Radio telescope 30 times the diameter of Earth

China will launch an observatory orbiting the Moon to create a radio telescope with a diameter of 400,000 km.

Network simulation of a very long stand radio interferometer in space. Photo: NASA

The new radio telescope will be built in two phases and be ready to operate within two years. First, a communications relay satellite for China's Chang'e 7 mission will launch and transform into an orbiting lunar observatory. After that, a number of observatories on Earth will participate in a project called Very Long Base Radio Interferometer in Space, forming a giant network of antennas, equivalent to a radio telescope nearly 400,000 wide. km technically. Compared to that network, the world's largest single telescope is the 500 m Aperture Spherical Radio Telescope (FAST) in China.

It is expected that the Very Long Base Radio Interferometer project in space will launch before 2025. This will be the largest facility ever created for astronomical observations. The system can provide images of a number of important astronomical phenomena such as black holes and gravitational lenses with unprecedented resolution in the X-ray range.

In theory, a telescope extending from Earth to the Moon could capture action during a football game on Mars. The greater the distance between the two observatories, the higher the resolution of the image. The method of combining several small telescopes to form a large instrument is called a very long baseline interferometer (VLBI) and was invented in the 1950s. The first image of a black hole was produced in the 1950s. 2019 by the Event Horizon Telescope, a VLBI network that uses observatories around the world to reach Earth-sized diameters. Russia and Japan have both launched satellites to extend the scope of the VLBI observatory beyond the Earth, but cannot fly as far as the Moon.

However, the project still raises some questions about its feasibility. To function as a telescope, data collected at various locations must be precisely timed. This requires an atomic clock called a hydrogen maser (a device that generates and amplifies electromagnetic radiation mainly in the microwave region of the spectrum), which can work for long periods of time with extremely high stability. . But the size and weight limitations mean that the accuracy of satellite hydrogen clocks is often lower than that of large machines on Earth. Researchers don't know for sure if the small observatory in the Moon's orbit can operate in unison.

In a study published March 28 in the journal Acta Astronomica Sinica, a research team led by Professor Liu Qinghui at the Shanghai Astronomical Observatory said that atomic clocks are not a big deal. They draw their conclusions based on recent experiments with Tianwen 1, a Chinese spacecraft orbiting Mars. Liu and colleagues tracked the extremely weak signals from Tianwen 1 with a hydrogen maser built for the telescope program. They found that the small atomic clock and the larger version on Earth differed much less than expected.

If the project goes as planned, China will launch more satellites and set up permanent observatories on the Moon or even Mars to create an interplanetary telescope.