the integral operational ground segment 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 orbit 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 satellite is to be Phase, the spacecraft 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. rocket 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 modulation, demodulation 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 57 r bulletin 111 — august 2002 Figure 1. The Redu Integral maintain a copy of the archive generated by the Operational Ground Segment (OGS) are the ground station: central ISDC, thereby providing an additional interface ground stations, the Mission Operations Centre monitoring 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 telemetry 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 orbits. 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 radio-frequency communications at S-band to the science community, so as to allow (2 GHz), and track it during its pass 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 heart 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