Atmospheric dust electrification is a highly probable phenomenon in the Martian atmosphere. To gain a more thorough understanding of the potential for electrostatic discharge of different materials on Mars, the Electromagnetic Physics Laboratory at KSC developed an aerodynamic electrostatic multisensor that will measure the electrostatic and triboelectric properties of Martian atmospheric dust (figure 1). This knowledge will provide necessary information for the design of landers, rovers, and habitation facilities in future missions to the planet.

Figure 1. Diagram of the Prototype of the Aerodynamic Electrometer and Its Associated Electronic Housing With Sensor/Guard Probes Embedded in 6 Cylindrical Insulators

The multisensor electrometer consists of an array of insulating materials with each material backed by a miniature electrometer. The instrument was designed to be exposed to mineral particles similar in composition to those in the Martian environment. To simulate a windstorm, mineral particles are propelled toward the instrument at speeds reaching 20 meters per second. The overall sensor array has an aerodynamic configuration to minimize turbulent flow. The electrometer sensor uses a simple reference capacitor design similar to the one used on the Mars Environmental Compatibility Assessment (MECA) Electrometer (figure 2), a flight-ready instrument designed by the Jet Propulsion Laboratory and KSC that includes five sensors in a line array with a resolution of 5 million elementary charges.

Figure 2. Circuit Diagram for Each of the
Electrometer Probes

The probe consists of a field-sensor electrode that is enclosed by a guard electrode, which in turn is enclosed by an electrically grounded shield (figure 3). The probe is embedded in a cylinder to within 2.5 millimeters of the surface. The overall gain of the electronic circuit is 0.25 picocoulomb per millivolt. The current version of the instrument contains six sensors to measure the electric field induced by any net charge on six different insulator surfaces. The charge develops through frictional contact between the cylindrically-shaped insulators and incident granular material.
Windborne dust particles were generated using a dust particle impeller that was developed at KSC to simulate a Martian dust storm in a vacuum chamber (figure 4). Constant wind speeds of 20 meters per second were measured with the dust impeller operating at gas pressures ranging from 5 millibars to 1 bar.

Figure 5 shows the electrostatic responses of polytetraflouroethylene (Teflon) and fiberglass-epoxy G-10 to Martian simlant dust particles. The cylinders were exposed to windborne dust particles in separate experiments. Data were taken in a vacuum chamber containing a room-temperature carbon dioxide (CO2) atmosphere at 9 millibars. Other granular materials such as silicon dioxide (SiO2), iron oxide (Fe2O3), and aluminum oxide (Al2O22), found by Viking and Pathfinder instruments to be major components of the Martian soil, were also used in these experiments.

Figure 3. Diagram of One of the Electrostatic Probes Inside an Aerodynamically-Shaped Polymer (The shield, guard, and sensor electrodes are embedded below the surface of the windward face of the cylindrical insulator.)

Figure 4. KSC Dust Particle Impeller Operates at Low Pressures and Is Capable of Propelling Dust Particles at Atmospheric Pressures and Pressures as Low as 7 Millibars

Figure 5. Martian Soil Simulant Particles Propelled to the Aerodynamic Electrometer With the Probe Embedded in Teflon and Fiberglass-Epoxy G-10 Cylinders

Contact: Dr. C.I. Calle (Carlos.Calle-1@ksc.nasa.gov), YA-C2-T, (321) 867-3274
Participating Organizations: Florida Institute of Technology (Dr. J. Mantovani), YA-C2-T (E.E. Groop), Swales Aerospace (Dr. C. Buhler), and Dynacs Inc. (A.W. Nowicki)