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Liberty Bell. The recent recovery of the Liberty Bell 7 space capsule, lost after its Atlantic splashdown in 1961, was achieved with the help of the latest underwater technology. The spacecraft had been lying for 38 years in 4875m of water some 300 miles off Cape Canaveral, having flooded moments after astronaut Virgil 'Gus' Grissom had been winched to safety. In an expedition funded by The Discovery Channel, Oceaneering International Inc was contracted to conduct the search and recovery, and a two-man team from John E. Chance & Associates - Chris Gladwin and Brad Chaumont - were sub-contracted to provide the necessary survey and positioning expertise. Because of the extreme water depths, Sonardyne's recently launched Big Head USBL transceiver was supplied as the best acoustic solution for providing precise ROV positioning during the recovery. Being so new to the offshore industry, there were no Big Head USBL transceivers in stock, and one had to be specially built by Sonardyne's UK factory. The capsule's recovery followed a towfish scan of a 24 sq-mile search grid. Eighty seabed targets were identified, but the first one investigated by the Magellen 725 ROV - the same vehicle used to film the Discovery Channel's documentary of the Titanic - proved to be the historic 2.5m tall Liberty Bell 7 capsule. It was discovered sitting upright on the sandy seabed 3 miles down. To the team's amazement, a discarded Coke can lay a few feet away. Capsule recovery took some 8 hours of slow and cautious lifting, during which the Big Head USBL transceiver tracked the ROV acoustically by providing range and bearing between the surface ship and a Sonardyne 7823 transponder mounted on the vehicle. 'Happy with Big Head' Reviewing the Big Head's performance after the event, the John E. Chance surveyors were enthusiastic. 'I was really happy,' said Chris Gladwin 'the system never missed a beat.' Brad Chaumont was equally pleased. 'We acoustically tracked a depressor in 16,000ft - I don't think that has ever been done before.' The strength of the Big Head USBL transceiver is 'its unique ability to listen downward from the surface vessel in a cone extending 50 degrees from the vertical', says Sonardyne, of Yateley, England. This enables it to reduce acoustic interference from the surface vessel, making it suitable for use in ultra-deep-water and high-noise environments. This listening ability is claimed to be matched by exceptional positioning accuracy, with an additional 33 per cent of transducer spread compared to Sonardyne's standard USBL transceiver design. With an outside diameter of just under 30cm, the 'Big Head' name was, say Sonardyne, chosen to reflect the performance of the unit rather than its physical size. The Discovery Channel filmed the expedition for a documentary, In Search of Liberty Bell 7, which premiered in the US on December 12, 1999, and in the UK on December 29. |
