# Review and Evaluation of MAC Protocols for Satellite IoT Systems Using Nanoatellites
## 2 Overview of Space and Communications Systems
### CubeSats  
Traditionally, most of the projects for designing and building satellites have been excessively expensive. They involved complex designs and, consequently, long development time spans. However, starting in the 1980s, a new paradigm was established that significantly reduced the size of some satellites, leading to the appearance of microsatellites and, in the 2000s, the creation of nanosatellites or CubeSats: aircraft whose weight is equal to or less than one kilogram.  
The CubeSat standard was created in 1999 at the California Polytechnic State University in conjunction with the Stanford University's Space Systems Development Lab. The development of this standard aimed at improving access to space by providing opportunities for satellite development, design, and construction to institutions that could not do so with the classical paradigm. Figure 3 shows the number of Cubesats launched and operational to date.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Company** & **Number of Satellites** & **Orbit** & **Services** \\ \hline Inmarsat & 13 & GEO & Broadband \\ Viasat & 4 & GEO & Broadband \\ Intelsat & 52 & GEO & Broadband \\ O3b & 16 & MEO & Broadband \\ Iridium & 66 & LEO & Voice, broadband \\ Globalstar & 24 & LEO & Voice, broadband \\ \hline \hline \end{tabular}
\end{table}
Table 1: A set of commercial constellations providing communication services as of 2018.  
The basic design of a CubeSat consists of a 10-cm cube--called 1U--which must contain the primary subsystems for the operation: an onboard computer, batteries, transmitters and receivers for communication, and attitude determination and control system (ADCS), among others. The cubic shape and volume defined for this new standard considerably reduce launching costs, but, at the same time, incorporate restrictions regarding availability of computational resources, energy, and volume, among others.  
Initially, the development of nanosatellites was intended to test components and study their behavior in the space environment. Nowadays, applications have spread widely with projects led by universities, governments, and commercial entities. Moreover, and of interest to the authors, this technology represents an excellent opportunity for developing countries to exploit space resources in addition to providing a tool to democratize the use of space [20].  
In South America, for example, several countries have taken advantage of nanosatellite technology to promote educational initiatives within universities, including, the Libertad-1 in Colombia (Sergio Arboleda University) [21], PUCSAT in Peru (Catholic University of Peru) [22], SUCHAI-1 in Chile (University of Chile) [20], to mention just a few. In the commercial field, new companies have appeared in the market for developing and selling CubeSat parts and pieces; other companies make use of CubeSats for applications such as satellite imaging collection. Government agencies, such as NASA and ESA, developed nanosatellite-related missions. One of the most notable examples is the experimental use of two CubeSats--Mars Cube One (MarCO) A and B--as communication relays for the InSight-1 probe that landed on Mars in November 2018.