David Findlay wrote:
If you could hypothetically block off all sound created aft of the engine
core, what would it sound like? How loud would it be? I don't know the
answers to those questions... In any case, I don't think working on a live
running engine would be such a good idea. If something as complicated as
an engine was that badly broken that it would need human repairs, it
wouldn't be running anyway.

Well I was actually thinking more from the aspect of maintinence of a second
engine while one was running. A mars spacecraft would really need the
ability to be maintained in flight, so having pressurised access to almost
everything would be useful. An ion or vasimr drive would be quite easy to
quieten enough for inflight monitoring and maintinence. Thanks,

The drive does not need to be maintained in action.
At any time other than takeoff you have at least days, possibly months
before getting the engine working again is critical.

And there is limited stuff you can do to an operating liquid fueled engine,
as it tends to be kind of hot and high-pressure.

--
http://inquisitor.i.am/ | | Ian Stirling.
---------------------------+-------------------------+--------------------------
If you've been pounding nails with your forehead for years, it may feel strange
the first time somebody hands you a hammer.
But that doesn't mean that you should strap the hammer to a headband just to
give your skull that old familiar jolt. -- Wayne Throop, during the `TCL Wars'