The rapid proliferation of satellites in Low Earth Orbit (LEO) has dramatically increased the risk of orbital collisions, generating space debris that threatens the long-term sustainability of space operations. Left unaddressed, cascading collisions could render entire orbital shells unusable — a scenario known as the Kessler Syndrome. As of the project's inception, more than 30,000 tracked debris objects were already present in orbit. Debris Avoidance Maneuvers (DAMs) and Post-Mission Disposal (PMD) performed by onboard propulsion systems have been identified as the most effective countermeasures; however, these demand propulsion systems that are simultaneously compact, efficient, storable, and environmentally benign — a combination that existing technologies struggle to provide.
HYPER-CAT was conceived to address this gap by exploring a novel propulsion concept for small satellites: a catalyst-free hydrogen peroxide (H2O2) and kerosene bipropellant system integrated into an aerospike rocket engine. Two well-established challenges were the central motivation. First, the widespread use of H2O2 in space propulsion has long been hindered by catalyst degradation — stabilizers added to preserve propellant storability gradually poison the catalyst bed, reducing decomposition efficiency over prolonged missions. Second, aerospike engines, despite their well-known advantages in pressure-adaptive performance and compactness, have never reached operational deployment, largely because the spike structure is exposed to extreme thermal loads throughout the entire firing duration.
The central scientific hypothesis of HYPER-CAT was that these two problems could be solved simultaneously through a single mechanism: transpiration cooling using liquid H2O2. Rather than treating the thermal challenge of the spike as a constraint to be managed, the project proposed to exploit it as a thermodynamic asset. Liquid H2O2 injected through a porous metallic wall would absorb heat convectively, then vaporize and thermally decompose — generating a protective gas layer between the hot combustion gas and the structure. This thermal decomposition process, driven by heat from the core combustion rather than an external catalyst, would inherently eliminate the need for a catalyst bed while simultaneously protecting the spike. The resulting concept — referred to as hybrid combustion — represented a genuinely novel integration of cooling and propellant management functions within a single flow architecture.
The project was structured around three scientific objectives. The first was to experimentally characterize the hybrid combustion phenomenon using a vitiated-air heater that emulates the fuel-rich, high-temperature environment of an aerospike combustion chamber, with H2O2 injected through additively manufactured porous Inconel plates. The second was to develop a low-order mathematical modeling tool, capable of predicting transpiration cooling performance and combustion efficiency under reactive conditions, to be made openly available to the research community. The third was to translate these findings into a preliminary spike module design for the existing 500 N etholox aerospike engine at TU Dresden, followed by additive manufacturing and functional testing.
The project was hosted at the Institute of Aerospace Engineering, Technische Universität Dresden (TUD), in collaboration with the Fraunhofer Institute for Material and Beam Technology (IWS). TUD brought world-leading expertise in aerospike engine development, having achieved the first successful hot-fire test of an aerospike engine in Europe, and was concurrently developing a 6 kN H2O2/kerosene aerospike engine. The researcher brought complementary expertise in H2O2 propulsion systems, catalyst development, and low-order dynamic modeling, developed through extensive work at KAIST Rocket Lab. The collaboration was thus designed around a well-defined and mutually reinforcing knowledge exchange.
