Last night we all went to bed feeling sad for leaving our AUV in the freezing cold waters of the Antarctic, under thick blocks of ice. We had a rough idea of its position; its last reliable location was known and an avalanche beacon helped range to it but pretty much all other communications were down. Jeff had deployed his tethered underwater robot that he had brought along precisely for emergencies like this, and actually located the AUV and had a tight grip on it with its metallic claws. However the captain called the recovery a off at 2100 hours, and the ROV was pulled back on board. SeaBED stayed under the ice, with its acoustic profiling instrument loudly chirping until its batteries died – we stopped hearing the chirp about midnight. For most of us it was like being separated from a loved one in a cold, dramatic way. I image Hanu did not sleep much last night.
This morning however, no matter what, we were up and ready on the deck to continue the recovery mission at 8 AM. The night before when the ROV was pulled in, Jeff had noticed some incoherent behavior such as the robot going straight when he actually commanded a left turn. So it was overhauled first thing in the morning. At the initial inspection no obvious problems were found, and it was put back in the water for a quick test. The steering problems continued, and this discouraged everyone a little bit. At this time, we had two people getting ready to go on the ice on the port side of the ship, where the avalanche beacon pointed towards to drill holes, and see if they could somehow attach a line to the AUV from the surface. Jeff’s ROV had one spare thruster, but soon it became obvious that 2 of the 3 thrusters were bad; so one spare thruster would not fix the problem; if the vertical one was replaced with the spare, ascending and descending motion could be controlled but the horizontal motion would not be. And we really needed that since navigating under the ice is a pretty difficult task. Luckily, within the next hour, it was discovered that the locking pins in the ROV propellers were damaged enough that when it actually went it the water and spun, the blades would slip. We replaced the pins and by noon, we had a coherent, responsive ROV again.
At this point, I should note that SeaBED is designed to be positively buoyant. This means that when it sits in water, it will not sink; it will float at the surface. If SeaBED’s batteries ever die, or for whatever reason we fail to communicate with it from the surface, at the end of its pre-programmed mission it will always drive or free float to the surface, and as you can imagine, looking for a 400 pound yellow robot is easier at the surface than it is at the bottom of the sea. To aid this behavior, SeaBED also has a really heavy drop weight on its bottom hull, held in place by a corrodible wire. Depending on the type of wire, it will break after a certain amount of time passes, i.e. 12 hours after it goes in the water. This is to ensure that if we lose all communications to it, by dropping its weight it will become more positively buoyant, and if it can not drive itself up, it will simply float.

The ROV goes back in the water for the recovery mission.

The ROV was working now, but the problem of how to bring SeaBED back out from the ice layer was not solved. Although last night in the bar some suggestions like using explosives, or inserting T-shaped blocks under the ice sheet and then using the ship’s crane to lift the entire ice sheet up were proposed, they were kindly rejected because, well, in a bar most people are intoxicated.
It was decided that a lightweight, preferably neutrally buoyant hook would be manufactured, tethered to a line, and it would be attached to the ROV’s claw. Once the ROV is navigated to the AUV, it would hook this plastic hook onto it, and those holding the bitter end of this line on the deck would feed weights on it, in order to make the line heavier, which would in turn make the AUV heavier, thus less positively buoyant and eventually, negative. Otherwise with the simple, gentle jerks of the ROV with a grip on the AUV would not pull it out of where it was stuck, and perhaps would force the ROV tether to break (then we would really be in trouble).

The newly manufactured plastic hook, attached to the ROV's claw.

Long story short, the plan worked, thanks everyone onboard but especially the infinitely patient and helpful JCR crew, the captain, and Jeff, who, only 2 days ago turned 30, and spent his entire birthday drilling holes on the ice, and the following two days flying his ROV under ice blocks with a scenery that could have inspired “Lucy in the sky with diamonds”. Happy birthday Jeff and welcome back SeaBED!

SeaBED and the JCR crew who were standing watch today during the final stages of the recovery.

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1 Comment on Happy Ending

  1. Deniz says:

    Hurray for the team, hurray for the crew and the ROV. Please tell your AUV to behave itself next time.

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