airspike

An airspike is a type of rocket engine nozzle that does not have a traditional bell shape. Instead, it features a central spike or cone that extends outward from the engine's combustion chamber. This spike is designed to interact with the ambient air, creating a high-pressure region around its base. This interaction effectively simulates a larger nozzle, improving engine efficiency at lower altitudes where atmospheric pressure is higher.

The concept of the airspike was developed to overcome the limitations of conventional rocket nozzles, which are optimized for a specific altitude range. At sea level, a standard nozzle is over-expanded, leading to thrust losses. At high altitudes, it is under-expanded, also causing inefficiency. The airspike aims to provide a more adaptable solution by dynamically adjusting its effective nozzle area through its interaction with the surrounding atmosphere.

The central spike can be designed in various shapes, including conical or parabolic. The combustion gases are expelled from an annular slit or a series of ports around the base of the spike. As the rocket ascends and the atmospheric pressure decreases, the airspike's performance changes. The effectiveness of the airspike is most pronounced in the lower to mid-ranges of an atmospheric ascent.

While promising, airspike technology has faced significant engineering challenges, including thermal management of the spike and the complex fluid dynamics involved. Despite these hurdles, research and development in airspike propulsion have continued, with potential applications in single-stage-to-orbit vehicles and other atmospheric-lifting concepts. The primary goal is to achieve greater rocket performance across a wide range of altitudes without the need for complex nozzle-throat adjustments.