allowed the Shuttle to communicate by relay with a Tracking and Data Relay Satellite during re-entry, through a "hole" in the ionized air envelope at the tail end of the craft, created by the Shuttle's shape. Space weather Radio blackouts on Earth caused by solar flares are measured by the National Oceanic and Atmospheric Administration on a scale from 1 (minor) to 5 (extreme). Solar position Communications can also be lost when the Sun is blocking or behind one station in the same line of sight; Sun outages periodically interrupt communications with geosynchronous satellites. It is also a common problem for interplanetary space missions. See also Sudden ionospheric disturbance Sun outage References Further reading Radio frequency propagation Telecommunications engineering Technological failures