Communications Satellites, Part 3: The First Geosynchronous Satellites

Communications relay satellites in low Earth orbit (see Part 2) allowed transmitting signals between continents and required modest antennas, solar power, and launch vehicle capacity, but moved quickly in the sky and were only visible for a limited time from the source and destination before setting below the horizon. They required antennas that could track their rapid motion across the sky, which added cost and complexity to sending and receiving stations.

Long before the launch of the first communications satellites, it was realised that if you could place a satellite in an equatorial orbit around the Earth whose orbital period exactly matched the Earth’s rotation rate with respect to the distant stars (sidereal day, around 23 hours 56 minutes and 4 seconds or, if you’re picky, 86164.0905 seconds), it would appear to remain stationary in the sky from anywhere in the (almost) hemisphere visible from the satellite. With three or more such satellites and relays on the ground or between satellites, global coverage could be achieved. Plus, since the satellites did not appear to move as seen from the Earth, a fixed antenna aimed at their positions would suffice: no need to track a moving target or hand off from satellite to satellite.

But such a geostationary orbit has its own disadvantages. A circular orbit 35,786 km above the Earth’s equator takes a lot more rocket power (delta-v) to reach, and to receive and send signals over such a distance requires a satellite with a bigger antenna, more powerful radio transmitter, and correspondingly larger solar panels to run it, all of which make the satellite larger and heavier, requiring an even larger rocket to carry it to orbit. It wasn’t until August 1964 that the first geostationary satellite, Syncom 3, was launched and entered service, being used to broadcast the 1974 Summer Olympics from Tokyo live to the United States. (Syncom 2, launched in July 1963, was the first geosynchronous communication satellite, but as it was in an inclined orbit, it moved up and down in latitude over the day as seen from the Earth, requiring a steerable antenna that restricted its usability.) Syncom 3 was transferred to the U.S. Department of Defense which used it for communications between the U.S. and its forces in Vietnam. It was decommissioned and turned off in 1969 and will remain in orbit essentially forever unless somebody goes up and brings it back to put in a museum.

The first commercial geosynchronous satellite, Intelsat I (“Early Bird”), was launched in April 1965, and in the second half of the 1960s, one would often see “Live via Early Bird” on television news items from Europe.