Vanguard 1


Vanguard 1 is an American satellite that was the fourth artificial Earth orbital satellite to be successfully launched. Vanguard 1 was the first satellite to have solar electric power. Although communication with the satellite was lost in 1964, it remains the oldest man-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 was described by the Soviet Premier, Nikita Khrushchev, as "the grapefruit satellite".

Spacecraft design

The spacecraft is a 1.47 kg aluminum sphere 16 cm in diameter. 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 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 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 654 x 3969 kilometers, 134.2 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 nearly seven years as it orbited the Earth.

Radio beacon

A 10 mW transmitter, powered by a mercury battery, on the 108 MHz band used for International Geophysical Year scientific satellites, and a 5 mW, 108.03 MHz 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 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 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.

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 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 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 16 cm 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 with their drag properties essentially unchanged, they form a data set on the atmosphere of Earth that is over 60 years old and continuing.

After the mission

After its scientific mission ended in 1964, Vanguard 1 became a :Category:Derelict satellites orbiting Earth|derelict object—just like the upper stage of the rocket used to launch the satellite had after it finished the delta-v maneuver to place Vanguard 1 in orbit in 1958. Until otherwise noted, both objects remain in orbit.

50th anniversary

The Vanguard 1 satellite and upper launch stage hold the record for being in space longer than any other man-made object, and as such have traveled farther over the Earth's surface than any other man-made object.
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 17 March 2008. The meeting concluded with a simulation of the satellite's track as it passed into the orbital area visible from Washington, D.C.,. The National Academy of Sciences scheduled seminars to mark the 50th anniversary of the International Geophysical Year, which were the only official observances known.