The PAGEOS space balloon: One of NASA's most successful failures

On July 24, 1966, NASA launched the Passive Geodetic Earth Orbit Satellite (PAGEOS) satellite, and it would forever make history.

This incredible satellite served as a tracking target, connecting 46 stations from every continent on Earth — supporting real science with ground-shaking implications.

But it didn't end well for PAGEOS, according to an overview from NASA's website.

The massive shiny satellite was made of a thick mylar plastic film coated with vapor-deposited aluminum that surrounded a volume of 524,000 cubic feet (14,800 cubic meters).

The primary purpose of PAGEOS

The satellite was "a 100-foot (30.48)-m inflatable sphere [that] had no instrumentation on board, read the overview on NASA's website. "It was the second (following GEOS 1) NASA satellite in the National Geodetic Satellites Program. PAGEOS 1 was made up of 84 gores and 2 pole caps of 0.0127-mm aluminized mylar film. The gores were [157.4 ft (48 m)] long with a maximum width of [4.06 ft (1.24 m)] and the pole caps were [3.35 ft (1.02 m)] in diameter."

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The satellite was built to provide a tracking target for geodetic purposes and connected 46 stations 1,864 to 3,106 miles (3000 to 5000 km distance) from around the world with an incredible accuracy of 9.8  to 16 ft (3 to 5 m). With a specular reflectance of 0.862 and a diffuse reflectance of 0.029, it boasted a reflecting light source whose brightness was relatively independent of observer-satellite-sun phase angles. Its surface was capable of reflecting 97% of microwave energy in the range from 17 to 4E5 kHz.

Disintegration

But all did not go well for PAGEOS. Once its construction was complete, it was inflated in orbit to serve as a giant reflector of sunlight that could be photographed from the Earth. However, after the spacecraft was placed into a polar orbit in July 1975 — with an inclination between 85° and 86° — at an altitude of roughly 2,600 miles (4,184 km), it partly disintegrated.

Then in January 1976, PAGEOS suffered a second break up resulting in the release of a large number of fragments from the balloon, most of which re-entered the atmosphere during the following decade. Finally, in 2016, one of the largest pieces of PAGEOS de-orbited, marking the end for the balloon. But it was still worthwhile.

Observable from everywhere

During its heyday, PAGEOS had an apparent magnitude of 2 mag, thanks to its higher orbit. This meant the satellite could be observed across a wide swath of the Earth's surface, from Europe to North America.

And boy was it a sight to look at it! PAGEOS appeared from Earth like a slow-moving star even at night. It boasted a high orbit and polar inclination that would allow it to avoid the Earth's shadow and make it observable any time of day or night.

NASA had previously estimated that "to fulfill the mission requirements, the structural integrity of the satellite's load-bearing PET film and the reflectance of its vapor-deposited aluminum surface must be maintained for five years." PAGEOS, however, managed to last for 10 years in mint condition (before disintegration began), which is why it's considered a great success.