In the previous month, we gave you an overview about the hardware architecture of our Command Module. That means that this month we will be covering the general electrical architecture as a further continuation of our Command Module overviews.
The electrical architecture’s scope includes almost every part of the Command Module, as it has to power and enable safe and reliable electrical supply between the three main boards which are:
– The COM Board (Communications)
– The EPS Board (Electrical Power System)
– The CDHS Board (Command and data handling Subsystem)
The main components of the electrical system are located on the EPS board as it receives power from the CubeSat’s EPS and then distributes it to the other two boards and associated systems within the command module. Therefore, the majority of the focus will be on the EPS board itself as it is the most important component regarding stable and reliable voltage regulation to the Command Module, otherwise the whole system will not function properly.
The main goal of the Command Module (CM) project is to create a primary command and data architecture with signal processing capability that can be used in a variety of CubeSats, not just in the upcoming ESTCube-3. An EPS system that is independent from the satellite itself is needed as different future CubeSats might use different input voltages from the satellites EPS. Therefore the CM having its own power system that draws from the satellite’s onboard batteries eliminates the need to redesign the CM for each different CubeSat and it improves its flexibility and operability.
Redundancies & Protection
The purpose of the EPS (Electrical Power System) board is to provide a safe and reliable way of supplying power to the different boards and systems aboard the CM, those being the wider COM and CDHS boards. The intended function of the board is to monitor and control the flow of power. If it detects any irregularities, such as a sudden surge in voltage or anything that could damage or prevent normal operations of subsystems, it will cut the power to the affected system and attempt to restore nominal functions through power cycling that system. To achieve this, a watchdog IC (Integrated circuit) is connected from the CDHS board to two power switches on the EPS board. If it detects any irregularities, it will disable the power switches and attempt to automatically restore nominal functions.
The EPS’s ability to power cycle different subsystems means that it can completely power them down, remove any residual power and then attempt to restart the system. This is not only useful for electrical issues but also for any software issues as this refreshes the affected systems RAM (Random Access Memory) and forces the system to initialize a clean reboot. It is mainly intended to be used for the SoM (System on a Module) which is the main processing unit of the CM. The EPS acts independently from all other systems within the Command Module, this is because if a failure were to occur within the system, the EPS will not be affected. The EPS is also independent because if the SoM which is the main processing unit of the satellite were to have a failure, the EPS can power cycle the SoM and restore operations. Therefore, by having the EPS operate independently from other key boards, we can ensure that the smallest amount of external factors can inhibit the EPS’ functionality.
Power Input from the Satellite to the EPS
The EPS is the board responsible for safely distributing power to everything within the Command Module. The external EPS of the CubeSat supplies regulated 12V voltage through the power connector, but it is up to the Command Module’s EPS board to make sure power is regulated down to lower voltages for specific components and monitor them to make sure that those lines are at that specified voltage. The main 12-15V line runs from the EPS board to the SoM board, which is the main processing unit of the Command Module and satellite. The EPS board will also feature a secondary power source input which will be useful for debugging and it will use a USB Type-C port that is connected to a USB-PD (Power Delivery) chip which removes the need for voltage conversion later on, this will mainly be used for testing.
To achieve redundancy of the components on the power line, they will be doubled and will work simultaneously in a hot redundant state, meaning that if one of them fails, the other one will continue working immediately, ensuring there is no latency in the switch. This prevents the system from losing power for even a moment. In order to prevent uneven depreciation of power switches and converters, load sharing will be implemented to even the current arriving at both identical components to ensure operational stability. Additionally, as the components are not made for the conditions of space, and although resistant and good quality, the effects of radiation and other harsh external factors also demand the doubling of critical electrical components.
The Electronics systems of the Command Module are all managed by the EPS, an independent board and system within the Command Module itself. In order to ensure that the satellite remains functional in the harsh conditions of space and can withstand any issues, all major components of the EPS will be doubled to ensure that if one fails, the other component can immediately take over. The electronics system as a whole will have several failsafes and safeguards to protect against power irregularities, and to restore nominal operations immediately when an error occurs to ensure that the Command Module and the satellite by extension remains fully operational all the time throughout its lifespan.
Big thank you to the Command Module electronics team for their support and input!
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