The mesh antenna on the Skyterra-1 satellite, launched successfully from Baikonur in Kazakhstan on Sunday, is 72 feet across, the BBC reported Monday.
The antenna will relay cellphone and data signals for a start-up company called LightSquared.
Cellphone users whose carriers use the system will have their calls automatically switched to the satellite, built by Boeing, if they are out of range of a terrestrial cell tower, the company says.
LightSquared is the latest effort to try to establish a hybrid satellite-terrestrial system in the United States after two previous ventures ran into financial problems. LightSquared says it will be selling capacity to carriers who wish to offer go-anywhere connectivity to their consumers, phone and data users alike.
The 5.4-ton satellite is expected to have a service life of 15 years, the BBC said.
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