Hi everybody,
Steve has probably put his finger on the essence of the PTO
controversy with his observation of the quality of the lubricant.
Back in the early 80s I worked at JPL with a crack engineer whose job
it was to find out why the camera scan platform of the Voyager
spacecraft got stuck on the Saturn flyby. The scan platform slews the
camera and other instruments up, down, left, and right. (If you
remember, much valuable data and many pictures were lost because of
the failure.) The Lab was very interested in salvaging any movement of
the scan platform for the expected encounter with Uranus so that the
maximum science (photos) could be gained.
We made dozens of replicas of the scan platform's gearbox and then we
turned 'em on. Carl was a gearbox expert. We ran some continuously,
others intermittently, some rapidly and others slowly, still others at
high temp and others at cold temp, and collected statistics on them
all while they whirred frantically up in the gyro room. One by one,
they jammed up just like the original one.
When Carl finally finished his investigation, he concluded that a bad
batch of lubricant that prematurely hardened and clogged the precision
teeth of the gears was the cause of the failure, but he also found out
the exact parameters of movement range, frequency, and rate that would
allow NASA to maximize its very limited remaining gear box life. As a
result, the Uranus flyby was a success and Voyager 2's mission was
extended to include Neptune in 1989, which was at that time the
farthest planet from the sun.
I'm afraid that failures of gearboxes and PTO shafts can happen to the
best of us, but thank goodness that, here on Earth, we have the luxury
of merely opening up our PTOs and adding a little Teflon lube after
cleaning up the shaft. It's so much easier.
R,
Al W6LX
P.S. For fascinating info on the two Voyager spacecraft, check out
http://vraptor.jpl.nasa.gov/voyager/voyager.html
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