That question is entirely dependent on how the word “operating” is defined and how you interpret it. If it’s taken to mean what is the modest satellite in orbit that is still being studied and providing relevant data to those observing it, then the answer is Vanguard 1 which was launched by the United States of America on the seventeenth of March nineteen fifty eight and was, and still is the fourth artificial satellite to be launched into Earth Orbit.
Even though it stopped communicating with NASA (National Aeronautics and Space Administration) in nineteen sixty four, its orbital path is still being scrutinized and studied in order to further and better understand orbital decay and drag, and the flight patterns of satellites in Earth orbit.
Up until July two thousand and sixteen, the oldest working satellite and functional spacecraft in earth Orbit was the GOES-3, which was originally launched as, and was intended to be a Geostationary Orbital Environmental Satellite (hence the acronym it became known by), on June Sixteenth, nineteen seventy eight. The satellite monitored Earth’s ever-changing weather patterns for close to a decade until its orbital imaging capability stopped functioning which rendered it useless as a weather satellite,
However, as it could still send and receive geostationary information, the GOES-3 entered a new stage in its life and for the next twenty-eight years was used by a variety of different scientific organizations as a communications satellite, that served in a multitude of different capacities and proved to be an indispensable scientific tool.
Having outlived multiple administrations and the operational life of the Space Shuttle and the greatest period of upheaval in NASA’s long history, the decision to retire GEOS-3 was finally made in the opening months of two thousand and sixteen. At the beginning of June, NASA started to enact their complicated plan and began the first of a series of twenty complicated orbital adjustments and maneuvers that were designed to alter the position of GOES-3 and shift it into a higher “graveyard” orbit.
After two weeks of careful positioning and tracking, GOES-3 was at long last taken out of its orbital geostationary path and was decommissioned on June Twenty-Ninth, two thousand and sixteen. After thirty eight years of faithful service, the longest-serving, still functional satellite in the history of space exploration was retired. And if it hadn’t been forcibly taken out of the game, GOS-3 would probably still be in use today.