The In-Orbit Testing of the European Mobile Services Payload on Italsat-2

B.J. Clymans

Projects Division, Directorate of Telecommunications Programmes, ESTEC, Noordwijk, The Netherlands

M. Jones

Serco Europe Ltd., ESTEC, Noordwijk, The Netherlands

A. Wenz

Polygon Control Systems, Zurich, Switzerland

The European Mobile Services (EMS) payload was launched on board Italsat-2 in August 1996. The payload, which is partly experimental, consists of one forward and one return transponder. The forward transponder is able to receive voice and data communications transmitted in Ku-band from fixed ground stations and transmit them to earth mobile terminals in L-band. After the satellite had reached its allocated position in geostationary orbit, it was commissioned by Nuovo Telespazio with the assistance of ESA engineers for the EMS payload

Introduction

For some years the Directorate of Telecommunications has maintained a specialised satellite-monitoring facility, which has proved extremely useful on numerous occasions for evaluating communications satellite performance. This facility, known as the Backup Satellite Support System (BSSS), has enabled ESA engineers to analyse satellite telemetry data received either directly from antennas located at ESTEC or via a PSTN line, using analogue modems, from the Redu (B) and Fucino (I) ground stations. The facility has been used over the years for the on-station monitoring of both the Marecs and ECS series of satellites, as well as for the initial In-Orbit Testing (IOT) of, and the later control/recovery operations for the Olympus spacecraft in May 1991.

Currently, such systems are in use at ESOC, ESTEC and the Redu station, as well as at other non-ESA sites. They have been kept up-to-date in hardware and software terms and are maintained in a state of readiness for immediate use as and when needed. Its unique combination of capabilities and flexibility made the BSSS the perfect facility to support the Italsat EMS payload In-Orbit Test (IOT), for which additional BSSSs were procured from Polygon Control Systems.

Given that the IOT was planned to take place from the Redu ground station, it was decided to locate the monitoring facility there also to provide direct availability of the EMS information needed to conduct the tests. The BSSS's role was to:

• process and monitor all of Italsat's telemetry parameters

• archive the telemetry data and provide convenient retrieval capabilities

• present the processed telemetry data in the form of alphanumeric-, graphic-, hexa-decimal and synoptic displays

• provide a protocol-based interface to IOT test computers in order to dynamically exchange test data via the Local Area Network (LAN).

System configuration

The BSSS installation (Fig. 1) used during the IOT consisted of two off-the-shelf PCs, one acting as a data server (hereafter called the 'Server') and the other as a processing and monitoring work station (known as the 'Master'), with an X.25 link for data transfer between the two (Figs. 2a,b). In fact, it was decided to use two such systems for the EMS IOT in order to have full redundancy. The Italsat telemetry data was input to the Server in the form of a NRZ-L coded serial data stream at a bit rate of 1024 bit/s. The format of 16 frames, each 128 bytes in length, implied an update interval of 16 seconds.

Figure 1. The BSSS installation

Figure 2a. IOT system hardware configuration

Figure 2b. Post-IOT system hardware configuration

Server station
The tasks performed by the Server included:

• synchronisation with the incoming serial data stream

• buffering, when necessary, of up to 15 minutes of unprocessed (raw) telemetry data

• various checks on the Italsat format (i.e. satellite identifier, format- and frame counters)

• displaying the raw telemetry format in hexadecimal form, including the identification of bad-quality data.

Master station
The following tasks were performed by the Master station:

• support of alphanumeric (AND), graphical (GRD), hexadecimal (HEX), out-of-limit (OOL), mimic (MMD), and parameter observation (POD) displays

• processing and monitoring of the raw telemetry data received from the Server

• archiving and provision of retrieval facilities

• export of processed telemetry data in various ways

• maintenance of the satellite database

• provision of database management tools.

Database management tools
As the BSSS is fully compliant with the database syntax used by ESA, the Italsat database built by ESOC could be used during the In-Orbit Testing. Several tools have been developed to simplify the database's maintenance, including: (i) a Database Editor that presents the database information in a context-sensitive manner; (ii) a Mimics Editor that provides an interactive means of generating the static elements of mimic displays; (iii) a Parser/Pre-compiler, which allows the coupling of parameters and mimic objects with real-time data. Figures 3 and 4 show examples of mimic displays used during Italsat's in-orbit testing. Figure 5 shows a typical database update cycle. The BSSS Desktop application handles all real- time-related tasks, as indicated in Figure 6.

Figure 3. Mimic display of the Italsat EMS payload

Figure 4. Mimic display of the Italsat EMS IF processor

Evolution

The successes achieved with the Backup Satellite Support System over the past years have prompted ESA to support the development of the next generation of low-cost satellite telemetry data monitoring and commanding facility manufactured by Polygon Control Systems®, called SatView^TM. Running under the MS-Windows NT^TMoperating system, it has inherited many of the proven features of the BSSS, but some significant extensions are also being added:

• Packet Telemetry Standard: Through the integration of special third-party hard- and software, SatView^TM conforms with this telemetry data standard.

• Relational Database: SatView^TM uses the MS- SQL^TM Server as its satellite database management tool.

• Account Management: The tight integration with the MS- Windows NT^TM account management services prevents unauthorised use of SatView^TM.

• Security Profiles: Modifiable security profiles allow user-dependent access privileges.

• Report Generation Facilities: SatView^TM provides the capability to schedule and generate reports automatically.

• Mailing Facilities: Normal or event-driven messages can be generated and mailed by SatView^TM.

• Event Logging: All events are archived by category and can be retrieved at a later time.

It is intended to use SatView^TM in the in-orbit testing of Artemis, as well as for its on-station operation.

Figure 5. A typical database update cycle

Figure 6. The BSSS Italsat real-time monitoring