Fractional Orbital Bombardment System

A Fractional Orbital Bombardment System (FOBS) is a warhead delivery system that uses a low Earth orbit towards its target destination. Just before reaching the target, it deorbits through a retrograde engine burn.

The Soviet Union first developed FOBS as a nuclear-weapons delivery system in the 1960s. It was one of the first Soviet efforts to use space to deliver nuclear weapons. In August 2021, the People's Republic of China tested a weapon that combined a FOBS with a hypersonic glide vehicle.

Like a kinetic bombardment system but with nuclear weapons, FOBS has several attractive qualities: it has no range limit, its flight path would not reveal the target location, and warheads could be directed to North America over the South Pole, evading detection by NORAD's north-facing early warning systems.

The maximum altitude would be around 150 km. Energetically, this would require a launch vehicle powerful enough to be capable of putting the weapon 'into orbit'. However the orbit is only a fraction of a full orbit, not sustained, and so there would be much less need to control a precise orbit, or to maintain it long term.