1. Satellite On Board Computer Software
ECE Computer Engineering Design Project
Satellite On Board Computer Software
Brendan Bruner, Divyank Katira, Oleg Oleynikov, Jeffrey Ryan
2015
Project Motivation
QB50 invited 50 Universities to send in proposals for Cube Satellite projects. In response to this a group of people at the University of Alberta created AlbertaSat, and are now building Alberta’s first satellite, Ex-Alta 1.
A Cube Satellite is roughly 10 cm in all dimensions. The satellite being built by AlbertaSat consists of 3 of these sections, so it will be a 3u CubeSat.
The University of Alberta is also designing and developing its own scientific probe, a Digital Fluxgate Magnetometer (DFGM). The objective of the DFGM is to measure magnetic waves.
The On Board Computer
The On Board Computer (OBC) is at the center of all the systems that run on the satellite. It logs status information and scientific data for all payloads and support systems. In addition, it interprets and executes incoming commands, along with controlling data flow to and from the ground stations.
The layout of all these systems can be seen in Fig There are three support systems: the Electronic Power Supply (EPS), the Attitude Determination and Control System (ADCS), and the Communications (COMM) board. There are two scientific systems, as previously described: the MNLP and the DFGM. There is also an external memory card, and a GPS connected to the ADCS.
State Machine of OBC
The satellite is state driven, there are four states used for initial startup and three states for regular operations, which can be seen in Fig. 2. First, there is a simple “Powered On” state before the satellite is deployed. There is then a “Post Ejection” state where, by QB50 specifications, the satellite cannot do anything for 30 minutes in order to not interfere with other satellites. Then, according to power levels, the computer will either start up or wait for power to be at a sufficient level.
The three operational states are quite simple and are determined by the power level and the physical orientation of the satellite. The Electronic Power Supply (EPS) and Attitude Determination and Control System (ADCS) will communicate these properties to the On Board Computer, respectively. According to them the satellite will be in a “Power Safe” state, where only vital operations are allowed, a “Detumble” state where the satellite is physically orientating itself, and a “Science” state, where the satellite is operating normally and collecting scientific data.
Artist rendition of a Ex-Alta 1. [Andy Kale]
For colour ideas, University Visual Identity Guidelines can be found here:
The satellites will be launched in early aboard a Cyclone IV rocket from Alcântara Launch Center in Brazil. They will be released at an altitude of 400 km and have a lifespan of roughly 2 years before burning up in the atmosphere due to a decaying orbit.
QB50 requires that the satellite contains and opreates a scientific probe called a Multi-Needle Langmuir Probe (MNLP). The purpose of this probe is to measure plasma density in Earth’s upper atmosphere.
Fig. 2 State diagram of On Board Computer. [Brendan Bruner, Jeffrey Ryan]
For up to date information on the Ex-Alta 1, please visit:
This project would not have been possible without the hard work of the members of AlbertaSat, or without the help and cooperation of QB50.
The NanoMind A712, the OBC hardware. [ a712c]
Fig. 1 Block diagram of satellite systems. [Oleg Oleynikov]
Department of Electrical & Computer Engineering