"Debut" a success! The space station's massive sun-facing device is a real eye-catcher.

On July 28, 2022, four days after the launch of the Wentian experimental module, China's first large-scale solar-facing device—launched aboard the module—made its official debut. It successfully completed a series of in-orbit performance tests, with all indicators performing exceptionally well. As a result, China's space station has now achieved dual-degree-of-freedom solar orientation.
What is a "Solar Orientation Device"? Simply put, it primarily manages the rotation of the solar panels and facilitates the efficient transfer of energy both inside and outside the spacecraft—making it one of the key technologies that was first prioritized during the early stages of China's space station project. Once the space station is fully constructed, all kinds of scientific instruments and payloads housed within—including critical equipment essential for sustaining astronauts' life support systems—will rely on this large-scale Solar Orientation Device to deliver electricity efficiently and reliably from the exterior to the interior of the station. In essence, it truly serves as the space station's "energy guardian."

Full of energy, yet still able to turn.

To ensure the space station's electricity needs, the Wentian experimental module is equipped with large, flexible solar wings, each measuring 27 meters in length with an effective power-generating area of approximately 110 square meters. These wings can continuously supply the station with a steady flow of energy. However, smoothly maneuvering these two flexible solar wings in orbit—allowing them to "circle" effortlessly and capture sunlight around the clock—is no easy feat. Imagine holding a 27-meter-long "banana leaf fan" in one hand, using your wrist as the center point to rotate it 360 degrees; this would require your wrist to possess exceptional strength and rotational power. In this analogy, the module’s sun-facing orientation mechanism acts like your wrist, tasked with steadily rotating the solar wings while keeping them precisely aligned with the sun. The space station’s sun-tracking system provides an uninterrupted source of energy for the entire spacecraft, yet the harsh space environment faced by components constantly exposed outside the cabin poses a severe challenge to large-scale rotating mechanisms. Ensuring that the sun-tracking device drives the solar wings with pinpoint accuracy, while simultaneously preventing any mechanical jamming or stalling, has proven to be a monumental challenge for the development team. To tackle this issue, the team launched an intensive brainstorming session and devised a groundbreaking, domestically pioneered "distributed rotary support drive and transmission solution." This innovative design guarantees that even when the massive guide rails experience thermal expansion and contraction due to extreme temperature fluctuations, the drive mechanism can still operate smoothly, enabling the two colossal solar wings to continuously track the sun in real time. Additionally, the team has added a specialized "temperature-control jacket" to the sun-tracking system, ensuring that the mechanism remains within an optimal temperature range despite enduring prolonged exposure to both scorching heat and freezing cold in the unforgiving space environment.

Efficient and also needs to spread quickly.

Our daily electricity usage is delivered to countless homes and businesses through the vast grid system of power plants, but in our solar system, the Sun itself acts as a natural "large-scale power plant." Yet, how do we efficiently transmit the tens of thousands of watts of electricity generated by those massive, flexible wings directly to the space station—establishing a stable and highly efficient "energy lifeline"—to ensure the station truly achieves "uninterrupted access to power"?
Typically, most spacecraft rely on the conventional slip-ring method for electrical power transmission. Simply put, a slip ring serves as a "rotating joint" that connects and transfers energy. However, due to the inherent sliding wear associated with this approach, it’s generally suitable only for spacecraft handling kilowatt-level power transmission. In contrast, space stations require power transmission levels more than 20 times greater than those of ordinary spacecraft—and they demand exceptionally long operational lifetimes. Faced with the significant energy losses caused by sliding friction, the space station leaves no room for compromise: it insists on "zero tolerance" for such inefficiencies! To address this challenge, the development team has pioneered an innovative rolling-ring electrical transmission mechanism that delivers ultra-high power while boasting an unprecedentedly long lifespan. This marks the first time in China that rolling contact technology has been successfully applied to achieve high-power transmission, replacing the traditional sliding method. To rigorously validate the rolling ring's exceptional reliability, efficiency, and durability, the team conducted an accelerated life test on the ground, pushing the mechanism through 200,000 continuous rotation cycles—equivalent to 34 years of in-orbit operation under real-world conditions. This rigorous testing ensures 100% product reliability, guaranteeing a consistently efficient and uninterrupted energy supply for the space station throughout its entire mission lifecycle.

Get it right, and keep it steady.

During the space station's in-orbit flight, how is it ensured that the solar wings remain precisely aligned with the sun at all times? The Sun-Pointing Device is equipped with a rotary transformer—hidden within its "body"—that continuously captures real-time data on the sun's rotational angle. Once this information is received from the attitude control system, which dictates the desired motion pattern, the Sun-Pointing Device can autonomously plan its movements and finely adjust its orientation, enabling the solar wings to steadily track the sun, much like a "sunflower" turning toward the light. "Beyond achieving accurate alignment," the development team shared during the design phase, "the real challenge lies in controlling such large, ultra-flexible solar wings smoothly and stably." With an effective total power-generating area of approximately 220 square meters and each wing stretching a full 55 meters in length, these solar panels are as delicate as ordinary printer paper—so soft that even the slightest vibration could cause them to sway unpredictably. If the solar wings fail to rotate smoothly, it would severely complicate the space station's attitude-control maneuvers. To address this critical issue, a groundbreaking "Highly Stable Servo Control System for Large, Flexible Structures" was developed specifically for the Sun-Pointing Device. This tailor-made control solution empowers the solar wings to "dance gracefully," ensuring stable and precise tracking of the sun throughout the mission.
Even more impressive is that when the solar array wings experience external disturbances causing them to shake, the control system of the sun-pointing mechanism can detect these movements with remarkable sensitivity and swiftly "calm them down"—much like the art of Tai Chi, transforming the tangible into the intangible. Within just 30 seconds, it effectively dissipates the elastic vibrational energy of the solar wings, ensuring the space station enjoys "steadfast happiness."

High reliability also requires a tight grip.

This time, the Wentian laboratory module was carried by the Long March 5B launch vehicle—specifically customized for the construction of the space station. Known for its safety, precision, and reliability, this rocket is dedicated to providing premium services to the space station, our "major client." However, during the rocket's flight phase, the Wentian module inevitably endures significant loads, especially at the ascent stage. In particular, the sun-facing orientation mechanism, mounted on the resource module at the very rear end of the experiment module—and positioned right at the top after entering the rocket's fairing—faces the brunt of the intense pressure. "As countless paths may lead to success, safety remains the first priority." To prevent the sun-facing mechanism's delicate components from being overwhelmed during the launch phase, the design team ingeniously introduced a new W-shaped wrapping strap, effectively equipping the mechanism with multiple layers of protective "safety belts," ensuring it can withstand the rigors of flight with greater peace of mind. Once the experiment module successfully enters orbit, these "safety belts" receive an automated release command, allowing the sun-facing mechanism to freely activate its tiny motor and embark on its remarkable journey of tracking the sun across the sky. This in-orbit test marks the debut of the large-scale sun-tracking system in China's space station assembly process. The successful completion of this critical trial will lay a robust foundation for future space station construction and long-term operational activities in orbit.

Translated from China Science and Technology Net

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