MIT Wins The 1999 AUVSI AUV Competition

Mission

The International Autonomous Underwater Vehicle Competition challenges teams of college students to design and build underwater vehicles to navigate a submerged obstacle course. While operating autonomously under computer control, vehicles must pass through a series of gates, then enter a specified recovery zone, drop a marker, and surface, all within a specified time interval.

The contest arena for the AUVSI competition is the P-253 test pond at the Naval Coastal Systems Station in Florida. Six gates, with two uprights and a crossbar made of PVC pipe, are submerged along the perimeter of the pond, on the 3 m depth contour. From the sixth gate, a submerged pipeline will lead to the target zone, a 3 m square underwater raised platform. Each team's fully autonomous underwater vehicle must pass between the uprights and under the crossbar of each gate, follow the pipeline, enter the target zone, release a marker, and surface in the target zone in under 20 minutes.

The vehicle is not permitted to communicate with any off-board entity, including navigation beacons and the Global Positioning System. Points are awarded for each gate traversed, for marking the maximum depth in the target zone, for surfacing in the target zone, and for time.;

Competition Weekend

Teams arrived at the P-253 Test Pond an the Coastal Systems Station on Friday, August 6 for the 1999 competition. The weather was hot and sunny. Friday afternoon was given over to vehicle testing in the competition arena. The team set to work perfecting the isobath-following code that was used to navigate through the six gates. While some team members worked on the isobath code, others attempted to interface to a mechanical scanning sonar unit which we hoped to use to locate the gates. While the vehicle was capable of following the isobath at low speed, it tended to pitch out of control at high speed. At 1800 hours the test pond closed and we retreated to our motel pool to develop an active pitch control system using the vertical thrusters mounted fore and aft.

Saturday saw more testing at the P-253 test pond. Overnight we had perfected a pitch control system and a safety system to slow the vehicle if its depth deviated from our command. With these changes the vehicle was able to navigate the perimeter of the test pond in under 10 minutes. At that point we turned our attention to the final competition task, the location and marking of a submerged target zone. Hampered by the limited range of our sonar altimeter, we left the test pond Saturday without a successful target zone acquisition program.

Saturday night we settled upon a strategy for navigating to the deeper isobath of the target zone, and in the motel pool we discovered that our altimeter was capable of detecting the edge of the target zone. By the end of the evening we had an untested program for finding and marking the target zone, and we planned to use our one hour of alloted testing time for debugging. Despite the imminence of the competition we felt we had a good chance of completing the competition mission.

Sunday dawned rainy with electrical storms passing over head periodically. The competition day testing runs were delayed first for an hour, then for another two. When we got to the arena, each team's test time had been cut from one hour to only 40 minutes. Almost as soon as we got in the pool the sky darkened and thunder rumbled in the distance. After only a few minutes of testing, the competition officials pulled us out of the water as an electrical storm passed overhead. Remaining test time was cancelled, and the competition began immediately with the passing of the storm.

When MIT's turn came up, the University of Florida's vehicle had just put in an impressive performance, passing through four of the six gates on the pond's perimeter after a couple of false starts. ORCA-2 had to make it through at least five gates to ensure victory. Although we had demonstrated the ability to pass through all six gates at 40% of full power, we chose to reduce our speed to make the vehicle track straighter. At the prompting of the competition officials, we rolled ORCA-2 to the edge of the P-253 test pond and set up our wireless communication system. Matt logged into the vehicle and checked some last-minute parameters. At our command, ORCA-2 was lowered into the test pond, the lift rope was cast off, and Matt commanded the vehicle to start it's autonomous mission.

Like magic, ORCA-2 submerged to 1 meter depth, headed for the center of the pond, then turned back toward the shore, turning sharply to the right as it aquired the 3 meter isobath. With two divers from the Navy Experimental Dive Unit in hot pursuit, ORCA-2 passed through the first gate and headed for the second. Slowly but surely, our vehicle passed through all six gates, returning to the launch site for recovery by the divers. Project ORCA had triumphed again.