The Integrated Test and Operations System (ITOS) is a generic system of software for controlling spacecraft and components of spacecraft during development, testing, and operation in orbit. The ITOS software is an inexpensive, portable, highly configurable system that runs under a variety of UNIX operating systems — including Solaris, FreeBSD, and Linux — on workstations or personal computers. The ITOS evolved from the ground support equipment built in 1990 to support integration and testing of SAMPEX, the first Small Explorer (SMEX) mission, and now is supporting SAMPEX and eleven other missions.

Figure 1. A Typical Ground Data System for integration, testing, and flight operations of a spacecraft includes several workstations and external systems connected via a local-area network.
The ITOS software is executed on a cluster of workstations (see Figure 1) interconnected over a local-area network (LAN). Each workstation runs the complete ITOS software. One of the workstations is designated as the primary operator console; this console receives telemetry data from a spacecraft interface and sends commands to the interface via an Internet-Protocol (IP) Ethernet connection.

The primary console relays the spacecraft telemetry data to all other ITOS workstations on the LAN. Such computation-intensive operations as real-time, high-rate processing, distribution, and plotting of telemetric data can be distributed among workstations to achieve high performance at minimal cost of hardware. Each ITOS workstation unpacks the telemetry data packets and performs such data-processing tasks as limit checking, conversions of engineering units, and monitoring of configurations.

The primary ITOS console can distribute telemetry data, via an IP Ethernet connection, to external scientific, engineering, flight-dynamics, mission-planning, and command management systems attached to the LAN. These data are provided in a variety of formats and can be transferred by frame, packet, or individual datum. The ITOS uses a protocol that enables each of these external systems to request a particular type of data.

Figure 2. The ITOS Software System comprises five subsystems. The software is modular; most of its components can be replaced or augmented.
One ITOS computer can be connected to the Internet as a server to provide telemetry and event displays that are viewable through any Java-capable web-browser software. This feature enables engineers to monitor and participate in tests and flight operations from remote locations, including their homes and offices. The server can also provide telemetry and event displays to the public via the Internet.

The ITOS software is customized from mission to mission, through an operational data base (which contains mission telemetry and command specifications), and through a small set of configuration files.

The ITOS can accept telemetry from multiple sources simultaneously. It can, for example, process spacecraft telemetry and ground-station status blocks or telemetry from a dynamic simulator. It can also control and monitor such external devices as receivers, bit synchronizers, and simulators by use of IEEE-488, RS-232, or network connections.

With respect to functionality, the ITOS software system can be characterized as divided into five subsystems: telemetry, command, control, data base, and events (see Figure 2). The telemetry subsystem contains programs for ingesting, unpacking, displaying, and checking telemetric data from spacecraft. The command subsystem contains programs for generating and transmitting spacecraft commands. The control subsystem includes programs for controlling and monitoring the spacecraft and the elements of the ground system. The data-base subsystem comprises programs for creating and gaining access to the operational data base. The event subsystem manages the recording, display, and forwarding of all messages generated by the ITOS programs and by the spacecraft.

The cost of replicating the ITOS is low. This is partly because (1) the only commercial component of the ITOS software is a plotting program for which run-time licensing is not required and (2) the ITOS software is based on open standards. The ITOS software was developed by use of the Open Source GNU development suite. Its graphical user interface is based on Motif and the Java Development Kit. The development team made every effort to ensure that the ITOS code conforms to all relevant standards for maximum portability across UNIX implementations.

This work was done by Karen M. Keadle-Calvert and Sharon Orsborne of Goddard Space Flight Center; Brian Goldman and Mark Richardson of AlliedSignal Technical Services; Danny Lewis of SGT; and Greg Greer, Tim Singletary, and Bruce Wendel of Hammers Company. For further information, access the Technical Support Package (TSP) free on-line at  under the Electronics & Computers category. GSC-14012