The Ariane Passenger Payload Experiment (APPLE) was ISRO's first indigenous, experimental communication satellite. It was launched into GTO (Geosynchronous Transfer Orbit) by the third development flight of ESA'a Ariane vehicle from Kourou on June 19, 1981.
It was boosted into Geo-synchronous Orbit (GEO) by apogee motor of ISRO, derived from fourth stage motor of SLV-3. It was designed and built in just two years with limited infrastructure in industrial sheds.
It gave ISRO valuable hands on experience in designing and developing three-axis stabilized geostationary communication satellites as well as in orbit raising manoeuvres, in orbit deployment of appendages, station keeping, etc.
APPLE was used for nearly two years to carry out extensive experiments on time, frequency and code division multiple access systems, radio networking computer interconnect, random access and pockets switching experiments.
To commemorate this event India Post also issued a stamp in 1983, this stamp illustrated the image of the satellite orbiting the earth.
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Image Courtesy: isro.gov.in