## 1 Introduction
Even institutions and students without previous specific knowledge of space engineering are able to participate with outstanding results [14], enhancing the outreach of such projects. The European Space Agency's (ESA) Fly Your Satellite! (FYS) program, which started in 2013, is an example of competitions that provide technical and institutional support to the winning projects alleviating their funding constraints [16]. A total of 13 groups have already been supported by the program. Among them, the signal processing group at the Polytechnic University of Catalonia has been quite active publishing the results of several CubeSat missions. For example, they have contributed to the literature with the architectures of the onboard data handling, electrical power supply and communications systems for a technology demonstration mission [17]. They also published the mission analysis and a trade-off analysis for various configurations considered in a Global Navigation Satellite System Reflectometry (GNSS-R) mission [18], and the mission analysis of a different Earth Observation and GNSS-R mission [19]. In the literature, one can additionally find some CubeSat development teams that report their missions with very specific technical information [20; 21], while others prefer to put the emphasis on the mission description, but barely mention the technical details [22; 23]. Some of these works in the literature include a brief section on lessons learned, but such descriptions are typically short hints with little or no relevance to other missions [20; 24]. Some guidelines for carrying out CubeSat projects are presented in Reference [25], as a result of a survey from the CubeSat community. In addition, some (brief) recommendations are made in Reference [26] for designing CubeSats. NASA has also published a guide, especially written for beginners, which sets the bases for starting a CubeSat mission, including descriptions and advice for all phases of the project [27]. The aim of this paper is to provide a structured approach to developing CubeSats, which can serve as a complement to the current literature on CubeSat engineering, through providing technical details, materials and procedures as well as criticism to current practices. The paper uses a reference project based on the data resulting from the design, development, verification and operation of an actual CubeSat, which was conducted at the Lulea University of Technology (LTU), namely qbee50-LTU-OC (SE01). Such a project was part of an international collaboration within the QB50 mission [28]. The mission consisted of a constellation of 36 CubeSats to characterize the composition and the electrical and thermal properties of the Earth's lower thermosphere, between 200 and 380 km of altitude. Each CubeSat was equipped with one of the three different mission payloads, namely, Flux-Phi-Probe Experiment (FIPEX) for measuring the time-resolved behavior of atomic and molecular oxygen, Multi-Needle Langmuir Probe (mNLP) for rapid measurement of electron density, and Ion-NeutralMass Spectrometer (INMS) for identifying the influx of major particles, such as atomic and molecular oxygen, nitrogen and oxides of nitrogen. The present paper reports the necessary steps to initiate a CubeSat project in Section 2. Section 3 focuses on the technical tasks including manufacturing, assembly, and integration phases. Section 4 discusses the test campaigns for the satellite. In Section 5, the paper proceeds with a discussion of issues regarding the shipment of a CubeSat to the launch facilities. Section 6 briefly reports the operation of the CubeSat. Some conclusions are made in Section 7.