MONDAY, 05.11.09

0222: Day 34 (Yesterday, May 10)
Well, I hoped the last week of this job would be uneventful, but it’s not to be. Let me say outright that both vehicles are okay, but one is in a situation. After Ginger came up yesterday, she was launched back in to survey box 15/17C at 0957. Mary Ann came up at 1302. During Mary Ann’s pre-dive checks, it was discovered she suffered a thruster fault. The stator in her thruster motor failed, very similar to the failure she had around the time Ginger was struck by the boat.

We do not have a spare stator, so Mary Ann went into her van. When Ginger returned from her dive today at 0945, we decided to put her thruster on Mary Ann because we knew Mary Ann still had a functional pencil beam and it was easier and less invasive to change out the thruster unit than it was the pencil beam. We took off Ginger’s tail, installed the thruster onto Mary Ann and put Ginger in her van. We then launched Mary Ann this morning at 1134 to image box 17/18C. At 1325, just as she was getting close to depth, she suffered a vehicle re-set and aborted. We believe this is the same abort condition we’ve been seeing all along, an issue with the EdgeTech interface with the overall system.

We noticed very quickly Mary Ann was returning to the surface too slowly. We soon determined she had not released her ascent weight (a 45-pound weight resting on the underside of the nose of the vehicle). Like the descent weight, the ascent weight has a magnesium link that will decay after roughly 30 hours in the water. We watched the vehicle rise through the water column for four hours, coming up at roughly a thousand meters an hour. As it approached the surface, it slowed down. Greg Packard called me aside and explained they expected this: in essence, saltwater is actually denser near the surface, probably due to salt content, than the water at depth. This increased density means that the vehicle has less buoyancy.

When the vehicle hit this layer, it stopped rising. We spent about two hours trying to drive it to the surface using manual commands sent through the underwater modem. We were able to drive it from roughly 200 meters to within 50 meters of the surface, but no further. Every time we stopped trying to drive it to the surface it would sink back to around 165 meters. We are only getting the most basic of ranges on it at this distance, and we are using these in coordination with moving the ship to keep track of its position through triangulation. Greg is afraid if we keep banging it with the underwater modem, trying to drive it up, that we may burn out the modem on the vehicle and lose the ability to communicate with it at all (and thus lose the ability to track it and give it commands).

We’ve decided our safest action is to passively track the vehicle until its magnesium link used to secure the ascent weight dissolves and the weight falls out. The vehicle will float to the surface after roughly 30 hours in the water, which we estimate to be tomorrow at about 1800 — roughly 20 hours from now. Until then, we will do nothing to endanger the vehicle or our ability to communicate with it. We anticipate a positive resolution to the situation. I will update you tomorrow morning on our status.

1534: Mary Ann Is Aboard
We were following the vehicle and she was maintaining a drift at 190 meters. We ran the ship over her to hit her with the ship’s fathometer and just after that pass, they tried to drive her up again and she finally released her ascent weight and rose to the surface. We are going to look at the problems and try to get her back down for one more dive. We had a little photo session scheduled for noon today that will be postponed so we can keep the team working on the vehicle for a quick turnaround (big sigh of relief).

1702: Update To The Update
We are motoring back the 45 kilometers that Mary Ann drifted over the last 24 hours. While we do that, the teams are prepping to remove the tail section from Mary Ann to reinstall it aboard Ginger. Greg feels more comfortable about the survivability systems on Ginger right now as we have no explanation as to why Mary Ann’s ascent weight did not release when commanded. Mary Ann has also developed a ground fault that so far has not been isolated — it may or may not have something to do with the ascent weight release, but now we are willing to do the work to get the other vehicle running rather than spend the time with Mary Ann when she has a survivability issue. We are also going to remove the pencil beam altimeter from Mary Ann to install into Ginger. This will probably take four hours or so, and then we will put Ginger in for our last dive. Right now both teams are working both vehicles in an all-out effort to get one more dive down.