Reusability has changed the space industry. Hardware that can be flown again does not have to be built from scratch every time, which lowers the cost per kilogram to orbit, shortens turnaround times and opens the market to new players. It also cuts manufacturing emissions and helps limit space debris. For Europe, mastering reusable launchers and re-entry vehicles is both an economic and a strategic priority.
Reuse comes at a price in risk. Extended operational lifetimes, the severe loads of re-entry and higher flight cadence push propulsion systems to the limits of their materials, so faults cannot be designed out entirely. Propulsion is already responsible for roughly 54% of all launch vehicle failures. During re-entry such a fault is particularly unforgiving: the vehicle follows a narrow corridor bounded by thermal, structural and load constraints, and the time available to react is far shorter than any intervention from ground allows. The established mitigations, fixed redline thresholds, redundant hardware chains and pre-computed contingency trajectories, add mass, cost and complexity and are largely unworkable in this phase.
REACT closes this gap with software instead of hardware. The project develops an onboard, autonomous digital building block that diagnoses propulsion faults and recovers the flight trajectory before the vehicle destabilises. Three elements form one closed loop. Fault Detection and Identification at propulsion level, developed at TUM, combines physics-based models with data-driven classifiers to separate sensor, actuator and plant faults more accurately than conventional threshold monitoring, and fast enough to keep pace with the control algorithm. Fault Tolerant Guidance and Control, developed by Orbital Paradigm, re-optimises the re-entry trajectory in real time using the diagnosed propulsion capability as a constraint. A hardware-agnostic execution framework from Klepsydra Technologies lets these computationally demanding algorithms run in real time on representative onboard avionics.
Making propulsion faults survivable raises the availability of space transportation systems and avoids the cost and delay that follow a major failure. Because the result is portable software that integrates without a hardware redesign, it lowers the barrier for European companies, launch service providers and research groups and strengthens Europe's position in reusable space transportation.
REACT runs from July 2026 to June 2029 and is coordinated by the Chair of Space Mobility and Propulsion at the Technical University of Munich, with Orbital Paradigm (Spain) and Klepsydra Technologies (Switzerland) as partners. It receives around 1.5 million EUR under Horizon Europe (grant agreement no. 101296430).
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Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Health and Digital Executive Agency (HaDEA). Neither the European Union nor the granting authority can be held responsible for them.
