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Early submarines were incapable of diving very deep or moving very fast because their engines required air. When they submerged deep enough that their conning tower or snorkel went underwater, they had to switch to battery-powered electric engines with limited life and power.
Published reports describe how in the 1950s, this problem was solved with the introduction of nuclear power, which did not require air to generate large amounts of electricity. This change permitted submarines to stay submerged for longer periods of time. These more powerful nuclear engines also allowed the subs to move much faster, while their smooth turbines made them quieter than the banging pistons of internal combustion engines.
In 1954, under the leadership of Admiral Hyman C. Rickover, nuclear power was introduced to the fleet on the U.S.S. Nautilus. Together with advances in hull design, silencing techniques, and sonic detection, nuclear power dramatically improved the speed, stealth, and range of U.S. submarines. The USS Thresher, which became the submarine class name as well, was launched in July of 1960 and, after preliminary trials for seaworthiness, was commissioned a little over a year later in August of 1961.
As the first in her class, she underwent lengthy trials at sea over the next two years, of the new design, such as the ability to travel 1300 feet deep at over twenty knots. While on exercises in Florida, she was hit by a tug while moored at Port Canaveral and in the spring of 1963, after repairs and an overhaul for upgrades, she was sent back to sea off the coast of Massachusetts for post-overhaul trials. participating in exercises that demonstrated the capability.
Launched in 1960, the USS Thresher
A submarine disaster in April of 1963 destroyed the USS Thresher and killed 129 American Sailors.
The proximate causes :
1. Bad brazing in the sea water cooling system
2. Poor quality assurance in the installation process
Underlying Issues :
1. Poor ballast system design
2. Extreme depth of water for initial deep dive test after extensive overhaul
What Happened??
Deep Waters
On April 9th, as described in public documents, the USS THRESHER was escorted by another Navy vessel, the USS SKYLARK, out to the edge of the continental shelf off Cape Cod, Massachusetts, where the Atlantic Ocean floor drops precipitously to 8000 feet.
The USS SKYLARK was standing by for rescue if anything went wrong at a few hundred feet, though at the depths at which they were operating there would have been little she could do if the USS THRESHER went too deep. At 6:35 AM on the morning of April 10th, USS THRESHER spotted USS SKYLARK through her periscope to ensure she was in range, and prepared to dive in stages down to their maximum depth for testing.
The crew presumably attempted to restart the reactor and probably also attempted to get their crippled vessel back to the surface. This would explain the “positive angle” as they attempted to point upward and climb with the propellers. Without the reactor, however, they would have been relying on auxiliary power, with far weaker thrust than the reactor had. The boat probably also had negative buoyancy, meaning that it would sink if no active measures were taken, and simply didn’t have enough thrust to lift its weight to the surface.
A section of brass sea water piping recovered from the USS thresher
Emergency Measures
In order to lighten the vehicle, so that the weakened propellers could get it to the surface, or even allow the sub to float up on its own, the normal procedure would be to blow the water out of the ballast tanks and fill them with air, increasing the submarine’s buoyancy. That the sub’s crew were attempting to do so is evidenced by the next message from the stricken craft, shortly after the first troubling message—“Attempting to blow.” The microphone then picked up sounds of compressed air being blown through the lines to the ballast tanks.
At this point, Navy investigators believe, based on tests performed later on another vessel, strainers in the lines upstream of the ballast tank valves iced up. This occurs because the high volume of air moving past the strainers at such high velocity would have caused them to cool rapidly. Icing up of the strainers would have reduced the air flow such that either the tanks couldn’t be cleared at all, or at least not fast enough, because it’s clear that the boat continued to sink. There was only one more ominous voice communication: “...test depth.”
From this point on, the only sounds picked up by the open microphone were the distinctive and dismaying creaks of straining metal and fasteners as the craft sank deeper and started to crush under the unimaginable external pressure.
The submarine eventually broke into several pieces, killing almost instantly all 129 crew and observers aboard. It continued to sink, falling almost two miles to the floor of the Atlantic, prematurely ending the career of the most advanced submarine built to that date.
Proximate Cause
According to the Navy investigation, the proximate cause of the disaster was the leak of seawater into the reactor control electronics. This shut down the reactor, resulting in the inability of the boat to control itself or get back to the surface.
Underlying Issues
According to published reports, there were perhaps
several factors that came together to destroy the USS
THRESHER and its crew. The leak itself probably
occurred because of faulty brazing of the piping at the
shipyard. Prior to the USS THRESHER loss, the
installation procedure for pipes less than four inches in
diameter was to put a silver ring at the joint between two
points and braze it with a torch.
Poor Brazed Pipes led to the electrical shortage that led to the loss of the USS THRESHER
Subsequent investigation of other ships after the accident
showed that, though joints created in this manner
appeared solid, when broken apart there was no silver in
them, indicating that they were much weaker than had
been previously estimated. In general, the design and
standards for the non-nuclear portions of the vessel
seemed to have been more lax than those for the nuclear
reactor and its associated systems.
The icing of the line strainers, resulting in the failure of
the ballast tanks to empty themselves of water fast
enough, also contributed to events. This latter problem
was a failure to meet design specification. Had either of
these methods for surfacing been effective, the reactor
loss would likely not have been catastrophic, because the
crew could have dealt with the leaks and reactor problems
on the surface.
Finally, had the testing occurred in shallower water
(perhaps with the ocean bottom just slightly below test
depth), in which the USS SKYLARK could have
potentially come to their aid, the crew might have been
saved, if not the USS THRESHER itself.
Wreckage from the USS THRESHER's sonar dome can be seen on the ocean floor
Problem and Solution
As a result of the loss of the USS THRESHER, a major
new initiative was undertaken by the Navy, called
“SUBSAFE,” to reform design and manufacturing
processes (similar in many ways to changes at NASA
following the Apollo 1, Challenger and Columbia
disasters). Part of this initiative was to end the practice of
brazing smaller pipes, and to instead start welding and
doing x-ray inspection of joints to verify their integrity.
It also resulted in changes in designs of the system that
blows out the ballast tanks, providing a capability to do
so seven times faster than the system used in the USS
THRESHER.
It had another effect in that during the search for debris
and clues on the deep ocean floor, the Navy recognized
the need for better deep submersibles. This (combined
with other requirements) helped result in the remarkable
new designs that can now explore some of the deepest
trenches of the seas, and that helped discover the remains
of the Titanic. In fact, part of the legacy of this accident
was the development of the kinds of undersea rescue
vehicles that recently saved seven Russian sailors trapped
at six hundred feet off the Kamchatka peninsula, in early
August of 2005.
Applicability To NASA
Like the Navy, NASA operates vessels that must endure
harsh external environments (in this case a radiationdrenched
vacuum), though the pressure differential of
space is much lower (one atmosphere at most, compared
to potentially many atmospheres under the ocean’s
surface). It is also somewhat easier to deal with, because
constructing pressure vessels to keep pressure in is
structurally easier than to keep it out.
Nonetheless, both
types of failures are equally unforgiving, and can kill
people very quickly. This incident shows the importance
of having multiple layers of defense against harsh outside
environments, with redundant means of keeping
functional those vital systems that protect us from it.
It is
also critical from a safety perspective that NASA
simulate as close as possible to the real environments that
a spacecraft or manned system will experience during
flight and even include some margin above the flight
expected loads and environments. These factors would
include: Vibration; Acoustics; Thermal; Radiation;
Vacuum, etc.
This accident also indicates the importance
of redundant systems and that NASA must assure that
these systems will operate successfully when or if they
are called upon. Finally, highly coupled and complex
systems should have the benefit of a Failure Mode and
Effect Analysis (FMEA) to identify potential failure
modes and to control and mitigate them.
Refferences
Generally, for the common pressure :-
1 atm = 100 kPa = 760 mm per Hg (in manometer) = 10 m of H2O = 1 kg/ cm2 = 1 Bar
1 oz (ounce) = 28.35g
1 fl oz = 28ml
1 lb (pounds) = 454 g = 32 oz
