Test software monitors remote satellite station

The task facing companies that develop space and satellite monitoring and control systems can be daunting. Consider the challenge of developing a software package that controls dozens of instruments, from multiple vendors, with every imaginable interface scheme. Further, the equipment can be separated by hundreds of yards, and the control interface might even be hundreds of miles away. At Indra, we developed such a general-purpose software package that allows the coordinated control of all the elements in complex, distributed satellite stations.

Figure 1 shows the major elements that a satellite station typically includes:

• An antenna and antenna control unit (ACU) position the antenna or track a satellite.
• A transceiver subsystem amplifies weak signals from the antenna using a low-noise amplifier (LNA). The equivalent on the transmit side is a high-power amplifier (HPA).
• Upconverters and downconverters take satellite signals in the gigahertz range and drop them to an intermediate frequency between 50 and 90 MHz for processing.
• A baseband subsystem digitizes, modulates/demodulates, and multiplexes communication signals from user equipment.
• A system might use a variety of secondary and auxiliary equipment such as power meters, spectrum analyzers, antenna de-icing/blower units, frequency and time synchronizers, switching matrices, and even environmental or intrusion alarms for the satellite station.

Fig. 1  A satellite ground station consists of three major subsystems: the antenna, the transceiver/transponder, and the baseband subsystem that interfaces to the end user.

At the top level, the Genius system consists of two independent modules that are commonly located on networked computers. The first, called the ACQ (ACQuisition) module, interfaces with the station equipment. It works as a server, typically without a monitor or keyboard, and the equipment can run unattended. The second, called the MMI (Man Machine Interface) module, is a user-interface client often located hundreds of yards, if not many miles, away. With this architecture, an installation can have multiple ACQ or MMI modules as user requirements dictate, located at wide distances from each other.

Given the many suppliers of equipment for satellite stations, engineers need software that can support virtually any communications protocol, whether RS-232, RS-485, IEEE 488, TCP/IP, or even simple contact closures. This type of equipment generally does not come with drivers, so it is helpful if the development software makes it easy to write or test small sections of code. Using Agilent Vee let us verify that work in progress was correct before moving on to a larger program that might mask any problems. We could copy and paste a portion of graphical code to the main panel, add a "Start" button, and execute it for testing purposes.

The most difficult instruments to interface with are generally those with many operating parameters, such as modems, multiplexers, ACUs, telemetry, and telecommand processors. Even those with fewer parameters, such as an HPA, an LNA, a switch, or a converter, can pose problems. For example, the team found it challenging to set up a controller that moves a twin-antenna system mounted on an aircraft carrier. The transmission pattern of each antenna is restricted so as to not send energy close to the ship's cabins, hence the need for the two antennas to maintain communications no matter where a satellite might be.

Giving an operator an overview of all station operations requires a sophisticated display. An ASCII file in Genius defines the size of various display windows—an overall system representation, the main menu, a display of main operating parameters, and a message panel. Because a typical display is packed with information (Figure 2), software designers employ many special symbols with corresponding labels. To build this example panel, we started with a drawing package that creates a BMP, JPG, or GIF file. When the diagram was complete, the software designers determined the size and coordinates of each box and then linked each equipment interface to an object.

Fig. 2  In this portion of the screen of the PMCS software, different colors show the status of equipment.

To understand how Genius works in an actual application, consider the Polar Station Facility (PSF). Located on Norway's Svalbard Island close to the North Pole, the PSF is part of the EUMETSAT (European Organization for the Exploitation of Meteorological Satellites) Polar System. It provides the ground system responsible for the operation and acquisition of data from the MetOp (Meteorological Operational) polar satellites, which gather information about the atmosphere as well as land and ocean surfaces.

The station also acquires and processes global data from NOAA satellites and provides cross support for other NOAA operations during blind orbits not visible from other stations, such as a primary tracking facility in Fairbanks, AK. This PSF operates on the X, S, and L bands, and power output on the antenna is typically 45 dBW.

The PSF consists of two independent and identical command, data, and acquisition (CDA) stations, which consist of their own dish antenna and operations room. These facilities, unattended except for maintenance, are located on Svalbard Island. They connect over a WAN to a central monitoring and control station (MCS) in Darmstadt, Germany, a distance of more than 2000 km, where operators control the PSF site (although local operation is available for maintenance and emergency operations).

The polar facility monitoring and control station (PMCS) software periodically collects the status and parameters of the CDA equipment and sends them to the MCS; it also receives commands to schedule satellite-pass and self-test activities. From Germany, an operator can supervise the entire PSF station, altering the equipment configuration or reading back reports on equipment status when diagnosing possible operational failures.

The PMCS hardware architecture for each CDA consists of two major elements. One, in the operations room, is an industrial PC along with a LAN hub and a fiber-optic repeater. Software controls 18 pieces of equipment such as a GPS receiver, power meter, test modulator, and baseband processor. Roughly 200 m away, another computer setup in the Antenna Equipment Room likewise has a LAN hub and fiber-optic repeater. Here, the software controls 22 pieces of equipment such as tracking receivers, X-band converters, an antenna control unit, and a spectrum analyzer.

This installation shows that a satellite control program must be flexible in order to accommodate many types of equipment in many configurations. To create a system with Genius, the developer needs only instrument drivers and ASCII configuration files.