Standard for Spaceborne Fiber Optic Data Bus Uses Advancing Network Technologies

by Bruce Urbon

Historically, spacecraft data-handling subsystems have been implemented in point-to-point configurations that have proven to be extremely limited in flexibility and expandability. Existing bus standards have not sufficiently addressed requirements unique to spacecraft applications that would allow spacecraft designers to take advantage of rapidly advancing network technologies. P1393, Standard for Spaceborne Fiber Optic Data Bus (SFODB), is an effort sponsored by the IEEE Computer Society's Bus Architecture Standards Committee (BASC) to develop a standard that specifies a wide bandwidth, low-power, highly reliable, fault-tolerant fiber-optic network compatible with the harsh thermal, mechanical, and radiation environments of space missions.

The ever-expanding bandwidth of satellite-based sensor and communication payloads is placing increasing pressure on onboard data-handling systems requiring data throughput rates ranging from 100 Mb/s to 4 Gb/s. This onboard data traffic is characteristically sample based. The ability to handle both synchronous and asynchronous data with low, deterministic latency is a must.

Even at higher bandwidths, space systems will continue to be constrained by size, weight, and power limitations. In order to achieve the desired data rates while maintaining low size, weight, and power, data-handling subsystems must employ highly integrated components and cannot tolerate the luxury of unnecessary features commonly found in ground-based networks. Furthermore, any data-handling system implementation for space must be able to withstand the rigors of launch and the harsh space radiation environment. It must also be highly fault tolerant.

In order to meet these unique spacecraft data-handling requirements, a new standard is necessary. Adaptation of existing standards for space application is not practical. The SFODB protocol standard being defined reflects the RING-FODB currently under joint development by TRW and Honeywell featuring a ring topology and an ATM (Asynchronous Transfer Mode) cell data format to provide the basic functions of a distributed ATM Switch. The SFODB Working Group, organized in January 1995, has received a broad base of participation. For more information, contact Fred Orlando at (407) 951-3983.

Bruce Urbon is the Chair of P1393, Standard for Spaceborne Fiber Optic Data Bus.