Some projects fly under the radar. They’re your typical, run of the mill, done this 100 times, project. But others, well, they’re so exciting they belong in a movie.
Customer and Industry
Lockheed Missiles & Space Corp. was the prime contractor on this project for the United States Navy, which was working to develop a manned deep submergence rescue vehicle (DSRV). The DSRV would have to operate at extreme depths, link with a sunken vessel, bring crew members to the surface in groups and quickly return for more. It had to be transportable both by air and on the back of a mother sub.
This project was launched after the loss of the nuclear submarine USS Thresher, which sank in deep water in 1963, killing all hands on board.
Lockheed has a long history working with ENI, dating from our founders' work with Cornell Aeronautical Lab after World War II. We had extensive experience working with Navy labs developing welding parameters for high-yield steels, like the kind used in DSRV hulls. Although the steel developed was 40 percent stronger than other candidate materials available at the time, it was harder to work with and required precise welding procedures to achieve consistent, high-quality welds.
The Challenge
The pressure hull for the DSRV was made up of three intersecting spheres, each about 7-1/2 feet in diameter, with a hemispherical transfer skirt under the center sphere. The transfer skirt was the part that mated to the sunken sub. As depth increases, the external pressure that the hull must withstand increases. Spherical shapes were selected for the hull since a perfect sphere can tolerate external pressure better than any other shape.
By the time the project came to us, significant progress had already been made by the original builder – a large Navy contractor that no longer exists. They had built two DSRV hulls, but neither met all contract requirements because the hulls weren’t sufficiently spherical.
Our role was to build a backup hull, which eventually replaced one of the original hulls, and a set of the related oxygen storage, ballast and trimming tankage.
The challenges were immense.
The project combined welding, machining, non-destructive testing and A-Z planning. The project took place in the early 1970s, meaning there were no computer control machines — or any computers at all, for that matter. Teams used much of the same technology as that used on World War II planes. We had to do without future advances like five-axis machining technology and coordinated-measuring machines. Much of the welding would have to be done with the mating parts in the fully finished condition, so there was little margin for error.
The Journey
By the time we became involved, the design for the DSRV hull and tankage was fully developed. We had access to the original contractors comprehensive machining and assembly drawings and highly specialized – and expensive - tools and fixtures. We spent a month or two analyzing all of this in detail. It turned out that the specialized tools and fixtures cost more than the actual hulls. There were quite a lot of them – we had to rent an entire building just to store them all!
The Discovery
We quickly decided that it would be better to start from scratch. The original contractors process planning was more complex than necessary and not suited to our facilities, so the related drawings weren’t useful. The tools were cumbersome and, with a few exceptions, didn’t fit the manufacturing plans we developed. Using significantly fewer tools and developing new and simpler fabrication sequences and processes, we got to work.
The Solution
Since a perfect sphere is the best shape to withstand the intense pressures of deep ocean work, the key was to maintain sphericity and wall thickness of every section of the finished vessel or tank within very tight limits while minimizing overall weight.
Each of the spheres that made up the tri-sphere hull had thicker sections for viewports and electrical penetrations that had to be welded in place as finished parts.
All of these inserts were subject to the same geometric tolerances. The geometry of the intersections of the three spheres was also critical to avoid hard spots that didn’t react to external pressure like the spheres, creating failure points.
The finished hull also included optically clear Plexiglas™ viewports, which were an extremely precise fit in the machined seats in the vessel shell. We developed a set of tools to precisely measure the as-built seats and set a special lapping tool to match for perfect seating. Lockheed bought the tool and used it to make replacement viewports in the field.
The Results
ENI delivered a pressure hull and tankage to Lockheed and the Navy that was lighter than the design requirements and that exceeded the minimum test depth by 80 percent. Our team achieved a shape so close to perfectly spherical that it likely couldn’t be done better today with modern computer aided equipment.
The new pressure hull and tankage replaced the original units in DSRV-1. DSRV-1 worked flawlessly in training exercises and proved that crew members could be transferred safely in deep water. Thankfully, it never needed to be used in practice.
DSRV-1 remained in service until 2008, when it was replaced with new systems using remote operated vehicle technology.
The project expanded our weld distortion and sinkage knowledge base, and added some new machining techniques applicable to the equipment available at the time. The project also created a stronger relationship with the Navy, which resulted in direct work through the David Taylor Naval Research Center and with other Navy prime contractors like Northrop Grumman.
Although its services were never required for a real-world rescue, the DSRV-1, with its ENI built hull and tankage, enjoyed a second career as a movie star, appearing in several feature films, including 1990's "The Hunt For Red October."