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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
News: Press Kit

DEPTHX (Deep Phreatic Thermal eXplorer) Takes Flight

Stone Aerospace, of Austin, Texas, just completed integrated systems and subsystems checkout of the NASA DEPTHX fully autonomous underwater vehicle. Under NASA grant, Dr. Bill Stone, CEO of Stone Aerospace, said “this marks a key milestone in advancing the state of the art for future planetary robotic probes that could eventually plumb the depths of oceans on other worlds looking for life forms that we can only imagine today.” DEPTHX – a $5 M project – is the first in a series of NASA projects ultimately leading to a landing on Europa.

Jupiter’s moon Europa is distinguished by its global ocean of liquid water, which like the Earth’s Arctic Ocean is covered by a relatively thin layer of ice. Europa, about the same size as the Earth’s Moon, is the smallest of the four large satellites of Jupiter that were discovered in 1610 by Galileo. Unlike other icy satellites, Europa is heated by the friction of tides, enough so most of its water is in liquid form. In fact, the amount of liquid water in Europa’s ocean is similar to the total amount of water on Earth.

Evidence for liquid water comes from distinctive crack patterns formed by tidal stress; from effects on Jupiter’s magnetic field consistent with a global layer of salty water; and from theoretical predictions of the amount of heat available to keep the ice melted.

Europa’s orbital radius (distance from the center of Jupiter) is 670,000 km. Europa itself is about 1560 km in diameter. The ocean is about 150 km (100 miles) deep. The ice on top is probably about 10 km thick, or less. Under this very deep ocean is a rocky interior.

DEPTHX microbiologist John Spear (Colorado School of Mines) said, “the Europan ocean is the main deal – life at the microbiological level needs just four things: water, a carbon source, an electron donor, and an electron acceptor. The last three are likely present from meteoric sources on Europa, so we have in one place what is likely to present the highest possibility for first discovering life off Earth.”

If successful Stone’s vehicle will be transported through kilometers of the Europan ice cap with the help of yet-to be developed nuclear technology that NASA Lewis Research Center was to have developed for this capability. A Washington official close to this project said “Stone’s activity, done in a Skunk works fashion, is an example of creativity and prowess that we rarely see in the world.”

DEPTHX, which is a precursor to the follow on activity ENDURANCE , is providing insights and preliminary technical capability to autonomously detect and collect aqueous micro-organisms. DEPTHX’s first venture into the true unknown will be take place in Mexico beginning in January 2007 at the world’s deepest hydrothermal cenote. Stone said, “if this test is successful it will show that we can now easily investigate areas on Earth that would never have been accessable before.” Unlike the NASA Martian rovers Spirit and Opportunity – which require meticulous daily mission programming to make small moves forward -- DEPTHX operates on its own, seeking to achieve high level scientific objectives and reporting home only when it finds something “interesting”. In this sense, DEPTHX represents a dramatic leap forward in science autonomy – the next generation of planetary robotics.

After this grant is completed, Stone intends to start work on ENDURANCE which will leverage the technologies, systems and operational procedures developed in DEPTHX to support the even more ambitious challenge of exploring sub-surface Antarctic lakes – the next step on the path to mission to Europa. ENDURANCE will require the combined efforts of NASA, NSF and international partners to achieve its objectives. Once ENDURANCE is successfully completed, Stone will be in a catbird position to offer next-generation planetary robotics technology to explore the heavens.

Stone gives great credit to the NASA ASTEP (Astrobiology Science and Technology for Exploring the Planets) program, Science Mission Directorate, for its support of this important project in astrobiology.

Team DEPTHX, for which Stone is the Principal Investigator, is an extraordinary collection of talent. Carnegie-Mellon’s Field Robotics Center is developing onboard navigation and proxops code; SwRI is developing the science payload in collaboration with microbiologists from Colorado School of Mines and University of Colorado, Boulder. UT Austin is handling field logistics, access, and onboard environmental sensors. And the University of Arizona Lunar and Planetary Laboratory is providing science payload and vehicle design programmatic and technical review and strategic program guidance for path-to-mission planning. This lean, talented and devoted team of scientists and technologists have worked around the clock for months now to make DEPTHX a reality.

The DEPTHX vehicle itself represents a tour-de-force in rapid prototyping -- an astounding 8 months flat from completion of the paperless CAD design to an autonomous flying vehicle that bristles with dense high technology and sofware. Full system tests are scheduled for late October at the University of Texas ARL facility, including the integrated science payload. After that, Cenote Zacaton awaits. Team DEPTHX built a 3D map of Zacaton to a depth of -290 meters in May of 2005 to obtain real-world data for testing of the SLAM (simultaneous localization and mapping) algorithm that will be the predominant geometric mapping and navigation hat trick the vehicle performs when operating in unknown, unexplored space. In January of 2007 the team will return to Zacaton with the intention of flexing the vehicle’s full 1,000 meter depth rating and potentially exploring the hydrothermal spring to more than a kilometer depth and several kilometers horizontally from the only entrance, while returning home through the labyrinth on the maps just created by the tether-less vehicle.

Project leader Dr. Stone is not new to the exploration of the subterranean underworld. He has successfully launched two companies that have developed the world’s most advanced closed-cycle PLSS (portable life support system) backpacks for manned diving to depths of 200 meters. He has also logged more than 7 years in the field on expeditionary work to some of the deepest places ever reached by humans beneath the surface of the earth.

============== BACKGROUND MATERIAL – DETAILED=======

What is DEPTHX and how does it fit into the Europa Mission?

DEPTHX is a prototype AUV (autonomous underwater vehicle) for developing and testing two of the most critical capabilities that will be needed by the Europa lander third stage. Indeed, these two advances are essential to the success of the Europa mission. To review quickly, the Europa mission architecture, as envisioned by Stone Aerospace*, will likely include the following components:

• the parent spacecraft, which will remain in orbit either about Jupiter or about Europa and which will primarily serve as a data relay back to Earth from the Lander.

• the Lander, which will actually be a 3-stage device:

Stage 1: the physical landing system that will contain propulsion (rocket) systems, power, and data relay systems to communicate with the orbiter, and which will control and carry out the descent and automated landing on the moon.

Stage 2: the "cryobot" second stage, which will melt a hole through up to ten kilometers of ice cap before reaching the sub-surface liquid ocean. Although the design is far from completely defined, the concept will most likely involve a nuclear powered thermal melter that will be attached to the bottom of the third stage. It is highly likely that the second stage will also deploy an armored fiber optic bundle behind it as it melts deeper. The fiber bundle will be frozen into the ice after the melter passes through with the third stage;

Stage 3: by far the most sophisticated element of the entire mission will be the lander third stage. In fact, the lander third stage will likely be a multi-stage device itself, roughly along the following lines as envisioned by Stone Aerospace CEO Dr. Bill Stone: the melter tip from the second stage -- really just a shield and a sophisticated heat exchanger -- will likely be jettisoned upon reaching the subsurface ocean. The remaining vehicle will detach from the fiber optic system and will leave behind a powerful communications and navigation beacon as well as a rechargeable power pack. At that point what remains is the lander third stage proper: a novel torpedo-shaped "fast mover" that will be propelled by steam thrust generated by the nuclear power plant (or alternatively by traditional props or an internal thrust turbine driven by electric motors driven by thermoelectric conversion - or some variant of that theme). The "fast mover" will carry a collection (2-5) of redundant, electrically powered self-mobile smart sub-payloads that are sensor-rich devices capable of not only mapping into unknown territory and bringing the fast mover back to the navigation beacon at the bottom of the melt hole, but also able to "sniff" for indicators of environmental variables that might indicate the presence of microbial life and steer (home) the combined 3rd stage vehicle towards those sites. At that point one of the smart sub-payloads will be deployed and will "fly" off in pursuit of microorganisms. To find them it will have to employ a multi-stage (hierarchical) detection system that improves the odds of finding something at each stage. Ultimately, using these tools, and if successful, it will detect and characterize microorganisms (most likely Bacteria or Archaea) in the Europan ocean and return to the fast mover, which will then drive it back to the navigation beacon whereupon it will upload what it finds to the surface lander, which will then relay the info back to the orbiter, which will then relay it back to Earth.

DEPTHX, then, is the prototype (a test article) for the smart sub-payload of the 3rd stage fast mover. ENDURANCE (Environmentally Non-Disturbing Under-ice Robotic ANtarctiC Explorer) is the Phase 2 follow on research to design, build, and test a prototype for the 3rd stage "fast mover" in an Antarctic sub-surface lake. It is this latter program that is now in limbo because of the funding cuts to scientific research within NASA.

Finally, the purpose of DEPTHX is to test the following two hypotheses:

1) can we design a fully autonomous underwater vehicle that can explore into completely unknown territory, create maps of that unknown territory in three dimensions, and use those just-created maps to return itself "home" without any other navigation aids?

2) can we design a fully autonomous science system that will seek out places where there is a high likelihood of microbial life and make a decision to collect samples that will demonstrate, unambiguously, that science autonomy is feasible on Europa. Specifically, can we demonstrate that by tracking environmental sub-aqueous variable gradients (temperature, chemical concentrations etc), along with spectral (color) differentiation, we can improve the likelihood of machine detection of microbial life (which we will verify in-situ by microscopy of the samples collected while on an actual mission - that is, DEPTHX will have pressure-rated microscopes onboard to detect the presence of microbes).

These two things (as well as research related to the other vehicle stages mentioned above) form the fundamental underpinning of the success of the Europa mission. It is these two capabilities that we hope to demonstrate at the Cenote Zacaton beginning in January 2007.


Note for Aviation Week: The discovery of the first observational evidence for liquid water, based on crack patterns, was covered in an article in Aviation Week (June 21, 1999, p. 58-59) by Michael Dornheim. The discovery was the research team of Prof. Richard Greenberg at the Univ. of Arizona. Greenberg is a member of the DEPTHX team.

* the views presented in this article are the views of Stone Aerospace and do not necessarily reflect official NASA thinking.

Download high resolution pictures of the DEPTHX here (ca. 12 MB)

DEPTHX videos: