Wednesday, July 19, 2017

The Dance

By Teresa Atwill

Sunrise on the R/V Revelle at Axial Seamount.
To run a complex interdisciplinary research expedition like the Axial 2017 research cruise on the R/V Revelle requires coordination and communication between the ship’s crew, the ROV Jason and AUV Sentry teams, and the science team. Like a complicated dance company performance, each person has specific roles to be fulfilled and the timing of events is crucial. Mistakes could result in something as minor as lost data or samples or as major as damage to the ship or research instruments. Communication is key to keeping everyone’s efforts well-coordinated.

Navigation
One of the areas where there is the biggest need for communication and coordination is navigation of the ship and the ROV Jason as they move together during dives around Axial Volcano. When Jason is transiting between benchmark sites for pressure measurements on our cruise the Jason navigator uses software to let the ship’s dynamic positioning system know where it needs to move to next. They need to move at a speed that keeps the Jason ROV and its cable in the correct orientation to keep the vehicle and its cable safe.
Jason's view of the ship navigation.
The Revelle bridge officers monitor the bow and stern (both port and starboard) thruster output and the seas and winds and choose a heading for the ship to point into that minimizes how much the ship’s engines have to work. So right now as Jason and the ship move northward toward our next benchmark on the seafloor the ship’s bow is actually pointing to the southwest and the ship is crabbing backward to get there at a half a knot. The Jason cable is entering the sea from the winch on the port side of the Revelle and this also requires both the bridge and the Jason team to work to keep the Revelle moving in a way that keeps the cable free of the ship.

View this movie of the navigation (ship is blue, Jason is green and the acoustic buoy on the wire is pink):
video

Deployments and Recoveries
The Revelle’s marine technicians (referred to as ResTechs) Josh and Jim serve as the liaison between the scientists and the ship and oversee and run any deployment or recovery of instruments or vehicles over the side. They are responsible for the safety of everyone working on the deck and ensuring that no equipment is damaged during deployments or recoveries. For safety everyone involved has to wear hard hats and work-vest life jackets. For the ROV and AUV deployments the ResTechs and the rest of the ship’s crew must work in tandem with the Jason and Sentry teams that operate the vehicles.
ResTechs Jim (left) and Josh (right).
The ResTechs have radios to communicate with the bridge about what is happening with the deployments or recoveries and the bridge can also watch what is happening with shipboard cameras. The ResTechs also use hand signals to communicate with the Revelle winch or A-frame operator.

For example, to recover the Sentry AUV the following steps occurred. First the dives of both Jason and Sentry had to be pre-planned and designed by Chief Scientist Bill Chadwick to bring Sentry back from its long (24 hr) multibeam survey to meet the ship at a specific time and place as it moved with Jason to different sites within Axial Caldera. (This is sort of like the plan to have the Lunar Lander meet up with the orbiting Apollo space craft). In this case we have three moving objects (Sentry, Jason and the Revelle) in a 3D ocean world moving at different rates and hopefully not running into each other! The Sentry team kept checking on Sentry’s path and provided updates to Bill, the ship’s bridge, and the Jason team as the rendezvous neared.

AUV Sentry driving toward the ship.
When Sentry was about an hour out, Jason was lifted off the seafloor so that the ship would be better able to maneuver for the Sentry recovery. About half an hour out, Sentry dropped extra dive weights it was carrying so that it could leave the bottom and rise more quickly to the surface. Twenty minutes later Sentry was seen at the surface and the Sentry team drove Sentry closer to the ship with a radio frequency control console. As Sentry came up along the side of the ship, the Revelle dynamic positioning system was set to hold position and as the thrusters tried to do this they pushed Sentry back a few meters. Sentry was then driven closer to the ship again and the Sentry team had hooks on poles to latch onto and at the same time hold off Sentry from the side of the ship. The lifting hook was attached to the ship’s crane and Sentry was then lifted out of the water and onto the deck of the ship. Once Sentry was in its cradle on deck, Jason could then go back down to the bottom to continue its job of visiting pressure benchmarks with the Jason crew returning to coordinating the ship’s movements and driving Jason.

Science Data
There are crew from the Revelle, Jason and Sentry team members and the scientists involved in the collection and organization of all the science data during the cruise. The goal of this process is for all the navigation and science data to be cataloged and organized and made available to not just the scientists involved in the cruise but also for the general public to access. In the Jason Control Van there is always a combination of Jason team members and scientists discussing where to take samples or conduct experiments with people from the science party recording events. Photos, videos, navigation and other details are recorded continuously. This information will become part of a cruise report and will be available on-line after the cruise in what is called the Jason “Virtual Van” at this web site, click on our cruise "RR1712":
Virtual Van Website (http://www.whoi.edu/page.do?pid=12876)

R/V Revelle's computer tech, Brent.
The scientists and engineers have fairly heavy computer, network and printer needs and there is a Revelle computer tech, Brent, who is in charge of helping us with this. He has already fixed computers that were misbehaving and has helped set us all up with access to the ship’s network. The only way we can access the internet is through a satellite link and it is expensive, so there are limits to what we can do online.

Dance Missteps are Dangerous
There is risk in not managing the dance correctly - if Sentry gets to the end of its dive and the battery power gets lower than 5%, then it automatically aborts its dive wherever it is and comes to the surface. If the ship is not there to recover Sentry, it would start to drift away quickly in the surface currents. If that occurred away from where we were with Jason, we would have to abort the Jason dive, recover Jason and rush off with the ship to recover Sentry. So that's another reason "the dance" is so important and critical to get right. It could waste a lot of time and up-end our cruise plan for it to go wrong. Plus we don't want to lose Sentry!