ORPHEE

Innovative propellants in hybrid propulsion technology and its applications in space transportation

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 Obiettivo del progetto (Objective)

'Nowadays, chemical propulsion is based on solid (launch applications like first stage booster) or liquid technologies (upper stage engines). Complementary, hybrid propulsion technology, as defined in ORPHEE (Operational Research Project on Hybrid Engine in Europe), appears as a new generation of advanced space transportation system. Engines based on this innovative propulsion concept provide advantages like thrust performance, throttling (thrust modulation), versatility (easy adaptation to various configurations), simplicity, safety. which significantly reduce the global engine cost. It will help to consolidate the long term sustainability and ensure a technology needed by the European propulsion space community to remain independent. Hybrid propulsion principle is based on the injection of a liquid oxidizer into the engine combustion chamber where it reacts with a solid fuel to generate hot gases providing the thrust. Enlarge the burning surface is the current proposed solution to reach the needed performance level. It dramatically increases the solid grain volume and the engine weight, limiting the applications. The regression rate is a key parameter controlling the solid fuel grain design. Its increase is a very attractive solution to reduce the grain volume. The main objectives of ORPHEE are to increase versatility of space propulsion system, ensure significant increase performance of hybrid engine, improve solid fuel technological maturity from TRL 1 to 3 and gather European skills on hybrid propulsion and ensure European access to space In near future, the availability of new hybrid engines will allow the access to new space transportation missions and to obtain significant costs reduction. It will consolidate the knowledge on this innovative technology, allowing the European space community to become non dependant. It may be considered as a competitive propulsion solution to be implemented in future space agencies roadmaps.'

Introduzione (Teaser)

Conventional rocket propellants are either liquid or solid. EU-funded scientists carried out important experimental and theoretical studies aimed at improved performance and lowering costs through the use of a hybrid propulsion system.

Descrizione progetto (Article)

Both solid and liquid propellants rely on combustion, or burning in the presence of oxygen, to produce hot gases. When the latter are forced out the back of the rocket, the rocket gets 'pushed' forward, just as Newton described in his Third Law of Motion.

Scientists sought to improve on the status quo with EU funding of the project 'Innovative propellants in hybrid propulsion technology and its applications in space transportation' (ORPHEE). Hybrid rockets burn a solid fuel in the presence of a liquid oxidiser. The solid fuel has the benefit of simplicity and lower cost while the liquid enables adjustable control of flow (throttling), ensuring more precise manoeuvring and safer orbital insertion.

Previous proposals for hybrid rockets have focused on increasing the burning surface to reach desired performance, but this causes unwanted increase in weight and volume. ORPHEE sought to optimise the solid fuel regression rate, the rate at which the solid recedes as it is burned. Increase in regression rate will reduce solid fuel grain volume thus improving performance.

ORPHEE studied three selected applications consisting of hybrid upper stages, Moon or Mars Landers and low-cost, first-stage boosters. Scientists first characterised candidate fuels for each application using small-scale combustion experiments. When the process was scaled up, novel insight into the mechanical properties of fuel grains led to adaptations in manufacturing that significantly enhanced fuel grain quality. During the last project year, new formulations were developed with the addition of metallic powders to increase solid fuel regression rate.

Firing tests did not demonstrate the same expected increases in regression rate seen at smaller scales. However, such observations enabled the inclusion of key parameters affected by a scale increase in the many numerical models developed. This knowledge should prove particularly important in subsequent design studies.

Demonstrators for the three applications have been designed and preliminary computational fluid dynamics (CFD) studies have been performed. In addition, a hybrid technologies roadmap has been prepared based on ORPHEE outcomes. In the long term, ORPHEE is expected to have important impact on the sustainability and competitiveness of the European space programme.