Opportunistic Bistatic Radar for Mars Helicopter

Bistatic radar is a technique that utilize the telecommunication link to obtain science data about a target body. The New Horizons mission used this technique to probe the atmosphere of Pluto via transmissions from the Deep Space Network, the Cassini- Huygens mission used this technique to characterize the surface of Titan, and the Rosetta mission (with the CONSERT instrument) used this technique between the Philae lander and the Rosetta orbiter. In opportunistic bistatic radar, the technique is applied by taking advantage of required transmissions that are not otherwise planned for science purposes.

In the case of a helicopter flying in the atmosphere of another planet, data transfer may be accomplished via helicopter relay of data through another surface asset, such as a rover. The transmissions from the helicopter to the surface asset would have not only a direct path, but a portion of the transmitted energy would be reflected from the surface and possibly subsurface. Interference between the direct and reflected signals can be used to probe the surface and subsurface between the helicopter and the rover, with the depth of penetration depending upon the wavelength used for the telecommunications and the material properties (e.g., permittivity and porosity).

We have constructed a field deployable model of the telecommunications system for the Mars Helicopter Scout, which is flying with the Mars 2020 rover. We describe a series of tests designed to characterize the performance of this system. As a motivating scenario, we consider the extent to which the bistatic radar technique would be able to probe into recurring slope linea (RSL) on Mars, specifically whether a helicopter-surface asset system would be capable of distinguishing between "wet" RSLs, i.e., those originating from the flow of a brine, and "dry" RSLs. An attractive aspect of the bistatic radar technique is that it would allow remote sensing of potentially planetary-protection sensitive RSLs.

Finally, while the focus of this work has been a helicopter on Mars, the bistatic radar technique would be more generally applicable to any aerial vehicle at a planet with an atmosphere.

Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.