Mission and system architecture for an operational network of earth observation satellite nodes

Highlights

• System concept to supplement in a progressive way the current European Earth Observation infrastructures.

• System architectures to provide competitive revisit time, data latency and image resolution for Marine Weather Forecast.

• Architectures built with several heterogeneous satellite nodes distributed in different orbital planes.

• Multiple cooperating nodes, leveraging on the fractionated and federated satellite system concepts.

• Mission and System Architecture for an Operational Network of Earth Observation Satellite Nodes.

Abstract

Nowadays, constellations and distributed networks of satellites are emerging as clear development trends in the space system market to enable augmentation, enhancement, and possibilities of new applications for future Earth Observation (EO) missions. While the adoption of these satellite architectures is gaining momentum for the attaining of ever more stringent application requirements and stakeholder needs, the efforts to analyze their benefits and suitability, and to assess their impact for future programmes remains as an open challenge to the EO community. In this context, this paper presents the mission and system architecture conceived during the Horizon 2020 ONION project, a European Union research activity that proposes a systematic approach to the optimization of EO space infrastructures. In particular, ONION addressed the design of complementary assets that progressively supplement current programs and took part in the exploration of needs and implementation of architectures for the Copernicus Space Component for EO.

Among several use cases considered, the ONION project focused on proposing system architectures to provide improved revisit time, data latency and image resolution for a demanding application scenario of interest: Marine Weather Forecast (MWF).

A set of promising system architectures has been subject of a comprehensive assessment, based on mission analysis expertise and detailed simulation for evaluating several key parameters such as revisit time and data latency of each measurement of interest, on-board memory evolution and power budget of each satellite of the constellation, ground station contacts and inter-satellite links. The architectures are built with several heterogeneous satellite nodes distributed in different orbital planes. Each platform can embark different instrument sets, which provide the required measurements for each use case.

A detailed mission analysis has then been performed to the selected architecture for the MWF use case, including a refined data flow analysis to optimize system resources; a refined power budget analysis; a delta-V and a fuel budget analysis considering all the possible phases of the mission. This includes from the correction of launcher injection errors and acquisition of nominal satellite position inside the constellation, orbit maintenance to control altitude, collision avoidance to avoid collision with space debris objects and end-of-life (EOL) disposal to comply with EOL guidelines.

The relevance of the system architecture selected for the MWF has been evaluated for three use cases of interest (Arctic sea-ice monitoring, maritime fishery pressure and aquaculture, agricultural hydric stress) to show the versatility and the feasibility of the chosen architecture to be adapted for other EO applications.

Introduction

Two trends have recently emerged in space systems and could even further strengthen in the future: small satellites, with the development of key modularization and miniaturization technologies, and the deployment of constellations and distributed networks of satellites. It is paramount for Europe to properly analyze those trends and determine whether or not they could provide advantages for Earth Observation systems. To address those challenges, the Horizon 2020 ONION project (Operational Network of Individual Observation Nodes), completed at the beginning of 2018, investigated the distribution of spacecraft functionalities into multiple cooperating nodes, leveraging on the emerging fractionated and federated satellite system concepts [1]. In the case of Federated Satellite Systems (FSS) conventional spacecraft establish a network to exchange resources (such as bandwidth and computing power) for mutual benefit. It bridges a gap between traditional space distributed systems, such as constellations, and novel approaches, such as fractionated spacecraft [2], in terms of component uniformity and independency. The baseline of the ONION concept consists of augmenting current mission profiles, like the Copernicus Space Component for Earth Observation and Earth Explorer missions, with missing observation bands, increasing data resolution, improving coverage and revisit time, reducing data latency, augmenting mission lifetimes and ultimately sharing the capabilities across multiple spacecraft platforms. To reach its objective, the project followed the steps listed below.

• Survey and analysis of stakeholders and end user needs [3] in the Earth observation field and identification of technological gaps [4]. A quantitative methodology has been applied to select 10 promising use cases that emerge from the combination of pressing needs and technological gaps: climate for ozone layer and ultraviolet assessment, land for basic mapping, risk assessment, marine for weather forecast, atmosphere for weather forecast, fishing pressure, land for infrastructure status assessment, sea ice monitoring, agriculture (hydric stress), natural habitat & protected species monitoring, and sea ice melting emissions.

• Identification of current infrastructure technological gaps in meeting user needs, based upon the measurements, instruments and mission components of the EO value chain [5]. The identified technological areas for improvement served as support for the following system requirements generation.

• Survey of fractionated and federated technology state of the art with the identification of key enabling technologies to fill the identified technological gaps.

• Formulation of system requirements for a cost-effective space-based Earth observation infrastructure, based on identified use cases and available technologies. System requirements include spectral bands, spatial and temporal resolution, coverage and data latency.

• Identification of architecture concepts that can fill the gaps identified in the observation requirements analysis, including pre-selection of sensors, orbits, satellite mass classes and ground station network architectures.

• Selection of a reference architecture, by means of a systems architecting methodology that optimizes the constellation design and the allocation of instruments. This methodology has two stages.

  • First, an exhaustive, multi-attribute, tradespace exploration process evaluates architectural trends resorting to Pareto-optimality concepts and the definition of qualitative criteria. Based on the findings in the tradespace exploration, which comprised thousands of potential architectures, the space of solutions is reduced to a small subset of the most promising designs.

  • This reduced set is then thoroughly analyzed with refined mission and system simulations in order to select the most optimal architecture in accordance to the elicited system requirements.

• Detailed analysis of the architecture selected, comprising payload, platform, mission and ground segment.

• Assessment of the relevance of the selected architecture with respect to other use cases identified at the beginning of the project.

The ONION User Advisory Board recommended to focus on the selected use case (Marine Weather Forecast) and to perform an end-to-end analysis with the aim of showing ONION's added value and its link to the existing and planned Copernicus infrastructure. After the completion of the analysis of the MWF use case, also the agricultural hydric stress use case has been analyzed, with the aim of deriving a general and generic concept regarding the benefits of ONION.

This paper presents the findings that resulted from the last stages of the ONION project, namely, steps 6), 7) and 8). The paper is organized as follows: Section 2 provides a brief overview of the generic architecture optimization process and summarizes the multi-attribute tradespace exploration methodology (step 6a). Section 3 defines the MWF use case and its elicited system requirements. Section 4 highlights the most relevant observations in the design-space exploration for this particular use case and summarizes the trends that allowed the pre-selection of 28 candidate solutions (step 6 b). Section 5 details the mission and system analysis workflow conceived in ONION to evaluate the reduced set of candidates (step 7). Section 6 explores in detail the specific characteristics of the optimal solution. Finally, Section 7 assesses its versatility with other use-cases in ONION (step 8), and Section 8 concludes with final remarks.