In order to satisfy the requirements of micro-satellite attitude determination and control system, northwestern polytechnical university and delft university of technology have jointly developed a low-cost micro wireless automatic sun sensor (μWASS). μWASS chooses a four-quadrant detector as its sensing part, uses the low-power 51 microcontroller unit Kernel with integrated ZigBee communication protocol as its processor, and utilizes two triple-junction GaAs solar panels as its energy generating part. And a super-capacitor is creatively be used as its energy storage part. In the meantime, the space environment radiation and high and low temperature variation have been considered during the system design, and the additional protective circuit has been added. The field-of-view of μWASS is 120°×120°, and the accuracy is better than 0.5° (1σ). The average power consumption of μWASS is 30 mW. Compared with the existing analog sun sensors, μWASS is a plug-and-play component. Its measurement data can be transmitted through wireless communication and does not need any special connectors or external A/D conversion circuit, which could not only reduce the installation difficulty but also improve the system reliability of the satellite. μWASS has achieved the low cost, miniaturization and wireless of sun sensor, and it can be widely used in various micro-satellites in the future.

@en

Most of the CubeSats have a volume range from 1U to 3U, which limits their applications due to the difficulty of miniaturizing payloads. To facilitate the needs on a larger but low-cost satellite platform, the AOXiang (AOX) project has been developed by Northwestern Polytechnical University (NPU). The primary objectives of AOX project are four-folds: 1) To demonstrate the world first 12U CubeSat Star of AOXiang and 12U orbit deployer which uses an innovative electromagnetic unlocking technology. 2) To investigate the feasibility of using polarized sunlight for spacecraft attitude determination and navigation, and perform microgravity research using a miniaturized gravimeter. 3) To test a fault tolerant on-board computer using the System On the Programmable Chip (SOPC) technology, and 4) To gain the experience from developing the CubeSat and the subsystems. The CubeSat was launched in June 2016. Now, the mission has achieved all the goals. This paper provides the detail information of the AOX project, with a focus on the introduction of the subsystems of the 12U CubeSat, the orbit deployer and the payloads. The recent in-orbit results of the first NPU are also presented. In addition to the educational objective that has been reached with more than 50 young scholars and students participated in the project.

@en

The speed control accuracy of micro-reaction wheel was improved in order to meet the accuracy requirements for the attitude control of pico-nano satellites and CubeSat. The speed measuring and control system was designed with the switch-type Hall sensor, a speed estimation method was proposed to ameliorate the measurement accuracy, which was combined of time measuring by variable prescalerT-method and average sliding filter with speed switching hysteresis loop. The discrete PID algorithm of integral separation was utilized to prevent the control saturation. Results show that the maximum error of speed control is less than 1.5%, the average error of speed control is less than 0.4‰ and the error variance of speed controlis about 0.25. The reaction wheel provided three-axis stability for the satellite, as an important part of the world's first 12U CubeSat "Star of AoXiang", which was launched by “CZ-7” on June 25, 2016. The satellite had successfully worked until atmospheric re-entry after 99 days. The ground test and in-orbit service of the satellite show that the proposed method is feasible and effective, both the speed estimation method and the control algorithm can satisfy the mission requirement of satellite attitude control system.@en

In this paper, a redundant and integrated avionics for 12U CubeSat is presented. The main innovation is to propose a method to enhance system reliability and fault tolerance based on the COTS(Commercial Off-The-Shelf) devices, as well as to deal with system recoverability for unknown failures without changing the original system hardware. A multi-node architecture based on COTS devices and standard I2C bus is designed considering low cost, modularization, simplification and high-reliability. In order to avoid the I2C bus stuck issue, a bus recovery technology generating 16 clock pulses on the I2C bus is proposed. The cold redundant strategy is utilized on the devices that have no flight heritage. The OBC employs a heterogeneous complementary dual-processor method. A high-speed processor acts the main processor for the normal command data management and attitude control tasks. A high reliability, low-speed processor works as the backup processor for monitoring and fault-tolerant operations, which can protect the system with minimum running cost when the main processor fails. The proposed avionics has been developed and successfully demonstrated on the world's first 12U CubeSat "Star of AoXiang", which was launched on June 25, 2016. the avionics worked without issues until atmospheric re-entry after 99 days in orbit. The in-orbit results of this avionics are presented in this paper.@en