Credits: NASA HANDOUT
NASA said the communication breakdown happened at about 9:45 a.m. ET when flight controllers in Houston were updating the station's flight computer software.
"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," NASA said.
Mission control in Houston communicated with the crew before 11 a.m. and told them to connect a backup computer to start the process of restoring communications. Communication was restored at 12:34 p.m., and all systems were back up and running, NASA said.
Canadian astronaut Chris Hadfield tweeted early Tuesday morning that the crew was getting ready for the software switch.
"Good Morning, Earth! Today we transition the Space Station's main computers to a new software load. Nothing could possibly go wrong," Hadfield tweeted at about 2 a.m.