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coming into the engine. This reduces fuel flow and thus chamber pressure. The reduced chamber pressure in turn reduces back pressure at the pump, causing more fuel to come in and repeating the cycle. In this way, a rocket engine experiencing pogo oscillations is conceptually operating somewhat like a
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test flights suffered pogo oscillations in the first stage on
February 21, 1969. The launch vehicle reached initial engine cutoff, but exploded 107 seconds after liftoff and disintegrated. There are other cases during uncrewed launches in the 1950s and 1960s where the pogo effect caused catastrophic
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Pogo arises fundamentally because you have thrust fluctuations in the engines. Those are normal characteristics of engines. All engines have what you might call noise in their output because the combustion is not quite uniform, so you have this fluctuation in thrust of the first stage as a normal
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Now, in turn, the engine is fed through a pipe that takes the fuel out of the tanks and feeds it into the engine. That pipe's length is something like an organ pipe so it has a certain resonance frequency of its own and it really turns out that it will oscillate just like an organ pipe does.
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lunar mission in 1970. In this case, the engine shut down before the oscillations could cause damage to the vehicle. Later events in this mission (an oxygen tank exploded two days later) overshadowed the pogo problem. Pogo also had been experienced in the
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The structure of the vehicle is much like a tuning fork, so if you strike it right, it will oscillate up and down longitudinally. In a gross sense it is the interaction between the various frequencies that causes the vehicle to oscillate.
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Modern vibration analysis methods can account for the pogo oscillation to ensure that it is far away from the vehicle's resonant frequencies. Suppression methods include damping mechanisms or bellows in propellant lines. The
38:, causing variations of acceleration on the vehicle's flexible structure, which in turn cause variations in propellant pressure and flow rate, closing the self-excitation cycle. The name is a metaphor comparing the
205:'s ascent caused the center engine to shut down about two minutes earlier than planned. The loss in thrust was compensated by longer burns from the second and third stages.
193:) experienced severe pogo oscillation on the flight of Apollo 6, which damaged the S-II and S-IVB stages above and likely would have triggered an
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If the oscillation is left unchecked, failures can result. One case occurred in the middle
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first stage during its development, which delayed man-rating the rocket for the
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NASA Technical Paper on
Flexible Propellant Lines Including Pogo Suppressors
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In general, pogo oscillation occurs when a surge in combustion chamber
88: in this section. Unsourced material may be challenged and removed.
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201:) had less intense pogo on other flights. The oscillations during
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launch failures, such as the first Soviet spacecraft to the moon
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Moonport: A History of Apollo Launch
Facilities and Operations
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465:"Die russische Mondrakete N-1 (The Russian moon rocket N-1)"
34:. The unstable combustion results in variations of engine
495:"Rockets and People, Volume 2: Creating a Rocket Industry"
440:"NASA Experience with Pogo in Human Spaceflight Vehicles"
367:"Launch Vehicle Design: Configurations and Structures"
331:
Benson, Charles D.; Faherty, William
Barnaby (1978).
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if the flight had carried a crew. The second stage (
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124:'s pogo oscillation to a congressional hearing:
523:Sci.space.shuttle newsgroup discussions of pogo
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104:Learn how and when to remove this message
162:. If the pulse cycle happens to match a
76:Relevant discussion may be found on the
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129:characteristic of all engine burning.
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341:. NASA. NASA SP-4204. Archived from
86:adding citations to reliable sources
16:Type of vibration in a rocket engine
333:"Two engines out but still running"
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234:test flight in 1968. One of the
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251:in September and October 1958.
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42:vibration to the bouncing of a
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177:Pogo oscillation plagued the
166:of the rocket then dangerous
397:Fenwick, Jim (Spring 1992).
303:"Apollo 13 Pogo Oscillation"
230:first stage of the uncrewed
217:engine of the second stage,
301:Tom Irvine (October 2008).
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257:Space Shuttle main engines
469:www.bernd-leitenberger.de
423:: CS1 maint: unfit URL (
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310:Vibrationdata Newsletter
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160:pulse detonation engine
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32:combustion instability
543:Spacecraft propulsion
263:line, but not in the
374:Princeton University
82:improve this article
345:on January 23, 2008
164:resonance frequency
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240:N1-L3 rocket
236:Soviet Union
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94:January 2021
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71:verification
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40:longitudinal
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471:(in German)
267:fuel line.
283:References
145:increases
120:explained
44:pogo stick
403:Threshold
355:Ch. 20-3.
223:Apollo 13
221:, of the
203:Apollo 13
78:talk page
24:vibration
537:Category
493:(2006).
475:June 17,
449:June 26,
379:June 18,
316:June 18,
271:See also
265:hydrogen
232:Apollo 6
187:Saturn V
179:Titan II
156:pulsejet
143:pressure
122:Apollo 6
500:. NASA
445:. NASA
399:"Pogo"
209:Hazard
185:. The
50:Origin
36:thrust
498:(PDF)
443:(PDF)
195:abort
506:2021
477:2014
451:2012
425:link
411:2009
381:2009
351:2021
318:2009
247:and
228:S-IC
219:S-II
199:S-II
191:S-IC
151:fuel
261:LOX
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215:J-2
158:or
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