China’s astronomers hope to leap from the 4-meter Large Sky Area Multi-Object Fiber Spectroscopic Telescope to a new 12-meter telescope.

Lu Feng

Spat over design of new Chinese telescope goes public

A deep division among Chinese astronomers over the design of a proposed 12-meter telescope broke into public view this week as statements from competing camps went viral on social media.

The dispute centers on whether to adopt a technically ambitious four-mirror design proposed by optical engineers or a conventional three-mirror option favored by astronomers. The stakes are high. It will be China’s largest optical telescope and serve as the workhorse observational facility for several generations.

In a 4 August letter to the Chinese Academy of Sciences (CAS), Jiansheng Chen, an astronomer at Peking University in Beijing, notes that currently the largest Chinese-built scopes are a 2.16-meter general purpose instrument and the 4-meter Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) that is dedicated to surveys. LAMOST “is not very successful,” he adds, noting that its performance doesn’t match that of the 2.5-meter Sloan Digital Sky Survey telescope at Apache Point Observatory in New Mexico. “You can imagine how much risk there is in leaping from this foundation to 12 meters!” Chen writes in the letter that was posted on WeChat, a popular Chinese social media platform.

Chen miscalculates LAMOST’s aperture, counter Xiangqun Cui, the instrument’s chief engineer who is at Nanjing Institute of Astronomical Optics & Technology, and Dingqiang Su, an astronomer at Nanjing University, in a joint WeChat response posted 8 August. They write that in terms of its engineering, the aperture is equivalent to almost 8 meters, thus it wouldn't be a great leap to 12.

Chen, Cui, and Su are all prestigious CAS academicians, adding spice to the acrimonious exchange, which is just the latest skirmish in an ongoing battle.

Cui and her colleagues are behind the four-mirror design, which has a primary plus three secondary mirrors and relies on what they call an SYZ optical system, named using the initials of three designers who pioneered the scheme on the 2.16-meter telescope. A team from Huazhong University of Science and Technology in Wuhan has proposed a more conventional Ritchey-Chrétien design that has a primary plus two secondary mirrors. They claim this simpler approach provides better resolution in the central field of view, and “generally better scientific performance.”

In April, an international committee convened by CAS’s Center for Astronomical Mega-Science, which is responsible for the project, reviewed the competing designs and recommended the three-mirror option. On 10 July, Cui organized her own review committee that picked the SYZ design as better. Cui’s panel “leaned toward one side,” Chen says. And one member says that the three-mirror design was not sufficiently presented, partly because no one from the Huazhong team was there. Cui and Su explain in their open letter that a member of their own group who knows it well introduced the Huazhong design. “Members were repeatedly reminded they could abstain from voting,” they write. One-third of the 21 committee members did abstain.

Meanwhile, to date, more than 130 young astronomers have signed an open letter to the astronomical community urging that the recommendations of the international panel be respected.

The fundamental disagreement, according to Chen, is “whether a large science project should be technically or scientifically oriented.” Cui and Su say the choice is between incorporating “rapidly developing new technologies” that ensure a long life for the facility, or “simply replicating a 10-meter telescope built 30 years ago.”

This week, more than 800 astronomers are attending the annual meeting of the Chinese Astronomical Society in Xinjiang. The 12-meter telescope battle is not on the program. The society “doesn’t want to cause embarrassment,” says one attendee who adds there is sure to be “a lot of [discussion] in private.”