1. Pg. 3, col. 1, par. 5, lines 8-9: read11•••at all times thicker than the electron beam penetration, so the X-ray.
2. Pg. 4, col. 1, par. 4, lines 1-2: read"The thruster body-anode assembly 0onstructed mostly of type 304 stainless steel) . 11
3. Pg. 4, col. 2, par. 1, lines 1-2: read". sputtered material, as be in Figure 9(bl; Samples of these deposits were collect;d .