Lunar and XXXVI (2005) 2206.pdf

THE DEPTHX PROJECT: PIONEERING TECHNOLOGIES FOR EXPLORATION OF EXTRATERRESTRIAL AQUEOUS CHANNELS. W. C. Stone1, R. Greenberg2, D. D. Durda3, E. A. Franke4, and the DEPTHX Team, 1StoneAeroSPACE,18912 Glendower Rd., Gaithersburg, MD 20879, [email protected], 2Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, [email protected], 3Southwest Research Institute, 1050 Walnut St., Boulder, CO 80302, [email protected], 4Southwest Research Institute, 6220 Cule- bra Rd., San Antonio, TX 78228, [email protected]

Introduction: Liquid water is not unique to our including irregular vertical surfaces, an open water own planet, and the strategy of following the path to column, floor sediments, and potential hydrothermal extraterrestrial water is likely to produce great discov- vents. The site is the 330-meter-deep (or more) hy- eries, especially in the area of . Reaching drothermal of Zacatón, Mexico [6]. The upper liquid water will involve not just landing on a target reaches of Zacatón are known to contain diverse mi- planet, but penetrating below the surface with tech- crobial mats, but even those upper reaches are un- nologies that will permit exploration and characteriza- charted, both spatially and biologically. Thus they tion of the aqueous environment. For example, Eu- offer an extraordinary opportunity to test the principles ropa’s global ocean lies below many kilometers of ice. and hardware under development. In a later phase, In anticipation of missions to explore of ’s after the autonomous exploration system is fully tested, ocean, considerable planning and technology devel- the DEPTHX project will extend its terrestrial trials to opment has addressed the problem of drilling, melting, settings in the Antarctic ice, where conditions may or punching through the thick ice with a variety of pos- more closely approximate cracks or other openings in sible types of robotic penetrators [e.g. 1]. Similarly, Europa’s ice. Other potential settings for testing (and consideration has been given to submarines that might possible practical applications) may include unex- be launched into the subsurface ocean after the ice is plored sub-aqueous environments like Lake Vostok, penetrated [e.g. 2]. Considerable attention has been other deep geothermal springs like Grand prismatic paid to Antarctica’s Lake Vostok as an analog to Eu- Spring of Yellowstone, various marine environments, ropa, because of these common issues of penetration and artificially created inhospitable environments (e.g. through thick ice to a pristine aqueous environment. the Berkeley acid mine drainage pit, Butte, MT, or The most interesting aqueous environments may be nuclear reactor cooling ponds. within channels of liquid through solid strata, such as The autonomous character of this cave-exploring where Europa’s ocean may penetrate hot springs on its robot will avoid well-known problems with tethered floor [3] or tidal cracks in its surface ice [e.g. 4, 5]. vehicles, which are vulnerable to snags even in terres- Those settings may provide conditions uniquely hos- trial applications. On Europa, linkages through many pitable to . kilometers of ice and, for exploring the sea floor, tens Therefore, advanced technological planning re- of kilometers of ocean depth, would certainly make quires development of vehicles, of autonomous explo- tethers impractical from the control and communica- ration and navigation systems, and of in situ analysis tions standpoint. Moreover, the communications lag to tools for exploring such channels. The issues are quite Earth would make control impractical even if links different from those involved in drilling through solids could be maintained between the craft and the surface or moving through wide-open submarine spaces. of Europa. Thus, at the heart of the DEPTHX project Moreover, technology for exploring confined channels is the development of a fully autonomous underwater may allow exploitation of cracks in Europa’s ice to scientific vehicle. minimize the need for penetration of solid ice. It will The DEPTHX vehicle will map the spatial setting also be useful within the thick oceanic layer, as well as in three dimensions, using a 2-Pi-steradian sonar im- in exploring any hot springs or other channels into the aging system consisting of 56 discrete highly direc- sea floor. In fact, it is likely that only such an intelli- tional transducers. Additional proprioceptive sensors gent autonomous search system is likely to have suc- (inertial guidance, Doppler sonar, depth) provide input cess in a Europan setting. along with the sonar readings to a simultaneous local- As a first step in attacking this problem, the Deep ization and mapping algorithm, which will form the Phreatic Thermal Explorer (DEPTHX) project is de- primary basis for vehicle exploration and navigation. veloping a fully autonomous architecture for intelligent The environment along the vehicle’s trajectory will be in situ discrimination of microbiological organisms spatially characterized with an environmental moni- and biological sample collection. The technology is toring package that will sense and measure tempera- physically realizable, using off-the-shelf sensors and ture, pH, dissolved oxygen, redox potential, sulfides, state-of-the-art intelligent robotic strategies. nitrates, and turbidity. Most of these sensors are avail- The concept and prototypes will be tested in an un- able as a suitable commercial package, but the latter usual terrestrial analog that presents many of the likely three will need to be customized for operation in this morphologic regimes where life may exist on Europa, environment. The autonomous navigation system will Lunar and Planetary Science XXXVI (2005) 2206.pdf

analyze this information to determining the trajectory rescence from DNA attachment sites, allowing sophis- and activities going forward in time. Gradients will ticated characterization of the organisms in the sample. drive navigation toward sites of biological interest in In addition to the samples brought on board for in open water and on the walls of the channels. situ analysis, the DEPTHX vehicle will be able to col- At sites of potential interest, a macro imaging sys- lect and store samples for return and later laboratory tem will examine locations on the walls or other sur- study, including both samples from open water or from faces, as well as free floating materials or organisms. underwater surfaces. For the latter, a sample collection This imaging system will include a 5 megapixel color probe will extend from the vehicle to the cave wall, CCD camera with off-axis strobe lighting. Images will extracting material from the surface and also coring be captured and analyzed with on-board image proc- and sampling within the wall material. essing software to identify patterns, colors changes in Initial field testing of the several key subsystems color or texture, and other features that indicate the for this ambitious development effort is planned for presence of algae mats or other life. mid-2005 at Zacatón. In addition to challenging de- For in situ analysis of microorganisms, DEPTHX tector, sampling, and analysis systems, DEPTHX will will contain a custom designed flow cell and micro- be pushing the limits of autonomous robotics. The scopic imaging system to study what is drawn in. The adaptability and autonomy at the heart of this project microscope under development will include specific- will be potentially applicable in a wide range of set- wavelength LEDs for back illumination and a high- tings on Earth and in various other sites in the solar sensitivity CCD camera. Water will be pumped system. through the flow cell (maintaining the ambient pres- sure) and images captured and analyzed. Sequences of References: Hartman, C., et al. Forum on Innovative images will be analyzed by the autonomous on-board Approaches to Outer Planetary Exploration 2001-2020 system to identify selected shapes, structures and pat- (2001), Lunar and Planetary Inst.; [2] Committee on terns using machine-vision techniques. The image Planetary Exploration (1999) A Science Strategy for processing system will also have the capability to de- the Exploration of Europa, National Research Coun- tect relative motion and geometry of objects in the cil; [3] McCollom, T.M. (1999) JGR 104, 30729; [4] field of view. Greenberg, R., and Geissler, P. (2002) Meteoritics and Moreover, this internal imaging system will have Planetary Science 37, 1685; [5] Greenberg, R. (2005) the capability of introducing DAPI stain into the sam- Europa, the Ocean Moon, Springer-Praxis Publ.; [6] ple flow system and illuminating it with UV LEDs. In Gary, M. O. (2002), Karst Waters Institute Special this mode, the microscope will be able to detect fluo- Publication 7, 141.