The mean dynamic pressure of a solid rocket motor (SRM) can range from about 1000 to 5000 psi, so when the combustion instabilities occur the pressure oscillations could be up to 100 percent of the mean pressure. These pressure oscillations can occur thousands of times a second, and this could quickly lead to the fatigue failure of a motor system. The combustion instabilities can lead to a detonation in the propellant, which would be catastrophic to a propulsion system. In order to test for combustion instabilities of SRM propellant there or a few different testing rigs currently being developed here at the Auburn University Combustion Physics Lab (C. P. Lab). The rigs being developed include a 1,000 pound thrust stand, an acoustically forced optically accessible propellant testing rig, and a 3,000 psi capable window “bomb” rig. The window “bomb” and acoustically forced facility will be used to test propellant formulations, while the thrust stand will be used to test the SRM systems as a whole. The 1,000 pound thrust stand is a 5 foot tall by 2 foot square steel frame with legs in both directions for stability during tests. 
It has a two-rail linear bearing system with a location for interchangeable load cells for measuring thrust output of the SRMs. The SRM case will be modified to have a pressure transducer ported into the head of the rocket motor to measure the absolute and dynamic case pressure. Other measurements will be used such as strain gauges and external case temperature gauges, other non-destructive testing devices are also being considered as we can develop the understanding with the experimental rig. The atmospheric pressure acoustically forced rig has the capability to flow nitrogen or air and is to be used as an early stage rig to develop optical measurement techniques. The rig is forced acoustically using a set of driving speakers. The measurement devices being implemented in this experimental rig include dynamic pressure transducer, thermocouples, and optical systems. 
We are also using this rig to look into novel measurement devices such as ultrasonic transducers and laser distance gauges for measuring propellant regression rate. The window “bomb” rig is being designed as a high pressure capable tube with a window cut into the side. A quartz glass window will be used for structural integrity against the pressure and to not filter certain wavelengths of light. The rig will be pressurized with nitrogen and the system will use a back pressure regulator in order to allow the gas to flow from the tube to eject the combustion products from the combustion chamber. Experiments planned on being conducted with this rig include strand burning, gap burning, and slab burning tests. All of these experiments are planned to be used to observe different effects and propellant regression rates along with combustion instabilities of different propellants.
