Pogo oscillation

Pogo oscillation

Pogo oscillation is the term for a potentially dangerous type of oscillation found in rocket engines. This oscillation results in variations of thrust from the engines, generally caused by variations in fuel flow rate, and placing stress on the frame of the vehicle. Although the term is frequently written POGO, it is not an acronym, but in fact a reference to the bouncing of a pogo stick.

There are several causes of pogo oscillation. The main one is when a surge in engine pressure increases back pressure against the fuel coming into the engine, reducing engine pressure, causing more fuel to come in and increasing engine pressure again. If the cycle happens to match a resonance frequency of the rocket then dangerous oscillations can occur through positive feedback, which can in extreme cases tear the vehicle apart.

The most famous pogo oscillation was in the Saturn V S1-C Stage, caused by the cruciform thrust structure. This structure was an "X" of two I-beams, with an engine on the end of each beam and the center engine at the intersection of the beams. The center of the cruciform was unsupported, so the central F-1 engine caused the structure to bend upwards. The "pogo" oscillation occurred when this structure sprung back, lengthening the center engine's fuel line below (which was mounted down the center of the cruciform), temporarily reducing the fuel flow and thus reducing thrust. At the other end of the oscillation, the fuel line was compressed, increasing fuel flow - causing a sinusoidal thrust oscillation during the 1st stage ascent.

If the oscillation is left unchecked, failures can result. One case occurred in the middle engine of the second stage of the Apollo 13 lunar mission. Fortunately in this case the engine shut down before the oscillations could cause damage to the vehicle. Later events in this mission overshadowed the pogo problem. Pogo was also the cause of some of the problems experienced by Apollo 6. There are other cases during un-manned launches in the 50s and 60s where the pogo caused catastrophic launch failures.

However, modern vibration analysis methods can account for the pogo oscillation to test that it is far away from the vehicle's resonant frequencies. Suppression methods include damping mechanisms or bellows in propellant lines. The Space Shuttle Main Engines each have a damper in the LOX line, but not in the hydrogen fuel line.

One of the Soviet Union's N-1 rocket test flights was destroyed due to pogo oscillations on November 22, 1972. Pogo oscillation at stage 1 initial engine cutoff. The launch vehicle was destroyed 107 seconds after liftoff.

External links

* [http://yarchive.net/space/rocket/pogo.html Sci.space.shuttle newsgroup discussions of pogo]
* [http://www.hq.nasa.gov/office/pao/History/SP-350/ch-3-5.html The Perils of Pogo]


Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • Pogo — may refer to:In entertainment: *Pogo stick, a toy used for hopping up and down **Stunt Pogo, the act of doing stunts or tricks on a pogo stick *Pogo ball, a toy consisting of a rubber ball locked into a sturdy plastic platform, used for hopping… …   Wikipedia

  • Pogo — Cette page d’homonymie répertorie les différents sujets et articles partageant un même nom. Le nom Pogo a été donné à l origine à un jeu d enfant : une barre munie d un ressort, l utilisateur a les 2 pieds et les mains posés sur 2 montants… …   Wikipédia en Français

  • POGO — Project On Government Oversight (Governmental » US Government) * Polar Orbiting Geophysical Observatory (Academic & Science » Geology) * Purchase One Get One (Business » General) * Pressure Oscillation Gee Oscillation (Academic & Science »… …   Abbreviations dictionary

  • pogo effect — A form of longitudinal oscillation in a vehicle that has very high ratio of thrust to its mass and whose thrust may suffer from short term variations …   Aviation dictionary

  • Efecto pogo — Durante el lanzamiento de la misión Apollo 13, el motor J 2 central del segundo tramo del Saturno V se apagó debido a oscilaciones pogo. El efecto pogo u oscilación pogo es la oscilación violenta de motores de cohete debido a la combustión… …   Wikipedia Español

  • Apollo 8 — Infobox Space mission mission name = Apollo 8 insignia = Apollo 8 patch.png command module = CM 103 mass 28,817 kg service module = SM 103 lunar module = Lunar Test Article (LTA B) mass 9,026 kg booster = Saturn V SA 503 crew size = 3 launch pad …   Wikipedia

  • Apollo 13 — Infobox Space mission mission name = Apollo 13 insignia = Apollo 13 insignia.png stats ref = cite web |url=http://history.nasa.gov/SP 4029/Apollo 00g Table of Contents.htm |title= Apollo by the Numbers: A Statistical Reference (SP 4029)… …   Wikipedia

  • Apollo 6 — Infobox Space mission mission name = Apollo 6 insignia = Apollo program insignia.png command module = CM 020 mass 25,138 kg service module = SM 014 lunar module = LTA 2R (dummy) mass 11,794 kg booster = Saturn V SA 502 spacecraft name = Apollo… …   Wikipedia

  • Space accidents and incidents — Space accidents, either during operations or training for spaceflights, have killed 22 astronauts (five percent of all people who have been in space, two percent of individual spaceflights), and a much larger number of ground crew. This article… …   Wikipedia

  • Saturn V — Infobox rocket caption = The first Saturn V, AS 501, before the launch of Apollo 4 name = Saturn V function = Manned LEO and Lunar launch vehicle manufacturer = Boeing (S IC) North American (S II) Douglas (S IVB) country origin = United States… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”