The dependences of the ion current on the angle of attack are shown in Fig. 5 at — 1 kV array potential for the various models. For all models the collected ion currents decrease with increasing the angle of attack, that is, when the electrodes of the solar array models face toward the wake direction of the ion flow. Characteristics of Ion Drag The experimental results of the ion drag are presented as a function of the array voltage in Fig. 6 at the ram mode in the constant plasma condition. The dependences on the angle of attack are seen in Fig. 7 at —2 kV array potential. They were obtained by measuring the displacement of the pendulum system in the biased condition from the floating condition which had already been affected by the aerodynamic force. The ion drags for all the models increase with progression of the array potential. The order of the models for the drag magnitude in Fig. 6 is similar to that of the ion current in Fig. 4. In Fig. 7 the ion drag of the baseline model shows maximum at the ram mode and turns negative, namely, acts as thrust at a positive angle of attack. This tendency can be seen for the others, but the magnitudes are low. The erosion rate of the baseline model with the tungsten electrode biased at — 2 kV was 1.93 mg/C (1.01 as the sputtering rate), which is in good agreement with the theory of the sputtering.
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