triple" remark was pulled out of nether regions...
Remember that this recover attempt came far earlier that most of us outside observers would have anticipated.
... it is indeed very advisable to be sceptic about schedule announced by SpaceX for anything. For example, this very flight was originally supposed to fly in 2008 on F1. Here is your data point. Want more?
Granted - My point was merely that while flights slip - capabilities are frequently introduced before us outsiders expect it.
- I think we all expected more v1.0 flights before the block-II/v1.1 was introduced
- And we did not anticipate propulsive re-usability tests (attempted soft water landing) on the very first flight of v1.1
- and so on...
