Skip to main content
European Commission logo
italiano italiano
CORDIS - Risultati della ricerca dell’UE

DISCOVERER – DISruptive teChnOlogies for VERy low Earth oRbit platforms

Periodic Reporting for period 4 - DISCOVERER (DISCOVERER – DISruptive teChnOlogies for VERy low Earth oRbit platforms)

Periodo di rendicontazione: 2021-04-01 al 2022-09-30

The satellite-based Earth observation (EO) market within the space industry has seen significant growth. Yet key design parameters for the satellites 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 ones. These benefits could reduce the cost of European and international initiatives for maritime surveillance, intelligence and security, land management, 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. We envisioned a radical redesign of EO platforms for commercially viable, sustained operation at lower altitudes.

DISCOVERER addressed the following research questions:

1. Are there materials which reduce drag on satellites?
2. Are there propulsion methods for drag compensation which use the residual atmospheric gas as a propellant?
3. Can we use orbital aerodynamics to control a satellite’s pointing and orbit?

We have also developed commercial and economic models of EO systems which include these newly identified technologies.
DISCOVERER contained several technology development activities enabling Very Low Earth Orbit (VLEO) satellites, all of which have made significant progress during the project:

1. Prospective aerodynamic material coatings have been developed and tested in two different ways:
a. Tests to determine how the materials behave in VLEO have been completed and initial results analysed. Samples of novel materials were launched to the International Space Station (ISS) and were exposed on the outside the ISS before being returned to Earth for analysis. These tests have confirmed the long-term survivability of the materials.
b. Our Satellite for Orbital Aerodynamics Research (SOAR) deployed from the ISS on 14 June 2021, re-entered the Earth’s atmosphere 9 months later. SOAR was a small test satellite to validate the aerodynamic performance of the materials in the space environment and demonstrate aerodynamic control of a satellite. Initial analysis of the aerodynamic experiments shows promising results.
c. Our Rarefied Orbital Aerodynamics Research (ROAR) facility has been fully assembled but commissioning is on-going. The ground-based facility reproduces the atmospheric flow in VLEO, at the correct density, speed and predominant composition, to measure the flow as it scatters off material samples. This will be used in the future to characterise the aerodynamic properties of materials.

2. Aerodynamic control methods have been developed to help control satellites in VLEO despite the variations in atmospheric density and high wind speeds they will encounter.

3. An advanced prototype Atmosphere-Breathing Electric Propulsion system (ABEP) has been developed. The system collects the residual atmosphere in VLEO by means of an atmospheric intake and uses it as propellant in an electrode-less electric plasma thruster to compensate atmospheric drag. The design approach enables maximum flexibility for the propellant in terms of density and composition, the thruster can use an inherent acceleration mode based on polarization, additionally to the magnetic nozzle effect, the plasma jet is quasi-neutral such that no neutralizer is needed.
a. Different atmospheric intake designs have been optimised to achieve high collection efficiency and, currently the three designs based on DSMC simulations are available providing up to 95% collection efficiency.
b. The RF Helicon-based Plasma Thruster has been designed, simulated, built, and tested. It is based on radio frequency and utilizes an innovative birdcage antenna, that maximizes electrical efficiency. Its successful ignition has been achieved in March 2020, its electrical properties verified, and its operation on atmospheric propellant such as O2 and N2 has been proven for different power levels.
c. Instrumentation comprising a B-dot probe and a momentum probe have been developed, commissioned and set in operation. The determined thrust efficiencies are 15%-20% at powers of 100 W and 150 W respectively. A comparison with Takahashi’s reference shows promising trends referring to the thrust efficiencies to be expected for higher powers - significantly more than 20% can be expected in future investigations.

Studies of business models and an analysis of stakeholders in remote sensing from VLEO have been carried out. Business roadmaps as well as technology roadmaps have been developed with stakeholder input to guide the future development of new businesses and technologies. Combined with studies of spacecraft system models, designs of future VLEO satellites using the technologies that have been developed.
DISCOVERER has developed novel material coatings, specifically designed for their expected combination of atomic oxygen erosion resistance and gas scattering properties, with a patent pending for their fabrication and use.

The launch of SOAR in June 2021 was a major milestone for the project allowing the aerodynamic performance of materials to be assessed directly in VLEO. Initial analysis of the data from the satellite, the only in-orbit assessment of these or similar materials to date globally, shows very promising results for the novel materials.

Samples of the developed materials have also been exposed to the space environment on the exterior of the ISS to test their long-term survivability. Data about the effect of the space environment on the materials, alongside data from SOAR and ROAR, will be used to develop a complete picture of the performance of the materials for use on VLEO satellites to significantly reduce atmospheric drag in VLEO and improve aerodynamic control performance.

Active aerodynamic attitude control algorithms to help VLEO satellites compensate for the changing atmospheric conditions which disturb their pointing have also been developed.

Based on the designs of the atmospheric intakes for the ABEP system, sub-scaled intakes have been designed specifically for testing in ROAR. The tests will provide a verification of the particle code PICLas and feedback into atmospheric intake design.

Helicon waves are key for high efficiency of plasma production. A B-dot magnetic inductive probe has been designed and commissioned as a plasma diagnostic tool to verify the presence of helicon waves within the plasma plume of the thruster, and will be used to characterise the thruster’s operational envelope. Previous experimental assessment of an inductively-driven plasma device (IPG6-S), and the operation of the DISCOVERER’s Inductive Plasma Thruster (IPT) show operational modes that already imply transitions to the Helicon mode. This was proven by an improved ignitability, a power increase and a “visual” collimation in the IPT. Thrust efficiency values determined for the collimated mode are significantly higher.

A baffle plate momentum probe has been designed and used to measure thrust, and derive specific impulse, and thruster efficiency. This data can be used to support system and mission analyses, and to optimise the design of a vacuum version of the thruster, reducing required power, mass, and volume.
Satellite in space