Tuesday, February 24, 2009

More On CEV Vibration

There is a bit more detail on the CEV's SRM (Solid Rocket Motor) vibration problem. Most structures -- rockets, buildings, what have you -- will vibrate at particular frequencies if you 'excite' or 'whack' them. These are called "natural frequencies/resonances". The burning SRM (the SRB on the shuttle -- try to keep up with the acronyms) acts a bit like a didgeridoo or organ pipe, with the obvious difference that burning rocket propellant is shooting through it, not air. The burning rocket propellant provides the energy to 'excite' the SRM to resonate at a very bass 12 Hz -- the old Shuttle SRBs resonated at 15 Hz. Apparently the CEV has a natural resonance around 11.7 Hz.

Since the CEV has a natural resonance around 11.7 Hz , NASA has a problem on their hands. If left alone, by the time the SRM is burnt out, you have "Bouille de Spatiaunaut" (blended or creamed astronaut) in the top of the rocket, or more likely the CEV has already disintegrated. To avoid this NASA is coming up with dampers to avoid having the CEV resonate at 11.7 Hz. Here's a link to the NASA story.