# Satellite Edge Computing for the Internet of Things in Aerospace
## 3 The Architecture and Application Scenarios of Satellite Edge Computing
### iSat System
#### 3.1.2 Software Architecture  
As an intelligent node for space edge computing, the core of iSat is the software. Unlike traditional satellites, the functionality of iSat can be defined in-orbit by loading apps. iSat cannot only operate separately to provide a variety of services but also form a space edge computing system through inter-satellite links. The software architecture and collaboration mode of iSat are shown in Figure 3.  
Unlike the tight coupling of traditional satellite software and hardware, the iSat satellite software uses an open hierarchical architecture. Each layer corresponds to the function of the terrestrial cloud computing platform, which facilitates the cloud-edge collaboration to provide services. The functions of each layer and the collaboration mode will be described in detail below.  
The hardware resource layer contains all the hardware units of the iSat. According to the hardware structure, all the devices will be abstracted into five categories of resources: computing resources, network resources, sensors resources, actuators resources, and storage resources.  
The virtual abstraction layer integrates various resources through resource virtualization technology to achieve unified management. Although there is currently no resource virtualization method for satellites, the virtualization methods for the cloud platform, such as virtual machines or containers, have been used in embedded systems [24; 25]. These technologies will be used to implement  
Figure 3: The software architecture and collaborative mode of iSat.  
the virtualized packaging of onboard devices. The virtualized satellite resources can be coordinated with the resources of the terrestrial cloud computing platform. By receiving and executing resource management strategies of the cloud, on-board resources can be deployed on demand.  
The system service layer provides APIs for calling on-board resources and three specific service modules, including control domain service module, data domain service module, and management domain service module. The control domain service module provides real-time services, such as perception of the environment, real-time communication, satellite control system execution, and device resource management. The data domain service module provides preprocessing operations for data. It reduces communication bandwidth by filtering useless data. It includes stream data analysis, video and image analysis, intelligent computing, and data mining. Through the module, satellites can implement data synergy with cloud computing platforms. The cloud develops a data transmission and execution strategy of satellite and delivers it to satellite for execution. The cloud provides storage, analysis, and value mining of the massive received data. The management domain service module provides optimized management strategies, including resources, services, and data. Satellites can implement management synergy with cloud computing platforms via the module. The satellite provides an application runtime environment and management APIs. The cloud realizes the management of the entire life cycle of satellite applications.  
The application layer contains various satellite apps. Satellites can run different apps to provide the corresponding service capabilities based on the needs of the cloud. The cloud needs to provide a corresponding deployment strategy for different satellites according to user requirements.