**3.1 Satellite management unit**

The Satellite Management Unit is an improved satellite research equipment. The design fully draws on the advantages of the previous satellite platform and has been optimized and expanded. The main completed functions are as follows:


up to 10 Mbps. For data rate higher than 10 Mbps, industry trend is moving toward SpaceWire data bus that can handle data rate up to 400 Mbps.

The SMU adopts the dual-machine cold backup working mode. In the case of the autonomous switching enabled, when the on-duty machine fails, the failure-tolerant module automatically completes the switch of SMU and power off the faulty machine. In the case of the autonomous switching not enabled, when the on-duty machine fails, the power failure and machine switch is conducted by ground station.

## **3.2 Integrated service unit**

The Integrated Service Unit (ISU) adopts modular hardware design [14, 15]. Each functional module is connected to the "bus interface management module" through an internal bus, which uses widely acceptable data bus such as 1553B bus. The ISU is mainly composed of a bus interface management module, a matrix instruction and matrix telemetry module, and an analog quantity acquisition and a discrete instruction output module.

The menu module is mainly composed of a bus interface management module, a matrix acquisition and command module, and an information acquisition and command module [16]. The module menu is shown in **Table 1** below.

The functions of each module are also modularized. The capability of each module is shown in **Table 2**.

After the module design is completed, the number of modules is determined according to the task requirements. Then, complete the assembly according to the standard interface. The number of modules menu is shown in **Table 3**.

## **3.3 Data bus network**

The data bus network is the information transmission hub of the avionics system. Through the data bus network, distributed data acquisition, and instruction output, centralized operation and control are implemented, thereby improving the efficiency of system processing. The avionics system first-level bus is 1553B bus [17]. Note that for data rate higher than 10 Mbps, SpaceWire data bus is recommended.

Data exchange between SMU and ISU and other equipment realized through 1553B bus. The master–slave response mode of the 1553B bus is used to transmit platform command data and telemetry acquisition data. In the data exchange process of the first-level bus, the SMU always acts as the controller of the 1553B bus


**Table 1.** *Function module list.*


#### **Table 2.**

*Modularized functions.*


**Table 3.** *Menu-style design.*

and initiates the communication. ISU and other equipment, as the RT end, receive instructions and send collected telemetry data to the SMU.
