The International Space Station (ISS) lost ground communications capabilities for around three hours this morning during a software upgrade, according to NASA.
As flight controllers on the ground in Houston were updating flight computers, the data relay systems malfunctioned, cutting off all communications with the ground. The Communication and Tracking System provides communications between the crew and Mission Control via Ku-band, S-band, and UHF frequencies.
During the upgrade, an anomaly resulted in the primary computer that controls critical station functions defaulting to a backup computer, but the system was not allowing the station to communicate with NASA's Tracking and Data Relay Satellites.
As the space station flew over Russian ground stations around 8 a.m. PT, Mission Control Houston was able to make contact and instructed the crew to connect to a backup computer to begin the process of restoring the main communications.
Listen to the audio as Expedition 34 Commander Kevin Ford talks with Mission Control Houston as station passes over Russian ground stations this morning:
Though communication is at the core of safe, reliable International Space Station operations, there doesn't appear to be any additional threat to the ISS as a result of the computer glitch. Expedition 34 Commander Kevin Ford reported that the station's status was fine and that the crew was doing well.
Mission Control Center, Houston, communicates with the ISS via 60-foot diameter, high-gain microwave ground terminals at NASA's White Sands Test Facility near Las Cruces, N.M. These terminals then relay signals to and from a pair of Tracking and Data Relay Satellite System satellites orbiting at an altitude of 22,300 miles. When everything is working smoothly, the satellites pass these signals directly to and from the ISS.
In 2010 the space station lost communications for about an hour when a computer crashed. See an interactive demonstration that further explains the process of space communications here.