# Satellite Edge Computing for the Internet of Things in Aerospace
## 2 Related Works
### New Concept Satellite Research  
Traditional satellites can be divided into two parts: platform and payload. The payload determines the function of the satellite. The platform provides relevant guarantee services for the payload. With the development of microsatellite technology, various new technologies are continuously applied to satellites, such as integrated circuits, digital signal processing, MEMS, and additive manufacturing, etc. Various countries are actively exploring the next-generation satellite. Many new concept satellites have emerged. These new concept satellites mainly focus on the following two aspects: module standardization and function software definition.  
In terms of improving the modularization level of satellites, some institutions carry out the relevant research work and have achieved some results. In the standardization of satellite structure, a low-cost spacecraft platform with multi-payload adaptability for low-orbit space missions, called CubeSat, is proposed [18]. It uses a cube with a side length of 10 cm as a standard unit and can flexibly combine according to task requirements. In the standardization of the satellite interface between hardware modules, a plug-and-play satellite (PnPSat) is proposed [19]. Its components are analogous to the USB components of a personal computer, which can be formed by simply plugging together. In terms of improving on-board resource sharing, a satellite is divided into a standard set of subsystems, called Satlets [20], which can \"sense\" they are aggregated and cooperate in sharing resources. These proposed satellites have promoted the standardization of satellite modules, the plug-and-play of devices, and the enhancement of satellite resource sharing capabilities. However, the application of these satellites is still the traditional model. To improve the capability of satellite service in-orbit, some institutions conducted related studies on satellite software.  
The software-defined satellite is inspired by software-defined radio (SDR). In 2012, the International Space Station carried out three SDR payload for technical verification. The \"Eutelsat-quantum\", designed by European Space Agency (ESA) and Eutelsat, is a software-defined payload satellite [21]. It changes the parameters of the communication payload by software defined to achieve functional reconfiguration. The satellite is expected to launch and conduct in-orbit experiments in 2019. The Institute of Software, Chinese Academy of Sciences (ISCAS) organized the Software Defined Satellite Technology Alliance in 2017. The alliance aims to create an open-source platform-level software solutions for satellites using a common computing platform, creating the conditions for flexible software definition and expansion of satellite capabilities. The first experimental satellite \"Tianzhi-1\" for verifying the technology was launched in November 2018. Currently, although some satellites already have a certain degree of software definition capabilities, the related technology of software defined satellites is not mature enough. However, such satellites have enormous potential for various applications. Moreover, some studies have combined satellites with edge computing to deploy edge computing servers on satellites for lower latency and boarder coverage of terrestrial-satellite communication [22; 23]. However, they pay attention to the performance of terrestrial-satellite communication, and neither of them considered the effects of satellite orbits. To improve the QoS of IoT system, we propose the iSat for IoT in aerospace. To the best of author's knowledge, it is the first satellite edge computing for IoT. iSat not only has software-defined capabilities but also can perform edge computing, such as onboard resource virtualization, resource on-demand scheduling, task offloading, and cloud-edge collaboration.