 Complete the following phrase:  Edwin Link spent the following two years designing an unmanned Cabled Observation and Rescue Device CORD that could free a trapped submersible. A second Johnson Sea Link submersible, nearly identical to the first, was launched in 1975. The two submersibles remained in operation for many years, examining the wreck of the in 1977 and helping recover the wreckage of the Space Shuttle Challenger after its 