data storage device, and could only send telemetry to the ground when it was passing over an Earth receiving station, so some regions had no coverage during the flight. Micrometeorite Detector Direct measurements of micrometeorites were made on Explorer 1 using two separate detectors: a wire grid detector and a crystal transducer. The parameters determined were the influx rates of each size interval, the impinging velocity, the composition, and the density of the micrometeorite. The wire grid detector consisted of 12 cards (connected in parallel) mounted in a fiberglass supporting ring which in turn was mounted on the satellite's cylindrical surface. Each card was wound with enameled 17-micron-diameter nickel alloy wire. Two layers of wire were wound on each card to ensure that a total area of completely covered. A micrometeorite of about 10 microns would fracture the wire upon impact, destroy the electrical connection, and thus record the event. The acoustic detector (transducer and solid-state amplifier) was placed in acoustical contact with the middle section skin where it could respond to meteorite impacts on the spacecraft skin such that each recorded event would be a function of mass and velocity. The effective area of this section was 0.075 m2, and the average threshold sensitivity was 0.0025 g-cm/s. Satellite Drag Atmospheric Density Because of its symmetrical shape, Explorer 2 was selected for use in determining upper atmospheric densities as a function of altitude, latitude, season, and solar activity. Density values near perigee were deduced from sequential observations of the spacecraft position, using optical (Baker-Nunn camera network) and radio and/or radar tracking techniques. Resistance Thermometers The Explorer 2 satellite was equipped with four resistance thermometers that made direct temperature measurements, three external and one internal. The primary purpose of the experiment was to study the efficacy of passive thermal control (in this case, insulation and exterior coatings) on the exterior and interior of a satellite, and to document the temperature of the instrumentation to study its effect on instrument operation. Thermometers The thermometer designated external temperature gauge no. 1 was mounted on the outer hull at the bottom of the upper (instrumentation) section of the satellite. This measured the cylinder skin temperature over a range of -50°C to +110°C, with an accuracy of 4°C over the range -10°C to +80°C. External temperature gauge no. 2 was mounted along the bottom of the nose cone to measure the nose cone skin temperature.