Fig. 7. Minimum Angle of Attack Allowed for the Noninteracting Limit to be Valid as a Function of Conductor Voltage. for £»1. Therefore, the projected area of the sheath is proportional to A sin p. Since cd is defined by cd=F-d/\piV2o^A sin P, cd increases for small P in the PIC result. This cd~P characteristic can not be found in the interacting limit where all the sheath interacts over the solar array and forms the planar sheath. However, from the limit of validity of the noninteracting limit we would expect that for P<— 45 we have to know the ion flow field over the whole array. In Table I we give the ion drag force relative to the neutral drag force as a function of altitute for two potential drops and for the numerical results of Ref. [2] and the PIC code results. We see that at high altitudes the ion drag force can significantly modify the total force on the array for large array voltages. This is important to understand since while the total force is small, an enhanced drag force acting for a long time will cause large changes in the orbit of the system carrying the solar array.
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