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The aim of this work is to study the effect of disturbances from startups and shutdowns of a restartable sustainer engine on the operation of control jet engines in their continuous and pulse operation with account for the integration of the engine feed lines. Abandoning the traditional feed of control engines from individual tanks increases the payload mass by eliminating the need for a gas displacement system and offers a more complete use of the onboard propellant. The main objectives of the system of control engines as actuators of the launch vehicle upper stage flight control system are roll, pitch, and yaw control in different operating regimes of the sustainer engine, the acceleration of the stage before sustainer engine restarts, and the removal of the stage to an utilization orbit with remaining propellant burn-up. Because the feel lines of the sustainer engine and the control engines are hydraulically connected, at sustainer engine startups/shutdowns the propellant component pressure at the control engine inlets is subject to disturbances in the form of surges and dips, in response to which the rocket stage flight control system must generate additional control actions. The control engine operation under disturbances from the sustainer engine was studied using the authors' comprehensive mathematical model, which describes the propellant component flow in the feed lines, electrically operated fuel valves, and combustion chambers of control engines, and the time profiles of disturbances recorded in full-scale ground tests of the Cyclon-4M launch vehicle upper stage. Calculations were conducted for the most strenuous combinations of the control engine operation under disturbances from sustainer engine startups and shutdowns. The calculated data show that the control engine thrust is within the limits specified in the requirements specification for the development of the control engines as a part of the liquid-propellant jet system.

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The aim of this work is to analyze the state of the art in the development and use of pollution-free (“green”) propellants in low-thrust jet engines used as actuators of spacecraft stabilization and flight control systems and to adapt computational methods to the determination of “green”-propellant engine thrust characteristics. The monopropellant that is now widely used in the above-mentioned engines is hydrazine, whose decomposition produces a jet thrust due to the gaseous reaction products flowing out of a supersonic nozzle. Because of the high toxicity of hydrazine and the complex technology of hydrazine filling, it is important to search for its less toxic substitutes that would compare well with it in energy and mass characteristics. A promising line of this substitution is the use of ion liquids classed with “green” ones. The main components of these propellants are a water solution of an ion liquid and a fuel component. The exothermic thermocatalytic decomposition of a “green” propellant is combined with the combustion of its fuel component and increases the combustion chamber pressure due to the formation of gaseous products, which produces an engine thrust. It is well known that a “green” propellant itself and the products of its decomposition and combustion are far less toxic that hydrazine and the products of its decomposition, The paper presents data on foreign developments of “green” propellants of different types, which are under test in ground (bench) conditions and on a number of spacecraft. The key parameter that governs the efficiency of the jet propulsion system thrust characteristics is the performance of the decomposition and combustion products, which depends on their temperature and chemical composition. The use of equilibrium high-temperature process calculation methods for this purpose is too idealized and calls for experimental verification. Besides, a substantial contribution to the end effect is made by the design features of propellant feed and flow through a fine-dispersed catalyst layer aimed at maximizing the monopropellant-catalyst contact area. As a result, in addition to the computational determination of the thrust characteristics of a propulsion system under design, its experimental tryout is mandatory. The literature gives information on the performance data of “green”-propellant propulsion systems for single engines. However, in spacecraft control engine systems their number may amount to 8–16; in addition, they operate in different regimes and may differ in thrust/throttling characteristics, which leads to unstable propellant feed to operating engines. To predict these processes, the paper suggests a mathematical model developed at the Institute of Technical Mechanics of the National Academy of Sciences of Ukraine and the State Space Agency of Ukraine and adapted to “green”-propellant engine systems. The model serves to calculate the operation of low-thrust jet engine systems and describes the propellant flow in propellant feed lines, propellant valves, and combustion chambers. To implement the model, use was made of the results of experimental studies on a prototype “green”-propellant engine developed at Yuzhnoye State Design Office. The analysis of the experimental results made it possible to refine the performance parameters of the monopropellant employed and obtain computational data that may be used in analyzing the operation of a single engine or an engine system on this propellant type in ground and flight conditions