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 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. Second generation In the second generation of the satellites, code named "Gelios", several improvements had been introduced, but due to lack of funds, only one satellite built on this platform has been launched: Luch-2 1 (Gelios-12L) on September 11, 1995 – it stopped working in 1998. Third generation - MKSR Luch Constellation Originally, during 2009, the Russian Federal Space Agency signed a contract with JSC Information Satellite Systems (previously "NPO-PM") for development of a new generation of satellites, Luch-4, Luch-5A and Luch-5B. It enabled the rebuild of the Luch network and provided the ROS with 45 minutes of coverage per orbit via the Lira and Regul communications systems. Luch-4 was based on the heavier Ekspress-2000 satellite platform, while the Luch-5A and Luch-5B was based on the lighter Ekspress-1000 and flew with companion satellites on Proton-M/Briz-M. That plan was suspended and the MKSR Luch Constellation was defined. It replaced the heavier and more expensive Luch-4