## 2 Methods and Materials
### Alfacrux Ground Segment
#### 2.3.1 Ground Station Architecture
Time update enforcement twice a day has been added to the task schedulers. This procedure was implemented after observing the impact caused by the delay or advance of a few minutes during the operation with AlfaCrux. Moreover, it guarantees a reliable and satisfactory satellite clock synchronization. The satellite clock synchronization is performed by the operator through specific telecommands, and it is regulated from the main server at the ground station. In this  
Figure 6: Ground station architecture. framework, the precision of the satellite clock is given by the precision of the ground station's main server and computers. The clock synchronization between the server and computer systems is achieved using the Network Time Protocol (NTP), specifically a server provided by the [[https://ntp.br/](https://ntp.br/)]([https://ntp.br/](https://ntp.br/)) (accessed on 20 September 2022). The maximum error of a clock set through an NTP client varies from fractions of milliseconds to a few tens of milliseconds, depending on the quality of the network. Asymmetric routes and network congestion can cause errors of 100 ms or more. Quantitatively speaking, for the proposed solution, values less than 100 ms were noticed, which should provide an idea of the precision magnitude. The impact of these delays is twofold: orbit propagation for the tracking system and data analysis and use for different applications. In the first case, considering the pointing tolerance of 5 degrees and the precision of the tracking system, it was noticed that a mismatch of less than 30 s is affordable. In the case of data use and analysis, a regularization procedure is executed at least once per day. The regularization of the satellite's current time is progressively performed in order to avoid jumps in time. Consequently, the time is not changed immediately. The duration of the regularization must be longer than the time span to be advanced or delayed. For example, if the on-board time is 20:30 and we want to set it to 20:15, the duration of the regularization should be set to greater than 900,000 ms. Moreover, in case higher precision is needed for data use, time corrections can also be applied in the mission control software. Another innovation in the architecture of the ground station was the use of containers, allowing for greater compartmentalization and isolation of solutions. To facilitate the container management, the free graphical manager Portainer was installed. In all, 5 containers are configured, namely, CouchDB for the MCS database, PostgreSQL for the MCS database, MCS server, Rotctld rotator control daemon, and an SDR container. Data registration is performed in an encrypted form in a CouchDB database and in a PostgreSQL database exclusive to the application. To comply with the need for data study and analysis, the MCS software has an API that allows access to data through web services. For this reason, a Python 3.6 program was developed with the objective of performing three operations during its execution: (i) update all existing parameter tables; (ii) update all executed remote controls; (iii) update all telemetry received. The result of this operation, in a way, is a backup of the data while creating a security layer for data access since, after updating, the data are provided through another API, developed by the AlfaCrux team to be accessed by students, researchers, and the amateur radio community. In addition to this API, the AlfaCrux team also developed an interface that allows the collaborative collection of telemetry from anyone that have received packages from the AlfaCrux satellite, recorded the telemetry and generated a KISS frame file. This interface, an online form, allows recording latitude, longitude, email, name, call sign, and KISS frame file. Finally, data duplication analysis mechanisms will be necessary and even, without prejudice to data quality, the creation of a composite primary key that allows differentiating the data source, which may lead to the possibility of telemetry duplication.