interstage

An interstage is a structural section on a multistage rocket that connects the lower stage to the upper stage. It provides alignment and attachment points for the stages and often houses hardware needed for stage separation. The interstage can also carry electrical and data interfaces and, in some designs, components such as sensors or protection for the interface during ascent.

Designs vary widely. In many vehicles the interstage is a detachable adapter or ring that sits between stages, while in others it may be an integral part of one stage. The interstage typically contains or supports the stage-separation mechanism, including clamps, bolts, and sometimes motors or springs used to push the stages apart when commanded.

During flight, the interstage must tolerate ascent loads and aerodynamic forces while maintaining precise alignment of the stages. At the moment of separation, the interstage works with the separation hardware to release the upper stage from the lower stage and to clear the exhaust path for the upper-stage ignition. Depending on the vehicle, the interstage may be jettisoned with the lower stage or released to remain with the upper stage.

Notable uses and terminology: The concept of an interstage is widespread across launch vehicles and is referenced in families such as Saturn V, Atlas V, SpaceX Falcon 9, Ariane 5/6, and various others, where the design of the interstage is tailored to the vehicle’s staging sequence and structural requirements.