The balloons are filled with helium gas , can carry payloads up to 3600 kilograms ( 7,936 lb ) , fly at altitudes of up to 42 kilometers ( 26 mi ) .
The balloons are can remain at float in excess of 40 days .
The balloons are filled with helium gas , can carry payloads up to 3600 kilograms ( 7,936 lb ) , fly at altitudes of up to 42 kilometers ( 26 mi ) , and can remain at float in excess of 40 days .