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Planetary Instrument Concepts for the Advancement of Solar System Observations

Next-Generation Ground Penetrating Radar for Mars, the Moon, and Asteroids

Completed Technology Project

Project Description

ALHAT - ETD Autonomous Landing & Hazard Avoidance Tech   Earth Science Technology Office

The exploration of planetary bodies has been dominated by remote sensing of the surface. The martian orbital radars have produced incredibly detailed stratigraphic mapping of the polar caps and have demonstrated that ground penetrating radar (GPR) is a powerful instrument to investigate the subsurface. A high-frequency (500 - 3000 MHz) high-bandwidth Stepped Frequency Continuous Wave (SFCW) GPR called WISDOM will fly on ESA's ExoMars rover mission. The 2013 Science Definition Team for the Mars 2020 rover recognized the benefits of GPR and included subsurface sensing including structural and compositional mapping in its baseline mission, but removed this capability from its threshold (i.e. minimum) mission. Therefore, GPR may get left off as it did on MSL. High-resolution subsurface mapping can also greatly benefit other missions such as: a lunar rover missions to investigate ice in the permanently shadowed terrain, and the Asteroid Retrieval Mission could use radar to investigate the internal properties of the small (<10 m) asteroid before it is captured and possibly destroyed. Our objectives is to construct a GPR that can easily be accommodated into any platform operating in proximity to surfaces, particularly rovers and that possesses a large bandwidth to enable resolution of several centimeters at depths of a few meters and total penetration depths of greater than 10 meters. A large-bandwidth system also enables discrimination of certain mineralogies and rock units based on their frequency-dependent electromagnetic (such as liquid water, adsorbed water due to clays or salts, gray hematite, magnetite, palagonite, and ilmenite) or scattering properties. Therefore, we proposed to build a SFCW with a bandwidth of 100 - 1000 MHz with a conformal fractal antenna that will minimally interfere with the primary design of the exploration platform. On a rover these form-fitting antennas would attach directly to the rover belly and protruds less than 10 mm. This is significantly different from the larger WISDOM antennas that must be place in the front or back of the rover. WISDOM antennas would be difficult to attach to a MSL-like rover, because the arm attached to the front and the nuclear power source attached to the back. The SFCW also allows us to minimize Electromagnetic Interference (EMI), by eliminating any radar frequencies that interfere with the avionics or instruments. To accomplish these goals, we will first design and fabricate a set of conformal antennas (Task 1), and then design and fabricate the SFCW GPR electronics that can later be easily adapted for spaceflight (Task 2). Next, we will integrate the flight-like VNA and conformal antennas into our prototype GPR (Task 3), and then field test the GPR (Task 4). Throughout the entire project we use radar-range calculations and full-waveform GPR models to show like results for mission to Mars, Moon, and Asteroids (Task 5). Lastly, we will both assess the system's imaging ability to extract geological structure and stratigraphy, and model our field data to show how different attenuation mechanisms can be measured in the field terrestrially (Task 6). The proposed radar will start at TRL 2 and obtain TRL 4+. We will achieve TRL 4 with the antennas and VNA in the laboratory. Once the radar is integrated, indoor testing becomes problematic without the costly construction of very large test-beds. Therefore, we will conduct our tests at well known field sites (USGS GPR test facility in Lakewood, CO, Great Sand Dunes National Park near Alamosa, CO, and at the Volcanic Tablelands near Bishop, CA), thereby obtaining TRL 4+. Our team has extensive experience in terrestrial GPR, building GPRs, understanding the attenuation mechanisms that a planetary GPR will encounter, and planetary analog investigation with GPR.

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