Photo by Matt Barton, Woods Hole Oceanographic Institution
Since the beginning of 2011, Alvin, the U.S. science community’s only human-occupied submersible dedicated to deep-sea research, has been undergoing a thorough overhaul and upgrade that will enhance its capabilities. The improvements include a new personnel sphere, updated command-and-control systems, enhanced lighting and high-definition imaging systems, new syntactic foam to provide buoyancy, and more and larger viewports, or windows.
The centerpiece is a larger personnel sphere with improved interior design to enhance the comfort of pilots and researchers who will occupy it. The titanium sphere is also designed to withstand pressure at depths of 6.5 kilometers (4 miles), with the eventual goal of allowing Alvin to dive beyond its current 4.5-kilometer (2.8-mile) diving capacity.
Now in the final stages of the first phase of the upgrade, the iconic sub is being painstakingly reassembled, piece by piece, by a one-of-a-kind team of engineers, technicians, and pilots at Woods Hole Oceanographic Institution (WHOI). They also carefully inspect and test each component to ensure its reliability and the safety of those who will use to sub to explore the depths.
Here, technician Jefferson Grau describes how the Alvin Group verifies that the acrylic viewports will withstand the intense pressures of the ocean depths:
When we set sail later this year, Alvin will have five windows: three up toward the front that are 7 inches across on the inside (17 inches across outside), and two smaller ones off to either side that are 5 inches in diameter on the inside (12 inches across outside). These are considerably larger than the windows we had before.
The larger sides of the windows face out to the ocean, so that as Alvin goes deeper and is subjected to greater pressure, the windows will be forced inward against the titanium hull. That will strengthen the seal between the window and hull.
The windows are acrylic, a type of plastic. At a test facility in Texas, the windows were subjected to a test pressure of over 12,000 pounds per square inch. This translates to about 680 tons of force on the small windows, and over 1,300 tons on the larger ones. That is almost twice the pressure Alvin will experience at its current maximum operating depth of 4,500 meters (about 15,000 feet). Eventually, Alvin will be rated for dives to 6,500 meters, or a little over 21,000 feet.
When we receive each window from the manufacturer via the test facility, we check its dimensions to make sure that the window has not changed shape under all that pressure. We also perform a visual inspection on the windows to make sure there are no inclusions (like particles or foreign objects) or voids (like bubbles) that might have crept into the acrylic during manufacture, and which could compromise the integrity of the windows under pressure.
In this photo, I am performing a visual inspection on one of our smaller windows. Working in the dark with a bright, handheld light placed at different positions and angles allows us to see the quality of the window in detail throughout its thickness. Fortunately, this window passed inspection and will soon be keeping the observers and pilots inside Alvin safe and sound, while permitting them an enlarged and crystal-clear view of the ocean depths around them.
I joined the Alvin Group in May of 2011, after the submarine had begun the current overhaul and upgrade process. As a mechanical technician, I work to rebuild, test, and integrate the components of all of Alvin's various mechanical systems—the variable ballast system that modulates the submarine's weight during a dive, the hydraulic system that drives our manipulators and tools, the thrusters that we use to move around the terrain of the ocean floor, and so on. It’s a lengthy process that involves a lot of rebuilding, testing, and installing components like relief valves, check valves, pipes, hoses, solenoids ... and oh yeah, windows.
Once the upgraded Alvin is fully reassembled and is under way again, I will officially move into the Pilot-in-Training program and begin the process of becoming an Alvin pilot. All of which is, to be honest, already a dream come true.
Alvin is owned by the U.S. Navy and operated by WHOI. The current upgrade has been funded largely by the National Science Foundation, with support from private donations to WHOI.