All four Cluster satellites will fly independently, controlled by radio contact with a ground station on earth, rather than talking among themselves about where they are.

ECONOMIST: Birds of a feather

CNN's Mike Hanna in Jerusalem said the plane was tracked by Israeli warplanes and helicopters, who established radio contact and made repeated attempts to contact the pilot, but he refused to respond or identify himself.

CNN: Israel shoots down light aircraft

They acknowledge the difficulties caused by choosing radio-frequency chips instead of a system where direct contact must be made with the reader.

ECONOMIST: High-tech passports are not working

Twice during the state-by-state tour, Lindbergh was lost in bad weather and each time several hours passed before radio contact with him was reestablished and he was able to let the country know that all was well.

NPR: Roth Rewrites History with a 'Plot Against America'