Two recently published SAE International standards (AS5725 and AS5653) address communications between aircraft and weapons systems.
AS5725 concerns the interface for miniature mission stores. The standard came out of the AS-1 Aircraft Systems & Systems Integration Committee. According to AS5725 standard sponsor Joseph Cammarota of EDO MTech, the U.S. Air Force approached the committee several years ago to develop a new weapon interface standard that “would provide many, if not all, of the services provided by MIL-STD-1760, but for a smaller class of weapons: 250 lb and below.”
This new open interface needed to provide three things, Cammarota said: a reduced release force solution to minimize the impact of connector separation on vehicle dynamics; a much smaller form factor than the existing 1760 connector; and all needed services using cost-effective components.
A subcommittee headed by Jerry Provenza of the Air Force Research Laboratory, Munitions Directorate, Eglin Air Force Base, was formed to explore options. Initially the group had almost no boundaries in the design concepts it evaluated, including contactless and single-pin interfaces. Pressures from the Small Diameter Bomb (SDB) program, however, forced the group to converge on a more conventional, connector oriented solution, Cammarota said. Fred Benedick of Wintek was tasked with creating and maintaining the detailed requirements and initial draft of the standard.
A separate working group was formed to tackle the requirement for a higher-speed and more cost-effective (than MIL-STD-1553) solution for the digital communications requirements of the new weapon interface. The findings of this Communications Protocol Working Group were handed over to AS-1A and led directly to the development of AS5652, the Enhanced Bit Rate (EBR) 1553, 10 Mbps protocol.
The first version of the new Miniature Mission Store Interface (MMSI) was completed in 2002 and submitted to the U.S. government for tri-service coordination. The competitive nature of the SDB program prevented the immediate adoption of the SAE document, and a similar interface, the Joint Miniature Munitions Interface (JMMI), was developed by the winner of the SDB competition. There were some attempts to reconcile the differences between the MMSI and JMMI interfaces, but they proved unsuccessful and the SAE document languished.
Then, in 2006, the U.S. Navy (PMA-263) recognized the need for a truly open standard to support the integration of miniature weapons on unmanned combat air vehicles. AS-1B was once again approached, this time by the Navy, to complete the work it had started in 1996. Cammarota said that in less than a year following the Navy’s request, AS-1B had resurrected the last known draft of the SAE document, compared that to the last draft of a proposed Department of Defense MMSI document, defined the allowable design trade space, and proceeded to formalize AS5725.
This new standard supports the original intent of providing 1760-like services to miniature weapons using a small connector and cost-effective, open components, but also incorporated some new requirements that were not defined as such in 1996, said Cammarota. “These new services added increased power and safety features into AS5725 over those in the 2002 draft, and did so using a smaller connector. Although not required by the Navy, AS-1B worked to make AS5725 compatible with JMMI and, in fact, JMMI can be mapped to a subset of the AS5725 signal set. That mapping is defined in Appendix B of the SAE standard.”
The AS5653 standard, according to standard sponsor Thomas Lystrup of the Naval Air Warfare Center, Weapons Division, China Lake, CA, “defines a high-speed fiber channel network to improve the capability of MIL-STD-1760 to transfer digital data between aircraft/platforms, carriage systems, and mission stores.” This activity, he said, was initiated at the request of the U.S. Navy in 2001 due to excessive length of time downloading GPS data to weapon systems through the 1760 Mass Data Transfer process on current platforms.
AS5653 (High Speed 1760) provides a digital data command and control interface similar to MIL-STD-1555 based on fiber channel protocol but operating at a 1-gigabaud data rate. This interface has been incorporated in MIL-STD-1760E, which was recently published. High Speed 1760 has replaced the previous coax interface identified as HB 2 and HB4.
This change is considered a Class 2 interface change, since High Speed 1760 is designed to replace the 1553 interface in the future.
“Implementing AS5653 will dramatically reduce the time it takes to download weapon GPS target programming data and will facilitate rapid retargeting of preplanned weapon-delivery missions such as the Joint Direct Attack Munition, the Joint Standoff Weapon, and SDB,” Lystrup said.