Vanguard 3
Micrometeorite Detector
### 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](/wiki/Micrometeorite "Micrometeorite") 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](/wiki/Magnesium "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 of the satellite shell through bombardment by [space dust](/wiki/Space_dust "Space dust"), [micrometeorites](/wiki/Micrometeorite "Micrometeorite"), and other particles was recorded by three [chromium](/wiki/Chromium "Chromium")\-strip erosion gauges mounted on the satellite surface, and by a photosensitive detector. Electrical resistances of the gauges changed as their surfaces were changed by erosion. The photosensitive detector, a [cadmium sulfide](/wiki/Cadmium_sulfide "Cadmium sulfide") cell protected by an opaque covering of [aluminized PET film](/wiki/Metallised_film "Metallised film"), also showed a resistance change as the covering was eroded or penetrated. Erosion measurements also were telemetered as channel lengths, which permitted estimates of the erosion rates. Four [barium titanate](/wiki/Barium_titanate "Barium titanate")\-type [microphones](/wiki/Microphone "Microphone") recorded micrometeorite impacts on the satellite's surface. The microphone output was amplified, shaped, and fed into a magnetic counter unit, which provided continuously, in three\-decimal digits, the cumulative count of impacts. The unit counted up to 1000 and then reset to zero. The satellite recorded 6600 micrometeorite impacts during 66 days of operation, of which 2800 occurred during a 70 hours interval from 16 to 18 November 1959, almost certainly due to the Earth's annual passage through debris from comet [Tempel\-Tuttle](/wiki/55P/Tempel%E2%80%93Tuttle "55P/Tempel–Tuttle"), which results in the [Leonids meteor shower](/wiki/Leonids "Leonids") which peaks on the 17 November 1959\. No penetrations or fractures were recorded in the sensors of the surface penetration experiment. Because the erosion sensors were not disrupted, no definite results could be drawn from that experiment. 


Why did so many micrometeorites impact the satellite in that short time?