On-orbit validation of the OpenHarmony real-time operating system based on the Dalian-1 Lianli satellite

In a research article recently published in Space: Science & Technology, researchers from Dalian University of Technology, COSATS CO., Ltd. (Xi’an), and Xi’an Aerospace Propulsion Institute together reported the ground tests and the on-orbit validation of the OpenHarmony RTOS after porting to 3 subsystems, i.e. a magnetometer, a digital interface sun sensor, and an attitude measurement unit, laying the foundation for future smicro/nanosatellites adopting subsystems ported with the OpenHarmony RTOS.

First, information about the Dalian-1 Lianli satellite’s attitude determination subsystem and an innovative software design using the OpenHarmony RTOS is presented. The Dalian-1 Lianli satellite was developed by the Dalian University of Technology (DUT). Fig. 1 displays the precise location of the Dalian-1 Lianli satellite at the China Space Station. Fig. 2 and Fig. 3 display the main technical parameters and the physical entity of the Dalian-1 Lianli satellite. There are 3 new micro/nanosatellite attitude determination subsystems: the COSMAG (high-performance magnetometer), COSSD (digital interface sun sensor), and COSAMU (attitude measurement unit).

• The COSMAG is a high-performance 3-axis vector-type sensor characterized by a high resolution, a low power consumption, and a strong anti-interference capability. The COSMAG’s dimensions are 34 mm × 34 mm × 10.3 mm, and its mass is less than 30 g. The COSMAG operates by measuring the magnetic field strength in the space environment and uses the International Geomagnetic Reference Field Model as a reference for Earth’s magnetic field.
• The COSSD determines the orientation of the sun vector in the coordinate system and is characterized by a small volume, a low power consumption, a high accuracy, and a high reliability. the COSSD’s dimensions are 47.6 mm ×19.6 mm × 9.3 mm, and its mass is only 21 g. When the 4-quadrant detector senses sunlight, it generates 4 sets of analog photocurrents, which are amplified by an amplifier, converted into digital voltage signals by a 16-bit ADC, processed to digital angle signals by a high-performance processor, and finally transmitted as output signals to the digital output interface.
• The COSAMU integrates a sun sensor, a 3-axis gyroscope, a 3-axis magnetometer, a temperature sensor, and a high-performance processor. It can measure the 3-axis attitude information of the spacecraft in real time and provide high-performance and reliable attitude information output. The COSAMU’s dimensions are 45.6 mm × 45 mm × 11.7 mm, and its mass is less than 55 g. When the spacecraft is in the sun irradiation area, the solar incidence angle and azimuth angle measured by the sun sensor, along with the magnetic field value, are combined to achieve attitude determination. When the spacecraft is in the shadow zone, out of sun irradiation, its attitude is determined by measurements from the inertial sensor and the magnetometer.

The OpenHarmony RTOS was ported to the above 3 subsystems. OpenHarmony is an open-source project incubated and operated by the OpenAtom Open Source Foundation. It is oriented toward application scenarios in the era of all-scenario, all-connected, and all-intelligent environments, building a framework and platform for the operating systems of intelligent terminal devices based on open source to promote the prosperity of the Internet of Everything industry. In 2021, the OpenAtom Open Source Foundation, DUT, Tsinghua University, and other organizations jointly established the OpenHarmony InSpace working group to promote the application of OpenHarmony in the aerospace field. A block diagram of the OpenHarmony structure is shown in Fig. 4. Task management, memory management, and interrupt management are the main functional modules of the RTOS core kernel.

• Task management determines its real-time performance. The RTOS supports multitasking with each task assigned a priority and adopts static priority assignment. OpenHarmony’s multitask scheduling mechanism is based on a priority-based preemptive scheduling mechanism supplemented by a time-slice rotation scheduling mechanism. Function calls and the execution time of services in OpenHarmony are predictable.
• Memory management typically includes memory allocation principles, memory protection, and memory allocation methods. Memory allocation principles include expediency, reliability, and efficiency. OpenHarmony protects the programs and data in memory. OpenHarmony’s dynamic memory allocation supports 2 memory management algorithms: bestfit (also known as dlink) and bestfit_little.
• OpenHarmony uses interrupt handling in interrupt management, which simply means that interrupts are handled on a different stack from normal tasks. This ensures that interrupts only trigger the storage of certain critical registers and do not switch the context of the task, thus greatly reducing interrupt latency.

OpenHarmony Performance is compared with representative RTOSs from around the world, as shown in Table 4.

Then, the ground test is present. The focus of the ground test will be on real-time performance and reliability. Specifically, the real-time test will include the task switching time and the optimal data acquisition rate test; the reliability test will include the system stability test and the verification of the triple modular redundancy (TMR) mechanism. In addition, vacuum and thermal cycling tests were conducted on the Dalian-1 Lianli satellite (Fig. 5).

• In the TST test, the test is performed using an improved algorithm based on Rhealstone, and the test is looped 6,000 times automatically. The hardware platform of the TST test system is STM32F103VET6 with a 72-MHz CPU and 512 KB of flash memory, and the software is OpenHarmony version 1.0 with the LiteOS-M1.0 kernel. Results show that the average TST of OpenHarmony is ≤ 2 μs. It can be concluded that OpenHarmony is suitable for micro/nanosatellites and other application fields that have strict requirements for real-time performance.
• In the data update rate test (Fig. 6), the COSMAG, the COSSD, and the COSAMU are used as the hardware platform, and the controller area network (CAN) analyzer software on the personal computer (PC) continuously sends telemetry commands to the COSMAG, the COSSD, and the COSAMU and saves the data. The maximum data acquisition rate of the COSMAG, the COSSD, and the COSAMU is determined, followed by the determination of the peak rate of CAN communication. When the telemetry commands are neither duplicated nor lost, this is the maximum stable data update rate of the COSMAG, the COSSD, and the COSAMU. Compared with COSSD without the OpenHarmony RTOS, the stable data update rate of COSSD has increased by 3.1-fold from 20 to 62 Hz. The stable data update rate of the COSMAG increased from 20 to 62 Hz, which is a 3.1-fold improvement, and the stable data update rate of the COSAMU increased from 20 to 50 Hz, which is a 2.5-fold improvement.
• In the system stability test (Fig. 7), over 1,000 h of continuous operation tests were conducted in a room-temperature environment, and all relevant data were strictly recorded for in-depth analysis. Results show that the data were received, parsed, and saved normally, indicating that the COSMAG, the COSSD, and the COSAMU exhibit high stability.
• In the TMR test, the COSMAG, the COSSD, and the COSAMU are protected from single-event upsets using TMR technology and the evaluation aimed to verify the program’s ability to perform a 3-module review and autostart loading and to confirm the presence of TMR functionality in the software system. Test results indicate that the COSMAG, the COSSD, and the COSAMU can automatically reboot through firmware checksum changes and load backup software on their own, which confirms that the 3 subsystems have the TMR function.

Finally, the on-orbit verification is reported. After the satellite was successfully released into orbit on 2024 January 18, the 3 subsystems worked normally, the telemetry data were normal, and the on-orbit operation status met the expected requirements. The on-orbit validation of the OpenHarmony RTOS was successful. In addition, the overall satellite is in excellent condition, and the 3 attitude determination subsystems, with their superior performance, have enabled the satellite to capture remote sensing images with a resolution better than 1 m, as shown in Fig. 8. The 3 satellite subsystems that have been ported with OpenHarmony have operated smoothly in the harsh space environment. Among them, these devices accompanied the China Space Station for 253 d of in-orbit storage. This long-term performance demonstrates the excellent performance stability of the satellite subsystems ported with OpenHarmony and also verifies their reliability in on-orbit operation.

Conclusion: Through ground tests and on-orbit validation, this paper demonstrates that porting OpenHarmony to subsystems can improve the real-time performance and reliability of the subsystems and then the overall performance of the satellite. In the future, we plan to port OpenHarmony to more satellite subsystems and apply it to more missions.