Vika or TGK is an oxygen generating system for spaceflight. It is a SFOG, or solid-fuel oxygen generator, a kind of chemical oxygen generator. It has been used on the retired Mir space station and the International Space Station. It was originally developed by Roscosmos to supplement the Elektron oxygen system on Mir. A Vika module, also known as a "candle", contains about one liter of lithium perchlorate and can provide oxygen for one person for 24 hours. After being adopted for use on the ISS, it had the NASA name SFOG, but they also sometimes use the Russian acronym TGK.