Safe-and-arm device for solid rocket motor ignition and destruct

This paper describes the development and qualification of an electromechanical safe-and-arm (S&A) device used for initiating solid rocket motors and ordnance destruct systems. The S&A device is qualified for use on the Delta II launch vehicle for firstand second-stage destruct and has been flown successfully on Ariane. STS, Atlas Centaur, Titan IIIC, Long March, Joust, and Maxxus launch vehicles. The S&A device described features two independent and redundant explosive trains that are used to initiate explosive transfer assemblies. Each explosive train consists of a 1-amp/l-watt detonator and an RDX transfer lead. Safety is achieved by rotating the transfer leads 90 deg out-of-line with the detonators. As required by NASA safety policy NHB.1700.7A for STS payloads. the detonators will not fire or dud after exposure to a static discharge of 25 kv applied through shorted pins to case without a resistor in series. \d The testing described demonstrates that the S&A device will function reliably over a temperature range of -65 to +16OoF and after exposure to sinusoidal and random vibration testing. The S&A device (with isolators) has also been successfully tested to a shock-response spectrum at a peak level of 4200 g's. Unique features of the S&A device design are containment of solid particulate matter during (iring and minimized outgassing through the proper selection of materials. These features allow the S&A device to be mounted anywhere on the launch .J vehicle or spacecraft. Capyright @ 1992 by the American Institute of Aeronautics and Astronautics. Inc. All rights reserved. Introduction In 1979, Thiokol Corporation/Elkton Division started the development of an electromechanical S&A device for the initiation of upper-stage rocket motors. This led to the qualification of this S&A device for use on the McDonnell Douglas Space Systems PAM D2 rocket motor. The S&A, designated Model 2134A, subsequently was used for rocket motor initiation and destruct applications in more than 50 flights on six different launch vehicles including Shuttle, Delta 11, Ariane, Japanese H-1, Titan IIIC, and China's Long March 3. One of the unique applications was its use as the initiator for the Magellan spacecraft STAR 48 orbital insertion motor. The Magellan was deployed from the Shuttle Atlantis on May 4, 1989, with two Model 2134A S&A devices aboard. These S&A devices were armed in deep space approximately 2 months after deployment. On August 10. 1990, after a 15month, 795-million-mile journey to Venus, the S&A devices were fired to initiate the STAR 48 motor. The success of the Model 2134A S&A device has led to its use in an increasing number of applications, especially in flight termination systems. Although official DoD and NASA safety approvals were received, each Model 2134A S&A device continues to fly with a waiver against the detonators. Waivers are required because each lot of S&A detonators typically experienced a 4 to 8% failure rate during electrostatic discharge (ESD) testing at the manufacturer. These detonators were discarded and the remaining detonators in each lot passed the ESD test and were acceptable for use. The need to eliminate the waiver and expand the environmental envelope for flight termination applications led to the development and qualification of the Model 21348 S&A device (Fig. 1). The Model 21348 retains most of the design features of the A model but incorporates several improvements. The primary improvements are integration of an ESD insensitive detonator and addition of vibration isolation. Flg. I. Model 21348 Safe-and-Arm Device