IS satellites (Russian: Истребитель Спутников, Satellite Hunters) is a family of Soviet military satellites developed in the 1960s with the ability to destroy enemy reconnaissance satellites in low orbit. The program, after being declared operational in 1973, was discontinued in 1993, following the fall of the USSR. The IS satellite is a kamikaze-type satellite that carries a conventional explosive charge that it explodes at a short distance from the targeted satellite after performing a series of maneuvers to approach it.

The IS satellite has a mass of 2,450 kg and consists of two subsystems: the first contains the guidance system and a 300 kg explosive charge, the second part contains the propulsion system. The satellite core is designed to fragment under the effect of the explosion into 12 groups of fragments to ensure the destruction of a target within a radius of 1 km. However, a frontal interception allows destruction only at a distance of 400 meters while an explosion occurring while the satellite catches up with its target allows its destruction at a distance of 2 km. The rocket engine can be reignited a large number of times and is designed to operate cumulatively for 300 seconds.

The IS satellite must be placed in the same orbit as the target to destroy it. This can be performed twice a day when the launcher can place the IS satellite on the same orbital plane as its target. Once launched, the satellite is guided by ground controllers to catch up with the target in 1 to 2 orbits. The IS satellite's radar then takes over to ensure guidance until the target is only a few dozen meters away. The explosive charge is then triggered, ejecting shrapnel which damages the target satellite. IS satellites have already destroyed other test satellites, but never other enemy satellites.

Cosmos 404 approached Cosmos 400, but due to a computer error, never destroyed it. Instead, it performed several maneuvers nearby to improve the control system.