Vanguard 1

Radio beacon

A 10 mW transmitter, powered by a mercury battery, on the 108 MHz band used for International Geophysical Year (IGY) scientific satellites, and a 5 mW, 108.03 MHz^[10] 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 very slight^[11] 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.^[8] The battery-powered transmitter provided internal package temperature for about sixteen days and sent tracking signals for twenty days. The transmitter powered by solar cells transmitted for more than six years. Its signal gradually weakened and was last received at Quito, Ecuador, in May 1964. Since then the spacecraft has been tracked optically from Earth, via telescope.^[8]

Vanguard 1 with its six solar cells attached^[12]

Satellite drag atmospheric density

Because of its symmetrical shape, Vanguard 1 was used by experimenters for determining upper atmospheric densities as a function of altitude, latitude, season, and solar activity. As the satellite continuously orbited, it would deviate from its predicted positions slightly, accumulating greater and greater shift due to drag of the residual atmosphere. By measuring the rate and timing of orbital shifts, together with the body's drag properties, the relevant atmosphere's parameters could be back-calculated. It was determined that atmospheric pressures, and thus drag and orbital decay, were higher than anticipated, since Earth's upper atmosphere does taper off into space gradually.

This experiment was planned extensively prior to launch. Initial Naval Research Laboratory (NRL) proposals for the project included conical satellite bodies; this eliminated the need for a separate fairing and ejection mechanisms, and their associated weight and failure modes. Radio tracking would gather data and establish a position. Early in the program, optical tracking (with a Baker-Nunn camera network and human spotters) was added. A panel of scientists proposed changing the design to spheres, at least twenty inches in diameter and hopefully thirty. A sphere would have a constant optical reflection, and constant coefficient of drag, based on size alone, while a cone would have properties that varied with its orientation. James Van Allen of the University of Iowa proposed a cylindrical satellite based on his work with rockoons, which became Explorer 1, the first American satellite. The Naval Research Laboratory finally accepted a sphere with a 6.4-inch diameter as a "test vehicle", with a diameter of twenty inches set for the follow-on satellites. The weight savings, from reduced size as well as decreased instrumentation in the early satellites, was considered to be acceptable.

Since three of the Vanguard satellites are still orbiting 23 October 2018 with their drag properties essentially unchanged, they form a baseline data set on the atmosphere of Earth that is over 50 years old and continuing.^[13][14][15]

50th anniversary

The Vanguard 1 satellite and upper launch stage hold the record for being in space longer than any other man-made object.^[17][18]

A small group of former NRL and NASA workers had been in communication with one another, and a number of government agencies were asked to commemorate the event. The Naval Research Laboratory commemorated the event with a day-long meeting at NRL on March 17, 2008.^[19] The meeting concluded with a simulation of the satellite's track as it passed into the orbital area visible from Washington, D.C., (where it is visible from the Earth's surface). The National Academy of Sciences scheduled some seminars to mark the 50th anniversary of the International Geophysical Year, which were the only official observances known.^[20]