Aft-body drag reduction by combined boat-tailing and base blowing atM = 3
the sphere in the pressure range 4x 10~ 6 5 which is now equal to +0.3 V. We have chosen to examine the influence of the slow ions on the electron temperature at the closest vicinity to the sphere downstream, since it is in this region that the effect of Te (wake) > 7; (ambient) is pronounced. 12~14 As is seen from Fig. 4, Te (wake) is larger than Te(ambient) for pressures smaller than about 1.6xlO~ 5 Torr. For the higher pressures, the enhancement in T e(wake) with respect to rc,(ambient) is close to the experimental error in the electron temperature determination. The trend seems, however, to be clear. Namely, as the pressure increases the influence of the slow ions on the electron temperature observations is more significant, which is similar to the influence of the slow ions on the electron current profiles (see Fig. 3). In summary, the findings of this study indicate that the effect of slow ions, when a<0.3, is not significant for measurements of ion current variations in the wake zone. However, this is not the case when studies are aimed at the quantitative examination of electron current and temperature variations in the near wake zone. In these instances, the measurements of electron properties in the wake should be done at very low systems pressures or over a range of system pressures in order to ascertain the effect of slow ions.