​Xuntian will be a Chinese space telescope that will be launched into roughly the same orbit as China’s Tiangong Space Station. That way, the telescope will be able to periodically dock with the space station and be visited by astronauts, but its launch, originally planned for the end of this year, has been pushed back to mid-2025.

With a main mirror diameter of 2 meters, Xuntian will try to unravel the mysteries of dark energy (dark energy) and dark matter (dark matter), thus entering the international race in this field together with the European Euclid telescope (launched on July 1, 2023) and with the help of the telescope NASA Nancy Grace Roman (to be launched in 2027). It appears that the observable universe makes up only 5% of the total mass of the universe, with the remaining 95% being dark matter and energy, about which we do not know many details today.

All of the science instruments aboard Xuntian are built in China, but the main instrument is a 2.6-gigapixel camera that will provide a field of view more than 300 times that of the Hubble Space Telescope. This means that Xuntian will be able to capture an area of ​​the sky in one image that would take Hubble a year of observations.

During its 10-year nominal lifetime, Xuntian will collect information on 40% of the sky in the near-ultraviolet and visible (while Euclid and Nancy Grace Roman will observe in the near-infrared). After its first decade of operation, the telescope will dock with the Tiangong Space Station, where it can be refueled and prepared for the next phase of its mission.

Xuntian will also be able to search for exoplanets, asteroids or supernovae with other scientific instruments on board. Given that it will be able to be visited and improved by tyconauts, its design is modular, and in the future it will even be possible to add new instruments for observing the sky, instruments that may result from future collaborations.

These things cannot be done with the Roman Euclid or Nancy Grace telescopes (or even the James Webb Space Telescope) because they are on a mission at the L2 Lagrange point, where a manned mission would be extremely difficult, difficult, and expensive. Of course, the fact that Xuntian is only 400 km high has its drawbacks, given its proximity to our planet (which is why Xuntian cannot make infrared measurements).

Xuntian requires a Changzheng-5B rocket, China’s most powerful launch vehicle, which can lift more than 20 tons into orbit. However, the launcher is not without controversy: the 5B variant, adapted for launches into low Earth orbit (as opposed to the initial version of the rocket designed for geosynchronous orbit), has a bulky primary stage that remains in an unstable orbit around the Earth and that after several days after launch, it will again enter the atmosphere uncontrolled, and fragments of this rocket can also reach populated areas.

This has not happened since previous Changzheng-5B launches, but this is no guarantee that things will be different in the future (although statistics are on our side, only 1% of the Earth’s surface is inhabited, and more than 70% of our planet is covered by water).

According to some rumors, the Xuntian telescope is in the early stages of assembly, which means that the launch date is still a long way off. Zhan Hu, a key figure in the Xuntian program, recently confirmed that the launch will not take place this year or even next year, but is scheduled for June 2025.

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