My father was an engineer and valve/fluid dynamics specialist for Rocketdyne for 30 years. He was the project manager for the SSME turbo pumps. When they they first tested the SSME it scared the hell out of the engineers to see that engine run!
Pretty much what grogadile said. All liquid fuel rocket motors experience combustion instability particularly on ignition. The motor is designed to self damp after oscillations such as the one shown occur. Keep in mind that this was taken with a high speed camera, the oscillation likely happened within 1/10 of a second and what you are seeing is likely the harmonics of a 4k-24kHz oscillation. The issue is more problematic on larger rockets which is why the Russians use small clusters.
@2ndAsstJizzMopper That is the engines gimbling. each nozzle moves independently to adjust inflight and to bring the shuttle back to straight up. The intial ignition makes the whole thing sway. You can see the pre-flight engine gimble check minutes before.
@yourjudgeandjury No, that wasn't gimballing. Gimballing is the directional pointing of the entire engine in a direction away from centerline. This was the bell of the engine "ringing" and flexing.
You see those ring-like structures on the nozzles? Those provide a substantial increase in nozzle rigidity while minimizing weight. It kinda works like a ribcage.
The ribs on the nozzles do provide some structural benefit, but they also serve another purpose. The hot exhaust would easily melt the nozzle during flight, so to solve this problem the liquid propellant (which is at ridiculously low temperatures) is piped through those ribs to cool the nozzles. The ribs coil around the nozzle top to bottom for cooling then shoot back up into the chamber for combustion.
Cold start under choke, idle system with mixture enrichment for warm up, acceleration sytem with a shot of fuel to cover idle bog and then power system with correct fuel/oxidizer distrubution under the power valve with final run cruise. Gret view of the engines and combustion. The BBC ran a great story on the F1 injector plate issues with their (fiction/fact) documentory called the "Space Race". Combustion instability affects all. Perhaps a Rochester 4MV Quadrajet?
@UAL1200 I'm even wanting to think I read somewhere that when the liquid is heated it tries to expand, and they use that pressure to spin the fuel pumps before the fuel goes into the combustion chamber.
you seem like a pretty knowledgeable guy, I've had this question bugging me about the SSME for a while. Prior to engine igntion with the pyro igniter, ~ T -5 coming from the edge of the bell nozzle a white vapor jet appears to shoot down into the flame trench, I've always wondered what this was for? I've thought maybe is it LH2 being dumped, but if it is why waste it? if you know what it is, and what its for, I'd really appreciate an explanation, it bugs the heck out of me!
@marmaladekamikaze - Actually I rechecked what your talking about. Do you mean the white horizontal "sparks" being shot across the engine bell outlet ? If so...its sparks to burn off any stray Hydrogen before ignition.
No I'm talking about the vertical white fluid coming out of the edge of the engine bell, that is directed down into the flame trench. The Horizontal sparks you're talking about are pieces of Zirconium metal from the NASA standard igniter IIRC.
Those are the gaseous oxygen dump lines. Prior to engine start, LOX and LH are circulating through the engine's pumps and valves to keep them at the proper temperatures and to prevent gas bubbles from forming. Any oxygen gas that does form prior to engine start is dumped through these two lines. Gaseous hydrogen is piped off and then burned off in a flare stack well away from the launch pad. Once the engine start signal is given, the valves to these dump lines are closed.
My father was an engineer and valve/fluid dynamics specialist for Rocketdyne for 30 years. He was the project manager for the SSME turbo pumps. When they they first tested the SSME it scared the hell out of the engineers to see that engine run!
Thirdmanin 18 hours ago
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kingofinferno100 1 week ago
Man, this is cool stuff. I'm glad I was able to see this before I die - and that may not be too far down the road.
MSLTUL 3 weeks ago
Pretty much what grogadile said. All liquid fuel rocket motors experience combustion instability particularly on ignition. The motor is designed to self damp after oscillations such as the one shown occur. Keep in mind that this was taken with a high speed camera, the oscillation likely happened within 1/10 of a second and what you are seeing is likely the harmonics of a 4k-24kHz oscillation. The issue is more problematic on larger rockets which is why the Russians use small clusters.
krebsderek 1 month ago
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@2ndAsstJizzMopper i concur
pcfaulkner 1 month ago
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pcfaulkner 1 month ago
@2ndAsstJizzMopper That is the engines gimbling. each nozzle moves independently to adjust inflight and to bring the shuttle back to straight up. The intial ignition makes the whole thing sway. You can see the pre-flight engine gimble check minutes before.
yourjudgeandjury 2 months ago
@yourjudgeandjury No, that wasn't gimballing. Gimballing is the directional pointing of the entire engine in a direction away from centerline. This was the bell of the engine "ringing" and flexing.
shockwave77598 1 month ago
Power!!!!
SquallyTeaLeaf 2 months ago
resonance, some times it can be destructive .. engineers takes it seriously into account
khalilovH 2 months ago 2
Wow...rings the nozzle like a bell. Sort of...
verstengenericks 3 months ago
tTHATS one helluva bunsen burner
bandito468 4 months ago
You realize how many of hundreds of thousands of pounds of thrust are coming out of those things? Its good that they are flexible :)
rockfilmers 6 months ago
If I were going to fly on the shuttle, I would have rather not known about this...
Ferrariman601 6 months ago
MIT has a 22 part lecture on the design of the shuttle on youtube. It is very worthwhile if thats your kinda thing.
MrUnclestupidhead 7 months ago
Looks like the nozzle hit its resonant frequency during ignition. About 12 oscillations in all.
Good thing NASA never really explained how completely close to the edge the shuttle is when taking off.
oracle2world 8 months ago 2
@oracle2world Close to the edge?
matrix49A 7 months ago
@matrix49A - "edge" = limits. LIke this stuff barely works at all on a good day.
oracle2world 7 months ago
Cool, ...I think... Never seen this. I wonder how the nozzles just dont tear like aluminum foil, they are so relatively thin.
badback22 11 months ago
@badback22
You see those ring-like structures on the nozzles? Those provide a substantial increase in nozzle rigidity while minimizing weight. It kinda works like a ribcage.
MichaelCox 10 months ago
@MichaelCox
The ribs on the nozzles do provide some structural benefit, but they also serve another purpose. The hot exhaust would easily melt the nozzle during flight, so to solve this problem the liquid propellant (which is at ridiculously low temperatures) is piped through those ribs to cool the nozzles. The ribs coil around the nozzle top to bottom for cooling then shoot back up into the chamber for combustion.
UAL1200 10 months ago 13
@UAL1200 Wow. Awesome explanation. And what a great idea!
cjmkael 5 months ago
Mixture burning.
Cold start under choke, idle system with mixture enrichment for warm up, acceleration sytem with a shot of fuel to cover idle bog and then power system with correct fuel/oxidizer distrubution under the power valve with final run cruise. Gret view of the engines and combustion. The BBC ran a great story on the F1 injector plate issues with their (fiction/fact) documentory called the "Space Race". Combustion instability affects all. Perhaps a Rochester 4MV Quadrajet?
grogadile225 3 months ago
@UAL1200 I'm even wanting to think I read somewhere that when the liquid is heated it tries to expand, and they use that pressure to spin the fuel pumps before the fuel goes into the combustion chamber.
Enatbyte 3 months ago
@UAL1200 And by doing so, the fuel expands with heat, requiring less of it to be burnt. Efficiency.
kinsley2108 3 months ago
@UAL1200
you seem like a pretty knowledgeable guy, I've had this question bugging me about the SSME for a while. Prior to engine igntion with the pyro igniter, ~ T -5 coming from the edge of the bell nozzle a white vapor jet appears to shoot down into the flame trench, I've always wondered what this was for? I've thought maybe is it LH2 being dumped, but if it is why waste it? if you know what it is, and what its for, I'd really appreciate an explanation, it bugs the heck out of me!
marmaladekamikaze 1 month ago
@marmaladekamikaze - I believe its the initial H2-O2 injection before its ignited. The turbo pumps have to get up to full speed before ignition.
dcb1138 3 weeks ago
@dcb1138
that sounds plausible! thanks
marmaladekamikaze 2 weeks ago
@marmaladekamikaze - Actually I rechecked what your talking about. Do you mean the white horizontal "sparks" being shot across the engine bell outlet ? If so...its sparks to burn off any stray Hydrogen before ignition.
dcb1138 3 weeks ago
@dcb1138
No I'm talking about the vertical white fluid coming out of the edge of the engine bell, that is directed down into the flame trench. The Horizontal sparks you're talking about are pieces of Zirconium metal from the NASA standard igniter IIRC.
marmaladekamikaze 2 weeks ago
@marmaladekamikaze
Those are the gaseous oxygen dump lines. Prior to engine start, LOX and LH are circulating through the engine's pumps and valves to keep them at the proper temperatures and to prevent gas bubbles from forming. Any oxygen gas that does form prior to engine start is dumped through these two lines. Gaseous hydrogen is piped off and then burned off in a flare stack well away from the launch pad. Once the engine start signal is given, the valves to these dump lines are closed.
zeke0101 2 days ago
This looks scary. Now I know why they choose to remove and inspect them after every flight.
Jacnas 1 year ago
this is incredible ! ,,,i wish there was a 1080p copy of it !
t0p0l1eve4 1 year ago