Modular Aerospike Nozzles for Upper Stage Applications

Aerospike nozzles represent a promising solution for upper-stage propulsion due to their compactness and ability to achieve high expansion ratios within constrained envelope dimensions. While annular plug configurations offer excellent theoretical performance, they present critical challenges, such as narrow throat gaps and severe thermal loads, which can be mitigated by adopting clustered modular designs. However, in upper-stage applications, the use of conventional bell-shaped modules can lead to poor clustering efficiency or require an impractically large number of nozzles, undermining the system feasibility. This work explores alternative module geometries with more annular-like exit cross-sections, aiming to improve the trade-off between single-module performance, clustering efficiency and total number of modules. CFD simulations were carried out for both gapless configurations and cases with a fixed number of modules. Results indicate that the so-called RESA geometry provides the best compromise for the application under scrutiny, achieving performance comparable to the annular reference configuration. A final comparison with conventional bell nozzles across a range of expansion ratios representative of upper-stage designs confirms a potential gain in specific impulse, quantifying the advantage of the proposed configurations.