Vanguard 1 (Harvard designation: 1958-Beta 2, COSPAR ID: 1958-002B) is an American satellite that was the fourth artificial Earth-orbiting satellite to be successfully launched, following Sputnik 1, Sputnik 2, and Explorer 1. It was launched 17 March 1958. Vanguard 1 was the first satellite to have solar electric power. Although communications with the satellite were lost in 1964, it remains the oldest human-made object still in orbit, together with the upper stage of its launch vehicle.
Vanguard 1 was designed to test the launch capabilities of a three-stage launch vehicle as a part of Project Vanguard, and the effects of the space environment on a satellite and its systems in Earth orbit. It also was used to obtain geodetic measurements through orbit analysis. Vanguard 1, being small and light enough to carry with one hand, was described by the Soviet Premier, Nikita Khrushchev, as "the grapefruit satellite".
Spacecraft design
The spacecraft is a aluminum sphere 6 inches (152 mm) in diameter, with antennae spanning 3 feet. It contains a 10 mW, 108 MHz transmitter powered by a mercury battery and a 5 mW, 108.03 MHz transmitter that was powered by six solar cells mounted on the body of the satellite. Six long antennas, diameter spring-actuated aluminum alloy aerials 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 the ground stations.
A backup version of Vanguard 1 is on display at the Smithsonian National Air and Space Museum, Steven F. Udvar-Hazy Center in Chantilly, Virginia.
Mission
On 17 March 1958, the three-stage launch vehicle placed Vanguard into a , 134.27-minute elliptical orbit inclined at 34.25°. 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 about 240 years. Vanguard 1 transmitted its signals for over six years as it orbited the Earth.
Radio beacon
A 10 mW mercury-battery-powered telemetry transmitter on the 108 MHz band used for International Geophysical Year (IGY) scientific satellites, and a 5 mW, 108.03 MHz Minitrack transmitter powered by six solar cells were used as part of a radio phase-comparison angle-tracking system. The system transmitted signals through the satellite's six spring-loaded aluminum alloy aerials. Satellite tracking was achieved using these transmitters and Minitrack ground stations situated around the globe.
These radio signals were 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 16 days and sent tracking signals for 20 days. The solar-cell-powered transmitter operated for more than six years. Signals gradually weakened and were last received at the Minitrack station in Quito, Ecuador, in May 1964. Since then the spacecraft has been tracked optically from Earth, via telescope.
Design for atmospheric density measurements
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 in diameter and hopefully .