Vertical Launching System - Hot Launch and Cold Launch

Hot Launch and Cold Launch

A VLS system can be either hot launch, where the missile ignites in the cell, or cold launch, where the missile is expelled by gas produced by a gas generator which is not part of the missile itself, and then the missile ignites. "Cold" means relatively cold compared with rocket engine exhaust. A hot launch system does not require an ejection mechanism, but does require some way of disposing of the missile's exhaust and heat as it leaves the cell. If the missile ignites in a cell without an ejection mechanism, the cell must withstand the tremendous heat generated without igniting the missiles in the adjacent cells.

An advantage of a hot-launch system is that the missile propels itself out of the launching cell using its own engine, which eliminates the need for a separate system to eject the missile from the launching tube. This potentially makes a hot-launch system relatively light, small, and economical to develop and produce, particularly when designed around smaller missiles. A potential disadvantage is that a malfunctioning missile could destroy the launch tube.

The advantage of the cold-launch system is in its safety: should a missile engine malfunction during launch, the cold-launch system can eject the missile thereby reducing or eliminating the threat. For this reason, Russian VLSs are often designed with a slant so that a malfunctioning missile will land in the water instead of on the ship's deck. As missile size grows, the benefits of ejection launching increase. Above a certain size, a missile booster cannot be safely ignited within the confines of a ship's hull.

American VLSs have the missile cells arranged in a grid with one lid per cell and are "hot launch" systems; the engine ignites within the cell during the launch, and thus it requires exhaust piping for the missile flames and gasses. France, Italy and Britain use a similar hot-launching Sylver system in PAAMS. Russia produces both grid systems and a revolver design with more than one missile per lid. Russia also uses a cold launch system for some of its VLS missile systems, e.g., the Tor missile system. The People's Republic of China uses a circular "cold launch" system that ejects the missile from the launch tube before igniting the engine on the Type 052C destroyer, and also a rectangular ”hot launch" system with one lid per cell arranged in a grid on the Type 054A frigate.