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.
