Light from the sun is converted by a solar cell to recharge a tiny battery, so the units don't operate at night. The PTTs generate a signal every two or three minutes, although the transmission cycle can be adjusted to as often as 61 seconds. For this project, the PTTs are preprogrammed to operate for three years. North Star PTT as used in FalconTrak. The PTTs are mounted on the back of the falcons with teflon webbing, attached much like a backpack with a crossover on the chest.
Scientists attach the webbing to young falcons when they have reached nearly full physical size.
The webbing is carefully integrated with feathers to prevent any injury or discomfort, or any interference with the falcon's normal lifestyle or activities. Each transmitted message contains an individual identification number so the birds can be differentiated. These satellites are in polar orbit, which means they travel over the north and south pole on each 102-minute orbital revolution. The satellite can see all transmitters within a 5,000-kilometer diameter circle at any time. The Argos messages are received by the satellites from six to 28 times each day.