// PROPULSION SYSTEMS AND ENGINE TECHNOLOGY TERM
Aerospike Nozzle
An aerospike nozzle is an unconventional rocket nozzle that maintains high efficiency across a wide range of altitudes. Instead of a traditional bell shape, it uses a central spike or ramp that the exhaust flows over, using the ambient air pressure to form the outer boundary of the nozzle.
TECHNICAL DEFINITION
An aerospike nozzle is an altitude-compensating rocket engine nozzle where exhaust gases expand along a central spike (annular aerospike) or ramp (linear aerospike), with ambient atmospheric pressure acting as a virtual nozzle wall. This expansion-deflection design optimizes thrust efficiency from sea level to vacuum, making it a key technology for single-stage-to-orbit (SSTO) vehicle concepts by adapting the exhaust plume expansion ratio dynamically.
BACKGROUND
The aerospike engine is a type of rocket engine that maintains its aerodynamic efficiency across a wide range of altitudes. It belongs to the class of altitude compensating nozzle engines. Aerospike engines were proposed for many single-stage-to-orbit (SSTO) designs. They were a contender for the Space Shuttle main engine. However, as of early 2026 no such engine was in commercial production, although some large-scale aerospikes were in testing phases.
READ MORE ON WIKIPEDIASYNONYMS & ALIASES
- plug nozzle
- altitude-compensating nozzle
- spike nozzle
- expansion-deflection nozzle
- linear aerospike
- annular aerospike
- E-D nozzle
USAGE NOTE
While famed for its theoretical performance and association with the X-33 program, the aerospike's complex cooling requirements have limited its operational use in flight vehicles.
DEVELOPERS
Organizations developing technology related to Aerospike Nozzle.
A Spanish startup actively developing and testing a 3D-printed, methalox-fueled aerospike engine called ARCOS. They are one of the leading commercial ventures focused on bringing this technology to market.
This company has a long history with aerospike development, most notably designing and building the XRS-2200 linear aerospike engine for NASA's X-33 program. They retain significant expertise in this advanced propulsion technology.
A German aerospace company designing a reusable, aircraft-like spaceplane named AURORA. The design's primary propulsion system is a linear aerospike rocket engine, which is a core part of their vehicle concept.
A private aerospace company that has developed and flight-tested aerospike nozzles on its rockets, including the Demonstrator 2B and subsequent vehicles. They have focused on steam-based and other unconventional propellant systems integrated with aerospikes.
Firehawk develops hybrid rocket engines using 3D-printed fuel grains. Several of their engine designs incorporate an aerospike nozzle to improve performance and efficiency over a range of altitudes.
NASA has been involved in aerospike research for decades, from the original concepts to managing the X-33 project. Marshall continues to conduct research and development on advanced propulsion, including additive manufacturing techniques for aerospike and other novel nozzle geometries.
Developer of a fully reusable second stage, which utilizes a unique engine configuration in a ring at the base of the vehicle. While not a classic aerospike, its multi-thruster base design acts similarly to an altitude-compensating nozzle, drawing on aerospike principles.