MIL-STD-1553: The Global Standard for Military and Aerospace Data Buses

By Brian Conway | October 15, 2024

MIL-STD-1553 has been incorporated in every type of air, land, and sea vehicle built by the U.S. military in the last half-century. There is something eminently satisfying about a technology that simply works.

One of the more enduring standards in the mil-aerospace industry is MIL-STD-1553, which defines the mechanical, electrical, and functional characteristics of a serial data bus. This standard has been incorporated in about every type of air, land, and sea vehicle built by the U.S. military in the last half-century. There is something eminently satisfying about a technology that simply works. For over 50 years, designers have known they can absolutely rely on MIL-STD-1553 connectors to get the job done.

MIL-STD-1553 is now one of the most common means around the world of integrating defense and space systems. The standard is also seeing increasing adoption in the commercial aerospace sector.

Evolution of the Standard

In the early 1970s, the US Air Force created specifications for an avionics data bus, which became an official Air Force standard in 1973. First used in F-16 Falcon fighter jets, that bus and its associated specification, MIL-STD-1553, were subsequently adopted by the other branches of the U.S. Armed Forces.

Fig 1. F-16 Falcon Fighter Jet

MIL-STD-1553 is also the basis for bus standards adopted by the United Kingdom and the North Atlantic Treaty Organization (NATO).

The National Aeronautics and Space Administration (NASA) also standardized that bus for spacecraft on-board data handling (OBDH) systems.

Over time, the standard has seen few changes. The original was superseded by MIL-STD-1553A in 1975. That was followed by another revision in 1978, MIL-STD-1553B. Different vendors had been implementing MIL-STD-1553A in diverse ways, leading to incompatibilities between the products of the various suppliers. The 1553B version addressed the issue by allowing for manufacturing variations but strictly specifying the electrical interfaces.

From 1978 through 2018 the Department of Defense (DoD) issued only a handful of change notices to the standard. In 2018, the DoD published MIL-STD-1553C, which, despite the designation as a major revision, is considered functionally equivalent to MIL-STD-1553B.

Elements of the Standard

MIL-STD 1553B covers the data bus itself, the method of communication on the bus, and the electrical interface requirements for systems connected to it.

System elements defined by the standard include a bus controller and bus monitor, two kinds of terminal, the twisted shielded pair wire data bus, and optional isolation couplers.

The bus controller provides data flow control for all data traffic, using a command /response method. The bus monitor makes it possible to gauge the system’s operational status and supports the ability to record and store data.

For a sensor or any other subsystem to connect to the data bus, it needs to incorporate interface circuitry – that circuitry constitutes an embedded remote terminal. An embedded remote terminal is not required to have a bus controller, but it can be useful to include one and MIL-STD-1553 allows for that.

Fig 2. Diagram Outlining the Basics of Databus and Cable Assembly

That is one kind of terminal. The other, the stand-alone remote terminal, is used to interface with other systems that are not compliant with MIL-STD-1553.

The standard also defines the characteristics for twisted pair shielded cable. The ultimate purpose of the optional data bus coupler, meanwhile, is to reduce potential distortion on the main data bus.

Some of the specific characteristics of the standard include:

Equipment must be rugged and able to hold up to harsh environments.
Equipment operates at low frequencies, less than 500 megahertz (MHz).
Implementations must be dual redundant systems. There must be two signal paths: one main signal transmission line plus a backup.
Data rates are up to 1 megabit per second (Mb/s)
The transmission protocol is time-division multiplexing (TDM).
The integration of up to 31 remote terminals must be supported.

MIL-STD-1553 in Action

As noted, the data bus defined in MIL-STD-1553 has become the default for most US combat vehicles, ships, satellites, and missiles, as well as for many systems developed by NATO allies. It is so ingrained in global defense design that it is reported to have been used in the Russian MiG-35 fighter jet.

Space applications include the James Webb space telescope and the International Space Station Program. Long a military data bus standard, MIL-STD-1553 has attracted the interest of commercial aircraft manufacturers who seek to benefit from the standard’s demonstrated reliability, robustness, and EMI performance.

MIL-STD-1553 and Interconnects

MIL-STD-1553 specifications require all devices to be connected by a redundant and shielded data bus to ensure reliable data transmission, which is essential for challenging environments. To this end, all connectors and RF cables, which collectively form the primary physical layer of the system, must strictly meet all requirements.

Fig 3. Cinch’s CJ3450ACS-221 Connector

Key factors contributing to connectors’ reliability include the use of high-quality materials as well as the implementation of twinax cables, which feature a twisted pair of wires (as opposed to one in a standard connector), canceling electromagnetic fields to create RF shielding.

Fig 4. Cinch offers the TWC-78-1 series, the TWC-78-2 series, both PVC jacketed, and the M17-176 series, which has a PFA jacket for high-temperature resistance.

Devices connect to the bus through tributaries called stubs. Stubs for remote terminals, bus controllers, and bus monitors are connected to the bus through coupling boxes that provide single or multiple stub connections. These couplers provide the necessary shielding, isolation resistors, and transformer interface. The data bus passes through the coupler by connecting to two connectors.

The Enduring Role of MIL-STD-1553 in Defense and Aerospace

For over 50 years, MIL-STD-1553 has stood as a testament to the reliability and robustness required in mission-critical military and aerospace applications. Its ability to integrate seamlessly across various platforms, from fighter jets to spacecraft, has made it a global standard. As the industry continues to evolve, this trusted data bus will remain an integral part of defense and aerospace designs, offering unmatched performance in the most demanding environments.

Learn more about MIL-Spec solutions at Cinch Connectivity Solutions.

Cinch products are available from Interstate Connectivity Solutions (ICC).