The purpose of the Harvester test-target planting system was to place unexploded ordnance (UXO) surrogates (or targets) at various burial depths and orientations in waters ranging from the beachline through the surf into water depths of up to 30 meters. A key feature was the ability to precisely deposit the targets in a re-acquirable and verifiable location. The concept referred to as the `Harvester` was based on using proven technologies such as pumps, caissons, gravity feeds, and plows.

Technology Description

A design challenge was to fit all the components on a delivery platform, including power. The main drive platform is based on the Sea Beast autonomous, amphibious, bottom crawler (now referred to as the B350-HD) with an 800-lb payload capacity. The fully loaded Harvester system has a low dry ground pressure of 6.0 kilopascals (0.88 psi) or half that when submerged, enabling transit across weak soils. The Harvester payload consisted of the navigation and communications package, the munition dispenser, and the excavation and burial system.

Two dispenser designs were constructed and tested that allowed the system to carry and release multiple targets. The simpler drop rack used gravity feed to drop targets on the ocean floor. The system had a high sail area and is restricted to predictable shapes but could hold sixteen, 155mm artillery shells (or smaller diameter rounds).

Control is based on either radio frequency command, man-in-the-loop or autonomously based on prearranged positions. Placement precision is centimeter accuracy using a mast-mounted real-time kinetic as a guide, or .5-m accuracy using inertial measurement unit guidance only. Clusters of five targets could be placed in a 3-m square body-centered pattern with an accuracy of 0.15-m.

Demonstration Results

The following key objectives were accomplished:

  • Designed and built the Sea Beast (light) vehicle.
  • Tested navigation systems and determined precision of placement.
  • Wrote, tested, and verified a vehicle orientation algorithm to enable the vehicle to place a tight pattern of targets in various directions.
  • Wrote and preliminary tested placement control software.
  • Redesigned and built a heavier duty motor and transmission system: Sea Beast (heavy).
  • Tested drop-off of a limited number of munitions (4 x 105mm) using a `wing’ dispenser design.
  • Tested the power necessary to plow-in (bury) munitions.

Experiments were performed on excavating emplacement holes for placing buried targets at various angles and depths to 1 meter, but the desire to optionally bury the targets was overly ambitious. The process was power-intensive, highly soil-dependent and imparted a high risk of catastrophic failure. Alternate approaches were conceived but not tested and none offered a risk-free solution. In particular, if the system failed mid-way during the excavation or insert process the vehicle would be anchored in place requiring manual dismantling. Ultimately the decision was made to focus only on surface laid targets.

The cost advantages and suitability of the Harvester are site dependent. Where surface laid targets are permitted, the logistical advantages over divers and support craft are significant. The Harvester can carry from 6 to 16 munitions, depending on size, and travels at 0.5m/second. Setup and programing waypoints take less than an hour, leaving 6 hours for operations. Where dead-heading is minimal, a full 50+ field can be planted in a workday. If burial is required the power consumption, battery change out and burial cycle time reduces the production rate by roughly a half.

Implementation Issues

The economic impact of the pandemic and the need to redesign the vehicle to accommodate heavier loads curtailed completion of the program. Component costs doubled, beach access restrictions prevented testing, and delivery delays all led to elimination of the final refinements and demonstration. The technology was demonstrated at a subsystem level to be a success, meeting capacity and placement accuracy goals in sea State 3 surf conditions (poor surf with some (30%) FAIR waves to ride). The dispensing of targets on the surface or in shallow partially buried sites, is achievable. Deeper 1-m burial is possible but with greater development cost and a much greater reliability risk.