## 2 The \({}^{3}\)ColStar Satellite Mission
### Preliminary Design
#### 2.3.5 Communication Subsystem  
To transmit data effectively, the system must take into account the speed of the orbit, the distance and a limited power budget, and the location of the electrical components in the CubeSat is difficult due to its small size, which represents a challenge in the design of the communications system. Satellite communication requires an Automatic Identification System (AIS), this communication system is designed to have three subsystems: AIS, data communication and Telemetry, Tracking and Control (TT&C) [88].  
The Cubesat communication system is composed of one dipole antenna compact and efficient with necessary radiation pattern, gain, and reconfigurable polarization. The transceiver is capable of VHF and UHF operation; it receives the Telecommunand and IoT  
Figure 8: \({}^{3}\)ColStar ADCS interfaces.  
data and transmits the payload and Iot data to the ground station. The architecture of the communications system is shown in Figure 9.  
Satellite operating in LEO orbit have the advantage of affordable launch costs, as well as less stringent communication link power limitations due to the shorter distance for the communication link [88]. However, LEO satellite ground station antennas must track and follow the satellite as it passes the ground station. The Doppler effect present in a satellite communication link is very harmful for applications based on Frequency Shift Keying. Satellite tracking through specialized software allows to maintain the best transmission and reception characteristics when connecting to the satellite [89; 90]. This tracking is performed in the Ground Station through the use of the following elements:  
* SDR: The software-defined radio allows one to process the message signal improving favorable characteristics for a correct demodulation.  
Figure 9: Schematic for \({}^{3}\)ColStar communication system.  
* The general control system: Manages message reception and antenna positioning; often this task is performed by software such as orbitron.
* Prediction: From the georeferencing of the ground station, it predicts the time and direction of possible links with the satellite.
* Rotator System: Allows one to orient the antennas towards the satellite to ensure the highest power gain in the link.  
The communication system for ground station transmission and reception operation is shown in Figure 10.  
For the link budget, the VHF uplink and UHF downlink could be used as the communication network for CubeSat in TT&C applications [89; 91; 92]. The main characteristics evaluated on the Spacecraft-Ground Station link are shown in Figure 10.  
IoT nodes will be designed for ground segment purposes. The self-development is compatible with the commercial transceiver for the operation of this project, which is portable and has the ability to achieve the uplink with the satellite. The design parameters are listed below:  
* Portable with self-sustaining power supply.
* Operation by reception of satellite alert signals.
* Unique identification code for each node and intercom system with satellite for logging tasks and access for IoT data upload.  
The Collect Mission Data Activity is shown in Figure 11.  
Accessing the satellite requires the implementation of an identification system, which also allows distinguishing between Telecommand or IoT data upload [93] using the uplink, according to the process shown in Figure 11[94], where TFPH is the Transfer Frame Primary Header, SH is the Segment Header and FECF the Frame Error Control Field [95]. The RAC (Remote Control Access Code) and IAC (IoT Access Code) allow the OBC to switch between these two uplink tasks. For the satellite construction the Astrodev Hellium from Pumpkin's radio is available; it operates on commercial and amateur radio links, and these have low power consumption and low mass budget and the adaptability to change the data rate and frequencies in flight mode. Its main technical characteristics are shown in Figure 12:  
Figure 10: Uplink and downlink characteristics.