The Oldest Orbiting Satellite

When a satellite is launched into space it is not expected to last forever. The satellite carries on board a limited amount of fuel which will run out in a couple of years, or decades, or even months depending on how long the satellite was designed to remain operational. Eventually, its batteries will run out and its solar cells will degrade. Once the satellite stops responding to signals from operators on earth, or when it’s fuel depletes, it will lose the ability to correct its orbit. The thin atmosphere will slow the satellite down and degrade its orbit, and in a matter of years or decades, the satellite will fall back to earth. Some satellites are also purposefully brought down once their mission objectives are completed so as not to contribute to the space junk. There are already 20,000 artificial objects in orbit above the Earth, including 128 million pieces of space debris—the result of collision between dysfunctional satellites. While most satellites stay in orbit for only a couple of years, there is one that has been circling the earth for more than sixty years.

A backup copy of Vanguard 1 satellite built by the Naval Research Laboratory, now at the National Air and Space Museum of the Smithsonian Institution.

Vanguard 1 was only the fourth artificial satellite to be successfully launched, following Sputnik 1, Sputnik 2, and Explorer 1. It was a small and shiny metal sphere with protruding antennas, less than 1.5 kg in mass, and with a diameter of only 16.5 cm. Soviet Premier Nikita Khrushchev mocked it as “the grapefruit satellite,” comparing it with the 84-kg Sputnik 1 and the half-ton behemoth, that was Sputnik 2.

Although tiny, compared to its predecessors, Vanguard 1 had quite a few mission objectives. It carried on board instruments that could measure the densities of the upper atmosphere and the electron content of the ionosphere, which was then used to determine the effect of the space environment on a satellite. It also obtained geodetic measurements through orbit analysis, and these proved that the Earth was indeed pear-shaped with the stem at the North Pole. The launch itself was a test to determine the launch capabilities of a three-stage launch vehicle as a part of Project Vanguard. It was only the second satellite launched by the U.S., the first successful satellite of the Vanguard series, and the first satellite to use solar cell power. And it is the oldest satellite still orbiting the Earth.

Vanguard 1 was launched on 17 March 1958 from the Atlantic Missile Range in Cape Canaveral Florida. Unlike the hushed affairs of the Soviet Sputnik launches, the Vanguard launches were a major public event attended by politicians and senior military figures, as well as throngs of people and the world’s media. The first attempt on 6 December 1957 ended in a disaster when the rocket rose only four feet and then fell back on the launch pad and exploded. The Vanguard 1A satellite was thrown clear and landed on the ground a short distance away with its transmitters still sending out a beacon signal. The satellite was damaged, however, and could not be reused. It is now on display at the National Air and Space Museum of the Smithsonian Institution.

Vanguard rocket explodes seconds after launch at Cape Canaveral.

The failure was widely derided in the press. It was called variously a kaputnik, flopnik, puffnik and stayputnik. Fortunately, the US managed to salvage some pride when they successfully launched Explorer 1, a few weeks later. It was the first US satellite. But while Explorer 1 remained in orbit for only 12 years, Vanguard 1 is still circling the earth. The Soviet satellites of the period had an even shorter period of operation—Sputnik 1 fell back to earth after only three months and Sputnik 2 stayed in orbit for 5 months.

Vanguard 1 circles the earth in an elliptical orbit with a perigee of 654 km and an apogee of 3,969 km. Because of its high orbit, where atmospheric drag is less, Vanguard 1 was expected to last 2,000 years. But scientists underestimated the effects of solar radiation pressure and atmospheric drag during high levels of solar activity. When these were taken into account, it was found that the satellite would last only about two centuries—still significantly more than some of the current generations of satellites.

Vanguard 1 transmitted its signals for over six years as it orbited the Earth. During its greatly extended lifetime (the satellite was designed to operate for only 90 days), Vanguard showed how our planet bulges out around the equator. It also provided the first-ever measurements of the Earth’s tenuous outer atmosphere and an estimate of the number of micrometeorites surrounding the planet. It showed that atmospheric pressures, and thus drag and orbital decay, were higher than previously anticipated. These information were vital for future launches.

Although Vanguard 1 is no longer operational, a piece of space debris, it continues to aid scientific research by allowing ground based tracking systems to determine the orbit as it decays over time, which in turn helps scientists understand the influence of the Earth’s atmosphere on satellites.