Micrometeorite Detector

Description

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 1 cm by 1 cm was 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 sq m, and the average threshold sensitivity was 0.0025 g-cm/s.

During launch on February 1, 1958, one or two of the 12 grid detectors were apparently broken. The recorded grid data, valid for approximately 60 days after launch (February 1, 1958, to April 1, 1958), showed no more than one and possibly no detectors broken from meteorite impacts. Data from the acoustical sensor were obtained when an impact occurred while the satellite was over a ground recording station. Over an 11-day period (February 1, 1958, to February 12, 1958), 145 impacts were recorded (minus eight impacts that registered during the launch and injection into orbit). Due to poor signal-to-noise ratios, very elaborate data reduction procedures had to be developed. The high impact rates on one portion of the orbit and the subsequent failures in the satellite's electronic system have been attributed to a meteor shower.