which detected alpha particles between 2 and 10.2 MeV, and (4) PN3, which was sensitive to particles of Z greater than 3, including carbon-12 between 0.58 and 9.5 MeV per nucleon, nitrogen-14 between 0.514 and 13.9 MeV per nucleon, and oxygen-16 between 0.466 and 18.8 MeV per nucleon. GM1 and SSD were oriented perpendicular to the spacecraft spin axis, GM2 was oriented parallel to the spin axis, and GM3 was oriented antiparallel to the spin axis. Data from GM1, PN1, and PN4 were divided into data from quadrants oriented with respect to the Sun (sectors I, II, III, and IV were centered 180°, 270°, 0°, and 90° away from the Sun, respectively). Data were read out every 82- or 164-seconds, and the experiment performance was normal. Energetic Particle This experiment consisted of a Neher-type ionization chamber and two Lionel type 205 HT Geiger–Müller tubes (GM). The ion chamber responded omnidirectionally to electrons above 0.7 MeV and protons above 12 MeV. Both GM tubes were mounted parallel to the spacecraft spin axis. GM tube 1 detected electrons above 45 keV that were scattered off a gold foil. The acceptance cone for these electrons had a 70« full-angle and an axis of symmetry that was 20« off the spacecraft spin axis. GM tube 2 responded to electrons and protons above 22 and 300 keV, respectively, in an acceptance cone of 70° full-angle centered at the spacecraft spin axis. Both GM tubes responded omnidirectionally to electrons and protons of energies above 2.5 and 50 MeV, respectively. Pulses from the ion chamber and counts from each GM tube were accumulated for 39.72-seconds and read out every 40.96-seconds. In addition, the time between the first ion chamber pulses in an accumulation period was also telemetered. This experiment performed well initially. GSFC Magnetometer The experiment consisted of a boom-mounted triaxial fluxgate magnetometer. Each sensor had dual ranges of minus to plus 24 nT and 64 nT, with digitization resolutions of ± 0.094 nT and 0.250 nT, respectively. Zero level drift was checked by periodic reorientation of the sensors until 20 May 1969, when the flipper mechanism failed. Past this point, data analysis was more difficult as the zero level drift of the sensor parallel to the spacecraft spin axis was not readily determined. Spacecraft interference was less than 0.125 nT. One vector measurement was obtained each 5.12-seconds. The bandpass of the magnetometer was 0 to 5