Vanguard 1

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Vanguard 1 (ID: 1958-Beta 2 [1]) was the fourth artificial Earth satellite launched and the first satellite to be solar powered.[2] Although communication with it was lost in 1964, it remains the oldest manmade satellite still in orbit. It was designed to test the launch capabilities of a three-stage launch vehicle as a part of Project Vanguard, and the effects of the environment on a satellite and its systems in Earth orbit. It also was used to obtain geodetic measurements through orbit analysis.

Contents

Spacecraft design

The spacecraft is a 1.47 kg (3.2 lb) aluminum sphere 6.4 inches (165 mm) in diameter. It contains a 10 mW, 108 MHz transmitter powered by a mercury battery and a 5 mW, 108.03 MHz[3] transmitter that was powered by six solar cells mounted on the body of the satellite. Six short antennas protrude from the sphere. The transmitters were used primarily for engineering and tracking data, but were also used to determine the total electron content between the satellite and ground stations. Vanguard also carries two thermistors which measured the interior temperature over sixteen days in order to track the effectiveness of the thermal protection. A backup version of Vanguard 1 is on display at the Kansas Cosmosphere and Space Center.

Mission

The three stage launch vehicle placed Vanguard into a 654×3,969 km (406×2,466 mi.), 134.2 minute elliptical orbit inclined at 34.25 degrees on March 17, 1958. Original estimates had the orbit lasting for 2,000 years, but it was discovered that solar radiation pressure and atmospheric drag during high levels of solar activity produced significant perturbations in the perigee height of the satellite, which caused a significant decrease in its expected lifetime to only about 240 years.[4]

Mission results

Radio beacon

A 10 mW mercury battery powered transmitter on the 108 MHz band used for International Geophysical Year (IGY) scientific satellites, and a 5 mW, 108.03 MHz[5] transmitter powered by six solar cells were used as part of a radio phase-comparison angle-tracking system. The tracking data were used to show that the shape of the Earth has a north-south asymmetry, occasionally described as pear-shaped with the stem at the North Pole. These radio signals were also used to determine the total electron content between the satellite and selected ground-receiving stations. The battery-powered transmitter provided internal package temperature for about sixteen days and sent tracking signals for twenty days. The solar cell powered transmitter operated for more than six years. Signals gradually weakened and were last received at Quito, Ecuador in May 1964 after which the spacecraft was optically tracked from Earth.

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