Harry Adirim

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.

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.

Dynamic Derivative Computation of a Sub-orbital Vehicle

The computation of the dynamic derivatives is presented for a sub-orbital vehicle in transonic and supersonic flow regimes. The dynamic derivatives are calculated by analyzing the aerodynamic response of a three-dimensional model to small amplitude forced oscillations. Steady and unsteady flow solutions are achieved with a time-dependent Navier Stokes solver. A moving grid technique is adopted to simulate the forced oscillations of the model. An experimental campaign is carried out within the project in similar flow conditions. Close comparisons with the available experimental data are discussed to validate the approach. The activity is the result of a funded research project of the European Community aimed at exploring new technologies for the high-altitude and high-speed transportation.

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.