Design and Management of Reusable Rocket Engines: Trade-offs among Performance, Lifetime, and Complexity
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etzenbach-lillyetz-ms-aeroastro-2026-thesis.pdf
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81.91 MB
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4d29a94d94551cd96e6eb85b636ba808
Author(s)
Etzenbach, Lilly
Advisor(s)
De Weck, Olivier
Date Issued
May 2026
Publisher
Massachusetts Institute of Technology
Abstract
Over the past decade, reusable launch vehicles have fundamentally reshaped the economics of spaceflight. However, realizing their full economic potential introduces major engineering challenges and new trade-offs among reliability, performance, durability, and complexity. Beyond vehicle design itself, the economic viability of reuse depends not only on the ability to recover hardware, but also on the efficiency of the associated inspection and refurbishment processes. Reusable liquid-propellant rocket engines lie at the heart of these challenges, as they are among the most expensive and failure-prone subsystems of a launch vehicle. While previous studies have examined specific facets of engine reuse in isolation, a gap remains in understanding how these considerations interact across both abstraction levels and phases of engine development. This thesis addresses that gap by taking an integrated view of reusable engine design and management.
The thesis first examines design trade-offs between performance and reusability by considering combustion chamber lifetime alongside metrics that affect refurbishment protocols, including coking and soot propensity. Chamber life is characterized using a coupled thermomechanical finite element model tracking the doghouse effect, a fatigue-driven failure mode associated with the repeated cycling of regeneratively cooled walls. This failure mechanism is critical as it typically dictates the end of life of the engine assembly, since replacing a combustion chamber is rarely practical. These engine-level results are then propagated to the vehicle level through a first-stage trajectory model to evaluate their implications for payload capacity under different recovery strategies. The analysis shows that meaningful gains in reusability (reduction in coolant exit temperature of ~15 K and in peak heat flux of ~1.5 MW/m2) can be achieved at a limited payload mass capacity cost (~150 kg for droneship landings). In parallel, the results demonstrate that mission lifetime cannot be inferred directly from hotfire lifetime, since recovery profiles strongly alter thermal history and damage accumulation. Finally, performance–reusability trade-offs extend across abstraction levels. For instance, throttling the engine down to 80% during re-entry can extend chamber lifetime by up to 9% but increases the launcher's peak dynamic pressure by 42%.
Building on this failure mode analysis, the thesis then investigates the stochasticity in engine degradation caused by both manufacturing deviations and operational variability. Due to the resulting dispersion in engine lifetime, the assumption of a fixed, universal lifetime introduces substantial prediction errors, leading to either life overprediction or underprediction in 50–70% of cases. Accordingly, the thesis builds on a Monte Carlo framework that tracks doghouse deformation from production through flight operations and refurbishment. Using this framework, the thesis compares different health monitoring strategies that combine data from inline monitoring systems and manual inspections, with the dual objective of improving lifetime prediction accuracy and reducing operational burden, both at the individual engine level and across engine clusters. By accounting for the distinct objectives of the different phases of engine development, the work then proposes an evolutive engine health monitoring and complexity management strategy for next-generation rocket engines. To outline practical implementation pathways, the thesis presents a data reconciliation framework for doghouse deformation monitoring.
Together, these contributions provide an integrated perspective on reusable engine development. Fundamentally, the work highlights the need for tighter coupling across abstraction levels and development phases to ensure that engines are not only high-performing by design, but also reliable, maintainable, and sustainable across repeated flights.
MIT Department
Massachusetts Institute of Technology. Department of Aeronautics and Astronautics
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