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Fat Man underwater propulsion vehicle ENDURANCE lands at Lake Bonney, Antarctica
Variable depth underwater habitat DEPTHX testing at the Applied Research Lab at UT
Bill Stone reads a paperback while spending 24 hours underwater using the MK1 rebreather Map of Wakulla Springs created using the Digital Wall Mapper MK1 rebreather
DEPTHX: Zacaton - Mission 3
Sunday, May 13 2007

John Kerr and Marcus Gary arrived on site at Rancho la Azufrosa on Friday evening May 11th to begin unpacking DEPTHX from the storage container where it had baked for the past two months.  John reported a positive system boot today that indicated the system was still stable.   Bill Stone left Austin, Texas mid-day with a truck load of late-arriving components that would be needed for the new high power underwater lighting system that would be used for the science autonomy experiments that will dominate this series of tests.  Jose Antonio Soriano, one of Mexico’s best known expeditionary explorers and a commercial nature photographer, began documenting the final field stage of the DEPTHX project.   Mexican biologist and DEPTHX collaborator Antonio Fregoso, from the Universidad del Noreste in Tampico, also arrived on site.  Over the weekend the floating science station in Cenote Zacaton was upgraded by Marcus and Antonio while John worked on wiring for the power supply for the new film lights.  Stone also brought two MK6 closed cycle life support backpacks and associated heliox and oxygen gas supplies for a hedge against possible need for emergency recovery of DEPTHX should there be a problem.  The MK6 is limited to 200m operating depth so any autonomous system failure in DEPTHX below that depth would be unrecoverable.

View of Cenote Zacaton looking northeast.  The round, green floating reed mats at the top of the image are known as “zacate”, hence giving rise to the name “Zacaton” for the cenote.  Normally these rotate and move about with changing winds;  however, in this case they were corralled into the northeast corner with floating line in order to keep them from interfering with the science missions.  The pit measures 120 m in diameter and the drop to the water is 17 m freefall.  Photo: (Jose Antonio Soriano / Stone Aerospace)

The view from the bottom –  a fish eye portrait of Cenote Zacaton taken from a kayak at the northwest corner of the shaft. It was at this location that cave divers Sheck Exley and Jim Bowden made their attempt to reach the bottom of Zacaton in 1994. Bowden reached a depth of 282 m.  Exley never returned and the mystery of what lay below remained until the arrival of Team DEPTHX in May 2005 during which the shaft was imaged to about the same depth (282m) using DEPTHX core instrumentation in a drop sonde configuration. The current autonomous missions hope to finally resolve the mystery of what lays below.  
Photo: (Jose Antonio Soriano / Stone Aerospace).

John Kerr working on the guts of the Science Payload to integrate a new PAR photo sensor that will measure incident ambient light levels at locations where DEPTH will begin taking biological samples from the wall of Cenote Zacaton.
Photo: (Jose Antonio Soriano / Stone Aerospace).

Marcus Gary assembling a shade canopy on the floating science base in Cenote Zacaton. 
Photo: (Jose Antonio Soriano / Stone Aerospace).



Monday, 14 May 2007

Today was spent moving the bot from the storage container and re-assembling the system and its syntactic floatation panels.  Two cranes were on site as of today – the main 60 ton unit that will be used to access Sistema Zacaton during the next two weeks – and a smaller 20 ton mobile unit.  We used the latter for final assembly of DEPTHX on its carrier.  By nightfall, all was ready for the first mission.

Cenote Zacaton at dawn.  In the background is Cerro Granito, a granite dome;  further to the east are ancient volcanic cones, whose residual heat warms the waters rising from Zacaton.  The cenote itself is carved from limestone.
Photo: (Jose Antonio Soriano / Stone Aerospace)

DEPTHX is rolled out from the field lab to begin the final series of tests at Sistema Zacaton.  
Photo: (Jose Antonio Soriano / Stone Aerospace).

Hoisting DEPTHX onto its carrier for transport to Cenote Zacaton.
Photo: (Jose Antonio Soriano / Stone Aerospace).

Loading the syntactic floatation panels that were stored on the bot carrier. 
Photo: (Jose Antonio Soriano / Stone Aerospace).



Tuesday, 15 May 2007

This was the big day:  the first autonomous exploration of Cenote Zacaton, the main entrance to Sistema Zacaton.   After a final code check at the field lab we towed DEPTHX to the 60 ton crane that lay waiting at the edge of the cenote.  With no incidents the bot made it to the water surface where it was towed to the floating science station.  A 500 m long 1 mm diameter fiber optic filament was connected to the vehicle to allow for data uplink during the mission.  This piped live information on what the bot was seeing and thinking to two laptops on the floating platform where two team members reviewed the behavior.   Following some short tests to verify basic functionality (dive, move in a  straight line, return to a point and hold etc) we sent it on its way down.  The platform had been moved to a location approximately on centerline of the shaft so that we could have an essentially straight drop.  We were not disappointed by the data coming back:  Zacaton morphed from a nearly circular 120 m diameter cenote into a rectanglular shaft, 80 m north-south by 45 m east-west.   On its way down the bot went into high resolution scanning mode.  Due to the axisymmetric form of the design, there is very little resistance to rotation, and hence it can emulate a surface-based scanning laser radar and produce exceptionally high resolution 3D maps.  It was this capability that allowed us to paint in the walls with such graphic density (see the map images from today).   At this point, at a depth of – 270 meters, two surprising things happened:  first, we began to see what appeared to be a bottom to the cenote – an inclined slope leading to a deep point at the northwest corner of the cenote.   Spin scanning ultimately illuminated the floor in a series of circular contours (see the bottom closeup image).   The second surprise was a sudden failure in the guidance system at a depth of -250 meters during the ascent.  This was manifested by a gradual divergence in the geometry data between the descent and ascent paths.  Had it happened on a fully autonomous mission it could have led to the loss of the vehicle.   We therefore began a detailed investigation of the causes of this failure.   Prior to beginning the ascent the vehicle, while hovering at -270 m, was able to image the northwest corner to a depth of -296 m underwater, currently the deepest known point in Zacaton.

Nathaniel Fairfield reviews the final code and mission plan for DEPTHX and its first mission at Zacaton.  Nearly 100,000 lines of software control the robot.
Photo: (Jose Antonio Soriano / Stone Aerospace)

The bot on its transporter heading to Cenote Zacaton from the field lab.  
Photo: (Jose Antonio Soriano / Stone Aerospace).

DEPTHX Principal Investigator Bill Stone connects the robot to the 60 ton crane that will be used to drop the bot into Sistema Zacaton for the first time. 
Photo: (Jose Antonio Soriano / Stone Aerospace).

Once in the water the bot is towed over to the floating science base. 
Photo: (Jose Antonio Soriano / Stone Aerospace).

At the science base in Zacaton a fiber optic filament is connected which will be used to activate the mission plan;  the fiber will remain connected to allow topside scientists to study the live data and ascertain if the bot is making proper decisions during the early dives. 
Photo: (Jose Antonio Soriano / Stone Aerospace).

The floating science platform follows the bot out (which is moving under its own power and its own program) to the point where it will begin a descent in the deepest portion of the Cenote.   Once the bot submerges we can see what it sees via the fiber data link but other than observing and detecting a dangerous error by the bot, we do not intervene. 
Photo: (Jose Antonio Soriano / Stone Aerospace).

On the first mission the bot descended to a depth of 270 meters.   There, beginning at a depth of 20 m below the vehicle, the presence of a sloping floor began to appear.   Using its high resolution scan behavior (which involves setting the bot into a steady rotation about its vertical axis, just like a spinning top) we were able to “paint” the floor with circular scans from the down-looking sensors.  The result was an unambiguous, and disssapointing, end to the entrance shaft – we had been prepared on the first mission to descend to at least -400 m;  the vehicle itself is rated to -1,000 m. 
Photo: (Stone Aerospace / Team DEPTHX).

The complete map from Mission 05152007-001, showing the entire height of the Zacaton entrance shaft.  Note the distortion in the upper ¾ of the image – this was a result of a data registration mis-match between the descent data and the ascent data due to failure of one part of the onboard guidance system. 
Photo: (Stone Aerospace / Team DEPTHX).

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