SENER Aeroespacial has successfully completed the delivery of the nominal version of the Attitude and Orbit Control System (AOCS) for the Euclid satellite, for which, as main contractor of this AOCS, SENER Aeroespacial leads the design, development and verification of this system.
This version, called v1, cover all the nominal functionalities and has allowed to demonstrate and test the outstanding subsystem's performance, achieving the most demanding pointing stability obtained to date in a space science mission. That achieved pointing stability is better than 25 milliarcseconds (1σ) is maintained during 11 minutes, which in macroscopic terms, is equivalent to maintaining pointing inside one-euro coin from 100 km distance.
The AOCS in charge of the determination and control of the satellite pointing, and of the maneuvers necessary for the control the satellite trajectory/orbit. In Euclid, the AOCS provided by SENER Aeroespacial includes the sensor and actuators units, as well as the logic and on-board software necessary to process the obtained data and to manage and control the satellite's dynamics, being one of the most complex systems in the satellite.
Among the different state-of-the-art sensors integrated in the system it stand out a high-performance inertial unit, a fine guidance sensor integrated inside the telescope and a star sensor with multiple optical heads. With regard to the actuators, the system includes five reaction wheels subject to a complex start/stop operation cycle, necessary to avoid disturbances, whether generated by the wheels themselves, or by other mechanisms in the telescope; this type and number of reaction wheels star-stop operations has never been used before and has required a dedicated qualification process.
In combination with the reaction wheels, the system uses multiple micro-cold-gas thrusters, with high-precision amplitude modulation, to keep the very precise pointing while the wheels are motionless.
In the words of Salvador Llorente, Project Manager at SENER of this system, "In the Euclid mission, SENER Aerospacial is overall responsible for the complete AOCS system, from the preliminary design to acceptance in orbit, including the detailed design, production, integration, verification and on-ground and in-flight validation." Llorente added that "SENER Aeroespacial is proud to have delivered this version to Thales Alenia Space Turin, the mission's integrator and prime contractor, after having demonstrated and tested the compliance of the most demanding AOCS specifications.
Prior to the delivery of this version, we have also delivered representative units of all the AOCS equipment, enabling its joint application and testing at the satellite avionics bench at Thales.” Meanwhile, most of the flight units for integration into the satellite have already been delivered, and version 2 (the final one) is expected to be completed in the first half of 2020.
Euclid is a cosmology mission of the European Space Agency (ESA) dedicated to the study of the nature of the dark universe, meaning both dark matter and dark energy. To do this, the satellite features a 1.2-m diameter telescope with which it can make observations in the visible and near infrared spectra, and with wide bandwidth and spectroscopy. Euclid's goal is to investigate the evolution of cosmic structures by measuring shapes and redshift of the light from distant galaxies, which information dates back as much as 10 billion years.
Among the issues it seeks to resolve are how the universe was created and why it is expanding at an increasing speed, rather than decreasing, as we would expect given its current, known mass. The dark energy is expected to be the cause of this effect that Euclid will analyse through the impact it has on the shapes and locations of galaxies.
