Self-healing space materials: ESA and European partners develop a composite that detects damage and “heals” cracks
Europe is looking for ways to reduce launch costs and increase the reliability of future spacecraft, especially those that could be used multiple times. One of the biggest costs of such systems is not only propulsion or logistics, but also maintenance: after each flight, structures must be inspected, microcracks located, and damage repaired that over time can compromise load-bearing capacity. This is exactly where the CASSANDRA project comes in, a development program supported by the European Space Agency (ESA) within the FIRST! – Future Innovation Research in Space Transportation initiative, linked to ESA’s FLPP program for future launchers.
The project brings together the Swiss companies CompPair and CSEM and the Belgian company Com&Sens, with the aim of adapting existing self-healing composite technology to the requirements of space transportation. At its core is the HealTech material (carbon fibers with a polymer matrix), which, with the help of controlled heating, can “close” again in places where cracks or impact damage have occurred. What is new in CASSANDRA is not only the ability to heal, but the combination of three elements in one structure: a sensor network, a heating system, and a composite with a built-in repair mechanism.
What is CASSANDRA and what “autonomous” repair means
The name CASSANDRA in the project documentation is interpreted as an acronym for Composite Autonomous SenSing AnD RepAir, which in translation describes two key functions: autonomous reading of the material’s condition and autonomous repair. The concept is designed so that the composite structure itself detects the early stages of damage, determines where it is located, and then – without classic service intervention – activates local heating to initiate the “healing” process of the resin inside the structure.
Unlike classic solutions, where a composite is repaired by cutting, adding layers, and re-curing (which can be time-consuming and expensive), here the focus is on repair at an early stage. The logic is simple: microcracks in composite structures are often not immediately visible, but with load cycles they can spread. If a crack is stopped at the beginning, the service life of the part is extended and the need for replacement is reduced.
Why composites are both an advantage and a problem
Composite materials, including carbon fiber-reinforced polymers (CFRP), are being used increasingly often in space structures because of their strength-to-weight ratio, corrosion resistance, and the ability to optimize the design. In recent years, ESA and European industry, through future launcher development programs, have been intensively seeking technologies that increase reusability – the reuse of components and systems – while maintaining safety margins. In that framework, FLPP (Future Launchers Preparatory Programme) represents the technological base from which solutions are selected for the next generations of European transportation systems.
But composites also have a weakness: they are sensitive to certain types of damage, especially impact events and micro-damage that can accumulate through repeated load cycles. For systems that return through the atmosphere and then fly again, the risk of progression of small cracks becomes a practical maintenance problem. Classic repairs can be expensive, time-consuming, and sometimes lead to changes in local stiffness or other properties, which complicates certification and reuse.
How HealTech “heals” and what the temperature trick is
According to available descriptions of the technology, HealTech is a composite whose resin component contains a repair mechanism that is activated by heating. When the material is brought to a certain temperature range, a “healing agent” in the matrix becomes mobile again and can fill micro-damage, after which the structure stabilizes and retains mechanical properties closer to the original than with improvised field repairs.
In the CASSANDRA demonstrator, heating is carried out by integrated 3D-printed aluminum meshes (heating elements) that locally raise the temperature to approximately 100 to 140 °C, depending on the configuration and sample. The idea is to ensure homogeneous heating of the critical zone – enough to activate healing, but without undesirable thermal stresses. For space transportation this is especially sensitive because components can pass through extreme temperature gradients, and cryogenic fuel tanks add another layer of requirements: materials must survive thermal shocks and operation at very low temperatures.
Optical fiber sensors: the structure’s “nervous system”
The key of the project is not only healing, but also precise localization of damage. The CASSANDRA demonstrator therefore includes a network of sensors integrated into the structure. Partner Com&Sens specializes in composite monitoring solutions, and in the demonstrator optical fibers are used as sensors that can register changes related to strain, deformation, or the occurrence of damage.
Such a sensor network can serve as the construction’s “nervous system”: instead of carrying out lengthy inspection campaigns after a flight, the system continuously records the condition and alerts when a change occurs that indicates damage. In practice, this opens the possibility of two levels of autonomy:
- Autonomous diagnostics – the structure itself recognizes that damage has occurred and where it originated.
- Autonomous intervention – the heating system is activated and healing is initiated, with the aim of restoring functionality before the damage spreads.
What has been tested so far and why cryogenic tanks are the next step
According to information published in partner statements, samples of different dimensions were tested – from small formats (about 2 × 10 cm) to larger panels (about 40 × 40 cm). The tests focused on three basic questions: can damage be reliably detected, can heat be evenly distributed in the material, and can the heating procedure achieve a visible and mechanically relevant repair effect.
Additional thermal shock tests were carried out to monitor the behavior of the material under conditions similar to those experienced by a cryogenic tank – a component that in modern rocket systems often operates at extremely low temperatures and must withstand changes during filling, emptying, and operational cycles. According to the project’s plans, the next phase includes adapting the technology to a larger geometry, for example a demonstrator of a complete cryogenic fuel tank, which would be closer to real conditions of use in reusable systems.
Where CASSANDRA fits into ESA’s reusability programs
Through FLPP and related initiatives, ESA emphasizes the need to develop technologies that reduce costs and accelerate the development of European transportation systems, including concepts “to space, in space and back”. FIRST! is designed as an instrument that, through open competitions and rapid demonstrators, supports “derisking” – the reduction of technological risks before solutions are introduced into larger programs.
In that sense, CASSANDRA can be read as an attempt to “move” part of maintenance into the structure itself. Instead of treating every suspicious mark on a composite as a potential replacement, the goal is to create a system that recognizes what really happened, how serious it is, and whether it can be repaired immediately. If this proves reliable, the gain would be twofold: less waste and less time out of operation, which for launch systems is directly linked to the cost per flight.
Statements from ESA and industry: focus on cost, autonomy and sustainability
In publicly available statements, the project is described as a step toward “reusable space infrastructure” and reducing mission costs. ESA representative Bernard Decotignie emphasized that integrating such technology could bring major benefits to space transportation, precisely through developing reusability and reducing mission costs.
From the industry side, CompPair, through statements by its CTO Robin Trigueire, highlighted that the project brings the autonomy and durability of future spacecraft closer to practical application, while Head of Research and Development Cecilia Scazzoli emphasized the demonstration results: the combination of condition monitoring and heating systems showed autonomous damage reading and healing and high resistance to micro-cracking, which is important for demanding components such as propellant tanks.
Broader meaning: from “just” repair to managing the material life cycle
Behind such projects there is also a broader change in the approach to engineering: instead of viewing a structure as a “passive” element, it becomes an active system that monitors its own condition. In the composites industry this is often described by the term structural health monitoring (SHM) – systematic monitoring of structural health. When SHM is combined with the possibility of intervention, a new category is obtained: real-time management of the composite life cycle.
In the space sector this is especially important because safety margins are strict, and every kilogram and every hour of preparation have a price. If damage can be detected earlier and repaired before it becomes critical, the entire maintenance model potentially changes. At the same time, in an era when Europe wants to strengthen autonomy in access to space and the competitiveness of launch services, technologies that reduce costs and increase system availability also have a strategic dimension.
What the next challenges are: scaling, certification and real conditions
Although demonstrations on samples and panels are an important step, the real test will be transferring the technology to larger and more complex structures. Cryogenic fuel tanks are a natural candidate because they combine requirements for mass, strength, tightness, and resistance to thermal cycles. But along with that come questions:
- how many times the healing process can be repeated without degrading properties and without “hidden” consequences;
- how to ensure that the heating and sensor system works reliably after multiple cycles;
- how, within certification frameworks, to prove that the repair has truly restored the required level of safety;
- how to manage energy and heat so that the repair is carried out locally, without affecting surrounding systems.
For now, publicly available materials present the project as technological maturation – step by step – exactly in line with the logic of the FIRST! initiative, which focuses on rapid prototypes and testing. Final success will depend on whether the demonstrator can be turned into a solution that industry can integrate into operational systems.
Why this matters beyond space
Technologies developed for space applications often find their way into other industries. Self-healing composites and integrated condition monitoring could also be relevant for aviation, energy (e.g., wind turbine blades), and mobility, where composites are present and inspections are costly. In that sense, CASSANDRA is not just a story about rockets and fuel tanks, but also about how the European composites industry is trying to combine durability, sustainability, and smart materials.
If the next phase – demonstration of a larger form such as a cryogenic tank – confirms the results so far, Europe would gain another technology that supports the goal of reusing launch systems and reducing the cost of access to space, with potential spillover into civilian applications where a longer service life of structures and less waste are sought.
Sources:- ESA Commercialisation Gateway – explanation of the FIRST! initiative and campaign goals ( link )- ESA Space Transportation – description of the FLPP program and focus on modular and reusable systems ( link )- CSEM – press release on the CompPair/Com&Sens/CSEM collaboration on the CASSANDRA project ( link )- CompPair – post about ESA support for the CASSANDRA project and notes about the contract and partners ( link )- CompositesWorld – overview of the CASSANDRA project and quotes from industry ( link )- ESA – activity on healable composites for space applications and the activation temperature range ( link )
Find accommodation nearby
Creation time: 2 hours ago