Navigation Systems For Deep Ocean Mining

ABSTRACT The advent of commercial deep ocean mining of manganese nodules appears quite near. Extensive geological surveys of the ocean floor during the past decade, coupled with more recent tests of experimental and prototype mining equipment have required significant advances in many areas of technology including navigation. A variety of navigation sensors and systems have been utilized to support deep ocean operations in the past. In the near future, detailed mine site surveys and nodule mining operations will place increased demands on the accuracy and reliability of navigation systems. A study has been performed to evaluate the application of current and future navigation sensors to deep ocean mining operations. INTRODUCTION Manganese nodules are potato-sized lumps composed of metallic compounds and sediment, which are found in a variety of locations on the ocean bottom at depths between 12,000 and 18,000 feet. The abundance and distribution of nodules varies widely over relatively small geographical areas and the economic feasibility of commercial mining is based on near continuous operations in areas of high nodule abundance. Therefore, high-accuracy pre-mining surveys must be conducted to determine areas of sufficient nodule abundance and to map topographical features of the ocean bottom in the mine site. Once a detailed mine site survey has been performed, the mining operations can commence. The general mining system will be composed of:A surface support ship for transporting, deploying, towing, and recovering the subsea mixing systems.A lift system composed 6f a 15,000 to 20,000 foot pipe string or equivalent device to transport the manganese nodules from the ocean bottom to the surface.An ocean-bottom mining device or dredge head at the end of the lift system to remove the nodules from the bottom.Surface transport ships for on-loading the nodules pumped up from the ocean floor and transporting the ore to land-based processing plants. SITE SURVEY NAVIGATION Early geological and bathymetric survey operations utilized astronomical and dead reckoning navigation techniques, but in more recent years, automated satellite navigation systems in conjunction with gyrocompass and speed-log (electromagnetic or doppler) sensors have been employed. In localized areas where detailed information on nodule abundance or topography is desired, acoustic transponder systems have been utilized. A post-mission performance analysis of navigation data from a preliminary survey operation was conducted at the C.S. Draper Laboratory to generate an optimal estimate of ship's track during a thirteen day period and to establish quantitative confidence in the track accuracy. The data consisted of one hundred and seventy-five satellite navigation fixes along with single-axis electromagnetic log speed information and gyrocompass heading information. An error model of the navigation system was constructed and computer programs were developed to process the satellite and dead reckoning information and to estimate the error terms.