China’s giant Xuntian space telescope faces further delay until late 2026
The leaked slides, which have since been removed from Chinese social media but were independently verified by the South China Morning Post with a CSST team member, show that the telescope’s major components are complete and are undergoing rigorous performance tests. The final flight model will be assembled by autumn next year.
The CSST team member who spoke on condition of anonymity said there were no insurmountable technical hurdles in Xuntian’s development. “Overall, the telescope’s specifications are very high by design, which made it extremely challenging to build,” he said.
Xuntian will be the largest and most complex scientific facility China has built in space and have a field of view more than 300 times larger than that offered by the Hubble Space Telescope. The country is domestically developing all five of its instruments, including a 2.6-gigapixel survey camera that will be the telescope’s main instrument.
Astrophysicist Quentin Parker, from the University of Hong Kong, said the new launch date, if confirmed, would be close to that of Nasa’s 2.4-metre Nancy Grace Roman Space Telescope, which is now expected to lift off in mid-2027.
Both the Xuntian and Roman telescopes will survey billions of distant galaxies and test theories of dark energy, the elusive but dominant force behind the universe’s ever accelerating expansion.
“There was going to be a bigger lead time for China to gain more scientific success ahead of the Americans. Now that advantage is not so strong,” Parker said.
However, he added, Xuntian and Roman were designed to work in different wavebands with some overlap and were, therefore, complementary.
Like Nasa’s James Webb Space Telescope, the Roman telescope will operate from the so-called Lagrange point 2, which is about 1½ million km (930,000 miles) from Earth.
“The James Webb has been very successful, but you can’t go out and fix it if something goes wrong. It’ll be the same for the Roman telescope,” he said.
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But Xuntian, he said, would be co-orbiting with the Tiangong space station in low-Earth orbit and so astronauts could be easily fix the telescope, replace or upgrade parts, or even install new instruments.
The delays were probably out of good technical and practical reasons. “After all, you are not going to risk putting up something that might fail or not work so well,” he said.
Xuntian was proposed as part of China’s plans for a space station, and approved by the Chinese government in 2013. It is expected to serve the entire Chinese astronomy community for a wide range of research, from cosmology to exoplanets and black holes, after scientists had waited for decades to have their own version of the Hubble telescope.
It is not uncommon for the deployment of large space telescopes to be postponed. For instance, the James Webb Space Telescope was launched in 2021 after more than a decade’s delay and huge cost overrun, and is now changing our understanding of many aspects of the universe.