the integral operational

The Integral Operational Ground Segment

P. Maldari Mission Operations Department, ESA Directorate of Technical and Operational Support, ESOC, Darmstadt, Germany

The mission profile The nominal operational parameters for The International Gamma-Ray Astrophysics Integral are given in Table 1, together with the Laboratory (Integral) is designed for two years combination of ground stations planned to of in-orbit operation, with the on-board support the Routine Phase (RP) of the mission consumables sized for a possible mission and the stations that will be used in the Early extension of a further three years. The Proton Orbit Phase (EOP). launcher will deliver Integral into a highly elliptical transfer orbit, similar to the final The driving requirement in the selection of the operational orbit, but with a lower perigee at ground stations to support the routine phase of 685 km. During the subsequent Early Orbit the mission was that the is to be Phase, the will be gradually injected operated in real time from the ground (no on- into its final orbit by a series of manoeuvres board data storage provided). The combination performed using the on-board resources (fuel of the ESA Redu and DSN Goldstone ground and thrusters). stations will provide coverage of the complete operational orbit above the Earth’s radiation Integral will be launched in October this year by a Russian Proton belts (approximately 90% of the total orbit), i.e. into a highly elliptical orbit. The mission will be controlled from the part of the orbit of scientific interest in which the Integral Operational Ground Segment, which will take charge of the on-board Instruments can be operated. the satellite’s operation from its separation from the launcher until the end of the mission. This article describes the ground-segment Integral is an observatory-type mission and as architecture and specifically the functionality of the Integral such will be operated based on a pre-planned Operational Ground Segment. The latter’s design is based on the command schedule for each orbit, containing latest ESA infrastructure develpments in the fields of mission-control all scientific observations and spacecraft systems (SCOS 2000), station , and tracking operations activities to be carried out during systems, and interoperability between ESA and NASA/JPL for cross- the orbit. The command schedule will be support of the mission. automatically executed within the Integral Mission Control System at the Mission Operations Centre. Table 1. Integral operational-orbit parameters and supporting ground stations The ground-segment architecture The mission’s ground segment consists of two Parameter Operational Orbit distinct elements: the Integral Operational Ground Segment and the Integral Science Apogee altitude 153 000 km Ground Segment (Fig. 2). The former will be Perigee altitude 10 000 km responsible for spacecraft and instrument Inclination 51.6 deg operations throughout the satellite’s lifetime, Argument of perigee 300 deg from its separation from the launcher until the Orbital period 72 hours end of the mission. The latter includes the RP ground stations ESA Redu Integral Science Operations Centre (ISOC) DSN Goldstone located at ESTEC, Noordwijk in the ESA Villafranca (backup) Netherlands, and the Integral Science Data EOP ground stations ESA Villafranca Centre (ISDC) located at Versoix in Switzerland. ESA Redu The ISOC is responsible for planning the DSN Goldstone scientific utilisation of the satellite, based on ESA Perth inputs from the gamma-ray science community and taking into account the on-board instrument characteristics. The ISOC will also

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Figure 1. The Redu Integral maintain a copy of the archive generated by the Operational Ground Segment (OGS) are the : central ISDC, thereby providing an additional interface ground stations, the Mission Operations Centre and control to the science community for the distribution of (MOC), and the communications system. The position and IFMS racks the mission’s scientific products. OGS is the sole interface to the satellite; all commands to the spacecraft and on-board The ISDC is responsible for the scientific instruments are generated at the MOC, and all processing of the satellite and for the telemetry from the satellite (spacecraft and archiving of the mission’s scientific products instruments, housekeeping and science and distribution to the science community. In telemetry) is received at the MOC and distributed addition, the ISDC will detect Targets of within the Ground Segment as necessary. Opportunity (TOOs) and Gamma-Ray Bursts (GRBs) from the telemetry received in real-time In the nominal mission scenario, the OGS will from the Operational Ground Segment. TOO take charge of Integral’s operation 1 h 32 min alerts will be provided to the ISOC for the after lift-off, when the satellite separates from possible re-planning of observations during the the Proton upper stage, within visibility of the current or future . GRBs are transient Villafranca (E) and Redu (B) ground stations. phenomena, which will be detected in real time The OGS’s role will terminate with the end of from the incoming science telemetry and will the mission. automatically generate real-time commands to the satellite, for specific setting of the Optical The ground stations will acquire the satellite via Monitoring Camera (OMC), and real-time alerts the -frequency communications at S-band to the science community, so as to allow (2 GHz), and track it during its over the additional specific observations using Integral station. They constitute the front-end interface and other space and/or ground-based between the OGS and the satellite. It is through observatories. The ISDC is supported by the this interface that the commands received from Principal Investigator teams, who are providing MOC and processed at the ground station are instrument-specific software and expertise for modulated in accordance with the relevant ESA processing of the received scientific data. Standards, frequency up-converted and transmitted to the satellite. On the receiving The Integral Operational Ground Segment side, the telemetry received from the satellite is The main architectural elements of the Integral frequency down-converted, demodulated,

58 the integral operational ground segment

decoded and pre-processed at the station to development in the domain of mission-control extract its main components (satellite systems. housekeeping and science telemetry virtual channels) before transmission to the MOC. In The Integral Flight Dynamics System (FDS) is addition, the ground stations will measure the based on the ESOC ORATOS infrastructure satellite range and range-rate. The and provides the functionality required for measurement data will be sent to the MOC, satellite orbit and attitude determination and where they will be used for satellite orbit control, and for mission planning. On the orbit determination and maintenance. During the and attitude side, the system inputs are Early Orbit Phase of the mission in particular, respectively range and range-rate (Doppler) range and range-rate measurements are measurement data received from the ground essential for the initial orbit determination and stations and the spacecraft telemetry from for the calculation and verification of the selected onboard subsystems (AOCS, RCS, manoeuvres required to achieve the final star-trackers, fine star sensors, reaction wheels) operational orbit. received on-line from the IMCS. This telemetry is processed within the FDS on the basis of the The MOC is the of the OGS. It is from the FDDB (Flight Dynamics Data Base), which MOC that all satellite operations, remote consists of a subset of the ODB enhanced with operation of the ESA ground stations, and specific parameters characterising the satellite communication-network operations are from a mechanical and dynamical point of view performed. The main building blocks of the (distribution of masses, alignments, thruster MOC are the Integral Mission Control System specific impulse, etc.) provided by the satellite (IMCS), the Flight Dynamics System and the manufacturer and re-calibrated in flight. The Integral Simulator. attitude profile for the satellite throughout its orbit is determined at the mission-planning The IMCS provides the functionality required for stage and is corrected in real time, as satellite operations, including the final step of necessary, based on the telemetry being the mission-planning process, satellite received. The FDS is also available in real time monitoring and control, and transmission in to the operator to provide any AOCS real-time of the received satellite telemetry to commanding information needed to handle the ISDC, together with the appropriate contingencies. auxiliary data. In addition, the IMCS provides the facilities required for handling the on-board On the mission-planning side, the FDS software-maintenance activities and the generates a Planning Skeleton File for each short- and long-term archiving of telemetry, orbit, defining the windows for spacecraft telecommand and auxiliary data. The archive operations and scientific observation. Once the will be regularly consolidated with the satellite file has been populated by the ISOC with the playback telemetry received from the ground science observations to be conducted during stations after the pass; the consolidated the orbit, the FDS performs a final validation of archive will be regularly dumped (in portions of the resulting product and converts it into a 12 h) onto CD-ROMs, which are to be provided format suitable for the IMCS to derive the to the ISDC for scientific processing. Telemetry Command Schedule for that particular orbit. access to the archive is to be provided, for diagnostic purposes, to authorised external The Simulator is an essential tool for system users (the ISOC and the satellite manufacturer) testing of the MOC components, including the via the Internet. interfaces to the other elements of the ground segment, for validation of the flight-operations A key element for the operation of the IMCS is procedures, and for pre-launch simulations and the Operational Data Base (ODB). For modern the training of the staff responsible for mission , with sophisticated on-board operations. It provides a realistic simulation of functionalities and increased on-board the ground stations and of the satellite’s in-orbit autonomy, the ODB becomes very large, and functionality through accurate software that for Integral contains more than 200 000 modelling based on the Satellite Data Base records. Powerful editors are provided by the satellite manufacturer. Figure 3 required to handle such massive amounts of is a schematic of the MOC computer installation. data efficiently. These have been developed by the Integral Operations Team, based on The OGS Communication System provides commercially available software (Microsoft connectivity between the MOC and the ground Access) and have been adopted for several station, and between the MOC and Science future ESA missions (see article in ESA Ground Segment (ISOC and ISDC). It is based Bulletin No. 103). The IMCS is based on the on leased lines interconnecting the various SCOS 2000 infrastructure, the latest ESA Integral ground-segment elements and

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Figure 2. The Integral Ground Segment architecture

GOLDSTONE REDU OPERATIONS GROUND SEGMENT (OGS)

ESOC

MISSION OPERATIONS CENTRE (ESOC)

INTEGRAL FLIGHT DYNAMICS INTEGRAL MISSION CONTROL SYSTEM SIMULATOR SYSTEM

OBSERVATION RAW PLAN DATA

INTEGRAL SECURE DISTRIBUTION SYSTEMS (ISDS)

SCIENCE GROUND SEGMENT (SGS) ESTEC UNIGENEVA

LONG/SHORT TERM INTEGRAL SCIENCE INTEGRAL SCIENCE REAL-TIME + OFF-LINE OBSERVATION PLANNING OPERATIONS CENTRE (ISOC) DATA CENTRE (ISDC) SCIENCE PROCESSING

INSTRUMENT ON-BOARD SOFTWARE IMAGES

OBSERVATION PI INSTRUMENT TEAMS PROCESSED PROPOSAL DATA

SCIENCE COMMUNITY

providing sufficient to support the adopting similar infrastructures in their ground- required operational traffic. Two protocols are segment designs. Three of the newly developed used for communications within the Integral infrastructure elements used in the Integral ground segment: the traditional protocol based OGS are described in more detail below. on ISO X25 Recommendations for the operational communications between the MOC The SCOS 2000-based Integral Mission and the ESA ground stations, and the more Control System modern TCP/IP protocol suite (as per RFCs) for SCOS 2000 is the latest ESA development in the communications between the MOC and the the field of Spacecraft Control Systems (SCOS) Goldstone ground station and between the and Integral is the first science mission to MOC and the Science Ground Segment. exploit its full functionality and performance for its mission-control system. The IMCS has been State of the art elements in the Integral build around the SCOS 2000 infrastructure, OGS which comprises a telemetry chain for State of the art design has constantly been processing the satellite telemetry received promoted within ESA in the Operational Ground through the ground stations, a generic Segments of ESOC-supported missions, and telecommand chain, and an on-board Integral is no exception. On the contrary, it is software-maintenance subsystem for handling serving as the pilot mission for several new on-board memory images. This infrastructure ground-segment infrastructure elements has been complemented by additional software developed in parallel with the implementation of developments required to accommodate the Integral OGS. The pioneering work of the Integral-specific satellite design elements, both Integral OGS team in the extensive operational in the areas of telemetry and telecommand and validation of these latest developments will be ground-segment interfaces, and specifically of significant advantage for future missions those between the OGS and SGS.

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Other SCOS 2000-provided functionalities Table 2. SCOS-2000 / IMCS functional mapping have been adapted to best fit the satellite’s operational requirements, as indicated in Table Operational Data Base IMCS specific 2. Telemetry Handling The highly distributed architecture of the IMCS- Telemetry reception (Packetiser) IMCS specific SCOS 2000 is based on the innovative SCOS Telemetry processing SCOS 2000 2000 concept of sharing the processing load On-board events handling IMCS specific within a family of servers. Specifically, the IMCS Telemetry displays SCOS 2000 Variable packet display SCOS 2000 includes a main server where all of the kernel Time correlation and stamping IMCS specific telemetry and telecommand functionality are provided, and a secondary server hosting the Telecommand Handling long-term archive, mission archive, archive Command sender (Releaser) SCOS 2000 consolidator and telemetry distribution to Manual stack SCOS 2000 enhanced with IMCS specific external users (SGS). IMCS-SCOS 2000 also Auto stack SCOS 2000 enhanced with IMCS specific has a modern and intuitive man/machine Command verification SCOS 2000 enhanced with IMCS specific interface. On-board queue management SCOS 2000 enhanced with IMCS specific On-board queue model display IMCS specific

On the telemetry side, the main server performs Infrastructure Services the essential general-purpose processing Short-term archive SCOS 2000 (packet extraction and inclusion of headers with Long-term archive SCOS 2000 enhanced with IMCS specific additional information); the telemetry is then Time correlation IMCS specific distributed to the peripheral client work stations Events and actions SCOS 2000 where the (configurable) part of the telemetry Events logging SCOS 2000 required by the specific application is Task launcher SCOS 2000 User-access management SCOS 2000 processed. The main advantage of such a design is optimal usage of processing OBSM Functionality SCOS 2000 enhanced with IMCS specific resources, and consequently increased system performance. MPS Functionality IMCS specific

With Integral being the first SCOS 2000 client External User Access IMCS specific mission, during the IMCS’s development and extensive testing, including operational File Transfer Service IMCS specific validation, intense dialogue between the IMCS Data Distribution SCOS 2000 enhanced with IMCS specific and the SCOS 2000 development teams has taken place, aimed at optimising the further Performance Analysis SCOS 2000 enhanced with IMCS specific releases of both systems. Significant effort has been devoted by the IMCS development team Mission Archive IMCS specific to system integration and configuration aspects, including failure and recovery analysis. Archive Completeness Checker IMCS specific This pioneering work will hopefully benefit CD-ROM Production IMCS specific future missions making use of the SCOS 2000 infrastructure for their ground segments.

inheritance from the XMM mission design. This The Intermediate Frequency Modem System results in the modulation characteristics of the (IFMS) received signal (in terms of carrier suppression) At the beginning of its main development phase being at the limit of the performance specified (Phase-C/D), the Integral mission was the for the standard receivers and demodulators in subject of several trade-offs. These were the current ESA ground-station network. The targeted on the one side at optimisation of the decision was therefore taken to adopt for the satellite’s orbit, taking into account both the main Integral support ground station (Redu), Proton launcher’s performance and the the IFMS, at that time under development, scientific mission requirements, and on the which had a performance specification other at maximising the telemetry allocation to compatible with Integral’s requirements. the various on-board instruments for scientific- return purposes. Ultimately, this has resulted in The IFMS integrates into a single unit the a high bit rate (92 kbps) being transmitted over functionality of the station receiver, including a large distance (orbital apogee: 153 000 km) diversity combination, the tracking subsystem via the radio-frequency link, keeping the on- for satellite range and range-rate board modulation scheme and the transmitter measurement, the remnant-carrier and output power unchanged in terms of its suppressed-carrier demodulator (the latter not

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Figure 3. The Integral applicable to Integral), and finally the uplink The IFMS has undergone several tests in the Mission Operations Centre modulator. The system is based on three newly context of the Integral Radio-Frequency computer-system developed modules: a front-end module Compatibility Tests and has also been validated configuration interfacing at the station intermediate downlink in-flight on the Cluster and XMM missions as frequency (70 MHz) and sampling at 280 part of the Integral system validation process. Msample/s, a number of Generic Digital Signal Processing (GDSP) modules implementing the The Space Link Extension (SLE) services for demodulation and ranging functions, and a Integral cross-support digital modulator module including digital-to- The NASA/JPL ground station at Goldstone analogue conversion and up-conversion to the (Calif.) will be used to cross-support Integral for station uplink intermediate frequency (230 approximately 20% of its operational orbit MHz). Subsystem control and auxiliary functions above the Earth’s radiation belts. For past (time code reader, interface to the station missions, inter-Agency cross-support has monitoring and control computer, etc.) are always been dealt with in an ad-hoc manner largely based on commercial off-the-shelf through mission-specific arrangements involving products. The GSDP modules make use of the exchange of equipment, or mission-specific Field Programmable Gate Arrays (FPGAs) designs for gateways in order to adapt the which, still executing as conventional digital interfaces between the ground-segment gates, can be programmed in software to elements involved in the cross-support (ground implement the specific functionality allocated to stations and/or control centres). the module. A particular feature of the IFMS is its suitability for remote operation and/or The inefficiency of this way of operating was maintenance through the so-called ‘Development recognised some years ago by the Consultative Control Position’. This uses the Internet as the Committee for Space Data Systems (CCSDS) communication protocol and provides a web- which, through its Panel 3, has developed a browser-based interface, allowing remote Cross-Support Reference Model from which control and/or maintenance of the IFMS system the recommendations for the SLE services, via the web. aimed at providing a uniform cross-support

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capability within the CCSDS member agencies, service user functions; and finally the Service have been derived. Management, which includes the exchange of trajectory-prediction, scheduling, resource- The Cross-Support Reference Model was allocation and operations-control procedures. published in a CCSDS Blue Book in May 1996 The parallel ESOC and JPL development work (ref. CCSDS 910.4-8-1). That same year, the was completed at the beginning of 2001 and Integral Project and JPL agreed on an initial the services have subsequently undergone SLE services development for the cross- extensive progressive testing in the Integral support by the Goldstone station of the Integral context, starting from a back-to-back testing of mission. That agreement was endorsed at the application for each service, and continuing agency level by ESA and NASA in 1997. The through trans-Atlantic testing between the basic set required for Integral operation, i.e. Integral MOC and JPL/Goldstone, until their Return All Frames (RAF) and Return Virtual recent final validation including the service- Channel (RVC) on the Return Link (telemetry) management functionality. side and Forward Space Packet (FSP) on the forward-link (command) side, was defined and Conclusions the development work was started both at The distributed architecture of Integral Ground ESOC and JPL. At the Plenary ITCOP meeting Segment has been presented, with the focus in in 1998, at which 7 CCSDS member on the functionality of the Operational Ground agencies were represented, CLTU was selected Segment (OGS), in which state-of-the-art for the forward-link service instead of FSP, for design has been applied. In particular, three reasons of compatibility with legacy systems new major infrastructure developments – the still present in some ground-station networks. main design features of which have been presented here – are being used for the first The SLE services design contains three key time to support the operation of a demanding elements: the Transfer Service Application and ESA scientific mission. The OGS has Protocol specified in the CCSDS Recom- undergone an extensive testing programme to mendation applicable to the service concerned; validate its functionality and interfaces to the the Application Programming Interface, a other Integral Ground Segment elements (ISOC generic design able to accommodate a variety and ISDC), and is now ready to support the of communication middleware technologies, Integral mission. r and supporting both service provider and

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