# Agile Stage-Gate Approach for Design, Integration, and Testing of a 1U CubeSat
## 1 Introduction  
A CubeSat is a cube-shaped satellite in which the unit is defined as U. A 1U satellite has limited dimensions and mass (volume of 10 \(\times\) 10 \(\times\) 10 cm\({}^{3}\) with mass up to 2 kg) according to the CubeSat program initiated in 1999 by California Polytechnic State University (Cal Poly) and Stanford University [1]. Since 2000, the National Aeronautics and Space Administration (NASA) has allowed nanosatellites to be launched through the CubeSat Launch Initiative (CSLI). The idea of this program is to launch secondary payloads via planned launch or as deployments from the International Space Station (ISS); for this possibility to be realized, the project must go through a process in which only strategic missions are selected. As of 2023, NASA has invested in the future of technology and science through the CSLI program, which has launched over 150 nanosatellites. The AztechSat-1 project started in 2017 at the Universidad Popular Autonoma del Estado de Puebla (UPAEP) in collaboration with the Mexican Space Agency (AEM). This project began as a requirementestablished by NASA in which the core mission was to develop the first nanosatellite designed and assembled in Mexico for further deployment from the International Space Station. The primary goal of the project is to enable intersatellite communications between the nanosatellites and the GlobalStar constellation. The GlobalStar first-generation satellite communication system operates in low earth orbit and originally consisted of a constellation of 48 satellites positioned at an approximate altitude of 1414 km; 12 satellites have since been added. These satellites are distributed among eight planes, each accommodating six satellites and following circular orbits with an inclination of approximately 52 degrees. Table 1 shows the parameters of the first-generation GlobalStar constellation. The GlobalStar constellation was upgraded with 24 second-generation satellites whose frequencies are within the L band (1-2 GHz), S band (2-4 GHz), and C band (4-8 GHz) [2]. In recent years, a new industry of nanosatellites has been created, and leading universities have now set a standard [3]. Nanosatellites are generally placed in low earth orbits (LEOs) [4]. Sometimes, such satellites rely on constellations that can improve the communication budget and simultaneously reduce costs [5]. Even with a reduced number of ground stations, the window of communication can be increased considerably compared with that of single stations. The AztechSat-1 proposal is based on the idea of communication between nanosatellites and an existing constellation of satellites. Although there have been attempts at constellation missions using nanosatellites, there are few proposals for nanosatellite communications using an existing satellite constellation. For example, the BIRDS Project started in 2015 as a constellation of five 1U CubeSat nanosatellites; however, each CubeSat communicates between its own ground station [6]. Aerospace projects depend on a sequence of methodological procedures for developing product solutions through various life cycle stages. The nature of these products is generally complex, and making decisions is a difficult task. Aerospace manufacturers, unlike those in many other industries, examine information and knowledge in a Stage-Gate process also known as the waterfall approach. Stage-Gate methods describe a product development process broken into phases, each with tasks and due dates [7]. Although different models for managing aerospace projects entail a unidirectional course, most of them provide dynamic approaches based on recursive and iterative methods. The Stage-Gate model utilizes sequential processes for a given pattern. In-depth studies have been carried out to review these practices using key elements such as stages (where activities take place) and gates (where information is assessed).