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Pacsats are low-orbit message-handling satellites that fly around the globe picking up typewritten messages from individual ham stations, storing them in memory, and relaying them to other terrestrial stations.
These mailboxes in the sky permit amateurs on one side of the world to place messages on the satellite's bulletin board to be removed by others when the satellite is on the far side of the globe. Mail stays in the satellite for long periods, of course, awaiting radio commands from an addressee.
Busy operators on the ground could put their satellite stations on autopilot. They would program their computers to determine when satellites would be overhead. Most pacsats pass over the North and South Poles every hour and a half and over any one point on the surface four times a day. One is overhead for only a dozen minutes or so at a time.
When operating automatically, a ground-station computer would fire up its radio at the appointed hour and send up a signal asking the satellite if any messages were on hand. If messages for that ground station were stored in the satellite, the satellite's computer would order them sent down. The computer on the ground then could store them for future reading by its human operator and turn off its radio as the satellite passed out of sight over the horizon.
A pacsat makes it cheap and easy to send messages, data and images in or out of developing regions. Scores of portable ground stations are linking underdeveloped countries to medical, weather, agriculture and engineering databanks.
These electronic mailboxes in the sky can link with inexpensive, portable ground stations built around a suitcase of computer, radio and battery where no power lines exist. A pacsat often flies low enough for small ground stations to use simple whip antennas, made from coat hangers if necessary, to hear the satellite.
A gateway is a satellite ground station acting as a bridge between a pacsat and a terrestrial network. Automated gateways upload and download traffic without human operators.
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