China gets closer to Jupiter mission by bringing Nasa’s StarNAV concept to life

Chinese researchers have tested a new way for spacecraft to navigate in deep space, putting a concept funded by Nasa into practice and paving the way for the country’s planned mission to Jupiter in 2030.

Known as stellar aberration navigation, the approach uses tiny shifts in the relative position of stars to work out how fast a probe is moving and in what direction, allowing autonomous real-time navigation without constantly relying on tracking and commands from Earth.

In a low-Earth-orbit experiment in January, the Tianhui-7 satellite used this method to determine its position to within about 5km (3.1 miles), a performance comparable to Nasa’s antenna-based Deep Space Network.

Jupiter can be up to 900 million km from Earth, with radio signals taking more than 50 minutes to travel one way. That made it impossible for ground controllers to intervene in real time, wrote researchers from the China Academy of Space Technology – the country’s main spacecraft manufacturer – in a paper that will be published in the Journal of Deep Space Exploration.

While China can track spacecraft as far away as Jupiter, it cannot track objects in deep space as precisely as Nasa or the European Space Agency, the researchers said. Tianwen-4 will be China’s first mission to explore the Jupiter system, studying the giant planet and its moons, including their evolution, environment and internal structures.

Tianhui-7 was launched aboard a Long March 4B rocket from northwestern China’s Jiuquan Satellite Launch Centre on December 30, 2025. At the time, state news agency Xinhua said only that it would be used for geographic mapping, land surveys and scientific research.

According to the new paper, the satellite carried three highly precise star cameras and an infrared sensor to test the navigation technology for 20 hours in orbit about 500km above Earth, with the planet standing in for Jupiter.

The cameras photographed different patches of the sky, while the infrared sensor observed Earth. Together, these measurements allowed the satellite to work out its own position and speed, which researchers then compared with GPS data to gauge the method’s accuracy.

Stellar aberration is not a new concept. It was discovered about 300 years ago by English astronomer James Bradley, who noticed that stars appeared to shift slightly in the sky as Earth travelled around the sun.

The stars themselves are not moving back and forth. They appear a tiny bit ahead of where they really are because Earth is moving forward to meet the incoming starlight.

The effect can be compared to watching rain through the windscreen of a moving car. Even if the rain is falling straight down, it seems to slant towards you because the car is moving towards the raindrops. The same happens with starlight as Earth or a spacecraft moves through space.

The effect is tiny, but predictable. For centuries, stellar aberration was something that had to be corrected when measuring the positions of stars.

However, scientists later realised they could use the effect as a navigation tool. By measuring how far the stars appear to shift, they can work backwards and calculate how fast a spacecraft is moving and in what direction.

In 2020, Nasa funded the StarNAV experimental project that aims to perform the extraordinarily precise measurements of star positions needed to navigate by starlight. Angles must be measured in milliarcseconds, equivalent to the apparent width of a grain of rice seen from 500km away.

The star cameras aboard Tianhui-7 were accurate to about 50 milliarcseconds. To make such measurements useful, the Chinese team added an optical reference system that kept track of tiny shifts in the cameras themselves, caused by launch vibrations and temperature changes.

Over the 20-hour test, the navigation settled at a margin of error of around 5km for position and 5 metres (16.4 feet) per second for velocity, compared with GPS data, the researchers reported.

Correcting systematic errors later improved those figures to better than 4km and 4 metres per second. But the team cautioned that conditions around Jupiter would be very different, and whether the technique could perform as well in orbit around the gas giant remained to be tested.

China is also developing a new generation of even more precise milliarcsecond-level star cameras.

A prototype has been built and put through ground tests, according to a 2025 article published on the China Aerospace Science and Technology Corporation website. -- SOUTH CHINA MORNING POST