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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - DISCOVERER (DISCOVERER â€“ DISruptive teChnOlogies for VERy low Earth oRbit platforms)

Teaser

Summary

The satellite based Earth Observation/remote sensing market is one of the success stories of the space industry having seen significant growth in size and applications in recent times. According to EuroConsult, global revenues from Earth imagery and data services set to exceed 4 billionâ‚¬ by 2024 up from 2 billionâ‚¬ in 2014. The market can be said to be booming.

Yet key design parameters for the satellites which provide the data for this market have remained largely unchanged, most noticeably the orbit altitude. Operating satellites at lower altitudes allows them to be smaller, less massive and less expensive whilst achieving the same or even better resolution and data products than current platforms. These benefits could greatly facilitate and reduce the cost of a number of European and international initiatives for maritime surveillance, intelligence and security, land management and food security, and disaster monitoring.
However, at reduced orbital altitude the residual atmosphere produces drag which decreases the orbital lifetime, and aerodynamic perturbations challenge the ability of a satellite to remain stable affecting image quality. DISCOVERER envisions a radical redesign of Earth observation platforms for sustained operation at significantly lower altitudes than the current state-of-the-art and overcomes these challenges. This vision requires foundational research in the aerodynamic characterisation of materials, in atmosphere-breathing electric propulsion for drag-compensation, and in active aerodynamic control methods. These activities are by their nature multidisciplinary covering atmospheric science, surface chemistry and material characterization, flight dynamics and control engineering, spacecraft design, payload engineering, and business modelling.

The proposed work aims to address the following foundational research questions:

1. Are there materials or processes which reduce the induced drag on spacecraft surfaces?
2. Are there propulsion methods which use the residual atmospheric gas as a propellant, providing drag compensation whilst removing the lifetime limits caused by carrying a limited amount of propellant?
3. How can we improve our understanding of, and make best use of, the orbital aerodynamics of a satellite and its ability to perform attitude (pointing) and orbit control manoeuvres?

In order to put these foundational developments in context, DISCOVERER will also develop advanced commercial and economic models of Earth observation systems which include these newly identified technologies. This will allow the optimum satellite designs for return on investment to be identified. DISCOVERER will also develop roadmaps defining the on-going activities needed to commercialise these new technologies and make very low Earth orbit, Earth observation satellites a reality.

Work performed

DISCOVERER contains several technology development activities, all of which have made significant progress during this period:

1. Prospective aerodynamic material coatings, those which are expected to scatter away the flow specularly, have been developed. These will be tested in a number of ways:
a. DISCOVERERâ€™s Rarefied Orbital Aerodynamics Research (ROAR) facility is currently being assembled and start experiments before the end of 2019. The ground-based facility will reproduce the atmospheric flow around satellites in very low Earth orbits, at the correct density, speed and predominant composition. This will be used to characterise the aerodynamic properties of the new materials.
b. An additional test to determine the survivability of the materials in the very low Earth orbit environment is underway. Materials samples were launched to the International Space Station (ISS) on 2 November 2019, and will be exposed outside the ISS for 6 months before being returned to Earth for analysis.
c. The engineering model of our Satellite for Orbital Aerodynamics Research (SOAR) will be assembled before the end of 2019 for testing, and will be quickly followed by the flight model early in 2020. Launch is expected in August 2020 from the International Space Station. SOAR is a small test satellite to validate the aerodynamic performance of the materials in the space environment, and demonstrate aerodynamic control of a satellite.

2. Aerodynamic control concepts have been developed to help control satellites in very low Earth orbits despite the variations in atmospheric density and high wind speeds they will encounter. Some of these are being refined so they can be implemented and demonstrated on SOAR.

3. A prototype Atmosphere-Breathing Electric Propulsion system (ABEP) is being developed. This collects the residual atmosphere in very low Earth orbits and uses it as propellant in a thruster to compensate atmospheric drag. The atmospheric intake has been optimised to achieve high efficiency, and a prototype of the thruster, a radio frequency based inductive plasma thruster, has been built and will be first ignited by the end of 2019.

In addition, studies of business models for remote sensing from very low Earth orbits have been carried out. These feed into on-going studies of future satellites designs, their applications, and the commercial environment in which they would operate.

Final results

The different aspects of DISCOVERER will all typically go through several major phases during the project: design, build, experimentation, obtain and analyse results, validation and publication. DISCOVERER is just entering the experimentation phase in many of the technology areas, with many exciting experiments due to take place or commence over the next year!