Comments on: SpaceX launches 22 Starlink satellites

By: Richard M

Richard M — Sat, 09 Sep 2023 21:12:04 +0000

Tory Bruno helpfully explains this a little today on Twitter:

Louis McCarthy @mccarthy_louis
What’s the pogo system?

Tory Bruno @torybruno 8:10 AM · Sep 9, 2023
Three broad categories of combustion instability in liquid fueled rockets: screech (acoustic resonance inside combustion chamber), buzz (resonance with the medical structure), and pogo (long fluid column resonance in feedlines). Mighty Atlas kills pogo via a fluid energy absorber

By: Richard M

Richard M — Sat, 09 Sep 2023 21:08:35 +0000

American private enterprise now leads China in successful launches 72 to 40. It also now leads the entire world combined, 72 to 65

I had this post in mind when I ran across one of the most wrong-headed takes in recent memory on Twitter (which is saying something): “My real problem is that space should not be privatized, anything and everything done in space should be done through publicly funded and operated organizations. SpaceX should not be allowed to be independent.”

By: Concerned

Concerned — Sat, 09 Sep 2023 19:29:29 +0000

Apparently there are electrically controlled bellows in the long main propellant feed lines that actively damp the longitudinal vibrations otherwise called “pogo”. They were so severe in the April 1968 Apollo 6 test launch that it would have seriously injured a crew had one been onboard. Other large rockets in the past have been destroyed because of it.

By: Robert Zimmerman

Robert Zimmerman — Sat, 09 Sep 2023 19:29:19 +0000

In reply to Ray Van Dune. Pogo was a problem during the second Saturn 5 launch, causing premature shutdown of engines. They got the capsule into orbit and were able to more or less complete the mission, but the very next flight of the Saturn 5 was Apollo 8, with three men on board going to lunar orbit. They launched in December 1968 because Von Braun's team in Huntsville was convinced they had found the issue and solved it.

By: Ray Van Dune

Ray Van Dune — Sat, 09 Sep 2023 19:20:55 +0000

Ps. I heard that pogo-ing got the last N-1, causing it to break up just before 1-2 staging, right at the hot-staging latticework as I recall. Heads-up, Elon.

By: Ray Van Dune

Ray Van Dune — Sat, 09 Sep 2023 19:15:48 +0000

Apparently the Atlas V 551 NROL-107 launch is put off again, until Sunday at 08:47 EST, due to electrical problems in the “pogo” circuit. Pogo is oscillatory feedback caused by fuel flow surging affecting thrust levels, but what circuit controls it God knows. I guess Tory Bruno does.

I have often heard the launch crew call out “pogo” late in the countdown for Falcon 9s, but never any explanation of it.