Among all the missions operated at ESA/European Space Operations Centre the ones that are impacted most by potential collision warnings are the Earth Observation satellites due to the distribution of the space debris within the low earth orbit (LEO) range.

These include more than 10 spacecraft launched and operated by ESOC: the Copernicus fleet (Sentinel 1A, Sentinel 1B, Sentinel 2A, Sentinel 2B, Sentinel 3A, Sentinel 3B and Sentinel 5P) and the Earth explorers (GOCE, CryoSat-2, Swarm constellation A/B/C and recently Aeolus), all of them launched between 2009 (GOCE) and 2018 (Aeolus) and before them the historical space missions Envisat, ERS-1 and ERS-2.

In the last 10 years all missions had required a constant analysis of the collision warnings received and in several occasions a debris avoidance manoeuvre was needed, even during critical operational phases mission such as the launch and early orbit phases, to reduce the risk to a predefined and safe probability level. In addition, each time a Collision Avoidance Manoeuvre (CAM) is performed, the continuity of the science data return is impacted, together with the fuel consumption and operational teams availability.

So far tens of thousands conjunction events have been assessed and few dozen resulted in a collision avoidance manoeuvre, confirming the reliability and robustness of the improved statistical model around LEO.

The space debris awareness and environment has changed a lot in the last decades with a huge increment of collision warnings. The access to more accurate and timely debris orbit predictions has allowed ESOC to implement a more robust and efficient collision avoidance process: the ESA Space Debris Office (SDO) could improve the characterisation of the collision risk due to single close approaches as well as their statistical distribution over mission lifetimes. This made focusing on the events presenting the highest risk more efficient, i.e. mitigating more risk without increasing the frequency of avoidance manoeuvres. At the same time it allowed improving the overall monitoring activities up to the Flight Control Team procedures that have been adapted to the new scenarios.

Several statistical parameters of the Collision Avoidance Manoeuvres (CAM) warnings, risk analysis and operations for the Copernicus and Earth Explorer missions since 2009 are addressed. Lessons learned and the impact to the spacecraft design including consumable budget are also assessed.

The Earth Clouds, Aerosol and Radiation Explorer (EarthCARE) mission is the sixth of the European Space Agency’s (ESA) Earth Explorers that are designed to form the science and research element of ESA’s Living Planet programme. EarthCARE, a cooperative mission with the Japanese Space Agency (JAXA), adresses the need for a better understanding of the interactions between cloud, radiative and aerosol processes that play a role in climate regulation. The mission aims to improve the representation and understanding of the Earth's radiative balance in climate and numerical weather forecast models by acquiring vertical profiles of clouds and aerosols, as well as the radiances at the top of the atmosphere.

EarthCARE will be the largest and most complex Earth Observation satellite operated at ESOC since Envisat. The spacecraft features four instruments – two passive and two active. The passive instruments are the Multi-Spectral Imager (MSI) and the Broadband Radiometer (BBR). The first of the active instruments is an ultraviolet LIDAR – the Atmospheric LIDAR (ATLID) – a sister instrument to the ALADIN laser on ESA’s Aeolus spacecraft. The second of the active instruments is provided by JAXA – the Cloud Profiling Radar – a microwave radar with a large deployable reflector to measure vertical profiles of clouds. A key advantage of the mission will be the synergistic products generated from all of these co-registered instruments working in parallel. However, this also imposes challenges on the operations of the payload to ensure maximum availability of simultaneous instrument operations. The paper will describe the concept that has been designed to cope with these challenges, particularly in the case of orbit maintenance activities that could impact the science availability. A novel method of operating the thrusters will be described – the small delta-v mode – that could allow regular orbit maintenance with minimal impact to ongoing science operations.

The mission is designed to operate in a sun-synchronous polar orbit at 393km altitude – chosen as a trade-off between the needs of the active and the passive instruments. This low altitude implies significant atmospheric drag, which has a high degree of unpredictable variability due to the response of the atmosphere to solar conditions. This therefore imposes challenges to the operations to ensure that the orbit is sufficiently tightly maintained to meet the science requirements – currently the routine operations target is a deadband of +/-25km from the reference ground track. As well as conventional ground track maintenance there is also the need for high prediction accuracy as the CPR instrument features a requirement to accurately locate mobile calibration equipment directly beneath the spacecraft to perform active radar calibration during overflights. In addition to the routine ground track maintenance, consideration for collision avoidance manoeuvres must also be made. The paper will describe the operational implications of these challenges and the proposed plan for biased deadband operations that should allow sufficient collision avoidance capability with minimal impact to the ongoing science mission.

Another of the major operational challenges of the EarthCARE mission will be to conduct all necessary activities, including planning and interagency coordination with JAXA, with a minimal resource profile. This foresees complete lights-out operations outside of working hours and a limit of two commanding passes per day in the mission’s routine phase. This must be combined with the maximum possible streamlining of the planning workflow to alleviate the need for a large team of engineers planning and monitoring the mission on ground. This has necessitated the development of an operations concept that is flexible enough to meet the needs of the mission while being as lightweight as possible to ensure that the resource constraints are met. In addition, latencies within the planning system have been carefully balanced to ensure that operations can be executed in a timely manner while still allowing for intra and inter-agency coordination. All of this must also take into account that at no point can spacecraft safety be impacted.

This paper will describe the EarthCARE mission and the operations concept that has been developed for it. It will cover the ways in which this concept has been developed to meet the challenges mentioned above – the complex operations of synergistic instruments, the challenges for orbit maintenance and prediction in a high drag environment and the optimization of resources despite the need for a flexible planning approach with both internal and external interfaces. In addition, the paper will describe how the operations concept has been developed to take advantage of new technologies present, such as position-based commanding and small delta-v manoeuvres.

The purpose of this study is to assess the improvement in terms of coverage and revisit time for Sentinel-1/2/3 when adding a third unit to the existing 2-satellite configurations, and also to address the injection operational issues arising from a 3-satellite configuration.
For Sentinel-1, we focus on the coverage over Europe and the Arctic. We first analyze the case where Sentinel-1B remains at its current position and determine the optimal position for the third unit, given the restricted amount of slots on the orbit. We then consider the optimal configuration where we relocate Sentinel-1B and add a third unit such that the coverage performances are maximal. The analysis for the cost of the relocation maneuver in that case is performed, and the trade-off between drift time and delta-V consumption is closely examined. Finally, the injection operational issues related to adding a third unit are addressed.
We proceed in a similar fashion for Sentinel-2 but the coverage area considered for the optimization is the latitude band 56°S 84°N which corresponds to the area targeted by the mission. We consider again the two cases, with and without relocating Sentinel-2B, and in the latter case we assess the cost of moving the B unit away from its current position. Similarly to the Sentinel-1 case, the question of the delta-V cost for the relocation maneuver and the operational issues linked to the injection of the C unit are answered.
For Sentinel-3, we only consider the possibility of adding a third unit to the existing 2-satellite configuration as there exist strong constraints on the ground tracks of Sentinel-3A and B. We optimize globally the 3-satellite configuration using the altimeter as a driver. Optimal solutions and near-optimal solutions are presented, depending on the science requirements. The possibility of a tandem phase for Sentinel-3C and its consequences are examined and the ground segment operational consequences for this third unit assessed.
On the basis of this study, it can be concluded that adding a third unit leads to significant improvements in terms and average and maximum coverage time with respect to the current 2-satellite configurations. Relocating the Sentinel-1/2 B units requires a reasonable delta-V for a drift time of less than 2 weeks, and allows for an additional gain in performances, as the coverage time decreases further and the longitudinal variability becomes less prominent.

The Sentinel-5p mission launched on 13th October 2017, is the first Copernicus mission dedicated to monitoring of the earth atmosphere, using the TROPOMI instrument to measure the concentration of trace gases. The objective is to provide daily global coverage of the atmosphere with a high resolution spectrograph covering UV, VIS, NIR and SWIR spectrums that enables measurements of particular atmospheric constituents to be taken.
The instrument operations are largely driven by predictable geometric events (rather than end user requests for imaging of particular targets) and can therefore be planned many days in advance with confidence, minimising the need for ground based ‘real-time’ control and monitoring. Two ground station contacts are scheduled for TT&C activities each day.
The satellite was developed by Airbus Defence and Space and is built on an Astrobus L 250 satellite bus, and equipped with S- and X-band communication antennas, a Payload Data Handling Unit to store the recorded science data, three foldable solar panels generating 1500W and hydrazine thrusters for orbit control. The instrument operations require that it remains nadir pointing permanently. The platform design is fully compatible with this except when Orbit Control Manoeuvres, OCM need to be performed.
The Failure Detection, Isolation and Recovery concept implementation means that all anomalies affecting the payload units: X-band, PDHU result in an abort of programmed OCMs. In order to mitigate the risk of interruption OCMs programmed as part of space debris collision avoidance activities, the ground stops and restarts the X-band and PDHU units as part of its CAM activities, thus complicating the time critical CAM operations and resulting in a science data gap of several hours.
We will describe how through the implementation of On-Board Control Sequences, on-board autonomy can be enhanced, thus simplifying nominal and contingency recovery operations and minimise the science data gap around critical manoeuvres as well as any operations resulting in payload switch-off.

Swarm is the magnetic field mission of the ESA Earth Observation program composed of three satellites flying in a semi-controlled constellation. Its history in-orbit began in the after-noon of the 22nd November 2013, when the three identical spacecraft separated perfectly from the upper stage of the Rockot launcher at an altitude of about 499 km. Control of the trio was immediately taken over by the ESA’s European Space Operations Centre (ESOC) in Darmstadt, Germany. Following the successful completion of the Launch and Early Orbit Phase (LEOP), commissioning was concluded in spring 2014 and precious scientific data have been provided since then.

In order to deliver extremely accurate data to advance our understanding of Earth’s magnetic field each Swarm satellite carries a magnetic package, composed by an Absolute Scalar Mag-netometer (ASM) and a Vector Field Magnetometer (VFM), an Electrical Field Instrument (EFI) and an Accelerometer (ACC).

Since the end of the Commissioning Phase varying and not fully unexplained phenomena characterised the behaviour of the Electrical Field Instrument thus affecting the quality of the data provided and limiting the sensing time available for science acquisition. Investigation and recovery measures have translated into a number of activities not foreseen before launch and, after six years of operations, still evolving to increase the data return in terms of quality and time, as well as to improve the understanding of the physics driving the unexplained be-haviours.

In order to better explain the scale of the changes implemented to adapt the new operational concept for the EFI, an overview of the Swarm operational concept as foreseen before launch will be presented. Starting from that the evolution required to support the prime investigators, the University Of Calgary (UoC), will be described in detail.

Three main areas will be considered:
• A history of the in-flight tests for the characterisation of the anomaly and to achieve a more suitable tuning of the calibration parameters;
• The concept and the tooling used to keep under configuration control the inputs re-ceived by the investigators against the flight configuration of the three satellites, dif-ferent in all three;
• The new instrument commanding approach which exploits a special, direct interface between the University Of Calgary and the Flight Operations Segment (FOS), both in terms of data exchange and share of responsibilities.

Finally, there will be some consideration on how a technology which is not well space proven might disrupt the operational concept designed before launch and how important it is to keep a degree of flexibility in both the space and ground segments to be able to accommodate such needs of missions flying technically or conceptually advanced instruments.

From the early days of ERS and ENVISAT, followed by the first Earth Explorers and continued by the Copernicus/Sentinels constellation, ESA/ESOC is and has been responsible for the daily operations, mission-planning and safety monitoring of a number of Earth Observation satellites and their associated Flight Operations segment.

Using a very stable, consolidated and available set of infrastructure (built around a set of commonly validated products as SCOS-2000 for Monitoring&Control, SIMSAT for Operational Simulators, the EO Kernel for Mission Planning, ESA KIRUNA S-band antennae for TT&C etc.) ESOC has developed, tested and integrated a core “Flight Operations Segment” for the entrusted EO missions, capable of successfully operating, in parallel, a number of different EO missions, platforms and phases, from multiple LEOP(s) to Routine through Commissioning, Tandem Operations, Constellations set-up, and satellite de-orbiting.

While the above “core EO FOS” has largely demonstrated its capabilities and shall be maintained beyond 2020 for the current missions in-flight and their legacy successors (e.g. planned Earth Explorers such EarthCare or C/D models for the Sentinel-1,-2 and -3), the plans at ESOC for what concerns new EO missions to be launched after 2020+, the associated infrastructure and operational concepts are under-going a deeper “renovation exercise” based on a number of technological developments, such as:

• The promotion of File Based Operations (FBO) as the underlying, baseline operational protocol to exchange operational products with the Space Segment, based on flight-proven standards such as CFDP
• The use of a new generation of M&C (Monitoring & Control) Systems based on the EGS-CC (European Ground Systems – Common Core) being developed in the context of a European wide initiative with the ambition to support all types of space systems, mission phases and categories. The M&C Core based on Common Core will implement FBO “natively” and is developed at ESOC. This can be extended to the new Operational Simulator infrastructure based on SIMSAT-NG.
• The modernization of Flight Dynamics software and the establishment of different development and deployment approaches
• The potential use of new TT&C and communications Bands, such as X-band for the TM/TC and Ka-Band/Optical for the science, requiring new investments and operational concepts, including distributed CFDP and Delay-Tolerant Networks (DTN)
• The progressive deployment of the new Packet Utilization Standard (PUS-C), defining the interface between Ground and Space at application level. PUS-C represents a major step forward compared to PUS-A by its solid PUS foundational model, clear interface definition separated from system requirements, together with its link to the ESA driven “Generic Operational Requirements ICD” (Gen-OIRD), defining a tailoring of such PUS common to all ESOC operated missions.
• Last but not least, the implementation of further automation elements tightly embedded within the operational concept, to be put in place and practice from the very early phases of a Project, in seek of deploying a “system of systems” whose operational concept is based on maximizing autonomy, automation and AI based-support since (almost) the beginning of the mission

We will describe the activities, technologies and the operational concepts being currently defined as part of ESOC plans, shaping the design of such future “EO FOS”. Evolutionary aspects, as well as the challenges linked to such investments (technological and financial) will be also addressed. Current schedule and major milestones will be discussed