Charge Decay Properties

Research and Technology 2002

I-V Curve for (a) Moist Simulant (Red) Along With a Best-Fit Curve Shown in Blur and (b) I-V Curves of Dry Simulant

Figure 2. I-V Curve for (a) Moist Simulant (Red) Along With a Best-Fit Curve Shown in Blur and (b) I-V Curves of Dry Simulant

Decay Curve for Both (a) Wet (Red) and (b) Dry (Green) Simulant Along With Best-Fit Curves

Figure 3. Decay Curve for Both (a) Wet (Red) and (b) Dry (Green) Simulant Along With Best-Fit Curves
(The colors match the curves with their equations.)

The Electromagnetic Physics Laboratory at KSC focused recently on testing and understanding the electrostatic properties of the Johnson Space Center Mars-1 Martian regolith simulant for future robotic missions to Mars. In a dry environment such as that of Mars, electrostatic discharge can become hazardous; therefore, characterization of this phenomenon is crucial for mission success. To characterize this phenomenon, experiments were designed to measure the charge decay characteristics of the simulant. Measurements were performed in a simulated Martian environment under both moist conditions (12-percent relative humidity) and dry conditions (less than 1-percent relative humidity). For the experiments under dry conditions, the soil was baked out to remove excess moisture and was evacuated to pressures below 1 torr before each experiment was performed. Figure 1 shows the time it takes dry simulant to discharge once exposed to a high-voltage corona under normal simulated Martian conditions at different temperatures. At lower temperatures the soil decays more slowly indicating the higher resistivity of the simulant. This behavior is understood in terms of the current-voltage (I-V) characteristics of the material. Tests of the I-V relationships (figure 2) show that the soil possesses nonohmic behavior when the soil is moist and ohmic behavior when the soil is dry. Using these forms of the I-V curves, theoretical relationships of the charge decay curves can be derived and match well with the experimental data in figure 3.		Analyses of the moist and dry simulant indicate that the most important mechanism behind the charge decay of the Martian regolith is the moisture content of the soil. Possible use of this mechanism in the search for water on Mars is being investigated. Figure 1. Average of Many Voltage Decay Curves at Low Temperatures Under Simulated Martian Conditions Contact: Dr. C.I. Calle (Carlos.Calle-1@ksc.nasa.gov), YA-C2-T, (321) 867-3274 Participating Organizations: Swales Aerospace (Dr. C. Buhler) and Dynacs Inc. (A.W. Nowicki)
Figure 2. I-V Curve for (a) Moist Simulant (Red) Along With a Best-Fit Curve Shown in Blur and (b) I-V Curves of Dry Simulant
Figure 3. Decay Curve for Both (a) Wet (Red) and (b) Dry (Green) Simulant Along With Best-Fit Curves (The colors match the curves with their equations.)