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Introduction BR-110 layout 2/21/01 10:57 AM Page 2 INTRODUCTION The mandate of the European Space Operations Satellite nativation is the process by which a Centre is to conduct mission operations for satellite is brought to and kept in the desired ESA Satellites and to establish, operate and orbit and by which the required body maintain the necessary ground segment orientation (attitude) is acquired. It involves infrastructure. determination, prediction and control of the satellite orbit hand in hand with determination and control of the satellite attitude. Changes in Mission Operations orbit and attitude are effected by the Mission operations is the process involving execution of often complex manoeuvres operations planning, satellite monitoring and under ground control, using for example the control, in-orbit navigation, and data processing on-board thrusters. and distribution, by which the satellite mission objectives are achieved, be they the collection of meteorological or scientific data or the Ground Segment Infrastructure provision of a telecommunication service. ESOC has established a comprehensive ground segment infrastructure suitable and ready to Monitoring and control starts as soon as the support various types of missions, each having satellite is separated from the launch vehicle, its different demands, requirements and purpose being to activate the on-board systems constraints. This infrastructure encompasses all for the tasks ahead in the challenging facilities and services needed for mission environment of space. Soon afterwards, the operations and includes a network of ground payload has to be configured to enable it to stations around the world, a number of control play its part in exploiting the mission according centres, payload data-processing facilities, to plans based on the wishes of the users. It is a spacecraft control systems, simulation systems round-the-clock task performed throughout the and communications systems. All ground duration of the mission. facilities have to be highly reliable and maintainable: cost-effectiveness in operations is Whenever the satellite is visible from the achieved by careful introduction of new ground, health and status are monitored, a task technology. Lift-off of an Ariane-5 involving the analysis of as many as five launcher thousand telemetry parameters every minute. The infrastructure is primarily intended for ESA Operations are effected through instructions missions, but can be made available to external sent to the spacecraft in the form of Agencies and industry. Depending on the type telecommands to change on-board settings or of agreement, ESOC can provide all types of to activate payload equipment. Continuous service, from full mission operations to monitoring is necessary to verify correct consultancy. execution of up to one hundred commands per minute. 2 BR-110 layout 2/21/01 10:58 AM Page 3 Mission Success The mission operations phase is generally the final and arguably the most critical phase in a space project, during which the return on investment is to be realised: the return in this case is the quantity, quality and availabiliity of mission products or services, which in turn depend heavily on the effectiveness of mission operations. Mission success is then gauged by the return of mission products, and by the ability to recover from deficiencies or anomalies in the orbiting spacecraft. Since 1967 ESOC has successfully conducted more than 40 satellite missions (Appendix 1), each presenting a different challenge to the operations staff, including: – Science missions in near-Earth, highly swing-by around the Earth in 1990 took One of the first Control eccentric and interplanetary orbits, Giotto into an orbit in which it was to Rooms for the ESRO-2 – Microgravity missions in near-Earth orbit encounter comet Grigg-Skjellerup two years Mission – Earth observation missions in near-Earth later: the operations involved in the orbit hibernation and blind reactivation of the – Meteorological missions in geostationary spacecraft are of historical significance. orbit – The successful execution of the Eureca – Telecommunications missions in (European Retrievable Carrier) mission, geostationary orbit including the deployment and retrieval of the spacecraft by the US Space Shuttle Of particular note are the following missions, proved ESOC’s ability to control from the for which ESOC had full responsibility: ground complex rendezvous and docking – The navigation of the Giotto spacecraft to manoeuvres in space, in close cooperation encounter Comet Halley in 1986 was a with another Agency (NASA). spectacular success. After surviving the encounter, a historical gravity-assist Multi-mission control Area at ESOC 3 BR-110 layout 2/21/01 10:58 AM Page 4 Image composition of MOP-2 and ADC – Between 1977 and 1995, ESOC conducted Olympus and Hipparcos, the latter being of the six European Meteosat missions particular importance. In August 1989, involving full spacecraft monitoring and Hipparcos, which was intended to undertake a control, navigation, payload control, payload 100 000-star survey from geostationary orbit, data processing, image data extraction, data was left stranded in transfer orbit when its Meteosat MOP-1 dissemination and archiving. The service apogee boost motor failed to ignite. Within provided to the meteorological community three months a revised mission had been was exemplary in its quality and continuous defined and the necessary modifications to the availability. ground segment and on-board software had been made, enabling the mission to be In total, four otherwise doomed missions have conducted in the unfavourable elliptical orbit. Eureca returning to the been recovered by ESOC, namely TD-1A, Geos-1, Outliving the planned mission duration, Space Shuttle Hipparcos operations continued for three years to successfully achieve all intended scientific objectives. The task of operations as conducted from ESOC is now a well-developed discipline involving highly skilled staff in intensive activities both in the preparations phase and in the operations execution phase. The philosophy for the control and operation of the various types of satellite intended to serve the needs of ESA’s different spheres of interest is founded on the principles established during more than 30 years’ experience. ESOC is recognised as a leading centre of excellence in Space Mission Operations that is unique in Europe. Conscious of the need to vigilantly maintain its high standards of quality, ESOC achieved ISO 9001 certification in 1999. This extensive expertise allied with the comprehensive and technologically advanced ground segment infrastructure, ensures that ESOC maintains its position as mission-operations authority for ESA satellites and guarantees that, as such, it constitutes an invaluable resource for the Agency’s future space projects. 4 BR-110 layout 2/21/01 10:58 AM Page 5 PREPARING THE MISSION Introduction The various units within ESOC then embark on In most cases, ESOC involvement starts when the execution of the preparatory tasks that the mission and satellite concept is being have to be completed during the period developed, especially as regards analysis of the covering the satellite’s development, integration type of orbit required, the provisions that need and test programme (usually about five years). to be included in the spacecraft design to The culmination of the preparatory phase is the facilitate the operational tasks and the ground- full readiness and availability of all facilities, segment facilities required to support the services and personnel and the ‘freezing’ of mission. Such involvement continues throughout all software systems, hardware and the assessment phase and the satellite Phase A documentation prior to the start of mission studies. operations. Once a mission has been selected, ESOC will be The principal activities to be undertaken by involved in providing operations requirements ESOC in the mission preparations phase cover a applicable to the spacecraft Phases B and C/D, in wide range of disciplines, as illustrated in the the formulation of a thorough specification of the Figure below and described in the following ground segment services and facilities needed to sections. support the mission and in establishing the necessary interfaces for exchange of data and information between the customer and ESOC. 5 BR-110 layout 2/21/01 10:58 AM Page 6 Mission Analysis Mission analysis is the term used to describe the mathematical analysis of satellite orbits, performed to determine how best to achieve the Table 1: Influence of orbit on satellite design mission objectives in terms of achievable orbit, launch vehicle, ground station utilisation, Mission Type will drive: operational complexity and lifetime. – Launch energy vs. satellite mass – Selection of launch vehicle and orbit injection strategy These very important aspects are considered by – Satellite Dimensions ESOC early in the formative stage of the mission design in close cooperation with the Project. Orbit Injection and Control requirements will determine: This is essential, since, later on, the results will – Orbit Control concepts (mono/bi-propellant/solid fuel) be given to the satellite Prime Contractor as – Number and type of manoeuvres needed design driving information, for the selected orbit – Fuel needed on board satellite and the derived operations concept will have an influence on many aspects of the satellite Actual Orbit will determine: design, as can be seen from Table 1. – Orbital lifetime
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