Command and Data Handling(C&DH) system, composed of a main computer, performs two important roles in a satellite. Upon receiving an uplink from ground station or getting a calculation result in the satellite, C&DH system sends commands, information about how subsystems should process. Moreover, C&DH collects data in a satellite and distribute data to the subusystems. After collecting data such as housekeeping data and mission data, C&DH saves the data, and then, sends the data to the Comm system to downlink or uses the data to generate a command to the other subsystems. In addition to these, C&DH system also has roles to control time and detect errors in a satellites.
C&DH system in Cute-1.7 + APD consists of PDA as the main computer, DAQ(Data AcQuisition) and USBHub expanding the interfaces PDA provides, and PDASwitch detecting errors in PDA. In spite of being inexpensive and having high performance, PDA provides only one USB port as the external interface, therefore, USBHub needs to be attached to the port to provide enough USB ports to the subsystems. In addition, DAQ is necessary because it is difficult to process analog data from sensor and digital data to send commands with USB interface. Being designed for terrestrial use, PDA does not cover space environment. Thus, two PDAs which PDASwitch switches on detecting errors are used in Cute-1.7 + APD after environmental tests such as radiation, thermal, and vacuum test are conducted.
C&DH System Block Diagram
Profile of Handling Data
Specification of the PDA is shown below:
| Specification of PDA | ||
| CPU | ARMV4I 400MHz | |
| OS | Microsoft Windows CE.NET | |
| RAM | 32Mbyte | |
| Flash Memory | SD Card 128Mbyte | |
| Interfaces | USB,MMC/SD Card slot | |
| Dimensions | 70(W) x 100(H) x 5(D)mm | |
| Weight | **g | |
PDA Board
DAQ, connected to PDA through USB interface, collects analog data such as gyro, power voltage and current, and magnet torquer current and handles digital data such as power on/off, reset command, tether deployment command, and magnet torquer output command. DAQ uses CISC type MPU, RAM:256Kbyte，FlashROM:8Kbyte，Freq:25MHzis, and provides 17ch DI/O and 49ch Analog interfaces through multiplexer, which can be accessed from PDA through USB.
DAQ System Block Diagram
DAQ Top View
DAQ Bottom View
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