Roger Lo

Investigation of the Burning Behavior of Cryogenic Solid Propellants

Cryogenic Solid Propellant (CSP)-technology is a new approach to develop more powerful rocket motors. CSPs include the advantages of classical solid propellants to save weight as well as those of a high energy content and safety of modern liquid propellants. The charges consist of liquid and/or gaseous fuels and oxidizers, both frozen. Two main versions of CSP-technology can be realised: 1. Mono-CSPs show the burning behavior of solid propellants. Experiments with mono-CSPs have been carried out under inert pressure conditions in a window bomb. Mono-CSPs have a stable burning behavior with a constant regression rate which follows the Vieilles law under varying pressure conditions. 2. The advantage of high safety is obtained by assembling oxidizer and fuel in sandwich configurations. The grain geometry governs the burning behavior. Such systems can be externally controlled, e.g. by the heat from a gas generator or they can work self-sustained. A Rod-in-Matrix burner shows self-sustained combustion in an inert pressure atmosphere with overall burning rates in a similar range as solid rocket propellants which obey also a Vieille-like pressure law. Disc stack burners have also been investigated, the combustion of which is strongly dependent on the disc thickness. For a short time Machs nodes have been observed in the exhaust plume of a disc stack burner. Currently, the temperature ranges are limited to the boiling temperature of liquid nitrogen. Therefore, liquid oxidizers like H2O2 have been used. However, for the first time a propellant strand of polymer rods embedded in solid oxygen was prepared and burnt. The experiments with CSPs end in the combustion of a small rocket motor showing no serious technical obstacles. Simplified models based on the heat flow equation can simulate the burning characteristics of the frozen energetic materials including phase transitions.

STRATEGIES OF DEVELOPING ADVANCED LUNAR POWER SYSTEMS

Abstract Electric and thermal power have to be available at the base site on the lunar surface before the first lunar crew arrives. Unlimited solar energy is available during the lunar day, but this must be stored for use during the lunar night unless nuclear energy systems are available. State-of-the-art candidate systems are reviewed and the production of solar cells on the moon is discussed. Various options for developing a lunar power plant are proposed. These must be simulated and optimized in a real life-cycle systems scenario to provide operations and cost data essential for choosing a strategy.

Modular Dissected Cryogenic Solid-Rocket Propellant Grains ☆

Abstract The paper deals with the concept of cryogenic solid-rocket propellant grains where the definition of solid propellants is not restricted to ambient temperature. Special cryogenic high-energy propellants, boundary layer combustion in solid propulsion and performance of cryogenic solid rockets are considered in turn.

A novel kind of solid rocket propellant

Abstract Cryogenic Solid Propellants (CSPs) combine the simplicity of conventional solid propulsion with the high performance of liquid propulsion. By introducing materials that require cooling for remaining solid, CSPs offer an almost unlimited choice of propellant constituents that might be selected with respect to specific impulse, density or environmental protection. The prize to be paid for these advantages is the necessity of constant cooling and the requirement of special design features that provide combustion control by moving from deflagration to hybrid-like boundary layer combustion. This is achieved by building the solid propellant grains out of macroscopic elements rather than using the quasi homogeneous mixture of conventional composites. The elements may be coated, providing protection and support. Different elements may be designed for individual tasks and serve as modules for ignition, sustained combustion, gas generation, combustion efficiency enhancement, etc. Modular dissected grains offer many new ways of interaction inside the combustion chamber and new degrees of freedom for the designer of such “multiple internal hybrid grains”. At a preliminary level, a study finished in Germany 1997 demonstrated large payload gains when the US Space Shuttle and the ARIANE 5 boosters were replaced by CSP-boosters. A very preliminary cost analysis [5] resulted in development costs in the usual magnitude (but not in higher ones). Costs of operation were identified as crucial, but not established. Some experimental work in Germany is scheduled to begin in 1998. However, almost all details in this article (and many more that were not mentioned - most prominent cost analyses of CSP-development and operations) wait for deeper analysis and verification. Actually, a whole new world of chemical propulsion awaits exploration. The topic can be looked up and discussed at the web site of the Advanced Propulsion Workshop of the International Academy of Astronautics. The author would be pleased to provide the necessary access data.

Experimental Investigation on Cryogenic Solid Propellants in a Combustion Chamber

The burning behavior of modular cryogenic solid propellants was investigated in two different test chambers. In a first stage, one optically accessible chamber allowed the observation of the diffusion controlled combustion of linear propellant grains using photographs, IR-cameras, pyrometers and spectrographs. The second phase led to the assembly of a rocket test chamber in which, for first time, a cylindrically symmetric 1kg propellant charge of cryogenic disc stacks of H2O2 as oxidizer could be investigated.

HOT WATER PROPULSION DEVELOPMENT STATUS FOR EARTH AND SPACE APPLICATIONS

Hot water propulsion uses water as propellant which is heated in a sealed pressure tank until it reaches a specified vapor pressure and a corresponding propellant temperature. Release of the nozzle initiates the “ignition” of a hot water rocket motor. The overheated water is then discharged through the nozzle, where it is accelerated by vaporization.

CAD-BASED MODELLING OF LARGE CRYOGENIC SOLID PROPELLANT MOTORS

Cryogenic solid propulsion (CSP) uses chemical rocket propellant combinations with at least one frozen component in solid rocket motors. As a result, CSP combines the simplicity and reliability of conventional solid propulsion with the high Isp performance levels of cryogenic liquid propulsion. In the framework of research and development under German (DLR) and European (ESA) sponsorship, the general feasibility of CSP was successfully demonstrated. An experimental combustion chamber holding up to 1 kg of CSP propellants was built at AI: Aerospace Institute and recently hot fired successfully at Fraunhofer Institute for Chemical Technology. Selected hybrid CSP propellants in specific configurations show good burning behavior with a regression rate that lies in the range of conventional solid rocket propellants. Due to the required cryogenic infrastructure, CSP operation can only be cost efficient for a certain minimum stage size. Therefore, the main field of CSP application should refer to large boosters and first stages of heavy lift launch vehicles. In the frame of preparatory work, it was shown that launchers with CSP boosters or CSP lower stages can be compared performance-wise with ARIANE 5 type launchers using conventional solid propulsion. Green hybrid propellant combinations using frozen liquids like solid hydrogen peroxide (SHP) or solid oxygen (SOX) in combination with hydrocarbon polymers like polyethylene (PE) in solid rocket motors proved best for entering CSP technology development. The paper presents the main results of the CSP motor mass and performance modeling that was accomplished by means of CAD/CAE based methods considering major modifications required for CSP application in large solid rocket motors.

MODULAR SOLUTIONS FOR VERY HIGH ENERGY SOLID PROPELLANTS

Cryogenic Solid Propellants provide access to clean high thrust, high Isp propulsion. CSP R&D under ESA and German sponsorship is well on its way. The experimental state-of-the-art, combustion chamber design for modular propellant grains and results of CSP combustion are described in the paper.

Concept and numerical model of a highly efficient thruster for a small reaction control system

Abstract The numerical design of a highly efficient satellite control system is described that uses free radical thrusters, converting into thrust the energy released by the recombination of atomic hydrogen. Free radicals are produced on board under microwave irradiation. Because of low power requirement the satellite control system (SCS) requires no additional energy sources. The investigation led to a numerical model, elaborated to calculate the thermophysical characteristics of a recombining hydrogen gas mixture in the chamber and nozzle. The geometry of the chamber and nozzle were optimized to minimize the thrusters mass. The dynamic characteristics of the thrusters were determined. This research was done in the framework of the scientific-technical cooperation between Bauman State Technical University Moscow (MGTU Bauman) and the Space Transportation Systems Branch of ILR at TU Berlin within the project “Investigation of highly efficient engines for auxiliary propulsion of space systems”.

Hands-on keyboard: The multifunctional tutorial for teaching and practical training of space-technology at the Berlin University of Technology☆

Abstract The multifunctional tutorial for teaching and practical training of space technology at the Aerospace Institute of Berlin University of Technology (BUT) is a research project designed to exploit certain features of expert systems for the management of a complex space education and information system. This paper describes this new approach to computer aided teaching and research. The system comprises databases, a complex of modelling features, a large technical library and files of the lectures presented during courses. The databases include a complete inventory of international launch vehicles and all major conceptual vehicle designs and their parameters (presently 125 systems) and details of rocket launches since 1957 (presently 3508 launches). Another base contains all major data of about 340 rocket motors and thrusters; yet another holds more than 700 data sheets concerning published data of cost and prices of the development, production and operation of launchers, stages, subsystems and related infrastructure. This paper presents the structure of the tutorial which is in accordance with the lectures offered and assures easy use accomplished by self-explanatory graphical menu-guidance and pictograms, visual representation of choices and a help-system based on practical experience. The structure of simulation and modelling has a wide range of degrees of freedom with strict separation between input parameters and derived values, strict indication of limitations (range of valid inputs) and with intelligent monitoring of inputs for possible contradictions.