The Luch (; lit. Ray) Satellite Data Relay Network (SDRN), also referred to as Altair and Gelios, is a series of geosynchronous Russian relay satellites, used to transmit live TV images, communications and other telemetry from the Soviet/Russian space station Mir, the Russian Orbital Segment (ROS) of the International Space Station and other orbital spacecraft to the Earth, in a manner similar to that of the US Tracking and Data Relay Satellite System.
First generation
thumb|Conceptual drawing of a Luch geosynchronous satellite, referred to in the West as "Altair/SR relay satellite". It was designed for voice and data relay with the Mir space station, in what was called the Satellite Data Relay Network (SDRN).
The first generation of satellites was created by NPO-PM using the satellite platform KAUR-4 (its first use) and had the code name "Altair" (index GUKOS - 11F669). The system was conceived as part of the second generation of the Global Satellite Data Relay Network (Глобальная Космическая Командно-Ретрансляционная система (GKKRS)) and was developed by decree of the Soviet Council of Ministers of February 17, 1976 (the other part of this decree authorized the construction of geostationary system "Geyser"). Five satellites have been built on this platform, but only four have been launched: Kosmos 1700, Kosmos 1897, Kosmos 2054 and Luch-1, none of which are currently operational. The fifth satellite has been, due to lack of funds for the launcher, donated to the A.S. Popov Central Museum of Communications in Saint Petersburg, Russia.
Platform design
Each satellite has a mass of 2.4 metric tons and featured two photovoltaic arrays, providing 1.8 kW of power. Three large antennas and numerous, small helical antennas permitted data relays in the 15/14, 15/11, and 0.9/0.7 GHz bands. causing concerns of a safety-of-flight incident. Attempts by Intelsat to contact the Russian satellite's operators were not successful, and no reason for the satellite's movement was given by the Russian government. The move sparked classified meetings within the Department of Defense.
The Luch-4 is speculated to have mutated into the Yenisey A1.