a charged plate, ac = 0.044 which corresponds to the PIC simulations and ac = 0 which is the result for a neutral flow to the solar array. The analytic result for ac=l agrees well with Kuninaka & Kuriki for low voltages but deviates for larger voltages as the sheath spreading neglected in the analytic model becomes more important. The analytic result for ac=0.044 is very close to the neutral result. The PIC code results fall in between the analytic results and the interacting limit results. This is because the PIC code results include thermal effects and the effects of sheath spreading away from the conductor. In Fig. 9 we show the drag coefficient as a function of angle of attack for A0 = — 250 V. In addition, we show the numerical result of Kuninaka & Kuriki (ac=l) for the case of only one segment («s=l). In Fig. 9 the interacting limit overestimates the drag at large negative angle of attack, since the whole array is at one potential. As the angle of attack P decreases, cd increases in the PIC result, while it decreases in the interacting limit and the analytical results. In the PIC result the sheath structure is spherical rather than planar as shown in Fig. 3. Therefore, the projected area of the sheath to the plane normal to the ion flow is larger than A sin for small p. On the other hand, in the interacting limit the sheath structure is planar if we neglect the round sheath at the edge of the solar array
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