How 1553 Remote Terminals Facilitate Data Networking in Aviation

MIL-STD-1553 is one of the oldest standards to be used in avionics today, and it is still the preferred one by network engineers for data communication in modern avionics. Thanks to its dual redundant physical layers, time division multiplexing (TDM) capability, and a differential network interface. However, what really sets it apart from its modern as well as ancient contemporaries is its handling capacity of several remote terminals (RT) or devices simultaneously. The most basic data bus setup of the standard can connect to up to thirty 1553 remote terminals, which not only makes data networking in avionics easier but also allows interfacing with multiple devices at once.

Here’s a quick look at how the support for 1553 bus terminal facilitates data networking in aviation along with a few examples.

Usage of 1553 Remote Terminals in Avionics

A remote terminal in MIL-STD-1553 is used for primarily two purposes. The most important one is for interfacing of the data bus with various subsystems. The secondary one is as a bridge between two subsystems (mentioned later in the article).

An example of this would be in a fighter aircraft like the F-20 Fightershark or F-16 Falcon, where the bus terminal acquires data from a navigational subsystem and sends it back to the 1553 card or the 1553 transceiver. This collected data, in turn, is forwarded to another subsystem (which is usually a display device in front of the control monitor or the aircraft crew) through support from another remote terminal.

This is a very crucial feature in a fighter aircraft where real-time data is absolutely necessary for the pilots to maneuver (and attack) with the highest precision. The same goes for features when the 1553 remote terminals are used for ordinary actions like switching ON the various lights in an aircraft.

The remote terminal connections are typically connected through 1553 bus couplers, stubs, and other connections which facilitate in lossless data communication. Although these components add to the overhead weight of the aircraft, these are usually considered indispensable cause of their necessity.

But this usage further points to the question of how, which can be answered by looking at how the military standard has helped avionics over the past few decades.

The Relevance of MIL-STD-1553 in 21^st Century

According to Intelligent Aerospace, a global aerospace technology network, MIL-STD-1553B (the upgraded version of the original MIL-STD-1553A, with predefined interfacing options) is still a major component in the field of data networking due to its wide variety of options.

In the 1960s, aircraft and military communication was mostly dependent on ‘single source, single sink’ application, which meant that a system could communicate with only another system or subsystem. In addition to that, the nature of this communication was simplex i.e. one-way communication. This was a very huge limitation for aircraft engineers, which got even worse when more and more subsystems came to being used. The lack of a bus system and the dependence on physical wires (which were bulky) gave rise to the formulation of digital computing. This heralded a series of new standards like the popular ARINC 429, which further paved the way for better standards with higher capacities and topologies.

The birth of MIL-STD-1553 was obvious, which immediately strengthened its position as the industry’s go-to standard. Below are a few of the reasons why it quickly became a popular standard not only in military avionics, but also in commercial aircraft, submarine, and space avionics systems:

• Error detection and prevention of malfunctioning in main system, attached 1553 cards, and extended subsystems (e.g. the ethernet)
• Predefined interfacing options that has resulted in simplified adoption across different platforms
• The ability to customize remote terminals and their connections

The last point is of the highest importance in 21^st century aviation. As more and more subsystems got added to an aircraft’s operation, partly caused by the rise of safety regulations and commercialization, the need for controlling them became the point of focus.

The Role of 1553 Remote Terminals

A popular example of the role of 1553 remote terminals is how the United States Air Force (USAF) saves over a thousand pounds of weight in its B-52 aircraft by employing them to connect to various subsystems using the data bus. The heavy wires and cables are done away with and instead the data is sent over electronic bus. This is not only space-effective but also is faster and power-efficient.

Another great example of how the 1553 remote terminal facilitates in data networking is to study how the National Aeronautics and Space Administration (NASA) uses it install laptop computers as physical interfaces. The NASA prefers the portable alternatives because they are easier to update, upgrade, and even replace. This is the reason why almost all vehicular commanding is done through laptop interfaces, event today.

The US segment of the International Space Station (ISS) chiefly employs Lenovo laptops for all physical interfacing, which are connected to the vehicle’s 1553 system as remote terminals. All of these laptops, called Portable Computer Systems (PCS), run on the open-source Linux operating system due to its high flexibility and customizable options.

Because they are installed as remote terminals, they have a series of advantages over other alternatives. Some of them are:

• Simplified duplex communication between the 1553 card and the physical interface
• Lossless communication
• Graphical interfacing for easy control by the spacecraft crew
• The laptops can double up as monitoring devices where graphical windows can alert the crew of various activities happening in and around the station

This is, by far, the best use of the 1553 bus terminal, which highlights the usage of a regular laptop (NASA uses the Lenovo T61P and A31P models) for complex monitoring and control activities over at the ISS.

It also shows how the 1553 standard can work with literally any type of electronic/electrical component and gadget because of the remote terminal support. These days, modern aircraft system engineers try to increase the number of RT connections so that one 1553 card can communicate with as many subsystems. Although two different subsystems can be joined together for this purpose, the research and development sections of different nations and organizations are still looking at expanding the appeal and usage of the good old MIL-STD-1553.

Final Thoughts

The above few examples – most importantly the one involving NASA and ISS – only point to the unfading relevance of 1553 remote terminals in data networking modern avionics. Although newer standards have been invented and used by modern aircraft systems, the 1553 is still a sought-after standard. And there are plenty of reasons for that.