Antony J. Musker

Development of hydrogen peroxide monopropellant rockets

Alta S.p.A. (Italy) and DELTACAT Ltd. (United Kingdom) are conducting a study, funded by the European Space Agency, into the development of hydrogen peroxide monopropellant thrusters using advanced catalytic beds. The present paper focuses on the design of two different demonstration thrusters with nominal ratings of 5 N and 25 N. Design requirements and specifications are presented, followed by the main results of a concept study, which was conducted to define the approximate dimensions needed. Some details about the specific design of the two prototypes and the choice of the main components are provided, with particular regard to the sensors and transducers to be used during the experimentation. Different catalytic bed configurations, including pure silver gauzes and pellets coated with manganese oxide or platinum, are going to be tested in the prototype thrusters, in order to find the optimum one for further industrial development. A dedicated test bench, designed and realized by Alta S.p.A. for tests on the thruster prototypes, is also illustrated.

Experimental Characterization of a 5 N Hydrogen Peroxide Monopropellant Thruster Prototype

In the framework of the LET-SME program funded by the European Space Agency, ALTA S.p.A. (Italy) and DELTACAT Ltd. (United Kingdom) jointly investigated the use of advanced catalytic beds on ceramic supports as a cost-effective alternative to metal screen reactors for the decomposition of high-concentration hydrogen peroxide in small monopropellant rockets. To this purpose ALTA S.p.A. designed and realized a reconfigurable test bench for the characterization of the operation and propulsive performance of small rocket thrusters. The present paper illustrates the experimental campaign carried out on a 5 N thruster prototype operating with two platinum catalysts on γ−alumina supporting spheres, especially developed by ALTA in collaboration with the Chemistry and Industrial Chemistry Department of Pisa University, Italy. The results indicated that Pt/Al2O3 is an effective catalyst combination for the decomposition of 87.5% propellant grade hydrogen peroxide, with good stability and performance comparable to silver screen beds of equal geometric envelope and operational conditions. Incomplete hydrogen peroxide decomposition and the onset of flow oscillations in the reactor were observed at the tested levels of bed loading, residence time and flow pressure. Thermal stresses due to the large temperature gradients occurring during the decomposition of high grade hydrogen peroxide (87.5% by weight) caused the ceramic pellets to break and the progressive occlusion of the bed. Based on the analysis of the test results, several ways to overcome these problems in future investigations have been tentatively identified, together with the necessary modifications to the present experimental set-up.

Experimental Characterization of Advanced Materials for the Catalytic Decomposition of Hydrogen Peroxide

Alta S.p.A. (Italy) and DELTACAT Ltd. (United Kingdom) are conducting a study, funded by the European Space Agency, into the development of hydrogen peroxide monopropellant thrusters using advanced catalytic beds. The present paper focuses on the design of a dedicated test bench to assess the effectiveness of different catalyst samples when immersed in hydrogen peroxide. To date, the apparatus has been used to study powdered silver and three oxides of manganese. The evaluation of an analytical technique for determining the observed decomposition rates is also presented. In addition to devising a quantitative method for assessing the efficacy of the candidate catalysts, some qualitative studies of proposed metallic catalysts, in the form of wires immersed in hydrogen peroxide, are also described. Of the catalyst materials tested so far, preliminary results suggest that dimanganese trioxide offers slightly better performance than both manganese dioxide and silver.

Experimental Assessment of Heterogeneous Catalysts for the Decomposition of Hydrogen Peroxide

With the increasingly stringent controls being placed on the use of hydrazine and its derivatives, “green” propellants such as hydrogen peroxide are receiving much interest from the space industry. This paper describes the development of an instrumented catalyst bed used to assess the performance and lifetime of catalysts used to promote the decomposition of hydrogen peroxide. The catalyst bed design and preliminary findings are described. Two catalysts have been tested with 87.5% concentration hydrogen peroxide: 0.5% platinum on alumina pellets and silver gauze. The preliminary results show that the 0.5% platinum pellets have a higher performance, achieving a steady state decomposition efficiency of 95.4%, with neither catalyst showing signs of exhaustion.

Design, Build and Test of a 20 N Hydrogen Peroxide Monopropellant Thruster

An engineering bread-board monopropellant thruster has been developed that uses hydrogen peroxide at 87.5% concentration. The design methodology is described and three variants of both the catalyst bed and injector have been manufactured. Different combinations of these components have been tested to allow comparisons based on pre-heat methodology, injector geometry and catalyst bed length to be undertaken. The results to date have identified an injector and catalyst bed combination which provides C* and decomposition efficiencies above 90%.

The Effect of Stabilizer Content on the Catalytic Decomposition of Hydrogen Peroxide

The decomposition of hydrogen peroxide by homogeneous catalysis was investigated experimentally. A theoretical thermo-chemical model of the decomposition process was used to aid the design of a dedicated test rig. Measurements of the decomposition temperature at various catalyst/oxidizer ratios were compared with the results of the thermo-chemical model. Despite the simplifying assumptions embedded in the model, the comparison was quite favorable. From the experimental data obtained, the reaction length required to achieve full decomposition of the hydrogen peroxide, under the conditions prevalent in the experiments, was estimated. It was demonstrated that stabilizer additives in very high proportions had a negligible influence on the react ion length.

An assessment of homogeneous catalysis for the rapid decomposition of hydrogen peroxide

Liquid catalysts for decomposing hydrogen peroxide in rocket engines have certain advantages over conventional gauzes or pellets. The most potent liquid agents for achieving this decomposition are the permanganates. However, permanganates have a tendency to precipitate at the outlet to the injector and this militates against their use for multiple engine restarts. Against this background, the authors have investigated the feasibility of using different liquid agents to achieve the rapid decomposition needed for use in both monopropellant and bipropellant rocket applications. The results to date suggest that it is unlikely that any of the candidate agents considered will match the performance of the permanganates. However, at least one of the agents (sodium iodide) was found to initiate a very high decomposition rate, albeit with an undesirable initial delay. It was found that ferrous chloride tetrahydrate had no such delay and was capable of producing useful decomposition temperatures.