At launch, a ballistic missile produces an enormous, hot plume. Infrared satellites in GEO and HEO see that plume against the cool background of the Earth and give a warning within a few tens of seconds, with the launch site and the initial trajectory. That gives time to take cover and to bring missile defence into action.
| Country | System | Orbits |
|---|---|---|
| US | SBIRS, successor Next-Gen OPIR; also a tracking layer in LEO (Space Development Agency) | GEO, HEO and LEO |
| Russia | EKS "Kupol" (Tundra satellites) | HEO (Tundra) |
| China | Under construction (open sources are limited) | Uncertain |
Modern systems also see smaller and shorter burns, such as launches of tactical missiles. Hypersonic glide vehicles are harder: they fly lower and less hot than a ballistic warhead in space — hence the new tracking layers in LEO.