Several generations of increasingly efficient DSP satellites followed one another until 2007. Since 2011 the DSPs have been replaced by the SBIRS system, which includes dedicated satellites in geostationary orbit (SBIRS-GEO) and in low Earth orbit (SBIRS-LEO), as well as sensors on board Trumpet satellites for mixed use (wiretapping/warning) located in a Molniya orbit. Soviet Union and Russia The US-K and US-KS satellites developed under the Oko program were the first generation of Soviet early warning satellites. 86 US-K satellites were placed in a Molniya orbit between 1972 and 2010 and 7 US-KS satellites, of a very similar design, were placed in geostationary orbit between 1975 and 1997, the system becoming operational in 1980. In 1983, a design error in the on-board software of the US-KS satellites led to the so-called fall equinox incident, which consisted of a false nuclear launch warning after a confusion between the heat caused by the reflection of solar radiation in clouds and that released by the launch of a nuclear missile. Unlike their US counterparts, the US-K and US-KS only detect surface-to-surface ballistic missile launches, due to less sophisticated electronics. Later, the US-KS were replaced by the US-KMO, capable of detecting sea-to-land ballistic missile launches as well. The first of them would be placed in geostationary orbit in 1991. In the early 1990s, after about ten years of operation, the coverage provided by these satellites was only partial, due to a reduction in the launch rate. In 2014, the last 3 early warning satellites in service ceased their activities. The US-K satellites were to be replaced starting in 2015 by a new generation of satellites: Tundra (EKS). Other countries In France, the Direction générale de l'Armement carried out preliminary tests for the development of an early warning satellite. Infrared sensors were tested on two small experimental SPIRALE satellites launched in 2009. However, an operational satellite was not expected to be launched before the end of 2020. China operates Huoyan-1 series satellites under the Tongxin Jishu Shiyan (TJS) program. Satellite series See also Missile defense Militarisation of space Space force Space domain awareness Space warfare References Bibliography Infrared technology Military satellites Satellites