CubETH is a joint satellite project between EPFL’s eSpace and ETHZ. The satellite is a next generation CubeSat, measuring about one liter of volume and weighing less than a kilogram. In many ways, it is the successor of SwissCube, following a similar form factor, but more advanced technologically. CubETH will be capable of calculating its own altitude and position in space with unprecedented precision thus paving the way for nano-satellite constellations with inter-satellite communication capabilities.
CubETH also serves as one of eSpace’s main multidiscplinary education tools. Close to a hundrer students have already worked on pars of CubETH, with more planned as we get closer to the launch date.
The mechanical assembly concept used in CubETH was developed by eSpace partner Astrocast. The structure allows a flexible and reliable assembly of different subsystems of the satellites in a versatile configuration.
Antenna Deployment System
The Antenna Deployment System (ADS) is one of the most complex mechanical parts of CubETH. Like SwissCube, CubETH is launched with antennas rolled up and held by a fishing wire. Once in orbit, a heating resistor is used to melt the wires, releasing the antennas. As this is effectively the only moving part of CubETH, a lot of effort is spent to properly chacterize the behaviour of the system, and make sure that it is reliable. The figure below shows several iterations of the ADS. And make to see the video of the deployment!
Electrical and software subsystems
CubETH is now at the end of its phase B development, which means that the satellite Electrical Model shall validate the majority of embedded functionalities. During the past semesters, the electrical subsystems were independently implemented by the students, based mainly on the SwissCube heritage.
Most recently, master student Adrien Corne could combine all subsystems together and validate inter-board communication capabilities. As seen in the diagram below, the Electronic Model architecture embeds most of the subsystems.
|Attitude Determination and Control System
|Sensor fusion between accelerometers, magnetometers and sun sensors. Control driving electronics for magnetic control.
|Contains the batteries necessary to power the satellite during eclipse, as well as thermal control and unlocking electronics.
|Command and Data Management System
|On-board computer. Data centralization, processing and storage.
|Radio link with ground station. RF electronics for modulation and decoding. Llinked to the satellite antennas.
|Electrical Power System
|Power generation and management system. Batteries control. Sensor to monitor voltage, current and temperature for every solar panel. Power distribution unit.
The CDMS is linked via UART to a computer to facilitate debugging and data gathering. The figure below shows the setup. A standard 104-pin interface exists on each board so they may be plugged to a FlatSat platform.
The inter-board communication protocol is I2C. The CDMS acts as master and requests flight data from the other subsystems. At this stage of the development, relevant data to gather is typically housekeeping parameters, as board current consumption, temperature, status flags, or battery voltage. Such data acquisition and I2C communication were implemented on all present subsystems.
Testing and ground support
The key to a successful satellite is testing, testing, testing! Throughout this project, several test setups were developed to validate different aspects of the satellites.
- An Helmholtz cage for validation of magnetometers and magnetorquers
- An air-bearing test beach for validation of magnetometers and magnetorquers, and antenna deployment
- A vacuum chamber for thermal vacuum characterization of the satellite and electronics
- A rotation table for characterization of the gyroscope