Stone Aerospace is the Principal Investigator for the NASA ASTEP project to develop and test the Europa Lander 3rd Stage Prototype.

DEPTHX (DEep Phreatic THermal eXplorer) is a fully autonomous underwater vehicle capable of not only maneuvering in true 3D but also of creating it’s own 3D maps of newly explored terrain and navigating home on those just-created maps. DEPTHX also has a sophisticated hierarchical life sensing, detection, and sampling Science Payload (see DEPTHX History).

DEPTHX is a 3-year development program that began in April of 2004 and which has two primary scientific objectives:

Astrobiology Science Goal: Develop a protocol for autonomous real-time processing of environmental indicators for the detection and discrimination of regions that provide a high probability for the presence of sub-aqueous microbiological life and the initiation of an in-situ sample collection on that basis.

Planetary Exploration Goal: Develop the DEep Phreatic THermal eXplorer (DEPTHX) vehicle, an autonomous maneuvering platform that acts upon the information sensed and processed by the hierarchical decision-to-collect microbiological subsystem and “drives” the sensor suite to areas of potential interest. Importantly, the vehicle must create a 3D map of the terrain it explores and then use those just-created maps to return home.

Vehicle designs were frozen in January of 2006 and system integration, test, and evaluation took place at the Stone Aerospace Armadillo Works (photos at left) through early July 2006. The vehicle is ellipsoidal shaped (2.1 m major diameter, 1.5 m height), has six onboard thrusters, 96 sensors, and more than 30 onboard processors. It weighs just under 1.3 metric tons in air.

For background details in how the DEPTHX design was developed see DEPTHX History). Initial neutral buoyancy and thruster testing took place in June 2006 (above) at the test tank at Stone Aerospace.

DEPTHX saw its first autonomous powered underwater tests in July of 2006 at the University of Texas at Austin’s ARL (Advanced Research Laboratory) test facilities, which include a 15m diameter x 12m deep water filled test tank. The first series of tests focused on pre-programmed mobility control with remote data and decision-making monitoring via a 1 mm fiber optic data link.

Later experiments in August of 2006 tested the “dead reckoning” navigation system, which consisted of a suite of sensors that included inertial navigation, Doppler velocity, and absolute depth. The highlight of these tests was the tracking of an underwater 3D cube based on goal states fed to the dead reckoning navigation system. In the actual field testing to be conducted at Cenote Zacaton in early 2007 the dead reckoning sensors only serve as the backup navigation system; the primary form of navigation will be via real-time 3D map building (based on custom sonar arrays) using a procedure known as SLAM (Simultaneous Localization And Mapping). Real-time SLAM will be tested in the upcoming September 22-26, 2006 experiments, again at ARL.

Some sample results from the August tests are shown below. In the figure at lower left we programmed a square wave ramp in commanded X (in this case, north-south) velocity. Command signals are sent to the thrusters to achieve this velocity while others maintain heading (direction) and depth. The blue lines are the pre-programmed command signal; the red line represents measured data. The noise in the red line data is a function of the various sensors being used to track the vehicle and is on the order of +/- 10 to 15 mm/s. The purpose of this experiment (and many others like it) is to characterize the response function for the vehicle -- how fast it can rise to a given velocity and, conversely, how fast it can be stopped. The target maneuvering velocity for the project is 0.2 m/s.

DEPTHX is not intended for speed, but rather for precision 3D maneuvering and stabilization for the conduct of exploration, mapping, and “prox-ops” (proximity operations) near a wall where there may be interesting microbiology. The figure at bottom right (previous page) shows a pre-programmed course where the bot descends from 2 m to 5 m, moves one meter, then returns to 2 m depth and returns home horizontally. The blue line, again, is the commanded goal state; the red line is the measured vehicle behavior. This behavior is well within the design parameters for DEPTHX. The targeted geometric localization accuracy is +/- 0.5 m over the entire course of a mission. Over short run distances (and using only dead reckoning) we can do better than that as shown here. Long range navigation will be a composite of the dead reckoning information combined with the SLAM data.

DEPTHX contains sufficient onboard power for an 8 hour exploration and science mission to working depths as great as 1,000 meters and distances of more than a kilometer from the mission initiation point. All of this will be tested in a fully autonomous (no tether) test series conducted at Cenote Zacaton (see News: Zacaton 1 Field Campaign) where the depths remain truly unkown and uncharted below the -290 m point that was imaged by the DEPTHX drop sonde core instrument.

For More information on DEPTHX click here.

For details on DEPTHX co-investigators, click here for Team DEPTHX.