[net.space] Specific impulse & chamber pressure

David.Smith@CMU-10A@sri-unix (05/14/82)

From: David.Smith at CMU-10A (C410DS30)
I have read a couple of times (AW&ST, not recently) that the SSMEs
develop a chamber pressure of 300 bar (atmospheres).  I have also
read a couple of times (FLIGHT International) that the Ariane's first
stage engines develop about 55 bar.  Is such a difference credible?
I would expect exhaust velocity and specific impulse to be directly
related to the chamber pressure.  Such a difference in specific
impulse seems hard to swallow.