"Pat Flannery" wrote in message
...
Henry Spencer wrote:
Right up till they got to their 30 engined N-1 Moon rocket it worked,
then it didn't work.


There was nothing intrinsically wrong with the N-1 design;

I disagree, I think it had too many motors to be reliable, and that the
decision to mount the kerosene tanks on top of the Lox tanks was
fundamentally flawed for the following reasons:
1.) One of the basic ideas that the N-1 was based upon was that of
having the ability to lose a motor or two during ascent, and have the
KORD system shut down the opposing motor to keep things balanced in
regards to thrust from the ring of motors so far from the rocket's
centerline. Good idea, but it relies upon a benign shutdown of the motor
before it suffers a catastrophic failure and damages the motors near it;
since the maximum number of motors that could be shut down was four (two
malfunctioning motors and two opposing motors shut down to compensate
for the asymmetrical thrust), and a catastrophically failing motor was
liable to damage the motors on either side of it...causing three motors
to shut down, and thereby exceeding the total of four shutdown motors
maximum- as three motors on the opposing side of the vehicle also shut
down- what you've effectively got is a rocket that will fail if it has
even one motor undergoes a destructive failure rather than a benign
shutdown, and of course this scenario actually happened during the
second launch attempt.

Catastrophic failure of liquid fueled engines is a "bad day" no matter how
many engines are in your cluster. Note that a catastrophic failure of an
F-1 engine on the S-1C stage or a J-2 on either the S-II or S-1VB stages
would have been a "bad day" for an Apollo Saturn V.

Note also that for benign failures of liquid fueled engines, the Saturn V
had a limited ability to continue with engines shut down, but that was only
a possibility later in the stage burns, and wasn't a possibility at all for
the S-1VB stage. In particular, loosing an F-1 engine early in the flight
would have been very bad.

Here's an article that mentions "Studies indicate that the immediate
structural dynamic transients at engine-out will not cause structural
failure. However, certain combinations of engine failure and wind direction
and magnitude may result in a divergent control condition which could cause
loss of the vehicle.":

http://www.apollosaturn.com/s5flight/sec2.htm

Here's an interesting article which talks about F-1 engine failure modes:

http://www.system-safety.org/~journal/techarticle.html

As you can see, the Saturn V, with fewer engines than the N-1, could also be
destroyed by an engine failure, even if that failure wasn't "catastrophic"
in and of itself.

Further, the large number of motors that need to be manufactured for
even a modest number of launches (the Soviets made a total of around
fourteen N-1's, or at least had that many at some stage of construction
although they only launched four- that's a total of 420 motors for the
first stages alone, and a total of 588 if you count the basically
similar second (8) and third (4) stage motors) means that you can't
afford to do strenuous tests on the individual motors if you want to get
up to a reasonable launch rate, and must minimize the man-hours spent on
making each motor. Neither of those choices is going to add to the
overall reliability of an individual motor.

This seems to be an unfounded assertion. A higher manufacturing rate
usually allows you to improve manufacturing in terms of repeatability,
tolerances, and the like. Manufacturing problems can easily happen when you
have a very small, limited production run, which means that your need for
"strenuous tests" is likely higher with a small run as compared to a very
large run, where repeatability in the manufacturing processes has already
been achieved.

Sounds like "damning with faint praise" to me. The strenuous tests of the
F-1 were required due to the small production run, and the high likelihood
of the Saturn V being destroyed by an F-1 engine failure early in the
flight.

Jeff
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