Introduction to Electrical Subsystem
Electrical subsystem is responsible for taking care of power and computational requirements of the system. It manages the power available on the satellite and regulates its distribution. Electrical subsystem equips the system with the required processing power which is used for controlling the satellite, power regulation, handling communication (between IC’s) and for various decision making involved during mission life. It provides and manages data storage onboard the satellite.
Contents
System Level Requirements on Electrical Subsystem
- Detect separation of the satellite from launch vehicle
- Receive and store power for future use.
- Provide adequate and regulated power to all components onboard the satellite
- Provide the necessary computation power
- Monitor status of the satellite
- Provide data storage
- Respond to KILL, RESET and other tele-commands through uplink
Electrical Subsystem Team has to take care of physical realization of all the hardware, firmware and software and associated interfaces required for fulfilling the above requirements and its testing.
Dependence of other Subsystem on Electrical and vice versa
Attitude Determination and Control (ADCS)
The ADCS subsystem is primarily concerned with determining the satellite's position and maintaining a stable orbit. The electrical subsystem is required to interface with sensors and actuators and execute the control-law calculations that determine the required actuation from the current position. The electrical subsystem ensures required power supply to the sensors and actuators. The onboard processor shall execute the control law as designed by the ADCS subsystem. This includes performing the requisite numerical calculations with the desired accuracy as well as according to the predefined sequence and timings. Control signals generated by the processor are used to provide required power to actuators which control the satellite.
Communications
Communication boards are to be provided adequate power for transmission which will ensure reception of the signal at the ground station with sufficient power. For the purposes of monitoring the status of the mission, the satellite will transmit the health of the various components during downlink. In this regard, the electrical subsystem is required to send parameters like health, temperature, latitude, longitude, altitude data etc which is suitably packaged using a packeting protocol like AX.25 which will allow detection on data corruption on reception at ground station. The electrical subsystem will be required to log some of these parameters while in orbit and save them in the data storage and downlink it at the time when it passes over certain specific ground station or on request from the user received via uplink. The communication may be designed such that it receives telecommand from ground station. Electrical subsystem has to decode the telecommand received and do the needful action.
Mechanical
Integration
The final PCB must conform to the requirements of the harness to be designed by the integration team. Typically, corners of the PCB and the places where it is to be mounted is grounded. Satellite body is the ground, all voltage levels onboard the satellite are with reference to it. Integration team has to bring connectors from solar panels which are outside the satellite body, inside the satellite and interface them with circuit of the electrical subsystem. A SNAP-RBF has to be placed and interfaced along with the launch vehicle interface so that separation can be detected and it can trigger the booting of the subsystems onboard the satellite
Thermals
Thermals Sub-System should protect the solar panels from heating above 70C. They should maintain the temperature range of the battery within 0C to 30C. They should maintain the temperature of the board within the operating temperature range of the components (industrial grade) i.e. -40C to +85C.
Quality Considerations
Quality Control requires the electrical subsystem hardware to be tested extensively to reduce chances of infant mortality. For the satellite to have a life of a couple of months, the estimate of the probability of failure should be below some threshold. The quality of the software plays a big role in the success of the satellite as a whole. The quality will be ensured by keeping proper coding conventions in mind including naming conventions and extensive in-line comments. The software will be tested by a code walk-through, coverage tests, unit tests to ensure that the software performs the requisite functions in the correct manner. Finally, the complete electrical subsystem will be tested using OILS (On board computer In-Loop Simulations) to ensure that the probability of failure is low.
Skills Required from Subsystem Members
The following skills are beneficial of the team member has them while joining. They should be imbibed if the team member lacks them while joining:
- Software Skills: C/C++, Embedded coding, EagleCAD, MATLAB, etc.
- Hardware Skills: Soldering, Multimeter operation, DSO operation etc.
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