|Ph.D Student||Dan Michaels|
|Subject||Interior Ballistics of a Combustion Chamber Discharging a|
|Department||Department of Aerospace Engineering||Supervisor||Professor Emeritus Gany Alon|
|Full Thesis text|
A unique concept for short action motors, based on a rocket-type combustion chamber discharging a concentrated mass through an exhaust tube is presented and investigated. The study considers a system comprising of granular solid propellant and a solid concentrated mass which may be an inert weight or a traveling propellant charge. Such short action motors may be beneficial for spacecraft and missile trajectory correction, applying mini-thrusters of this kind as well as for separating large space bodies such as missiles/launcher stages, satellites, etc., enabling the extraction of much higher impulse from available propellant mass and energy compared to rocket motors.
A theoretical time-dependent model has been developed, accounting for the two-phase gas-particle flow, propellant combustion, and concentrated mass motion along the exhaust tube. Calculations with a solid ejected weight of a few grams or less reveal that a specific impulse of above 400 seconds based on the propellant mass can be obtained, compared to a typical value of 250 seconds for solid rockets. This concept is also appealing for space body separation where each body acts as the ejected weight for the other body, with calculated specific impulse values exceeding 10,000 seconds. Additionally, a thruster ejecting a traveling charge composed of a very high burn rate propellant has been considered as a way of providing higher total impulse and eliminating the ejection of an inert weight. The results exhibit the benefits of using the traveling charge, and reveal important design consideration.
An experimental thruster ejecting small weights (5-8 g) was built in order to demonstrate the new idea. The impulse was measured both directly with a load cell and indirectly using a pressure transducer and high speed photography of the weight as it exits the tube. Both techniques produced similar total impulse measurements, resulting in specific impulse values of up to 430 seconds. Another experimental setup was built in order to demonstrate the concept for separation of bodies in space, with a heavy ejected weight (a cart of 13-26 kg). Specific impulses of 20,000 seconds and more were observed, which means that certain relative separation speed between two space bodies can be achieved by using the present concept with a fraction of one percent of propellant mass that regular rockets would need for this task. The good correspondence between the computations and the measurements validates the model as a useful tool for studying and designing such a thruster.