a count of micrometeoroid impacts. Mission results Proton Precessional Magnetometer This experiment had a proton precessional magnetometer to measure the Earth's magnetic field at altitudes ranging from to and at latitudes between ± 33.4°. The measurements were made on command as the spacecraft passed seven Minitrack stations in North and South America and one each in Australia and South Africa. When switched on by command, the polarization coil around the proton sample (normal hexane) was turned on for 2 seconds followed by a 2 seconds readout of the precession signal. Several readings were taken during each pass over a station. The experiment worked well during its 84 days active life, and approximately 4300 readings were recorded. The experiment is described in J. C. Cain et al., "Measurements of the geomagnetic field by the Vanguard 3 satellite", NASA TN D-1418, Goddard Space Flight Center, Greenbelt, Maryland, 1962, The overall accuracy of the field measurements was approximately 10 nT (gammas). X-Ray Experiment The objective of this experiment was to measure the X-ray emission from the Sun and its effects on the Atmosphere of Earth. The detectors were two identical ionization chambers sensitive to X-ray wavelengths produced in solar flares (2 to 8 Å, or 200 to 800 pm). The ionization chambers were located 120° apart in the equatorial plane of the satellite and received a maximum signal when an ion chamber tube "looked" toward the Sun. The instrumentation were designed to measure the 2 to 8 Å (200 to 800 pm) X-ray flux and record the peak solar flare intensity by means of a peak-reading memory device, during the daylight portion of each orbit. However, due to the overwhelming background radiation of the Van Allen Belts, its sensors were saturated, and no useful information on solar X-rays was gathered. Micrometeorite Detector This experiment contained two sealed pressure zones, extending along the interior walls of the satellite, which were designed to record the impact of micrometeorites large enough to pierce the satellite shell. These pressure zones were partial vacuums, each at a different pressure, and were protected by 0.66 mm magnesium walls that presented an exposed surface area of 0.162 m2, which was 20% of the area of the shell. A puncture in the walls of either zone was detected by a differential pressure gauge mounted between them, and telemetered as a change in the length of one of the telemetry channels. Erosion