Field notes: DEPTHX

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

The advance DEPTHX team arrived at Rancho La Azufrosa last night after an eventful set of days crossing the border. It is difficult to explain all of the details from our plight, but let me just say that it deserves a write-up of some sort.

We left Stone Aerospace in Del Valle, Texas Thursday afternoon, arriving at our hotel in Harlingen after midnight. Awaking the next morning, we crossed the Rio Bravo at the Los Indios crossing, one that I always try to cross since it is out of any urban area. The customs agents were very nice there, but since it is a satellite office, they said we needed to cross in Matamoros. We stayed at Los Indios for about 5 hours calling back and forth to the U.S. Embassy in Mexico City, trying to convince the Mexican officials to let us pass (we even set up our mobile satellite internet at the customs area!), but finally about 12:30 it was determined that we must turn around and go to Matamoros. One hitch…..we had to now go back through U.S customs towing a trailer with a submersible robot on it!

We spent 2.5 hours going through the commercial import line (with all the big trucks), and were lined up for a full-vehicle x-ray scan. After some convincing that this could fry all the electronics and ruin the project, the U.S. customs agents agreed to just manually scan to see if we had any radioactive material. Since we didn’t, they let us pass back into the U.S. Back where we started from in the morning, we regrouped in the parking lot of the hotel, printing out equipment invoices emailed from the U.S. Embassy, drafting a manifest list, and re-wrapping the bot frame in a tarp. By 4:00 PM we were on the road to Brownsville, destination Matamoros.

While approaching the bridge, we were met by a swarm of U.S. customs and "ICE" (I think it stands for International Commerce Enforcement) agents. Apparently, there are export restrictions on some stuff, and they were quite confused as to how to handle our interesting caravan. After sitting parked, poised to cross into Mexico, our "friendly" U.S. customs agents (in the sake of National Security, I’m sure) decided it was necessary to "detain the commodity" until they could run this up the chain of infinite bureaucracy. This meant it was locked up in holding yard Friday night. We had no idea how long this would take, and holed up in a nearby Best Western pondering our fate.

Saturday morning….Our options limited, I began to receive phone calls from the customs agent working our case. I have to say this guy was great. He went the extra mile to get us going again. After contacting our science liaison at the U.S. Embassy in Mexico City, he decided that it would be OK to let us go with "the commodity" and continue onto Mexico. We hooked back onto the trailer and crossed the Rio Bravo for the second time around noon on Saturday. I never felt so relieved to be in the hands of Mexican bureaucracy instead of the U.S.

Crossing through Mexican customs was very straight forward. A couple of hours getting forms filled out and documents stamped and we were heading south through the streets of Matamoros by 3:00 PM. The rest of the drive was quite uneventful, except for the fact that I was pulling a 8-foot wide trailer on roads that were 8 feet, 2 inches in each lane with radical drop-offs on the shoulders. I can attest to the "white-nuckle syndrome."

We finally arrived at Azufrosa around 8:30, and began the ominous task of unpacking. The internet seems to be working well, although not at light speed. It’s better than nothing at all. I’m sitting in the palapa drinking coffee writing this email, it’s pretty cool.

Marcus Gary
Ph. D. candidate
Jackson School of Geosciences
The University of Texas at Austin

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Having successfully arrived intact at Rancho la Azufrosa (site of Cenote Zacaton) and greeting ranch owner Alejandro Davila, we began setting up basecamp in ernest today for Zacaton Mission 1. This was very much a “MacGyver” day, with Marcus Gary showing an extraordinary collection of eclectic skills (welding, burning, electrical contracting) that go well beyond the experience of the average hydrogeology PhD student.

Marcus, who is in charge of site logistics in addition to managing the environmental sensor array for DEPTHX, arranged for the transport of a 12 m seagoing shipping container to the ranch to serve as the field lab. First order of business, however, was the construction of a “bot garage” for DEPTHX to protect it and the tech crew during assembly—the bot was transported to the site in pieces to avoid shock loading of sensitive electronics.

The day was mainly spent welding framing poles in place for the garage, stretching aircraft cable for tarp suspension, and running electrical lines into the shipping container for the lab benches. By nightfall we had fluorescent lighting inboard and bench power. Tomorrow begins the formal process of painstakingly re-assembling the bot.

Bill Stone
Stone Aerospace

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Marcus and Robin Gary left for Austin today – Robin returning to her job at USGS and Marcus to fetch an additional load of supplies for basecamp. This left us with a skeleton crew of John Kerr and myself to work the finer issues of setting up the field lab and re-assembling the bot until further reinforcements arrive.

First order of business was to uncrate the bot. At 1.5 metric tons DEPTHX is an industrial strength machine (rated to 1,000 m ocean depth), but this also means it’s not something you toss about by hand. Alejandro Davila, the owner of Rancho la Azufrosa, kindly made arrangements with a local Tampico-based crane company to ship a mobile handler to the site. We then began unloading all the electronics modules into the field lab for individual checkout.

Above: about half of the pressure vessels that go inside DEPTHX, at the field lab.

Although it seems like a simple process, DEPTHX has over 500 electrical connections, all of which run through scores of dis-connectable pressure rated cables… and each of those, along with the housing closures, have hundreds of orings, which are lubricated and therefore attract dust… of which there is plenty at Rancho la Azufrosa. So every make-and-break of a cable connection or housing lid means replacing orings, re-lubing, and sealing before any contamination can enter.

Today we managed to load the variable buoyancy engine (VBE) ballast as well as the two pressure housings for the redundant lithium-ion power supplies into the bot frame. We also charged up the VBE pressure drive tanks (5,000 psi carbon-epoxy construction) and mounted those.

The weather has been cooperative, partially sunny, a bit windy, and 70F. The only point of serious concern today was that while totally focused on our work we began hearing strange “clacking” noises outside the lab trailer and emerged to find a large herd of goats inspecting the bot at close range… in fact they had it surrounded and were licking the sonar transducers. Fortuitously we caught them before they got the idea to chew on the cables. New line item on the pre-flight checklist: remove goats from bot vicinity.

John Kerr attaches the Variable Buoyancy Engine (VBS) ballast tank to the top of the bot – the VBS has a differential displacement of 26 kg to compensate for compression-induced buoyancy loss as the vehicle descends.		Mounting the pressure housings for the twin Li-Ion power supplies that drive DEPTHX. The yellow cylinders are 5,000 psi carbon-epoxy pressure vessels that are used to drive the VBS. The gray cylinder at top center is one of two vertical ducted thrusters that work in concert with the VBS to vertically stabilize the bot and allow it to hover.

Bill Stone
Stone Aerospace

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Not everything goes according to plan. After unpacking most of the hardware into the field lab the previous day the first order of business was to top off the charge on the twin litihium-ion power stacks used to run DEPTHX, since all subsequent electronics check-outs are based on being on system power.

Unbeknownst to us (possibly from vibration on the trip down) a loose wire on the charging cable crossed circuits and sent full stack voltage (48 volts) down a line normally used for digital communications to control a number of electronics boards on the battery. Before we caught the problem it had fried all three (two primary and one backup) of the E-Stop (emergency stop) power disconnect boards on site here at Zacaton. For human safety reasons DEPTHX has the equivalent of a “big red STOP” button on the top of the vehicle. But because the full power draw from the vehicle can be large (scores of amps) that E-stop switch is not like your normal house light switch—it’s a digital switch that in turn “talks” to a very high power relay board in each battery which in turn enables high amp flow from the batteries. And it was the communications line (and all the microchips) to that “Disconnect” board that got fried. It took all of today to sort out the source of the problem that caused the loss of the boards and to permanently preclude the incident from re-occurring. But that still left us with a dead bot until the E-stop could be renabled. No solution had been found as of midnight and the team retired with the unpleasant knowledge that we had just 4 days in the jungle to sort this out before the arrival of the main research team.

Bill Stone
Stone Aerospace

Above: source of “El Nacimiento” (the spring) lies just 100 m west of the main field lab at Zacaton. The horizontal black slot at center is the entrance to the Pasaje de la Tortuga Muerta (dead turtle passage) leading upstream and underground to the main Zacaton cenote. It was first explored in 1989 by Jim Bowden and Gary Walton and leads 220 m underground to where it re-emerges on the southwest corner of Zacaton.

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

We awoke early to the knowledge that the bot was dead until we resolved the disconnect board issue. John Kerr began a continuous stream of emails with Nigel Jones back in the states while Vickie Siegel, myself, and two visitors coming north from the 2007 Tabasco caving expedition made our way into Aldama (the nearest town) in search of a Mexican cell phone to see if we could get voice communications out from the ranch. We considered Skype but it doesn’t work well when run off satellite relay (we were using a customized version of a HughesNet link).

Above: Nacho, the main ranch hand at Rancho la Azufrosa, brings over one of many loads of sand used to level out the “bot garage” so that sheets of plywood could be laid down to serve as a surface for maneuvering the bot (it’s lower orange frame rides on four heavy shop casters, but these need a flat surface to work on.

So off we went while John continued his asynchronous stream of emails with Nigel (our lead embedded systems electrical engineer). A plan was developed to produce more boards. Component parts were FedExed to Jones and he spent most of the day assembling the prototype boards – a tedious process that involved placing 2×3 mm surface mount chips on the board and using a large magnifying lens to help with guiding a fine point soldering iron to get all the chip pins properly soldered to their respective pads on the board. Nigel also programmed the onboard logic chips and then re-FedExed them to Harlingen, Texas where, if all went according to plan, they would be picked up by Marcus Gary who was due to begin driving back on February 2.

Bill Stone
Stone Aerospace

Above: John Kerr debugs the disconnect board following email discussions with Nigel Jones.

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

A good day today. We received word early via email from Marcus Gary’s Blackberry wireless that he had made it to Harlingen and that the replacement disconnect boards had arrived intact at FedEx. It would still be another six hours before he would arrive at Rancho la Azufrosa. Meanwhile it was a full day for those of us at the ranch. Vickie Siegel and I began an assembly line to clean all of the electrical connectors for DEPTHX and replace all of the oring seals associated with them. Given that this would be the final system assembly before DEPTHX could see service at up to 1,000 m water depth this was a necessary preventive maintenance task.

Above: Vickie Siegel takes on the tedious task of replacing all the oring seals on the electrical cables for DEPTHX. Some of the eleven electronics housings have more than a dozen such connections each, so this was an all day task.

Once that was done each cable end was individually sealed to prevent ingress of dust… of which there was a lot flying around outside as stormy weather blew in from the north.

While waiting for the disconnect boards to arrive John Kerr made good use of time by integrating the main cPCI computer housing, the science payload computer, and two of the sonar array digital signal processors into the vehicle.

Marcus Gary finally arrived at 7pm with the replacement boards. When installed, however, they did not deliver the necessary output voltages. Further emails ensued but by 11 pm the boards were still non-functional and the team went to bed. Nonetheless a lot of progress had been made today.

Bill Stone
Stone Aerospace

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Resolution. John Kerr was up at dawn and on the cell phone with Nigel Jones going over possibilities for why the new disconnect boards were not functioning. After a few rounds the problem was isolated to one particular chip. John then began methodically testing that chip and found one of the eight tiny solder connections to be non-contacting. When he re-soldered that the system came up. With this resolved we completed the checkout of the E-stop system with the batteries (now fully charged) back in the loop. John then powered up SIOP (the system basic Input-Output onboard interface computer) and was able to interrogate the various sub-systems and their associated sensors. The batteries were online and giving good readings and, following entry of the local GPS coordinates which Vickie Siegel collected outside the lab, the IMU portion of the guidance system came up with a proper alignment.

Above: Vickie Siegel doing final checkout on the 100m sonar array

Above: John Kerr (SAS) interrogating the bot with the microRAPTOR real-time interface tool from the lab.

Above: Screen capture from microRAPTOR showing both batteries online and charged (a very good thing indeed, considering where we were on Tuesday !).

Above: Vickie Siegel and John Kerr with DEPTHX at 10pm on February 2. We are now about one day from being fully operational, assuming no more field glitches.

At this point we continued with routine assembly tasks until 10pm. Marcus Gary meanwhile had completed installation of ceiling vent fans in the lab. Although seemingly unnecessary given the cold temperatures we’ve been experiencing the past few days, it will be required once the normal hot weather returns.

In all, a very good day. Barring any unforeseen problems we should have the bot close to complete assembly by late tomorrow and ready for transport to cenote La Pilita on Sunday, where we will begin the first true exploration field tests in a truly unexplored environment.

Bill Stone
Stone Aerospace

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

We made rapid progress today, despite the ever-increasing bad weather (from the same arctic front that dropped temperatures in Colorado far below zero – project microbiologist John Spear wrote by email indicating that it reached -25F in Golden, but here in Tamaulipas it came as a steady cold downpour).

Above: John Kerr carefully loading Battery Pod 1 into DEPTHX. Each of the two Lithium-Ion battery stacks contains the energy equivalent of 6 lbs of TNT.

Above: Vickie Siegel works on the water sampler sub-system of the biology payload for DEPTHX.

Both onboard battery systems were successfully brought online today and after a complete change of all canister and cable connection orings we loaded the two Li-ion packs into the bot (see photo). It is difficult to explain the care and attention that one must pay to such a high energy source, but the following energy conversion may be of help: each battery pack in DEPTHX carries the energy equivalent of 6 pounds of TNT. Having loaded all of the main computer and electronics pressure housings we turned our attention to the science package, where changes had to be made to place the water collection containers in an easily accessable outboard location so that they could be removed at the conclusion of a science mission without disassembling the entire probe sub-payload. By 10pm we had all systems installed and had confirmation of hardware powerup and software communications with the main cPCI computer pod, the guidance unit, velocity logger, environmental sensor suite, depth sensors, batteries, science package, and the 200m obstacle avoidance sonar array. Only the motor controllers and 100 m sonar arrays remain to be tested in the morning before the bot is fully operational. Marcus Gary left basecamp around 3pm to pick up the Carnegie-Mellon portion of the crew at the Tampico airport. They arrived just before midnight. The rain is coming down hard now.

Bill Stone
Stone Aerospace

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Today was an extremely busy day. With our crew now expanded to eight we held a team meeting at 8am and divided up the tasks for the day. Our crew contingent as of today includes:

• Dave Wettergreen (CMU), George Kantor (CMU), Nathaniel Fairfield (CMU), Dom Jonak (CMU)
• Marcus Gary (UT Austin)
• Vickie Siegel (SAS), John Kerr (SAS), Bill Stone (SAS)

Following final checkout of the electronics pods and software communications interfaces we rolled the bot out of the “garage” and began loading the four orange syntactic flotation blocks (see photos).

Above: Left to right: Alejandro Davila (owner of Rancho la Azufrosa), Nathaniel Fairfield, Marcus Gary, and Vickie Siegel look on as DEPTHX gets its final software verification.

Above: Nathaniel Fairfield (left) and John Kerr load the syntactic foam flotation blocks.

Above: the conditions we were working under.

Above: Marcus Gary ably drives the bot to cenote La Pilita, a 4 wheel drive journey of about a kilometer which we successfully completed in about 30 minutes.

The syntactic is a special glass-sphere-filled foam that remains nominally incompressible down to a kilometer depth underwater. We use this to make the vehicle initially precisely neutrally buoyant (neither sinking nor floating). The entire operation was complicated by the strong, steady dounpour as the unusual weather persisted.

Once the syntactic was bolted down Marcus Gary drove the bot to cenote La Pilita where the first true exploration field tests would begin tomorrow. Divers Jim Bowden, Ann Kristovich and others have made initial reconnaissance descents that indicate that La Pilita seems to have a bottom at around 100m, but very little else is known because of the reduced visibility and limited range of diving lights

Thus, the geometry remains unknown as does the potential presence of passages that extend off the entrance shaft. Because of this, we have prepared a safety tether for the initial descents that includes a fiber optic communications line and a 1500 kg test dyneema retrieval line. The entire umbilical measures only 3mm in diameter. However, because of the potential for line snags we planned to feed the safety tether through a high pulley suspended over the center of the cenote.

Above: Vickie Siegel scales a few phone poles to install a high line support for the vehicle safety tether at cenote La Pilita.

To enable this Vickie Siegel used Yosemite style aid climbing equipment to scale a series of telephone poles that had been installed for lighting around La Pilita some years ago. Once the high anchor points were in place the pulley was drawn up through a central second pulley at the mid point of the horizontal high line over the cenote.

Bill Stone
Stone Aerospace

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

FIRST DATA: Today was a milestone for Team DEPTHX. The vehicle made its first true exploration run at Cenote La Pilita (that is, it built a 3D map of terrain never before seen by man). Mission control was established in two large tents beside the 25 m diameter cenote. Marcus Gary and John Kerr managed the “sky trak” mobile hoist to get the vehicle in the cenote whereupon John spent a fair bit of time in the 32C water performing fine tuning of the vehicle buoyancy by adding small lead drop weights. For these initial missions, largely because of the unknown spatial extents of La Pilita, we equipped the vehicle with a 2.5mm diameter Dyneema safety tether (breaking strength 1.5 metric tons) and a 1 mm diameter fiber optic link for observing the real-time behavior of the vehicle at mission control.

Importantly, besides providing a huge stream of state and sensor data (see previous blog image of the microRAPTOR real-time vehicle state software output) we were able to monitor live what the vehicle was “seeing” through an openGL visualizer that showed a representation of the vehicle along with sonar beam models for the 54 discrete sonar transducers that build the world map about DEPTHX. The present onboard software can reject spurious readings in real time—important for the upcoming geometry-based navigation tests. Also piped up are video images from the three onboard cameras. An example of the output from the wide field science payload camera is shown below in the screen capture from one of the mission control laptops.

Left: DEPTHX being lowered into the 32C hydrothermal spring of cenote La Pilita.

Above: Dom Jonak (left) and Nathaniel Fairfield at mission control, La Pilita monitoring the live data uplink from DEPTHX. Current testing is being done on-tether for real-time performance evaluation.
Below: John Kerr releases the vehicle to begin testing.

Following a series of warmup runs the vehicle was commanded to undertake a vertical powered descent mission to a maximum depth of 100 m while insuring that it maintained a “keep out” zone of 10 m about the vehicle and a minimum 5 m standoff distance to bottom. The resulting map (see figure below) shows 340,000 sonar wall hits during the course of an approximately 1 hour duration mission. During the descent the vehicle was set in a uniform rotation so that the sonar arrays “scanned” the wall, creating a high density fill factor.

Left: George Kantor (left) and Dave Wettergreen (both from Carnegie-Mellon University) contemplate the performance of DEPTHX at cenote La Pilita.

The real power of the 4-Pi steradian imaging system is that DEPTHX can simultaneously look in all directions. This, and the fact that the vehicle is descending while it rotates, provides the maximum opportunity for filling in voids that would otherwise not be seen by normal planar line-of-sight imaging systems. This capability is crucial to the implementation of 3D SLAM, which we will begin testing towards the end of this week.

Of particular interest, the plan view of the map (left image below) shows the presence of a 20 m diameter tunnel leading off from the western wall of the chamber at a depth of approximately 40 m at the roof and leading in a northwest heading. Similarly, there appears to be a broad bulging in the room in the northeast corner at about the 30m depth level. The vehicle came closest to the floor on an eastward sloping incline; what happens to the west (which is in the direction of cenote Zacaton—the target of the DEPTHX finale field exercise in May) is unknown. We hope to fill in more data in the coming days leading to an untethered subsurface mission in a full 3D labryinthine environment.

Bill Stone
Stone Aerospace

DEPTHX 3D map of Cenote La Pilita, created February 5, 2007 during the first true exploration mission for the DEPTHX project. The map is comprised of 340,000 individual sonar “hits”. In general the vast number of points clearly define an enormous subterranean submarine void—the full extent of which will not be determined until further off-axis exploration in the coming days. Outlier points are raw data as recorded by DEPTHX; some of these were a result of an incorrectly cabled sonar transducer; some represent “multipath” signal bounce (and therefore non-existent geometry); and some likely represent sparse new data suggesting potential voids to be explored on subsequent missions. (click here for a bigger version of this map)

Screen capture at mission control showing wide field camera shot of the wall of La Pilita at 12m depth and live sonar imaging (right).

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Science Payload Powers Up:

We continued with vertical powered exploration profiles today, reaching a maximum depth of -98 m in cenote La Pilita. During this time we also tested the Science Payload wide-field camera at several depths and got our first look at the bottom of La Pilita, where, in true planetary robotic tradition, features began to acquire names, such as the “Iguana Rock” shown below.

Above: The eye of the bot-wide field camera on the Science Payload for DEPTHX.

Above: Bio film on the wall of cenote La Pilita at a depth of -12m.

Above: “The Iguana” rock on the bottom of La Pilita at a depth of -105m.

Above: Nathaniel Fairfi eld gets to experience the world of the bot (at shallow depth).

Above: The busy world of Mission Control at cenote La Pilita.

This evening Alejandro Davila picked up SwRI researchers Tom Lyons and Ian Meinzen who will be with us for the remainder of Mission 1 to tend to hardware and software relating to the Science Payload. Below is appended Dave Wettergreen’s summary of the technical results from February 7.

Bill Stone
Stone Aerospace

Tecnical Status and Progress – February 6

• Tested proximity operations. The robot typically tries to stay away from the walls, but in order to take images and collect samples it must move into close proximity of the wall and then position steadily (stationkeeping) to move along a transect. Proximity operations is our term for this mode. Not surprisingly La Pilita presents a much more complex geometry than the smooth walls of a test tank. The algorithm fits a surface to a collection of forward sonar range measurements and then tries to control the vehicle’s thrusters to move to a point relative to the vehicle (for example its probe tip) along the wall. When the wall has concavities and convexities, the tracking point can jump around or not move at all as the vehicle moves. To correct for this, the vehicle might move erratically. This is not a desirable behavior so we modified the algorithm to instead drive the vehicle smoothly and then reacquire a point on the wall. This was tested in a number of locations in la Pilita and we are now able to get the vehicle into position for science investigations of the complex geometry of la Pilita’s walls.
• Collect sonar data. It is important to characterize the performance of the sonars on the robot. We weighted the vehicle down (making it negatively buoyant) and then hung it at 22m and 42m depth to collect sonar data. In particular we adjusted the gain on the sonars, the maximum range, and low pass filtering. By hanging statically in the water we were able to see when the sonars were returning consistent (and believable) ranges. We adjusted all the major parameters to a variety of settings, trying to bracket the best values. There is no one perfect setting because each transducer behaves slightly differently—we have 32 of the 100m sonars and 24 of the 200m sonars so we were looking for a best overall performance. We think we’ve found that and furthermore have got settings that should work in Zacatón as well.
• Dropped to the bottom. With the sonars tuned we dropped the vehicle to the bottom of la Pilita, again on a tether for safety. We dropped in a different location and reached the bottom at 98.3m. This time we had added dive lights and so we took pictures of the bottom including a rock we called the iguana. The robot actually touched down gently. Using the live visual image (something we won’t have when we remove the fiber optic real-time data upload cable and go fully autonomous and un-tethered) we used the thrusters to hop around on the bottom. On this second drop to the bottom and return up we collected a second complete sonar data set of the cenote which we will use to build an even more accurate map.

Dave Wettergreen
Carnegie-Mellon University

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Wall and Water Sampling + Pre-SLAM: Most of the daylight hours today were consumed with tests of the various Science Payload sub-systems, mainly pre-programmed capture of up to five independent 2 liter water samples and the test firing of the coring tool, which extracts a 1 cm diameter x 3 cm long bio sample from a candidate wall location—see the images below for one of many such test sequences conducted today. In these photos you can see the Science Payload sampling probe in its extended position. The purpose of this design was to permit the main DEPTHX vehicle to “stand off&#x201#x201D; from areas of potential biologic interest and send in a non-disturbing probe. Bringing the entire vehicle up against any surface in a 3D labryinthine environment is fraught with possibilities for entanglement (and therefore potential loss of the vehicle) so in general we maintain a significant proximity fault “keep out” zone of 5 m radius from the vehicle. Only during proxops (proximity operations) do we intentionally allow the vehicle to get within 1.5 m of the wall; the probe then goes the last distance to look at what’s on the wall. This also has the benefit of minimizing thruster disturbance of wall materials.

Above: DEPTHX, with its Science Payload probe arm extended (left) moves in to acquire a biological wall sample (right)

Above: DEPTHX begins autonomous mission 7 after dark. The bot made a powered descent to 80m and successfully conducted exploration circuits at three depth levels.

Above: inside the mind of the bot—a 3D slice of the “evidence grid” from -40 to -60 m in La Pilita.

Later in the evening we began a series of more ambitious autonomous missions in which we sent the bot on a pre-programmed trajectory to various depths at which point it would then execute a triangular-shaped maneuver – moving 15 m along each leg of the triangle and then returning to the original vertex. The bot would then move to a shallower depth level, about 15 m higher than the first, and duplicate the maneuver. After doing this at many levels it would return to its “home” position, which is shown in the above night shot of the bot with its twin HID head lights blazing. The first such mission was attempting to reach 60 m depth when an over-temperature fault indicator on the inertial guidance unit tripped and the vehicle fell back to an abort behavior – surfacing along a path that placed it at the geometric centroid of the cenote. From the surface, except for the data being displayed on the microRAPTOR computer console interface, there was no indication that anything was different until the HID lights began making the entire cenote glow from a depth of around 20 m. After consulting the IMU operations manual we raised the temperature fault trip point and sent the bot back down, this time to -80 m. It then successfully conducted two back-to-back autonomous missions, returning to “home” each time… the first with a navigation error of just 9 cm; the second with about 0.5 m accumulated drift following more than an hour of operation away from base.

On each of these missions DEPTHX continued to collect a fire hose stream of geometric data, bit by bit filling in the unknown voids in La Pilita. Using these data a 3D “evidence grid”—a probabilistic density map showing “voxels” (cubes) of space likely to represent the internal boundary surface of the newly explored terrain—was constructed. One of the interesting features of this approach is that “negative probability” is deposited in the grid in places where the sonars detect nothing to exist. This negative probability accumulates over time to suggest that there really is nothing there, a consensus of many different sonar transducers seeing the same area over time. And thus, one can make a reasonably safe assumption that in such areas it is OK to drive the bot. Coincidentally, the converse is also true: that the places where true boundary surfaces exist will become better defined over time and have a higher probability rating that they are real. These, in turn, form the basis for the creation of a map, from which the vehicle location can be deduced in 3D. This, in a nutshell, is SLAM—Simultaneous Localization and Mapping. The green figure above shows the 3D evidence grid for La Pilita as it is being developed mission-by-mission. It is specifically a slice from -40 m through -60 m in depth. One can clearly see in this image that the core of the cenote is black, meaning high negative probability of occupancy of something real—and it is within that zone that it is safe to navigate. With some luck we will conduct the first full 3D SLAM navigation by Saturday. The expedition packs up on Sunday, February 11.

Bill Stone
Stone Aerospace

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Agenda

• Test reactive resurfacing behavior
• Execute multigoal dive with contingency plan
• Tune proximity operations parameters
• Exercise science payload

Status and Progress

• Tested reactive resurfacing behavior. When the robot detects any type of fault (like low battery, high temperature, process crash, or unexpected obstacle) is aborts its current plan and returns to the surface. In the simplest implementation, the robot runs its vertical thrusters and heads straight up. Very often this works fine, but in an environment like la Pilita which is shaped like a vase, it can run into the bottom of an overhanging ledge. It might still bounce around enough to eventually pop out through the opening, but maybe not. We have been testing a variety of algorithms for reactively moving away from walls or towards free space while also moving upwards. This behavior is reactive because it does not rely on any prior information or even knowledge of where the robot is located. Getting this to work reliably has involved deciding how far to stay away from walls, how rapidly (or forcefully) to move away, and what rate to ascend. After trying several schemes we settled upon a method based on repelling away from walls at rate inversely proportional to distance. We then set about testing this by getting progressively deeper and farther underneath the ledge. Eventually the robot was returning on its own from depths of 50m while more than 15m back underneath a ledge.
• Execute multigoal dive with contingency plan. Continuing on work from Wednesday we executed several 30 minute dives that involved navigating down to deeper areas where we have sparse sonar data and scanning intensely to try to collect enough readings to determine whether there is a tunnel present. These multigoal plans take the robot to the depths of la Pilita and must return on schedule otherwise the contingency plan is invoked and the robot begins to return home automatically.
• Tune proximity operations parameters. We continued refining the proximity operations behaviors and in particular worked on enabling the robot to move smoothly along walls while maintaining a constant standoff distance. It is now able to stationkeep quite steadily but motion relative to the wall can become erratic for very rough or fractured walls. We also observed that the robot sometimes drifts upward along an inclined wall. Work will continue on this after rethinking the current formulation.
• Exercise science payload. We performed our first sampling operations at depth just at dusk today. While at 50m and back along a wall beneath a 15m ledge, we directly commanded deployment of the sampling arm and pressed the vehicle forward against the wall to fire the coring mechanism. We also drew in water samples of the material that was stirred up, and of course took images. The core came back with a bit of wall material although not a complete core. The next step will be to integrate some of these science activities along with proximity operations into a longer multigoal plan.

Dave Wettergreen
Carnegie Mellon University Robotics Institute

Above: Probe Arm – Solid Sample Collection.

Above: This small pile of soft sediment was collected at a depth of 50 meters in the cenote La Pilita 40 meters back under the cave edge. The sample was collected by the solid core sample device on the end of the sample arm.

Above: Biogenic mineral crystal from the walls of La Pilita fell into the frame of the DEPTHX robot during a deep mission. These crystals are thought to be forming through biologic mediated processes.

Above: A top view of the DEPTHX robot with the sampling arm extending to test the operation of the solid core sample device. The coring devise is the gray cylinder at the front of the probe.

Above: A four-inch purple scorpion was found on the trail walking back from La Pilita. These scorpions are common in the caves nearby.

Above: Image taken with the stage 1 camera on the DEPTHX robot of the wall 50 meters deep in the cenote La Pilita. The texture of the wall is likely due to biogenic mineralization of crystals.

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Agenda

• Refine sample coring strategy
• Develop complex contingency plans
• Run multi-hour mission
• Operate without tether

Status and Progress

• Refine sample coring strategy. The rover’s sample coring mechanism can be triggered by a mechanical switch or by a signal generated by software. Our initial strategy was to station keep, while the arm extends, contacts the wall, and mechanically triggers the coring mechanism. The success rate has been low due to the difficulty in generating sufficient force on the trigger. Instead the rover was made to extend the arm and then move forward until motion stopped and the corer triggered and then the rover backed off retracting the arm. This method succeeded but suffered from occasionally bouncing off the wall before the coring mechanism fired. We are going to work alternatives.
• Tested water sampling plumbing. The rover can sample water from its environment and we are particularly interested in do this during the coring operation when material is dislodged from the wall of the cenote. After simplifying the plumbing somewhat and inserting operations into the sampling plan the rover now draws water samples while in proximity to the wall. It carries 5 1-liter sample bags and we verified that it was filling the proper bag. During the DEPTHX science investigation these will be sterile bags and we will have to go through a careful procedure to sterilized and flush all of the plumbing through the pump and manifold that directs water to the desired bag.
• Develop complex contingency plans. With the contingency plan based on moving upwards while repelling away from the walls working reliably, we began testing multiple stage contingencies. In this case the rover first tries to move back under its descent point and then ascends upwards to the surface. If any faults occur during the dive the rover begins execution of this plan, further faults associated with approaching walls or position estimation errors, cause the system to fall back to the purely reactive wall-avoidance behavior. The multiple fall-back contingency plan executed as expected.
• Operate without tether. With a plan to dive, fly a simple pattern, and return to the surface loaded and multiple contingency plans queued up, we removed the fiber optic tether from the rover. The tether had been used thus far to monitor onboard software in real-time, so this dive the robot was on its own. After 21 minutes and 5 seconds the rover resurfaced within a meter of its descent point having completed the mission. We loaded a second plan, running circuits down to 60 meters. In this dive the rover got within 10 meters of a wall (while at a depth of 50 meters) and triggered a proximity fault. While it didn’t complete the dive plan completely, it did successfully execute its contingency plan and return to the surface (in 00:18:55). After adjusting the plan and bounds on the contingency fault, the dive plan was repeated and completed successfully (in 00:33:10).
• Run multi-hour mission. We then programmed a longer mission, of vertical “boxes” pivoted off center to create a star pattern that would provide very dense observation of the lower chamber of the cenote. The plan was 2280m in length. The plan was given a timeout at 10800 seconds (3 hours). The vehicle dove at 10:24pm and resurfaced again at 1:34am about 1.5m from its descent point. The complex plan had required the rover to reach many waypoints and subsequent analysis revealed that it has spent much time making fine adjustments to reach the goals within 10cm. As a result its top speed of 0.2m/s was reduced to an average speed of 0.1m/s and it had timed out on the mission after 3 hours. Again the contingency plan functioned correctly and brought the rover back to the surface.

Dave Wettergreen
Carnegie-Mellon University

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Agenda

• Test altimeter-based coring
• Run map-based localization

Status and Progress

• Fire sample corer on altimeter. The rover’s sampling arm has an altimeter that was intended to allow it to adjust its distance to the wall the ensure proper focus of the close-up camera. We tied the altimeter to the coring operation so that when the range to the wall stabilizes to a constant (small) value the coring mechanism fires via a software signal. The proved more reliable than mechanical trigger which requires a smooth flat wall surface.
• Improved wall approach. We also worked to continue refinement of the wall approach proximity operation. In final approach the rover only uses its rear thrusters for more stable control. It also moves with constant steady thrust rather than thrusting towards the wall and then coasting in. This has reduced the bounce, rotation or both that can occur when contacting and irregular wall, which seems to be most surfaces in la Pilita.
• Ran map based localization. The dead reckoning algorithm, which uses an inertial measurement unit (IMU), depth sensors, and a Doppler velocity logger (DVL) along with a vehicle motion model has performed remarkably well. It’s drift is well under a meter and hour as long as all sensors remain locked. In particular a Kalman filter is able to maintain position across dropouts of the IMU and DVL but errors do accumulate. Using sonar-derived maps of prior and current dives, the robot can recognize its position and correct for any drift. (More specifically, the rover maintains a large number of possible maps and locations and determines based on probabilities its current best guess.) We ran a two hour dive to complete the mission of the Friday night and used the data previously collected to provide a map of the cenote. While the rover traveled it estimated its position from its sensors and also from the sonars and prior map. It completed mission in 01:43:00 (untethered). It’s dead reckoned estimate was off by about 1 meter, but its map-based localization was correct to 15 centimeters. This gives us some confidence that the rover will be able to complete dives in Zacatón that will require 6 hours or more and still reach goal and return to its starting point.
• Dove under a dome. In a last couple dives before wrapping up we ran a couple short missions into areas of the cenote that had been sparsely observed. In a 22 minute autonomous dive, the rover dropped down to 30 meters traversed, literally underneath our camp, and rose up into a dome in the ceiling of the cenote. It then dove down and returned to the opening. In a similar operation the rover dove to what we thought might be a tunnel opening at 55 meters. It collected more data and narrowed the area where a tunnel might exist but left the question of an underwater tunnel unanswered.

Dave Wettergreen
Carnegie-Mellon University

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Robin Gary, Marcus Gary and John Kerr make it back across the border into Mexico without a hitch.

Today was the day to make the 12 hour drive from Austin back to Rancho la Azufrosa in Tamaulipas, Mexico. John Kerr, Robin Gary and Marcus Gary loaded up 2 trucks with food, computers, and a ton of other miscellaneous items (including over 1000 pounds of books and journals being donated to a Mexican University from The University of Texas at Austin Geology Library. We made it out of Austin by 8:30 AM, and had a rather uneventful drive down. Quite a difference from our initial trip in late January. The crossing at the border went without any problems, and it was green lights all the way! We had a nice dinner at Resturante Tampico in the town of Sota La Marina and arrived at Rancho la Azufrosa by 9:30 PM. A few hours were spent unpacking food and storing it in the deep freezer, then we headed to bed to get some sleep for the very busy day ahead.

Trucks being loaded in Austin Wednesday morning

Old friends join the team. Seasoned Zacatón travelers Wyle and Mona load up for the trip. Mona has been traveling to Rancho la Azufrosa since 1995, making over 40 trips to the site. Wyle joined the crew in 2002, and has made almost 20 ventures.

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Site Setup

Our first full day back at Rancho la Azufrosa was a busy one. John, Robin, and Marcus had a long list of things to get done before the rest of the team showed up tonight. First on the list was to check the status of the bot and our shop. A strong windstorm, known locally as "El Norte" had blown through the previous weekend, leaving our shade canopy over the shop (a modified 40 foot shipping container) ripped to shreds. Not a major catastrophe, but a rather hot development. John Kerr emailed our geomicrobiologist, John Spear from the Colorado School of Mines to pick a replacement up in Denver and bring it on the plane. We will have shade again! Nonetheless, we opened up the shop and John checked the batteries. One of the battery banks had dropped to an uncomfortably low voltage over the past three weeks, but after an hour or so of pumping electrons into it, John breathed a sigh of relief as it became clear that it would work. On to the next item on the list.

The three photos above: A windstorm or "El Norte" had shredded our shade canopy (top), so we had to evaluate what to do next. Temperatures began to rise in the field lab….approaching 100 degrees (F)….Robin climbs on top to hose down the lab for some evaporative cooling (middle)….success! Temperatures dropped to a pleasant 81 degrees within 20 minutes (bottom).

Turning on the bot

John now booted up the system successfully, and we checked out the status of the science payload. Operation of this component is a primary focus for this week’s tests, so a list was made for what needs to be repaired and/or modified. At the moment, all we needed to do was reinstall the payload into the bot.

Left: John Kerr makes some adjustments on the science payload of DEPTHX before reinstalling the hardware on the bot.

Setting up Mission Control – La Pilita

Robin and Marcus Gary now headed over to La Pilita to set up the DEPTHX mission control. This entails tying in to the electricity grid and installing a breaker panel to provide power, setting up 4 large tents, and getting all the other odds and ends set up. Marcus handled the electricity. It is always an adventure when dealing with Mexican high voltage….440 V-three phase….had to be careful. Robin went ahead with the tent set up. First was the bot battery charging tent, then the science/biology tent, then the navigations ops tent. Finally we set up a fourth tent that will serve as the geology tent. Everything looks good, so we headed back to the ranch field lab to see what John had been up to.

Marcus Gary ties into the electricity grid to supply power for La Pilita Mission Control. The bot battery charging tent can be seen set up near the water.

Final bot assembly and transport to La Pilita

Upon return to the field lab, we found John had already installed the science payload, closed up the batteries, removed the bot from the container using the telescoping forklift, and had employed the help of local ranch hands Nacho and Gilberto to assist with bolting on the syntactic foam. Wow, things must be going well! Marcus jumped out and took over operation of the forklift so John could help guide the foam onto the bot frame. After another 30 minutes, it was ready to head to La Pilita. John and Robin continued to pack up computers, tables, cables, battery chargers, etc. to set up at La Pilita and Marcus headed over with the bot hanging from the forklift.

John, Nacho, Gilberto, and Marcus bolt on the syntactic foam to the bot. This was the final step at the field lab in preparing DEPTHX for operations at La Pilita.

Final Set Up and Arrival of Other Team Members

By 6:00 P.M. we have the bot poised for deployment into La Pilita, all support tents set up and operational. It was a busy day, but we were now prepared for the rest of the team to arrive and hit the ground running on Friday morning. Always a good feeling when things go well and you reach your goals. By 7:30 the three of us headed back to the ranch house to begin cooking dinner and preparing the rooms for other team members. Around 10:45 three sets of headlights rose up from the ridge and everyone made it to Rancho la Azufrosa safely. Antonio Fregoso led the caravan from the airport in Tampico, picking up:

• Dave WetterGreen (CMU)
• George Kantor (CMU)
• Dom Jonak (CMU)
• Nathaniel Fairfield (CMU)
• John Spear (CSM)
• Jason Sahl (CSM)
• Ernest Franke (SWRI)
• Ian Meizen (SWRI)
• Marc Airhart (UT-Austin)

We had a nice dinner and retired by 12:30.

The sun sets on La Pilita Mission Control with the DEPTHX bot ready for the next day’s round of tests.

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Back in the Water

John Kerr unhooks the bot from lifting slings as DEPTHX gets wet again in La Pilita. The first day back in the water saw positive success in the operations development of DEPTHX.

Morning Briefing

The team awoke at daybreak and assembled in the Rancho la Azufrosa Palapa (AKA Palapa Internet Cafe) to discuss the plan for the day. George Kantor wrote up the organization schedule for the goals, discussed what needed to get accomplished, and took questions. Most headed to La Pilita by 8:30 to get moving with the tests.

The DEPTHX team meets in the Palapa (left) to go over the daily plan (right), as shown by George Kantor.

Morning OPS

Update to come

The group breaks for lunch at La Pilita with the local menu favorite of tacos.

Afternoon OPS

Following lunch, the group began repairs and minor modifications of the science payload. A hydraulic leak was located and fixed, and a rebuilt sulfide sensor was installed on the bot. This work was led by Ernest Franke and Ian Meizen from Southwest Research Institute

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

 

Left: Dom Jonak in the navigation mission control tent with the day’s outline. Right: The Hydrotech used to verify salinity concentrations during the water sampling cleaning protocol tests.

Test Plan

morning dive:

• finalize autonomous wall sampling
• drive to depth, start sequence near wall
• complete sampling mission (tethered)
• collect wall images above and below photic zone
• collect pictures for texture analysis
• develop maneuvers for SLAM
• test Newton wall following

afternoon charge session:

• work out liquid sample sterilization routine
• determine sonar firing sequence

evening dive:

• collect microscope images
• short untethered mission (with wall and liquid sampling)
• long untethered mission (star mission)

Morning Ops:

Objectives this morning focused on completing a successful and repeatable sampling routine while the robot was on tether in order to prepare for a similar unteathered mission. Operations started with simply driving to depth, and initiating the sampling sequence near the wall. CMU worked on coordinating the timing for the sampling procedure, so the robot’s thrusters, sample arm extension, and coring device firing were working together. Several sampling attempts using the close-range sonar transducer integrated with the science package were made to trigger the coring device. The navigation team found that a timed coring device firing strategy produced better results. Once the sampling arm is extended, the robot thrusts forward for 30 seconds to fully contact the wall. 20 seconds into the forward thrust, the coring device fires. After the sampling sequence completes, thrusters reverse and navigation to the point of origin takes over. Establishing that the robot can successfully completing this sequence on-tether will allow the team to test off-tether operations against a known sequence.

Nathaniel Fairfield and David Wettergreen check the sonar firing sequence.

Afternoon Charging Session:

During the battery charging break mid-afternoon, the team focused on calibration of the water collection system and sensing probes. Jason Sahl, John Spear, Earnest Franke, and Ian Meinzen established a cleaning protocol for the sample bag collection system. They tested the cleaning protocol for cross-contamination using 5 saline solutions with varying concentrations. The team took samples of the prepared solutions and Marcus Gary verified the specific conductance of the solutions before and after sampling using a secondary Hydrotech water chemistry sensor. There was less than a 3% difference in original water and the sampled water. The sampling protocol was determined to limit the possibility of cross-contamination. Nathaniel Fairfield and David Wettergreen checked the sonar firing sequence to find that all sonars fire simultaneously.

Marc Airhart manually drives the robot using a wireless joystick to the point of origin before it begins its missions. George Kantor (right) and John Kerr (left) taught Marc to drive.

Evening Ops:

The evening mission attempted the same task, but this time the robot was untethered. Twice the robot aborted the mission. The CMU navigation team determined that while the robot was thrusting forward, the ADVM was too close to the wall to receive accurate readings which caused the DVL (Doppler velocity logger) to go out longer than the 30 seconds the filter allows. SCUBA divers Marcus Gary and Antonio Fregoso attempted to observe the robot’s performance, but given low visibility and distance thresholds required to not interfere with sonar readings, observation was unsuccessful. The team pulled the robot out of the water for the night and put batteries on charge at 10:30pm.

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Test Plan:

pre-morning dive:

• ring out stage 1 camera cable
• install pooper scooper (?)

morning dive:

• check stage 1 cable serial coms
• complete sampling mission (untethered)
• collect wall images below photic zone
• find good sample locations deep
• go to bottom, look at sulfide sensor, get water sample
• complete sampling mission at depth (untethered)
• test Newton wall following

afternoon charge session:

• remove science bottle and stage 1 camera
• look at microscope filter

evening dive:

• long untethered mission (star-like mission)

Morning Ops:

With fully charged batteries, morning operations began to attempt a fully autonomous sampling mission. Marcus Gary and Antonio Fregoso provided SCUBA support and video documentation of the sampling sequence. The robot was programmed to replicate yesterday’s mission: descend to 15 meters, acquire an optimal sample target, extend the sampling arm, thrust forward for 30 seconds to increase contact with the sample target, then fire the sample coring device 20 seconds into the thrust forward. The programming filter that compensates for the lack of appropriate ADVM readings was increased to account for up to a 60 second loss of data. Success! Divers observed a perfect sampling sequence.

Divers Antonio Fregoso (left) and Marcus Gary (right) observe a perfect sampling sequence at 15 meters depth.

The robot returned with 2 full bags of water samples and a wall sample. John Spear and Jason Sahl filtered the water samples, cut the filters, and preserved some of the filters in sample bottles with formaldehyde and others were stored in liquid nitrogen for transport.

Left: Earnest Franke retrieves the sample core arm and a water sample bag. Right: John Spear and Jason Sahl filter and preserve water samples.

A second mission ran the robot tethered down to 80 meters to scope out a deep sampling location. Maps of the cenote, which will later allow the robot to select sites autonomously, are not of high-enough resolution yet. A short 20-minute tethered dive down to 80 meters allowed the team to find a sample target. The autonomous run down to 80 meters went successfully. The robot retrieved 1 successful water sample, and during the second water sample pull, the tube clogged. The wall sample successfully triggered and the sample arm got stuck, the robot compensated by first trying to thrust backwards gently then by spinning. The science probe’s camera captured the sample sequence and navigation compensation. Once the robot was docked for charging, the biologists pulled the water and wall samples, processed them and called the mission a success.

During the Charging Break:

During the charging break, Earnest and Ian cleared the clogged intake hose on the water sampling system. They confirmed that all hoses could pull samples. Currently, the team tethers the robot after each mission to download data from that mission. Kantor worked on re-rigging the wireless antenna so that the navigation team can communicate directly with the robot while it’s on the surface. Nathaniel poured through the Doppler velocity log data and the DVL patch code to investigate how the robot deals with velocity spikes. Dom went through navigation code to further refine operation sequences.

Earnest Franke cleans out the sampling intake for the water sampling system.

John Spear (not shown in photo), Jason Sahl, John Kerr, and Ian Meizen (hand on right side) discuss the operation of the water sample collection system. Inset on lower left shows the diagram that John Kerr is drawing.

Evening Ops:

Once batteries were charged, the robot was lowered back into the water. The team waited 30 minutes for the sensors to equilibrate before aligning the IMU. The robot was launched at 7:15pm on an approximate 4 hour autonomous mission. The robot was programmed to cruise in a star pattern (also known as an inverse negative-hole donut pattern) at two depths. This particular pattern optimizes sonar coverage of the cenote walls to augment point density for the production of a high resolution map of the cenote. The mission was estimated to take approximately 4 hours.

DEPTHX prepares to collect a biologic solid core sample from the shallow walls of La Pilita.

No Return….

At 1:30am, David Wettergreen woke Marcus Gary with “The robot didn’t come back. It’s an hour and a half late.” The team hypothesized what could have gone wrong, and the fact that soon it would lose all battery power, lights would shut off, and only a faint red strobe mounted on top of the robot would last until morning. Marcus Gary planned to wake up early and search at daybreak.

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Marcus Gary gives the "thumbs up" after locating the bot Monday morning. After failing to resurface from a 4-hour mission the night before, the team was extremely relieved to see DEPTHX bob to the surface after Gary freed it from the rock it was stuck on.

Test Plan:

morning dive:

• find robot (DONE!!!)

afternoon charge session:

• analyze mission data
• install pooper scoopers
• visually inspect vehicle
• reconnect stage 1 camera
• work on dead reckoning bug

evening dive:

• systems check out
• test fly upward command
• scoop from bottom (tethered, teleop)
• wall sample at bottom (tethered, autonomous)
• triangle missions for localization (tethered)
• wall sample mission into chamber
• take lots of pictures near wall with stage 1 camera

Morning Ops – Bot Recovery:

Marcus was up before dawn. He geared up at La Pilita as the sun came up. Honestly, finding a robot (albeit a bright orange robot) that could be anywhere in La Pilita seemed like a futile task. But, being a game soul, he descended to 75 feet and began a slow dive following the walls of the sinkhole. The water was crystal clear. Beautiful biomat-covered lobes stood out under his HID dive light, which cut through the water like a laser beam. As he was swimming, he contemplated what divers would be recruited for a deep recovery mission. First choice, Jim Bowden, is currently in Italy diving at the deepest underwater cave in the world—the Merro Well. Approximately 15 minutes into the dive, one particular lobe caught his attention. He ascended a few feet and his light illuminated the word “DEPTHX”. Miraculously, he had swum right up to the robot.

All battery power had been spent, so the robot’s lights were dark. All systems had shut down. It was lodged under an overhang, a scant 6 feet from a clear shot to the surface. Being only slightly positively buoyant, Marcus was able to force the robot down a few feet and out from under the overhang where it was free to make a slow, unaided ascent to the surface. Surface team members were not expecting Marcus to find the robot so quickly. Third glance at La Pilita, no robot. A few minutes later, ROBOT! By 9:30am John Kerr had the robot out of the water and on charge. The batteries had shut off at 46 volts, so it would be at least 6 hours before the robot was ready for its next mission. This gave the team plenty of time to determine what caused the robot to get lost.

The CMU navigation team downloaded the data the robot gathered during its “star mission”. It had performed the ascents, descents, and traverses perfectly. The navigation fault occurred after the robot finished the “star” sequence at 60 feet, as it attempted to ascend to the surface in the middle of the sinkhole. Nathaniel analyzed the sonar firing patterns as the robot drifted off-course. After analyzing and re-analyzing the data, Nathaniel and George hypothesized that since data from several of the sonar transducers had been filtered out, this caused the robot to be pulled towards the wall. David and Dom joined the discussion. Dom confirmed, apparently as the robot drifted off-course, it was only being guided by one sonar transducer. That was a glaring error and a (relatively) easy fix.

Nathaniel Fairfield explains to the rest of the CMU team what happened on the previous night’s stressful mission. The bot made it almost out, but had a small glitch causing it to get wedged under a rock ledge 18 meters below the surface. The glitch has now been fixed.

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

The Full Scoop

Dom watches as the robot is lowered into La Pilita with two scooper attachments that will be used to sample bottom sediment.

The robot buried the scoopers in the bottom sediment then spun to take a sample.  The procedure worked so well that the amount of sample taken made the robot slightly negative.

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Wrap Up: Success!

This mission was not without challenges. But given the talent, resourcefulness, and positive attitude of each of the team members on this mission, it’s easy to call DEPTHX Mission 2 a success!

The DEPTHX Mission 2 Crew, from left to right: Dom Jonak, Raul, George Kantor, Marcus Gary, DepthX, David Wettergreen, John Spear, Jason Sahl, Alejandro Davila, Earnest Franke, Robin Gary, Nathaniel Fairfield, Ian Mienzen, Rene, John Kerr, Alonso Ramirez

Testing at La Pilita is complete.  On the next Mission (in May), DepthX will explore Zacatón.

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

John Kerr and Marcus Gary arrived on site at Rancho la Azufrosa on Friday evening May 11^th 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).

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

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).

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

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).

Rancho la Azufrosa, Aldama, Tamaulipas, Mexico
Reporting from Zacaton Basecamp

Today we re-ran the May 15^th mission, this time with what apparently was a solid guidance system alignment. Because of the disparate behavior of the IRU (with the previous day’s behavior) we kept the data tether on the bot in order to observe any anomalous behavior. The descent to -270 m went without error and the bot was performing with nominal parameters. Once we were relatively certain the system was stable we uplinked instructions for DEPTHX to proceed deeper into the northwest corner. The result of this timid exploration was the ability to see (with the sonar arrays) down to a new underwater depth of -319 meters. The main entrance shaft – with a well defined bottom now beginning at -276 m on the southeast corner and sloping down to the northwest to -319 meters – appears to focus into a deep alcove at the northwest corner. Tantalizingly, there remains a zone below this point (see today’s map) that was not able to be imaged because we did not drive far enough under the enormous overhanging roof for safety reasons. Although we have closed-cycle helium diving equipment on site the maximum safe depth for bot rescue with that equipment is 200m. So any errors below the northwest roof would result in a permanent loss of the bot. The unknown northwest void could be a closed alcove or it could be the entrance to a 16 m high by approximately 40 to 50 m wide horizontal tunnel. Beyond that we cannot speculate without further exploration, and that cannot take place until a positive explanation is reached for the IRU crash of May 15. We are pursuing a resolution to this while continuing to conduct fiber data tether science missions. It is important to point out that the source for the large river that appears at El Nacimiento to the west of Zacaton comes from whatever lies down in that alcove. Whether that souce is navigable to DEPTHX will have to be determined by untethered exploration. It should be noted that in addition to the 319 m of confirmed underwater depth, the shaft continues 16.5 m above the water in air (see the cenote photos for the May 13 blog), thus giving a total known entrance shaft depth of 335 m.

New 1,000 m rated underwater high power lighting (two 100 W diffuse illuminators) formed a new addition to DEPTHX and were given a ride with the vehicle today in preparation for the first science mission on May 17. Photo: (Jose Antonio Soriano / Stone Aerospace)

John Kerr attaches the fiber optic data link to the bot in preparation for the second mission to the bottom of the entrance shaft. Photo: (Jose Antonio Soriano / Stone Aerospace).

Dom Jonak (left) and Antonio Fregoso (Universidad del Noreste, Tampico) monitor the data as DEPTHX maneuvers away on the May 16 mission. Nathaniel Fairfield (seated left) works on code improvements while Dave Wettergreen (right) tends the data tether. Photo: (Jose Antonio Soriano / Stone Aerospace).

The floating science platform is maneuvered out to the center of the cenote while the bot descent is underway. Photo: (Jose Antonio Soriano / Stone Aerospace).

DEPTHX principal investigator Bill Stone maneuvers near the bot for crane recovery at the conclusion of the highly successful May 16 mission. Photo: (Jose Antonio Soriano / Stone Aerospace).

Following the May 16^th mission Nathaniel Fairfield (left) and Bill Stone discuss DEPTHX navigation control issues at the field lab while John Kerr (in background) wires up the first test circuit for interfacing the PAR (photosynthetically active radiation) sensor that will be used as the trigger for some upcoming science autonomy missions. Essentially it is a light intensity detector that is tuned to the wavelength of chlorophyll. Photo: (Jose Antonio Soriano / Stone Aerospace).

This map illustrates the May 16, 2007 data set for Zacaton. With a stable IRU the descent, exploration, and ascent portions of the data were automatically co-registered. This conclusively confirms the presence of a sloping bottom to the entrance shaft of Zacaton and also confirms the presence of an unexplored void to the northwest, the extent of which remains unknown. Photo: (Stone Aerospace / Team DEPTHX).

Refined closeup of the mysterious northwest corner at the base of the Zacaton entrance shaft. As the data indicate, there is a potential there for a passage approximately 16 to 20 m in height by 40 to 50 m wide. Or it may be a blind alcove…. Only further exploration will tell, but this seems to be the logical source of the hydrothermal spring. Photo: (Stone Aerospace / Team DEPTHX).