China is looking to build on its recent moon sample return success by attempting to retrieve material from an ancient near Earth asteroid.
The country will launch a spacecraft in 2024, reaching Kamoʻoalewa, a quasi-satellite of Earth, in 2025. When it returns home a year later it hopes to deliver invaluable samples from a body of rock thought to be made of remnants from the early solar system.
In keeping with China's long-term approach to space of developing and building specific and more advanced technologies, the mission will aim to be a milestone in Chinese exploration by apply newly-developed capabilities and science prowess in a novel scenario.
The mission will follow in the footsteps of the Japanese Hayabusa 1 and 2 missions, and NASA's OSIRIS-Rex, while presenting new and greater challenges for China. The country has so far launched just one interplanetary mission, Tianwen-1, which saw an orbiter and rover arrive at Mars earlier this year. And while it has collected samples from the moon with Chang'e-5, conducting operations in deep space means a greater signal delay, requiring greater spacecraft autonomy. The spacecraft will also need to maintain orbit around and approach a small body with very weak gravity. Long-life propulsion engines, high-precision navigation, guidance and control, and a small capsule capable of surviving ultra-high-speed reentry into Earth's atmosphere are also hurdles that need clearing.
And the sampling aspect itself will be a significant feat. According to a correspondence in Nature Astronomy, there are two typical approaches to sampling asteroids like Kamoʻoalewa, namely anchor-and-attach and touch-and-go.
The former requires delicate and dangerous interactions with the planetary body but allows more controllable sampling and more chances for surface analysis. The latter, used by Hayabusa 2 and OSIRIS-Rex, is a quick interaction facilitated by advanced navigation, guidance and control and fine control of thrusters.
China's mission will use both architectures in order to "guarantee that at least one works." The paper states that there is "still no successful precedent for the anchor-and-attach architecture," meaning a possible deep space first. A 2019 presentation reveals that China's spacecraft will attempt to land on the asteroid using four robotic arms, with a drill on the end of each for anchoring.
Chang'e-5 similarly opted to both drill for and scoop up its samples, providing redundancy and greater science value.
The mission is just one of China's ambitious sample return plans in the next few years. Chang'e-6 will follow up the complex Chang'e-5 moon mission, but even more ambitiously attempt to collect samples from the ancient and scientifically enticing South Pole-Aitken basin on the lunar far side. The mission will require assistance from a relay satellite as the moon's far side never faces Earth.
Around 2028 China plans to launch an audacious Mars sample return mission, a so-far not attempted quest (though NASA and ESA are also preparing a mission) that is one of the most sought-after goals of Mars science. Beyond this, a new Chinese company, Origin Space, has launched pathfinding missions and has its sights on utilizing resources from near Earth asteroids for commercial purposes.
But the sample return is just one aspect of the mission. After delivering samples to Earth in a return capsule, the spacecraft will continue its journey, heading out to Mars and using the Red Planet for a gravity-assist to send it on its way to the main-belt comet 311P/PANSTARRS.
Examining 311P/PANSTARRS with the spacecraft's suite of imaging, multispectral and spectrometer cameras and other instruments could provide vital information about the origin of the water on Earth and the theory that much of it was delivered by comet impacts. It would also provide insight into the differences between what are considered active asteroids and classic comets.
Notably both Kamoʻoalewa and 311P were discovered by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) at Haleakala in Hawaii within the last decade.
The spacecraft will also carry an experiment designed by students. Teams of students from primary schools up to universities have submitted proposals, with public voting now underway as part of the selection process.
The probe is likely to be named ZhengHe, after the famous Ming dynasty admiral and explorer. The name would be apt, both drawing on the country's exploration history and marking a new age of Chinese exploration, this time in the deep sea of space.
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