TECHNOLOGY AREA(S): Air Platform

ACQUISITION PROGRAM: PMA-201 Precision Strike Weapons

OBJECTIVE: Develop a sensor capable of detecting cracks in a propellant grain and transmitting that data through a hermetically sealed rocket motor case.

DESCRIPTION: The propellants used in Propellant Actuated Devices (PADs) and Cartridge Actuated Devices (CADs) can develop cracks while installed onboard an aircraft. If the device is initiated, the cracks would result in an increase of the burning surface area of the propellant, causing an increase in the gas production that may result in rupture of the device. The required work will employ innovative technologies to provide wireless through-case data transmission, in situ rocket motor health assessment, and appropriate miniaturization for CAD/PAD applications. The ability to detect a propellant grain crack was demonstrated in the past, but there were limitations in capability, which prevented transition to fleet service. The limitations of the previous designs included size (the design was too large to fit within the available device�s envelope) and inability to transmit information through a hermetically sealed rocket motor case. The Navy seeks a sensor system capable of detecting the presence of cracks greater than 2mm anywhere within the propellant grain, providing an indication if cracks are present as soon as they are detected, providing an alert (visual and/or auditory) to maintenance personnel, and maintaining data collected for download by engineering staff at the completion of a 10-year ordnance service life. The sensor system should record the installation date of the unit, temperature, and data dependent of method used for crack detection. The data should be collected once a day and wirelessly downloaded every three months. The use of multiple sensors may be required to ensure crack detection throughout the propellant grain and to assure system reliability (90% reliability at 90% confidence). The size of the sensor system should be kept to a minimum size but must not exceed 2�x 3�x 0.08� thick. The total weight of the sensor system must be as light as possible with a maximum weight of 6 ounces. The proposer must prototype and demonstrate the solution, before and after environmental conditioning, as described in MIL-P-83126 [Ref 4]. Evaluation criteria will be: (1) crack detection capability, (2) data transmission capability through a hermetically sealed rocket case (such as the MK 109 Canopy Jettison Rocket Motor), (3) system reliability, (4) 10-year ordnance service life, and (5) capability of surviving environmental exposures, documented in MIL-P-83126 [Ref 4]. The capability of detecting propellant grain cracks in-situ and in real time will improve warfighter safety and reduce total ownership costs for energetic devices.

PHASE I: Develop, design, and demonstrate potential alternatives for a sensor system to detect cracking in a propellant grain and transmit the sensor data through a hermetically sealed rocket case. Perform an analysis of alternatives and demonstrate feasibility of selected approach. Evaluation criteria are listed in the Description above. Produce prototype plans to be developed under Phase II.

PHASE II: Develop a prototype system that is capable of surviving and operating as designed while installed in a hermetically sealed rocket case, such as the MK 109 Canopy Jettison Rocket Motor. Demonstrate system capability to detect cracks in propellant grains and transmit data transmission through a hermetically sealed rocket motor. Validate a 10-year useful service life in an ordnance device through modeling and/or analysis. Demonstrate capability for system to be capable of storing recorded data for download at end of ordnance service life. Demonstrate compatibility of the developed sensor system with the propellant grain and other construction materials. Ensure the individual sensor systems be as small as possible, but not to exceed 2� x 3� X 0.080� thick. Ensure that the developed system meets DoD Hazard of Electromagnetic Radiation to Ordnance (HERO) when installed in the ordnance device.

PHASE III DUAL USE APPLICATIONS: Complete the tests specified in accordance with MIL-P-83126 [Ref 4] and transition the developed sensor for use on the F/A-18 canopy remover rocket motor (MK 109) Super Hornet and other propellant actuated devices. This technology will be of benefit to commercial CAD/PAD devices such as automobile and airliner gas generators and commercial space applications.

REFERENCES:

1. Liu, C.T. �Effects of cyclic loading sequence on cumulative damage and constitutive behavior of a composite solid propellant�, 28th Structures, Structural Dynamics and Materials Conference, Structures, Structural Dynamics, and Materials and Co-located conferences. https://doi.org/10.2514/6.1987-776

2. Liu, C.T. �Evaluation of damage fields near crack tips in a composite solid propellant.� Journal of Spacecraft and Rockets, 1991, Vol. 28, No. 1, pp. 64-70. https://doi.org/10.2514/3.26210

3. Military Specification (MIL)-P-83126A, Propulsion Systems, Aircrew Escape, Design Specification For, (08 Feb 1980). http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-P/MIL-P-83126A_9078/

4. Tang, B., Liu, C.T., and Henneke, E.G. �Acousto-ultrasonic technique applied to filled-polymer damage assessment.� Journal of Spacecraft and Rockets, 1995, Vol. 32, No 5, pp. 866-9. https://doi.org/10.2514/3.26697

KEYWORDS: Propellant Grain Cracks; Data Transmission; Sensor System; MK109 Canopy Jettison Rocket Motor; Environmental Exposure/testing; Composite Propellant