6 March 2012.
A group of tensed looking people in a tunnel access chamber finally receive the call everyone is waiting for: "The vehicle just made it through the tunnel."
The cavern Freudenweiler is one of four 100 m deep access chambers to the tunnel: a 25 km long pipeline with a diameter of 2,25 m, built in 1969 to supply Stuttgart with drinking water from Lake Constance. Since 1971 the tunnel is working without any incidents. However, the responsibles of the operating company asked for an inspection of the internal conditions.
A video inspection with an ordinary ROV could not be used due to a cable range of maximum a few hundred metres.
As a solution, the Tunnel Inspection Head came into life to inspect the whole tunnel without touching the walls in order to prevent possible water pollution. This idea was coupled with challenging requirements: The AUV had to be able to maintain a centered position within the tunnel. Furthermore it had to run the mission without GPS and acoustic Doppler speed sensor.
In the end the AUV had to recognize that the mission was completed and stop automatically at the tunnel access point.
Besides directing the AUV manually in the tunnel, the vehicle was required to work reliably over a time period of 7 hours without intervention of the operator.
The payload head was built within three weeks. As a special feature, the head featured a ring made of plexiglas that contained four wide-angle cameras for a 360 degree view within the tunnel plus one forward directed camera.
To maintain a central position, laser pointer were added to measure the distance between the vehicle and the wall. As an overall lighting arrangement, several LED lights were installed around the head.
During the last days, the team was working at full blast. The main problem was to find a solution for the AUV to automatically stop right at the tunnel access point, when the mission was completed. In the end, the team installed a light at the tunnel access point that sent a signal to stop the AUV. The whole system was realised within two days including the software.
On the mission day, the vehicle was desinfected and cleaned properly to prevent water polution. After a cordial welcoming on the occasion of such a unique mission, the SeaCat was launched into the tunnel. In 40 years, this was the first time, people got an insight into the pipeline.
With the help of a customized notebook, directing the SeaCat in the tunnel went well without any problems. After manouevring the SeaCat accurately centimeter by centimeter in the tunnel, the operator switched to the autonomous mode.
With a speed of 2 kts the AUV ran its mission by centering itself in the narrow pipeline.
At different locations along the pipeline listening posts were stationed to track the vehicle.
The last access chamber provided a 38 m deep well with a diameter of 8 m. Half filled with water, this was the point where the AUV should stop automatically after receiving a light signal.
15 persons were starring nervously in the well waiting for the AUV to approach. At 4:55 pm the SeaCat finally passed the chamber and reacted immediately to the light signal. Driving in reverse, the AUV positioned itself right in the middle of the access hole in the tunnel.To the applause of the spectators the lift engines were started and brought the vehicle to the surface. The mission was successful - a world's record.
After the mission, data was collected, all devices dismantled and further missions discussed. An interesting new market opened up for ATLAS ELEKTRONIK.