European Space Operations Centre Research Articles

INTEGRAL mission - Automation of Transponder Swaps Scheduling and Schedule Validation

Human-made satellites allow to broaden the knowledge of the world by discovering new stars, and exoplanets, observing Earth, performing X-ray measurements and more. All satellites need to be controlled from Earth by the Flight Control Team (FCT) consisting of experts from a wide range of fields. The satellite INTEGRAL is controlled from the astronomy control room in the European Space Operations Centre (ESOC) together with XMM-Newton and Gaia. Automation allows a single person to control three spacecrafts simultaneously and helps to reduce operational costs. This paper describes the automation of transponder swaps scheduling and mission schedule validation using tools developed in the programming language Python. Both tools were carefully tested in the defined verification process and marked as ready to be used. The developed tools allow faster mission planning for the INTEGRAL satellite thus saving the human resources of the FCT.

Analysis and Demonstration of First Cross-Support Interferometry Tracking in China Mars Mission

Delta-Differential One-Way Ranging (DeltaDOR) is widely used in deep spacecraft navigation, and cross support could enhance navigation accuracy with more interferometry baselines and longer baseline. In China Mars mission Tianwen-1, formal joint cross-support interferometry tracking between China Satellite Launch and TT&C General (CLTC) and European Space Operations Center (ESOC) under commercial contract was conducted around the critical stages of the mission, such as Mars orbit insertion. Cross-support interferometry is a new challenge to CLTC, as the correlator for routine DeltaDOR measurements do not fit for cross support, because of observable definition, blind station clock searching, and so on. This paper discusses the new method and algorithm adopted in joint cross support, especially for spacecraft tone signal processing and clock estimation when correlating with the data of two stations from different agencies. Results of the cross-support interferometry tracking activities are also analyzed. Observables from CLTC and ESOC are consistent with each other, and the difference in observables is in the order of tens of ps. All the baselines are induced to evaluate the accuracy of the spacecraft orbit determined and predicted by CLTC, and the DeltaDOR residuals have a root-mean-square (RMS) better than 0.5 ns (the goal is 1 ns), which could enhance the confidence of the orbit accuracy and the effectiveness of control parameters during critical orbit operation.

Accuracy evaluation of XUST’s global ionospheric products

The ionosphere research team of Xi'an University of Science and Technology (XUST) has been committing to high-precision global ionospheric modeling research since 2012. The agency adopted spherical harmonic functions to generate GNSS (Global Navigation Satellite System) global ionospheric product XANG and multi-source data fusion global ionospheric product XAMG. In this essay, we take International GNSS Service (IGS) global ionospheric maps (GIMs) products as a reference to verify and analyze the accuracy of GIMs products produced by XUST in detail from three different aspects. The internal and external evaluation results of GNSS dSTEC indicate that the GIMs products of XUST are consistent with the GIMs products of other analysis centers. In contrast to the Jason-2/-3 VTEC, the STD between XANG and Jason-2 during 2016–2018 is about 2.42–3.11 TECU. The STD between XANG and Jason-3 is about 2.40–3.11 TECU, which is equivalent to that of China Academy of Sciences (CAS) and Jet Propulsion Laboratory (JPL), better than that of the Center for Orbit Determination in Europe (CODE), European Space Operations Center of European Space Agency (ESA) and Wuhan University (WHU), and slightly worse than that of Universitat Politècnica de Catalunya/IonSAT (UPC). Besides, we figure out that the accuracy of GIM products in approximately 60% of the ocean areas has been significantly improved after adding space-based data by comparing the two developed global ionospheric products. Finally, we evaluated the product performance of XUST in single-frequency precise point positioning (SF-PPP) with convergence time and positioning accuracy of standard single-frequency PPP as reference. In terms of average convergence time, the ionospheric delay processing capabilities of XANG and XAMG are comparable to other GIMs and even better than ESAG and JPLG in some regions. In terms of positioning accuracy, the positioning accuracy of XANG as an external ionospheric constraint is better than that of XAMG, and both are better than ESAG, JPLG and IGSG, and slightly worse than CASG and CODG.

BepiColombo Ground Segment and Mission Operations

The ESA/JAXA BepiColombo mission to Mercury was launched in October 2018. It includes two scientific Mercury orbiters, flying as a single stack during the seven years interplanetary transfer, and as individual spacecraft operated by their respective space Agencies ESA and JAXA once deployed in their respective scientific orbit around Mercury. Three ground segments are closely collaborating on this mission. The European Space Operations Center of the European Space Agency, in Darmstadt, Germany, responsible for mission operations of the composite stack during the interplanetary transfer and of the Mercury Planetary Orbiter (MPO) once at Mercury, the JAXA Sagamihara Space Operation Center (SSOC) in Sagamihara, Japan, responsible for Mercury Magnetospheric Orbiter (MMO) operations throughout the mission, and the European Space Astronomy Center of the European Space Agency, in Villanueva de la Canada, Spain, responsible for MPO scientific archiving and Mercury science operations. The mission benefits from infrastructure and concepts developed on previous interplanetary missions of ESA and JAXA. However, it also includes specific operational challenges, such as electric propulsion, and a complex Mercury Orbit Insertion sequence, exploiting weak stability boundaries, and interleaving three module separations with 15 chemical propulsion manoeuvers to deliver MPO and MMO in their respective science orbits, requiring specific developments and operational approaches. In view of the nominal mission duration of 8.5 years, the mission also requires the adoption of specific measures for knowledge preservation and long-term maintenance.

Uncertainties in GPS-based operational orbit determination: A case study of the Sentinel-1 and Sentinel-2 satellites

ABSTRACTThe European Space Operations Centre currently operates five Copernicus Sentinel satellites in the framework of Europe’s Copernicus Earth observation programme. The routine operations rely on a daily orbit determination, carried out on-ground, consisting in a least-squares fit of a dynamical model to GPS navigation solutions generated on-board. The purpose of this paper is the estimation of realistic uncertainties on this daily determined state vector. By comparison with the orbit derived by Precise Orbit Determination, we estimate the 1-sigma errors at approximately 0.5m and 0.5mm/s. Non-stationary errors in the navigation solution preclude their characterisation with a constant covariance matrix. Error whitening is achieved by decreasing the signal-to-noise ratio in the errors through the use of underestimated weights on the data. The approach keeps the errors on the derived state vector unchanged and allows the covariance on the state vector to become realistic.

Yaw attitude modeling for BeiDou I06 and BeiDou-3 satellites

The estimated yaw angles of the BeiDou I06 satellite demonstrated that the satellite experienced midnight- or noon-turn maneuvers when the sun elevation angle above the orbital plane (β angle) was in the range of [− 3°, + 3°] and the orbital angle was in the range of approximately [− 6°, 6°] or [174°, 186°]. The behavior of yaw attitude maneuvers in the vicinity of the midnight and noon points was identical. An alternative yaw attitude model similar to that used for the Galileo Full-Operation-Capacity (FOC) satellites was developed on the basis of the estimated BeiDou I06 yaw angles with an accuracy of approximately 3.4° to reproduce the yaw attitude behaviors. However, a discrepancy in the form of a reversal in yaw direction during the midnight-turn maneuver was observed for BeiDou I06 when the β angle was extremely small (< 0.1°). The derived yaw attitude model was proved to model the yaw attitude of the BeiDou-3 experimental satellites, and reduces the observation residuals in the vicinity of the midnight and noon points to normal levels, and facilitates continuous satellite clock estimation during eclipse periods. Compared to the yaw attitude model developed by the European Space Operations Centre (ESOC), a similar performance has been achieved with maximum yaw differences up to 9.2° when the β angle is close to 0°. The average agreement between the models is about 1°. However, the ESOC model was developed based on a patented eclipsing model, the developed model in this study is open access.

Operational support to collision avoidance activities by ESA’s space debris office

The European Space Agency’s (ESA) Space Debris Office provides a service to support operational collision avoidance activities. This support currently covers ESA’s missions Cryosat-2, Sentinel-1A and -2A, the constellation of Swarm-A/B/C in low-Earth orbit (LEO), as well as missions of third-party customers. In this work, we describe the current collision avoidance process for ESA and third-party missions in LEO. We give an overview on the upgrades developed and implemented since the advent of conjunction summary messages (CSM)/conjunction data messages (CDM), addressing conjunction event detection, collision risk assessment, orbit determination, orbit and covariance propagation, process control, and data handling. We pay special attention to the effect of warning thresholds on the risk reduction and manoeuvre rates, as they are established through risk mitigation and analysis tools, such as ESA’s Debris Risk Assessment and Mitigation Analysis (DRAMA) software suite. To handle the large number of CDMs and the associated risk analyses, a database-centric approach has been developed. All CDMs and risk analysis results are stored in a database. In this way, a temporary local “mini-catalogue” of objects close to our target spacecraft is obtained, which can be used, e.g., for manoeuvre screening and to update the risk analysis whenever a new ephemeris becomes available from the flight dynamics team. The database is also used as the backbone for a Web-based tool, which consists of the visualization component and a collaboration tool that facilitates the status monitoring and task allocation within the support team as well as communication with the control team. The visualization component further supports the information sharing by displaying target and chaser motion over time along with the involved uncertainties. The Web-based solution optimally meets the needs for a concise and easy-to-use way to obtain a situation picture in a very short time, and the support for third-party missions not operated from the European Space Operations Centre (ESOC). Finally, we provide statistics on the identified conjunction events, taking into account the known significant changes in the LEO orbital environment and share ESA’s experience along with recent examples.

Rosetta mission operations for landing

The International Rosetta Mission of the European Space Agency (ESA) was launched on 2nd March 2004 on its 10 year journey to comet Churyumov-Gerasimenko and has reached it early August 2014. The main mission objectives were to perform close observations of the comet nucleus throughout its orbit around the Sun and deliver the lander Philae to its surface. This paper describers the activities at mission operations level that allowed the landing of Philae.The landing preparation phase was mainly characterised by the definition of the landing selection process, to which several parties contributed, and by the definition of the strategy for comet characterisation, the orbital strategy for lander delivery, and the definition and validation of the operations timeline.The definition of the landing site selection process involved almost all components of the mission team; Rosetta has been the first, and so far only mission, that could not rely on data collected by previous missions for the landing site selection. This forced the teams to include an intensive observation campaign as a mandatory part of the process; several science teams actively contributed to this campaign thus making results from science observations part of the mandatory operational products. The time allocated to the comet characterisation phase was in the order of a few weeks and all the processes, tools, and interfaces required an extensive planning an validation. Being the descent of Philae purely ballistic, the main driver for the orbital strategy was the capability to accurately control the position and velocity of Rosetta at Philae’s separation. The resulting operations timeline had to merge this need of frequent orbit determination and control with the complexity of the ground segment and the inherent risk of problems when doing critical activities in short times.This paper describes the contribution of the Mission Control Centre (MOC) at the European Space Operations Centre (ESOC) to this mission phase and the lessons learned that can be derived from this experience.

Rosetta: Making History!

The first spacecraft to orbit a comet was Rosetta, which was launched by a European Space Operations Centre. Its aim is to study the comet 67P/Churyumov-Gerasimenko. The details of the orbiter and lander have been explained here.

Goce flight dynamics operations from an orbital perspective

The Gravity Field and Steady-State Ocean Circulation Explorer mission GOCE was successfully launched on the 17 th of March 2009 from the Plesetsk Cosmodrome on a Rockot launch vehicle and is since controlled from ESA's European Space Operations Centre (ESOC) in Darmstadt, Germany. The spacecraft is the first Earth Explorer Core Mission of the ESA Living Planet Program and its main objective is to obtain detailed measurements of the Earth's gravitational field to an unprecedented accuracy. The purpose of this paper is to report on the experiences of operating such an unique spacecraft from a flight dynamics point of view with an emphasis on the orbital aspects of the mission during the different phases of the mission (LEOP, commissioning, routine phases, and contingencies).

New improved orbit solutions for the ERS-1 and ERS-2 satellites

Improved orbit solutions of the European Remote Sensing Satellites ERS-1 and ERS-2 have been computed in the ITRF2005 terrestrial reference frame using the recent models based mainly on IERS Conventions 2003. These solutions cover the periods 3 August 1991 to 8 July 1996 for ERS-1, and 3 May 1995 to 4 July 2003 for ERS-2. For each satellite, the final orbit solution is based on a combination of three separate orbit solutions independently computed at the Delft Institute of Earth Observation and Space Systems (DEOS) of the Delft University of Technology (The Netherlands), the Navigation Support Office of the European Space Operations Centre (ESOC, Germany) and the Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences (Germany) using three different software packages for precise orbit determination, but using the same models in the same terrestrial reference frame within the European Space Agency (ESA) project ‘Reprocessing of Altimeter Products for ERS (REAPER)’. Validation using radar altimeter data indicates that the new combined orbits of ERS-1 and ERS-2 computed by us are significantly more accurate, approaching the 2–3cm level in radial direction, than previously available orbit solutions.

Benefits of Using Innovative Tools for Diagnostics and Planning in ESA Mission Operations

Future European Space Agency (ESA) space missions are demanding and driving new operations concepts for increased on-board autonomy, for flexible and robust planning and scheduling services, and for ground capabilities to agglomerate and process a huge amount of downlinked data (e.g., tens of thousands of telemetry parameters) to extract high-level information and knowledge. Mission control will have to cope with maintaining and programming challenging missions such as interplanetary probes, complex scientific missions, and a constellation of earth-observation missions. The process of innovation in these areas is already progressing at the European Space Operations Centre (ESOC) of the ESA, and this paper highlights specific achievements and trends in the area of spacecraft diagnosis and mission planning and scheduling by making use of a variety of technologies and techniques. The discussion then focuses on the tools’ operational impact and on the expected trends in the future.

Managing knowledge for spacecraft operations at ESOC

PurposeThe purpose of this paper is to describe the current knowledge management activities at the European Space Operations Centre (ESOC), specifically in knowledge capture, sharing and preservation and focusing on the developed and adopted methods and on the results obtained related to the process of knowledge capture using video‐recording of experts.Design/methodology/approachThe knowledge management activities undertaken at ESOC during the past years have been organized into four phases: preliminary study and investigation on knowledge management systems including a review of already existing initiatives; a pilot project within the Flight Dynamics area (a key technical domain within ESOC taking care of the orbit and attitude aspects for the satellite operations) with respect to the questions of knowledge transfer and its barriers; the definition of the ESOC knowledge management system; and the introduction of knowledge capture procedures.FindingsThe inventory of the knowledge assets and the analysis of the knowledge coverage and criticality were essential to be able to identify the existing knowledge in specific areas and to perform a gap analysis. Through this analysis, it is now possible to identify those areas requiring improvement and to allow management to make reliable decisions for which areas the knowledge level should be increased.Research limitations/implicationsWith regard to the firm strategic behaviours, it seems particularly crucial to exploit all three dimensions of proximity, in order to guarantee openness and sustain innovativeness and competitiveness. Concerning policy implications, the local governments should address their actions to help and promote the openness of technology districts and the formation of technology clusters. With this aim, actions should be devoted also to sustain single local firms that are part of a technology cluster but not of a technology district. These, in fact, by increasing their competitive position, may generate positive externalities in the local area, fostering the diffusion and sharing of knowledge in the area and then, acting as knowledge gatekeepers for the whole area.Originality/valueThe paper describes the implementation strategy of the knowledge management within ESOC. Based on this practical experience, guidelines can be derived for the implementation of a more general knowledge management system in the aerospace industry.

Urban, regional, national and global knowledge capital

PurposeThe purpose of this paper is to introduce the JKM 2010 annual special issue on knowledge based development (KBD) with reference to the multi‐level analysis characteristic of the field.Design/methodology/approachA description of the knowledge management approach at ESOC (European Space Operations Centre of the European Space Agency) is provided first. At the core of this approach is the breakdown of knowledge in individual technical domains followed by coverage analysis and criticality assessment. Such a framework becomes the reference for best knowledge acquisition, transfer and storage locus identification and subsequent knowledge management practices and guidelines.FindingsKBD provides an integrated framework to account for multidisciplinary analyses and multilevel practices in knowledge capital generation, distribution and utilization.Originality/valueThe collection of papers included in the annual special issue on KBD provides a representative, composite view of the research topics and applications concerns in the field. Involving a number of disciplines and levels of analysis, issues ranging from the technological gatekeeper to global knowledge flows show the interdependence of KBD concepts and tools.

Infusion of innovative technologies for mission operations

The Advanced Mission Concepts and Technologies Office (Mission Technologies Office, MTO for short) at the European Space Operations Centre (ESOC) of ESA is entrusted with research and development of innovative mission operations concepts systems and provides operations support to special projects. Visions of future missions and requests for improvements from currently flying missions are the two major sources of inspiration to conceptualize innovative or improved mission operations processes. They include monitoring and diagnostics, planning and scheduling, resource management and optimization. The newly identified operations concepts are then proved by means of prototypes, built with embedded, enabling technology and deployed as shadow applications in mission operations for an extended validation phase. The technology so far exploited includes informatics, artificial intelligence and operational research branches. Recent outstanding results include artificial intelligence planning and scheduling applications for Mars Express, advanced integrated space weather monitoring system for the Integral space telescope and a suite of growing client applications for MUST (Mission Utilities Support Tools). The research, development and validation activities at the Mission technologies office are performed together with a network of research institutes across Europe. The objective is narrowing the gap between enabling and innovative technology and space mission operations. The paper first addresses samples of technology infusion cases with their lessons learnt. The second part is focused on the process and the methodology used at the Mission technologies office to fulfill its objectives.

IDS contribution to ITRF2008

For the first time, the International DORIS Service (IDS) has produced a technique level combination based on the contributions of seven analysis centers (ACs), including the European Space Operations Center (ESOC), Geodetic Observatory Pecny (GOP), Geoscience Australia (GAU), the NASA Goddard Space Flight Center (GSFC), the Institut Géographique National (IGN), the Institute of Astronomy, Russian Academy of Sciences (INASAN, named as INA), and CNES/CLS (named as LCA). The ACs used five different software packages to process the DORIS data from 1992 to 2008, including NAPEOS (ESA), Bernese (GOP), GEODYN (GAU, GSC), GIPSY/OASIS (INA), and GINS (LCA). The data from seven DORIS satellites, TOPEX/Poseidon, SPOT-2, SPOT-3, SPOT-4, SPOT-5, Envisat and Jason-1 were processed and all the analysis centers produced weekly SINEX files in either variance–covariance or normal equation format. The processing by the analysis centers used the latest GRACE-derived gravity models, forward modelling of atmospheric gravity, updates to the radiation pressure modelling to improve the DORIS geocenter solutions, denser parameterization of empirically determined drag coefficients to improve station and EOP solutions, especially near the solar maximum in 2001–2002, updated troposphere mapping functions, and an ITRF2005-derived station set for orbit determination, DPOD2005. The CATREF software was used to process the weekly AC solutions, and produce three iterations of an IDS global weekly combination. Between the development of the initial solution IDS-1, and the final solution, IDS-3, the ACs improved their analysis strategies and submitted updated solutions to eliminate troposphere-derived biases in the solution scale, to reduce drag-related degradations in station positioning, and to refine the estimation strategy to improve the combination geocenter solution. An analysis of the frequency content of the individual AC geocenter and scale solutions was used as the basis to define the scale and geocenter of the IDS-3 combination. The final IDS-3 combination has an internal position consistency (WRMS) that is 15 to 20 mm before 2002 and 8 to 10 mm after 2002, when 4 or 5 satellites contribute to the weekly solutions. The final IDS-3 combination includes solutions for 130 DORIS stations on 67 different sites of which 35 have occupations over 16 years (1993.0–2009.0). The EOPs from the IDS-3 combination were compared with the IERS 05 C04 time series and the RMS agreement was 0.24 mas and 0.35 mas for the X and Y components of polar motion. The comparison to ITRF2005 in station position shows an agreement of 6 to 8 mm RMS in horizontal and 10.3 mm in height. The RMS comparison to ITRF2005 in station velocity is at 1.8 mm/year on the East component, to 1.2 mm/year in North component and 1.6 mm/year in height.

DORIS processing at the European Space Operations Centre

This paper gives an overview of the DORIS related activities at the Navigation Support Office of the European Space Operations Centre. The DORIS activities were started in 2002 because of the launch of the Envisat satellite where ESOC is responsible for the validation of the Envisat Precise Orbits and a brief overview of the key Envisat activities at ESOC is given. Typical orbit comparison RMS values between the CNES POE (GDR-C) and the ESOC POD solution is 6.5, 18.8 and 23.1 mm in radial-, along- and cross-track direction. In the framework of the generation of the ITRF2008 ESOC participated in the reprocessing of all three space geodetic techniques; DORIS, SLR, and GPS. Here the main results of our DORIS reprocessing, in the framework of the International DORIS Service (IDS), are given. The WRMS of the weekly ESOC solution (esawd03) for the 2004–2009 period compared to the IDS-1 combined solution is of the order of 12 mm. Based on the long time series of homogeneously processed data a closer look is taken at the estimated solar radiation pressure parameters of the different satellites used in this DORIS analysis. The main aim being the stabilization of the Z-component of the geocentre estimates. We conclude that the ESOC participation to the IDS ITRF2008 contribution has been beneficial for both ESOC and the IDS. ESOC has profited significantly from the very open and direct communications and comparisons that took place within the IDS during the reprocessing campaign.

Exploration missions in the Sun–Earth–Moon system: A detailed view on selected transfer problems

The Astronautics and Space Station Department of the Universitaet Stuttgart has developed a design environment for the conceptual design of manned space missions. With the assistance of the ESA European Space Operations Center this design environment has been extended to cover exploration missions involving the areas of the collinear Earth–Moon and Sun–Earth libration points, which are of interest as an alternative staging location to the low lunar orbit approach for lunar exploration and for satellite servicing missions, respectively. To allow for a reliable mission design, the transfer times, the Δ V and variations in the Δ V for transfers between the different locations in the Sun–Earth–Moon system must be known, especially taking the rendezvous constraints and safety issues for human spaceflight missions into account. The results of the investigations presented in this paper cover transfer trajectories from Earth to different types of orbits about the collinear Earth–Moon libration points 1 and 2 and further on to the Moon. For the Earth to Earth–Moon libration point transfer, direct trajectories, fly-bys at the Moon and trajectories via the weak stability boundary region of the Sun–Earth system are treated.

Overview of the knowledge management system in ESA/ESOC

This paper discusses the knowledge management (KM) system as implemented in a pilot project at the European Space Operations Centre (ESOC) of the European Space Agency (ESA). By means of audits, we have identified the main knowledge fields in our domain, weighted their importance in the short, medium and long terms, and derived KM requirements in order to preserve, maintain, share and enhance relevant knowledge. The preliminary results from the knowledge audits were analysed and discussed by domain experts, showing that the KM process put in place has been successfully validated and appropriate measures, like continuous training, have to be put in place. The KM requirements were then mapped on the existing KM infrastructure and the available KM resources in order to assess the status of KM at ESOC and to recommend its evolution. Finally, some additional suggestions are made regarding the future of the initiative and potential steps that might be taken to further support KM within ESOC.

Development of a new three‐dimensional mathematical ionosphere model at European Space Agency/European Space Operations Centre

For several years a clear trend from the application of classical so‐called “single layer” models to attempts to model the ionosphere in accordance to its real three‐dimensional nature can be observed (see, e.g., Scherliess et al., 2003; Hernández‐Pajares et al., 1999). European Space Agency (ESA)/European Space Operations Centre (ESOC) commenced in 1998 employing a three‐dimensional (3‐D) model for ionosphere processing (Feltens, 1998; Feltens et al., 1998). This first version of a 3‐D model at ESOC model was based on a simple Chapman profile approach, assuming that the vertical component of the ionosphere could be mathematically expressed in terms of a single β‐layer Chapman profile function. The profile function's parameters, maximum electron density N0 and its height h0, were in turn expressed as surface functions of geomagnetic latitude and local time whose coefficients were estimated. In this way a horizontal variation of N0 and h0 was modeled, and the profile function varied vertically, depending on the actual N0 and h0 values at a certain location. The ionosphere, however, consists of several layers. Additionally, the plasmasphere on top of the ionosphere must be accounted for, and the scale height, needed to compute the profile function z‐parameter, is height‐dependent. Furthermore, some of the ionosphere layers are so called α‐layers and some parts of the ionosphere show special behavior. All these effects must be accounted for in a proper 3‐D mathematical modeling. It is the intent of this paper to give a substantial overview over the 3‐D ionosphere models developed at ESOC and their current testing and implementation status.