# Agile Stage-Gate Approach for Design, Integration, and Testing of a 1U CubeSat
## 2 Materials and Methods  
The main objective of the AztechSat-1 project is to develop a flight-certified 1U CubeSat-type nanosatellite for deployment from the International Space Station and to establish a communication link between the nanosatellite and the GlobalStar satellite constellation [14]. As a secondary objective, this project seeks to transmit tokens to radio amateurs on the 435 to 438 MHz bands. Upon receiving these tokens, the radio amateurs can decode the tokens and, thus, obtain a QSL (from the Q code \"I confirm receipt of your transmission) card endorsed by NASA, AEM, and UPAEP. Figure 1 illustrates the diagram of operation for the AztechSat-1 mission. The mission demonstration will motivate new CubeSat projects to use this resource so that they can download their mission data at higher speeds without the need for an intermediary ground station. AztechSat-1 consists of a single 1U CubeSat. The main component of the AztechSat-1 is the payload, which is a standard CubeSat board used for intersatellite communication. The payload is a circuit board designed by UPAEP which works as the core of the spacecraft by sending data from the nanosatellite to the GlobalStar LEO constellation, thereby enabling and demonstrating intersatellite communication. This satellite is also equipped with a communication board to allow Earth-to-satellite communication. The nanosatellite will also offer ground-to-satellite communication as a backup and is intended to be the trigger for the aerospace industry in the region. Some efforts have already been made to provide low-cost ground stations for nanosatellite missions, such as the Canadian Advanced Nanospace eXperiment program (CanX), in which the University of Toronto demonstrated the feasibility of an affordable S-Band ultra-high frequency (UHF) ground station by utilizing a terminal node controller (TNC) based on a Gaussian Frequency Shift Keying (GFSK) modem and an ARM computer with a Linux kernel [15]. Nevertheless, AztechSat-1 involves an intersatellite communication approach backed up by a communication system between the ground station and the nanosatellite following a similar approach proposed by the University of Toronto. NASA, AEM, and UPAEP collaborated on a project in which Mexican students could learn from experts throughout development from planning to mission operations. Some nanosatellite missions have already examined the constraints and impacts for CubeSats in low earth orbits, highlighting the design of the communication system [16]. Figure 2 shows the complete configuration details of the AztechSat-1 communication block. As illustrated, the nanosatellite possesses a backup system for its communications based on a standard communication system, through which it can receive commands and send telemetry. The nanosatellite computer can send information to the ground station through the communication module, after which the information is processed by a computer and can be analyzed by the user. In another possibility, the on-board computer of the nanosatellite sends information via the intersatellite module. In this scenario, the data are sent to the  
Figure 1: AztechSat-1 mission operation diagram. nearest satellite of the GlobalStar constellation. Then, the satellite redirects the information to the Earth gateways. Finally, the message goes through a simplex gateway connected to the Internet, and the user can access the information through any web browser. Importantly, the user must know the authentication credentials for this purpose. AztechSat-1 was intended to follow general guidance from NASA and AEM. The scope of this project included system engineering and project management performed by engineers from NASA [17; 18]. AztechSat-1 is the first nanosatellite designed in a Mexican university by a group of professors and students with no previous field experience. A level of experience is needed, however, for projects implementing the Stage-Gate process.