posted 02-28-2011 02:26 AM
I've always wondered what the "vapor" is that is coming from the nozzles (or whatever the actually are) that are on the outside of the SSMEs? Seems like I remember hearing what exactly it was and it's purpose but I've forgotten.
It also seems like it occurs up near the top of the external tank but it's always readily apparent near the SSME.
Ben Member
Posts: 1896 From: Cape Canaveral, FL Registered: May 2000
posted 02-28-2011 02:32 AM
Liquid oxygen venting.
fryson New Member
Posts: From: Registered:
posted 02-28-2011 03:02 AM
Awesome, I really appreciate the quick reply.
garymilgrom Member
Posts: 1966 From: Atlanta, GA Registered: Feb 2007
posted 02-28-2011 05:53 AM
I've read it took *years* to develop the 6 second starting sequence for these engines. I think even us geeks don't realize how complicated these systems are.
quote:Originally posted by garymilgrom: I've read it took *years* to develop the 6 second starting sequence for these engines.
Actually it is more like 3 seconds. The remaining time is for the vehicle to rebound from the twang.
The SSME is unique in that it is one of few engines to use a "head" start, that is only relying on the pressure of the propellant at the inlets. Most pump fed engines use solid cartridges or gas spin systems to start the turbo pumps spinning.
garymilgrom Member
Posts: 1966 From: Atlanta, GA Registered: Feb 2007
posted 02-28-2011 06:46 AM
NASA gives main engine start at T-6.6 seconds in the countdown and the thrust from the engines initiates the twang. The three engines start 100 milliseconds apart to reduce loads on the orbiter.
The following is from "Space Shuttle Main Engine: The First Ten Years" by Robert E. Biggs which is a PDF available on the web:
Start and Shutdown The first hurdle that had to be overcome in the engine test program was to learn how to safely start and shut down the engine. Five years of analysis had produced sophisticated computer models that attempted to predict the transient behavior of the propellants and engine hardware during start and shutdown.