FSSCAT was the 2017 ESA Sentinel Small Satellite (S^3) Challenge winner, and the Copernicus masters competition overall winner [1]. The ESA S^3 Challenge aimed at stimulating ground-breaking satellite design, testing and manufacturing solutions leading to small missions either complementary or providing added value to the current Sentinel family missions. FSSCAT data will provide soil moisture data, sea ice cover and coarse resolution sea ice thickness. It will also be a technology demonstrator of an optical inter-satellite link, and a test-bed of the concept of “federated” satellites using an UHF RF link, a precursor concept of the “Internet of Satellites.”

FSSCat consists of two 6U Cubesats (3Cat-5/A and 3Cat-5/B), and it is foreseen to be launched in the VEGA SSMS (Small Spacecraft Mission Service) maiden flight in a Sun Synchronous orbit at an altitude of 550 km [2]. Both spacecrafts are based in the same bus from Tyvak International.

3Cat-5/A includes the FMPL-2, the Flexible Microwave Payload-2 (FMPL-2), an evolution of FMPL-1 on board 3Cat-4 [3], which implements in a Software Defined Radio a GNSS-R instrument and an L-band microwave radiometer. The nadir antenna is a dual-band 3x2 microstrip patch array at 1413 and 1575 MHz covering the microwave radiometry band (1400-1427 MHz), and the GPS/Galileo L1/E1 band. 3Cat-5/B main payload is an evolved version of Cosine’s Hyperscout hyperspectral imager including three new Thermal Infrared (TIR) bands (8.6 μm, 10.5 μm and 11.4 μm) [4] and funded through the ESA’s In-Cubed. Coarse-resolution soil moisture data will be derived from microwave radiometry and GNSS-reflectometry data. High-resolution soil moisture data will be derived by combining the coarse-resolution one with the hyperspectral data [5,6]. Ice cover will be derived from the GNSS-reflectometry data as done with TDS-1 data [7], while coarse-resolution ice thickness will be derived from the microwave radiometry data, as it is done with SMOS data [8,9].

Other payloads in 3Cat-5/A and /B are the Optical inter-satellite links (O-ISL) and the UHF RF transceiver for the “Federated Satellite Systems Experiment” (FSSExp) to test communications and protocols concepts to pave the path towards virtual constellations (“Internet of Satellites” [10]) that could be created in the future in an ad hoc from manner by linking inhomogeneous satellites in a sort of “Space Uber” [11]. The Optical ISL payload is being manufactured by Golbriak Space oü (Estonia). The FSSExp transceivers hardware and firmware are being developed by the Universitat Politècnica de Catalunya (UPC) and Institut d’Estudis Espacials de Catalunya (IEEC).

The ground segment will be composed by a number of receiving ground stations at S-band to collect the scientific data, and by two UHF ground stations from Tyvak International to send telecommands and receive telemetry.

The Data Processing Ground Services (DPGS) will comply with the Copernicus free and open data products distribution policy and it will be based on Deimos Engenharia (Portugal) ground segment systems and expertise in satellite imagery commercialization (notably for Deimos-1 and -2). In particular Deimos’ SIMOcean platform [12] will provide data processing, storage, search and delivery cloud-based platform to support EO based products.

FSSCAT can also be consider as a precursor of a constellation of small satellites, notably when short revisit times are needed, such as for polar applications. This was one of the outcomes of the H2020 ONION project [13, 14], where the optimum constellation consisted of microsatellites each one with an X-band SAR and a multispectral imager, and nanosatellites each one with a GNSS-R payload.

At the conference, a detailed updated mission description will be provided.

References:
[1] FSSCat–Towards Federated EO Systems: http://www.copernicus-masters.com/winner/ffscat-towards-federated-eo-systems/ [last visited November 11th, 2018]
[2] Camps, A., et al., “FSSCAT, THE 2017 COPERNICUS MASTERS’ “ESA SENTINEL SMALL SATELLITE CHALLENGE” WINNER: A FEDERATED POLAR AND SOIL MOISTURE TANDEM MISSION BASED ON 6U CUBESATS”, 2018 IEEE International Geoscience and Remote Sensing Symposium, 22-27 July 2018, Valencia, Spain
[3] Things get critical for CubeSat teams, http://www.esa.int/Education/CubeSats_-_Fly_Your_Satellite/Things_get_critical_for_CubeSat_teams, [last visited November 11th, 2018].
[4] HyperScout: The intelligent hyperspectral imager, https://www.cosine.nl/portfolio/hyperscout/, [last visited November 11th, 2018].
[5] M. Piles, N. Sánchez, M. Vall-llossera, A. Camps, J. Martínez-Fernández, J. Martínez, and V. González-Gambau, “A Downscaling Approach for SMOS Land Observations: Evaluation of High-Resolution Soil Moisture Maps Over the Iberian Peninsula,” in IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, vol. 7, no. 9, pp. 3845–3857, Sept. 2014.
[6] G. Portal, M. Vall-llossera, M. Piles, A. Camps, D. Chaparro, M. Pablos, and L. Rossato “A Spatially Consistent Downscaling Approach for SMOS Using an Adaptive Moving Window,” in IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, vol. 11, no. 6, pp. 1883–1894, June 2018. doi:10.1109/JSTARS.2018.2832447
[7] A. Alonso-Arroyo, V. U. Zavorotny and A. Camps, "Sea Ice Detection Using U.K. TDS-1 GNSS-R Data," in IEEE Transactions on Geoscience and Remote Sensing, vol. 55, no. 9, pp. 4989-5001, Sept. 2017.
doi: 10.1109/TGRS.2017.2699122
[8] L. Kaleschke, L. et al., “Sea ice thickness retrieval from SMOS brightness temperatures during the Arctic freeze-up period”. Geophysical Research Letters 39 (5). (2012): S. L05501.
[9] L. Kaleschke, et al., “SMOS sea ice product: operational application and validation in the Barents Sea marginal ice zone”. Remote Sensing of Environment 180. (2016): S. 264-273.
[10] J. A. Ruiz de Azúa, A. Calveras and A. Camps, "Internet of Satellites (IoSat): Analysis of Network Models and Routing Protocol Requirements," in IEEE Access, vol. 6, pp. 20390-20411, 2018. doi: 10.1109/ACCESS.2018.2823983
[11] J. A. Ruiz-De-Azúa, A. Camps and A. Calveras Augé, "Benefits of Using Mobile Ad-Hoc Network Protocols in Federated Satellite Systems for Polar Satellite Missions," in IEEE Access, vol. 6, pp. 56356-56367, 2018.doi: 10.1109/ACCESS.2018.2871516
[12] SIMOCEAN: http://catalogue.simocean.pt, http://geoportal.simocean.pt, [last visited November 11th, 2018].
[13] E. Alarcón et al., "Design and Optimization of a Polar Satellite Mission to Complement the Copernicus System," in IEEE Access, vol. 6, pp. 34777-34789, 2018. doi: 10.1109/ACCESS.2018.2844257
[14] ONION H2020 (Project ID: 687490) – Distributed Satellite Systems space mission concepts - Project Animation Video: https://www.youtube.com/watch?v=LF7alaLTSyc [last visited November 11th, 2018].

The paper reports the results of CHRISTMAS, a feasibility study performed by an Italian consortium led by Università di Milano Bicocca in collaboration with Politecnico di Milano, Istituto Nazionale di Astrofisica and OHB-I, and financed by ASI.
CHRISTMAS targets to the Cryosphere Monitoring, operating with an innovative payload in the optical and thermal domain, to address challenges related to the snowmelt processes and on the impact of light-absorbing impurities on polar and non-polar glaciers in the context of fresh water management at catchment scale. CHRISTMAS mission requires to acquire information of radiation reflected (pan VIS-NIR - 0.4-0.82, RGB channels and two TIR bands - 0.8 –12 um) at high spatial and temporal resolution.
No space mission flew so far collect optical and thermal data at both high spatial and temporal resolution, for effectively monitoring snow and glacier dynamics. Although albedo and surface temperature can be obtained from several satellite missions, none allows capturing fast dynamics provoked by snow impurities appearance and their role in snow melting; CHRISTMAS proposes a new mission concept focused on the cryopshere Apparent Thermal Inertia (ATI) detection.
To satisfy all tight scientific requirements a formation flying constellation of micro-satellites has been designed, equipped with an innovative multispectral imaging system (MSI) of reduced size, weight and energy consumption in the required optical bands.
The on board-imaging payload is part of the research as well, being compacted and optimized from the detector to the telescope, to work in VIS-NIR and TIR spectral bands, and to design an optical telescope optimized for the VIS-NIR and TIR optical bands.
A spatial resolution of at least 30 meter in the visible and 80 meter (or less) in the thermal domain is imposed.
The retrieval of ATI on snow and ice surfaces requires at least two thermal acquisitions for monitoring the daily amplitude of surface temperature (e.g. early in the morning and at noon). Furthermore, a very-short revisit time of 1 day is required for monitoring fast dynamic processes of snow and ice such as rapid snow metamorphism, snowmelt, impurity depositions and resurfacing.
Therefore, a constellation of four satellites, flying in formation by couple, has been identified as the best-suited solution. The proposed architecture allows for further enlargement, being the satellite couple, flying in cross track formation, the atomic unit of the constellation, which can replicated at convenience, according to the desired temporal resolution. Being identical in shape and energy, orbits differ in LTDN to pass over the same target with a time delay of half a day: first formation to pass at 05:00 am, second formation to pass at 2:00pm. In particular, 551 km sun-synchronous orbits are selected, shifted of 0,8° at the equator to offer a 120km swath while nadir pointing, being the instrument FOV of 3°.
Even being nadir pointing, satellites have a good manoeuvrability to acquire data from the same target with inclined FOV as well. Fig.1 shows the constellation architecture base on the 2+2 formation flying satellites.
The payload is optimised to a 10kg, margined. Each space segment is equipped with two multispectral sensors.
The service module subsystems have been selected and sized to obtain a margined mass of 113kg, supplying 150W.
The satellite class can be further reduced, moving toward the mini satellite class ( 40 kg per s\c) and the strongly distributed swarm of sensors, if a single payload unit is put on board.
The paper presents and discusses in details the proposed mission, starting from the scientific objectives and requirements and going through the orbit design and platform sizing to propose a flexible, low cost-high performance EO mission.

Satellites flying in formation are boosting the capabilities of satellites missions due to the superior performance achieved by distributed systems. The concept of a distributed space system is to split the mission capabilities of a traditional monolithic spacecraft, or instrument, into two or more cooperating units. The elementary units may be identical or even different in functionalities. Such concept enhances the robustness of the overall mission architecture. Small satellites are the most promising solution for this type of missions because, whilst increasing the complexity and challenges of miniaturization, they sensibly decrease the cost of system acquisition. Most importantly, though, Formation Flying (FF) increases the flexibility of the mission by introducing the capability of orbital reconfiguration of the distributed system. The relative position between the satellites are varied using dedicated orbital maneuvers, yielding new geometric configurations, which essentially change the distributed instrument specifications. In particular, the orbital flexibility employed with respect to the relative orbital motion guarantees the fulfillment of different scientific payload requirements, potentially variable in time. Intersatellite baseline, achieved by controlled separation in drift or no-drift motion, and relative attitude of the two satellites are used to generate valid configuration to respond to payload requirements.
Moreover, train and tandem configurations can be obtained by employing satellites that were originally conceived as single spacecraft missions. Launched at different epochs, the satellites can later be coupled to extend Earth observation instrument or to increase its performance. The CNES-SPOT programme orbited five satellites with different functionalities and applications, with particular focus to Earth mapping, DEM and environmental monitoring. The five satellites were inserted in the same near-polar sun-synchronous orbit. A remarkable example of the application of reconfiguration of two satellites conceived as a constellation mission is the Sentinel-3 mission. Sentinel-3A was launched in 2016 and, since then, it has been monitoring the large-scale global dynamics of oceans, ice and land. In April 2018 Sentinel-3B was launched with the same radar altimeter, radiometer and imaging spectrometer; when operational, the latter will orbit Earth 140° from Sentinel-3A. However, Sentinel-3A and 3B are currently flying in tandem ~223 km apart from each other to calibrate and compare the instruments on-board the two satellites. After this tandem phase, a reconfiguration maneuver will take the two satellites to the nominal relative configuration.
In this paper, two different Earth observation scenarios are identified, namely optical and SAR, as significant examples of effective future distributed space sensors for EO which ask to approach the Mission and platform in flight control design ensuring more agility and flexibility, the space segment to be timely reconfigurable as needed. Regarding the optical scenario, two applications are identified: Panchromatic and Multispectral. The former achieves higher spatial resolution whereas the latter increases the spectral one. The two identified optical applications, even performing different tasks and having different configurations, impose similar constraints to the mission design: the payloads, sharing size, mass and power consumption, lead to a standardization of the platform design between the application provided the possibility to reconfigure the formation from cross-track to along-track separation with different intersatellite baselines, going from less than 500 km to ~6 km. On the other hand, three applications are identified for the SAR scenario that impose the formation reconfiguration. The creation of Arctic, Antarctica and Solid Earth DEM is performed using a two-satellite cross-track formation flying in sun-synchronous orbit at average intersatellite baseline from 200 to 2000 m; similarly, for sea ice drift detection two satellites flying in along-track formation are required in the same orbit with baseline above 20 km; finally, for ship detection, a four-satellites along-track cluster flying in tight formation, i.e. baseline smaller than 100 m, are necessary.
A coherent algorithm to evaluate and assess the fulfillment of the high-level payload requirements, such as intersatellite baseline, Earth coverage and instrument orientation, is developed based on concurrent constraints with respect to the system orbital configuration and orientation. The algorithm identifies the optimal configuration with respect to the high-level requirements and represent the input for the reconfiguration maneuver of the distributed system. In order to perform reconfiguration given the high-level payload requirements the proposed architecture employs an autonomous GNC algorithm, suitable to be implemented in small satellites. A continuous low-thrust control algorithm coupled with the decentralized navigation filter, suitable for distributed space systems reconfiguration, is designed. The on-board dynamical model of the satellites, representative of J2-perturbed elliptical orbits, is expressed in terms of the relative orbital elements (ROEs). Since the relative orbit determination measurements are typically referred to the Cartesian state, a linear mapping between the set of ROE and the Cartesian coordinates expressed in the local-vertical-local-horizontal (LVLH) reference frame is derived. A feedback control is designed to track the desired reference state, whose stability is analysed using Lyapunov theory. The key aspect in the development of the presented algorithm is the low computational power required, suitable for the implementation on small platforms. Indeed, guidance and control calculation is based solely on relative state knowledge and the semi-analytical model using relative orbital elements. The guidance, navigation and control algorithms are tested in a high-fidelity numerical orbit propagator for the abovementioned scenarios. The results demonstrate the effectiveness of the algorithm for reconfiguration maneuvers with limited fuel consumption and constrained available thrust ~1 mN.
In conclusion, small satellites Formation Flying for Earth-Observation applications, including orbital reconfigurations, are analyzed and the autonomous GNC architecture of the system is designed accordingly. In particular, system configuration is driven by the variable payload requirements in terms of relative orbital motion and intersatellite baseline and, above all, by the types of satellites building up the formation. The presented analysis demonstrate the enriching capability of distributed systems in meeting time-varying requirements imposed by the scientific payload employing autonomous GNC architecture. Moreover, it demonstrates the benefits that arise from the possibility to reconfigure the system depending on the single satellites characteristics and the available scientific instruments, yielding an incomparable mission flexibility towards the scientific outcome.

Planet designs, builds and operates the largest constellation of imaging satellites.
In four years, Planet has successfully launched over 300 satellites, called "Doves", tripled their imaging capability, developed a cloud-based imaging platform that delivers satellite imagery online the same day it was captured, and serves customers all over the world.
In November 2017, Planet acomplished its mission to image the entire Earth with high resolution every day and make global change visible, accessible, and actionable.
Next missions focus on the provision of information feeds based on Planet imagery. Beside the development of platform for analytics, built on modern Machine Learning and Artificial Intelligence approaches, it requires the availability of imagery with even better radiometric quality and temporal resolution.
While keeping the 3U form factor, our engineers were able to design a new generation of DOVE satellites. Inspired by the success of Sentinel-2 satellites and the wide variety of applications developed for Sentinel-2 imagery the band set of DOVE satellites was extended to 14 spectral bands covering wavelengths from 443 to 865 nm. These bands include visible bands, 3 RedEdge bands, 3 red bands, a NIR and a Water Vapor band.
The bands will have different spatial resolutions, ranging from 3m for visible to 12m for water vapor and coastal blue support bands. Important to mention, that Planet aims to maximize the percentage of parts "Made in Europe" for the sensor design. Prototypes of these so called SuperDOVE satellites are currently tested in space. The experiences collected during this operational tests are then used to fine-tune the sensor design and settings before Planet starts to manufacture enough satellites to replace the current generation of DOVE satellites. Planet will maintain the ability to cover the entire landmass of the Earth every daily.
The SuperDOVE generation of satellites will allow to contribute to and to complement ESA´s Sentinel-2 mission and applications based on it. Planet envisage a positive impact on the various Copernicus Services as well as on other monitoring programs. like for instance in the frame of the REDD+program.

VividX2 - the service demonstrator satellite for the forthcoming Vivid-i constellation of small satellites by Earth-i, was successfully launched in January 2018, from the Indian spaceport in Sriharikota into a low earth orbit at 505 km. The satellite, also referred to as Carbonite-2 by its manufacturer SSTL in Guildford, Surrey, UK, quickly began acquiring the first colour video data sets from space. SSTL worked through the commissioning phase tasks, collecting calibration data, verifying operational performance sequences and checking geospatial accuracy. VividX2 has demonstrated data acquisition over potential customer areas of interest and has verified the added value generated by analysing the video data to identify moving objects, improve situational awareness and enhance reconstruction of 3D structures to name a few. Earth-i is now working with one of its partners to deliver an operational processing chain to generate geolocated video from raw satellite data. This paper will address the activities and show results from early stages of the mission including various unpublished video sequences, 3D reconstructions and moving object detection & identification.

Such objectives are goals and planned outputs for a fully operational service from the Vivid-i constellation, with daily revisit, not once but at least three times a day, for any place on Earth and at high latitude even more often. With short notice tasking and near real time data downloads, the response times for the Vivid-i constellation will be highly attractive to potential customers. Adjusting data acquisition plans and implementing rescheduling activities due to cloud cover or operational changes will be semi-automatic and will optimise the utilisation of the full constellation of satellites. The derived information and integrated insights will be available as data feeds for direct integration into our customers’ interfaces, updating their database with the most recent analyses. Insurance, Mining or Security applications are amongst the sectors showing an interest. The Oil and Gas industry for example, where a ‘live’ common operating picture is crucial in ‘any emergency situation’, will be able to make better decisions, and better decisions save time, save resources and can help to save lives.

The RADARSAT Constellation is the next step in evolution of the RADARSAT Program with the objective of ensuring data continuity, improved operational use of synthetic aperture radar (SAR) data and improved system reliability.

The mission consists of three identical C-band SAR satellites flying in a constellation which will provide complete coverage of Canada's land and oceans offering an average daily revisit, as well as a potential daily access to 90% of any location on the globe.

The main objective of the RADARSAT Constellation Mission is on meeting Government of Canada User Department’s needs and requirements in Core Use Areas such as Maritime Surveillance, Disaster Management, Ecosystem Monitoring and Northern Development.

The greatly enhanced temporal revisit combined with accurate orbital control will enable advanced interferometric applications in between satellites on a four-day cycle that will allow the generation of very accurate coherent change maps.

RCM frequent revisit capability, near real-time SAR data availability and vessel identification capabilities (through an AIS payload) will provide the capability to identify and monitor ships up before they enter national waters or ports. It will also enable the detection of changes over time in Canada’s coastal, wetlands and wildlife habitats thereby contributing to the implementation of policies, programs and practices to protect ecosystems and biodiversity.

The RCM represents a major financial investment by the Government of Canada. In order to ensure that the use of RCM data will maximize benefits in service delivery to Canadians and others, a modernized data policy is being developed with the objective of expending usage of SAR data, stimulate economic growth and make the data accessible and affordable to the broadest extent possible, within the limit of the Canadian legislation.

The RADARSAT Constellation Mission is currently under construction with satellite launches planned for Q1 2019.

This presentation will describe the RCM space and ground segments, the expected utilization and the SAR data policy.

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