CAPE CANAVERAL, Fla. -

NASA lost communication with the International Space Station for two hours Tuesday because of a computer glitch. 

The six astronauts on the station, including American Kevin Ford, are OK. 

During the two-hour outage, crew members were able to talk with ground controllers through Russian ground stations.

NASA said the outage was caused by a computer software upgrade.

"Flight controllers in Houston were updating the software onboard the station’s flight computers when one of the station's data relay systems malfunctioned," NASA said.  "The primary computer that controls critical station functions defaulted to a backup computer, but was not allowing the station to communicate with NASA’s Tracking and Data Relay Satellites."

Two hours later, NASA tweeted, "Communications have been restored with the space station effective 11:34AM Central."

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