China targets its first planetary defense test mission

China’s first planetary defense test is taking shape, with the ambitious mission to both observe and impact a near-Earth asteroid with a single launch.

New information on mission planning indicates that China is not only looking to find answers to the threat that near-Earth objects (NEOs) pose to our planet but is also interested in using its first test mission to learn what these primordial planetary objects can tell us about the Solar System.

China has been getting increasingly serious about planetary defense. In 2023, indications were that a first kinetic impact deflection test mission would target the object 2019 VL5 with a launch in 2025. 

According to an article in the Journal of Deep Space Exploration (JDSE), a new proposal based on existing preliminary studies has identified 2015 XF261, a roughly 30-meter-diameter (98 feet) near-Earth asteroid, as the target for the dual-spacecraft observation and impact mission. The final target selection will be refined based on the actual launch window, with the launch expected before 2030.

Meanwhile, Wu Weiren, a Chinese lunar science luminary and now director of China’s influential Deep Space Exploration Laboratory (DSEL), said more concretely in April that the mission would launch around 2027, although he gave no explanation for the apparent shift in launch timing. Launch windows depend on the orbit of the target, mission objectives, and the readiness of the spacecraft. The mission, when it does launch, is expected to fly on a Long March 3B rocket.

One launch, two trajectories

Although it’s unclear why the China National Space Administration (CNSA) changed the mission’s target from 2019 VL5 to 2015 XF261, one reason could be the complex nature of the mission design. The plan is for the observer spacecraft to reach the target asteroid first and conduct three to six months of close and orbiting observations to study the asteroid’s size, shape, composition, and orbit. Then the impactor spacecraft will perform a high-speed kinetic energy impact test with the target asteroid. The observer will monitor the entire impact process and evaluate the aftermath for 6-12 months to ascertain the effects. 

This could have more payoff than an impact and flyby or an impact and follow-up observation in terms of learning about the asteroid and the effects of the impact. However, to allow for observation and later interception, the mission requires meticulous planning and optimization of launch times and two separate trajectories. This could possibly involve gravity assists for the observer spacecraft.

Objectives and observations

The single-launch mission plan is like a combination of that of NASA’s Double Asteroid Redirection Test (DART), which impacted the small asteroid moon Dimorphos, and that of the European Space Agency (ESA) mission Hera, which will make followup observations of the binary system. The key differences are that 2015 XF261 is much smaller than Dimorphos, and that up-close, detailed observations before, during and after the impact event will yield greater science value.

The new JDSE article also helpfully lays out hitherto undisclosed science goals and payloads, revealing what China hopes to learn from the mission. 

The main aims are, of course, conducting impact experiments and observing the entire impact process. Beyond this though, the mission aims to study the dynamic evolution, origin, and orbital migration history of the target asteroid, including any close encounters with planets. This could provide valuable data on asteroid populations, to which only a handful of missions have flown.

Key objectives for studying the asteroid are determining its size, shape, composition, internal structure, thermal radiation, and the presence of volatiles. Furthermore, estimating the asteroid’s mass, density, and porosity could bring insights into its formation and evolution. By extension, this could provide clues for understanding the origin and evolution of the Solar System.

Meanwhile,  a comprehensive observation of 2015 XF261 will be conducted to determine the asteroid’s orbital parameters, rotation, and reflectance characteristics. This data will help build precise asteroid evolution models and evaluate impact effects on near-Earth asteroids.

Payloads

Payloads will include spectral and Laser 3D detectors, color cameras, radars and dust and particle analyzers.

The spectrometer and laser payloads will be used to determine the asteroid’s composition and classification. High-resolution color cameras will be used to observe and model the asteroid’s surface features and to assist in impact point selection. A radar payload will be used to peek inside the asteroid and build internal structural models, created from reflected signals echoing back from the asteroid. Finally, particle analyzers will focus on the composition and environmental effects of dust and particles.

Together with the lessons from DART and Hera, China’s mission would significantly advance humanity's capabilities in planetary defense and our understanding of asteroids themselves, providing multiple new data points as we seek to safeguard Earth from potential asteroid impacts.

It would further verify kinetic impact techniques, with post-impact assessments providing greater insight into the effects of impact deflection.

Spotting new NEOs

Meanwhile, China is also stepping up its observation of near-Earth objects, not just nudging their orbits. The 2.5-meter Wide Field Survey Telescope (WFST) in Lenghu, Qinghai Province, saw first light in autumn 2023 and had spotted two new asteroids by November. Also up and running are the Lijiang 2.4-meter and the Xinglong 2.16-meter telescopes. Other survey telescopes for monitoring have also been proposed.

The “compound eye,” a 25-antennae network of radars, is under construction to bounce signals off deep space objects to determine their potential threat to Earth. The project is set to be completed in 2025.

There are also proposals for asteroid-hunting systems. These include a constellation of six surveyor spacecraft deployed in Venus-adjacent orbits. These would provide an early warning system for asteroid threats while providing better coverage of space within Earth’s orbit. 

China’s planetary defense plans are then continuing to take shape, with a growing number of papers, conferences, and forums on the topic. The country also says it is open to international collaboration in this arena, and also hopes to portray itself as a responsible space power through planetary defense.