pressure housings and life support and safety systems for the human operators. DSV endurance at the work site is limited by prolonged surface periods for crew change and vehicle replenishment. The cost per operating hour is usually much greater than for other vehicle types because of the extra cost attributable to crew accommodation and life support, the larger surface support ship needed to handle the heavier human-occupied vehicle in launch and retrieval, and the more limited availability—therefore, the normally higher day rate—of support ships. In addition, the capital cost component of the day rate for DSVs is potentially higher than for unoccupied vehicles because they can be operated fewer hours due to human limitations.

In comparison to DSVs, ROVs provide greater endurance and greater range, including maneuverability of surface support vessels, at lower cost. Because life-safety support is not required, ROVs can operate in hazardous environments and provide simultaneous real-time observation and control to multiple remotely situated observers (Robison et al., 1992; Bowen and Walden, 1993).

AUVs are free from the tether restraint common to ROVs and can perform tasks with little or no operator input. However, AUVs must operate on a limited energy budget and can provide little real-time feedback to the operator, who is limited by the bandwidth available when using acoustic communication. However, new advances in task-level control architecture will enable the human to command tasks at high-level in real-time, and acoustical advances are continually expanding the available acoustic communication bandwidth.

In the 1960s and 1970s many DSVs (with a human in situ) were in operation in a variety of different applications worldwide. Estimates indicate that more than 100 DSVs of all types were built during this time. DSVs have dominated ocean exploration, and some systems, such as Alvin, have been operational for the last three decades. DSVs continue to be used in support of certain military tasks and marine scientific research. However, few have been built recently (only four since 1990), and the number operating today is significantly less than it was 20 years ago. Since the 1970s, ROVs have replaced DSVs for most commercial work tasks, and the committee anticipates that ROVs will provide increasing support for marine science projects. However, there will continue to be certain vital exploration tasks that can be performed only by humans in situ.

Most contemporary DSVs require the on-site presence of a mother ship to provide logistical support for the vehicle and its personnel. The submersible's crew usually consists of a pilot and one or more observers. The observers are usually scientists, researchers, or technologists with an active part to play in conducting the mission. Due to limitations on human endurance and on-board power, mission times rarely exceed 8 hours, although some have extended to 16 hours or more. Emergency life support systems must be capable of operating for 72 hours beyond the maximum mission time.

The DSV places the crew directly at the site of interest. Visual observations are augmented for close-up inspections (less than 0.5-meter range) by video cameras, an important tool for direct observation (Robinson et al., 1992). Most DSVs are significantly larger than ROVs used in comparable missions. Its size makes the DSV a stable platform to support viewing and manipulative tasks, including biological and geological sampling. However, because it is essential for the DSV to be large enough to accommodate several persons, it is more difficult to handle at sea and more difficult to position when performing tasks in restricted work areas. Essentially, DSVs are vertical probes with limited horizontal range; therefore, they are less suitable for large-scale

Front Matter (R1-R14)

Executive Summary (1-6)

Introduction (7-17)

Undersea Vehicle Capabilities and Technologies (18-46)

Vital National Needs (47-69)

Priorities for Future Development (70-75)

Enhancing the Nation's Capacity for Undersea Work and Research (76-81)

Conclusions and Recommendations (82-84)

Appendices (85-89)

A Biographical Sketches of Committee Members (90-92)

B Foreign Developments (93-94)

C Development of Deep Submersible Vehicles in the United States: 1958-1994 (95-95)

D U.S. Government Agencies That Own and/or Use Submersibles (96-98)

Acronyms (99-100)