What exactly is the real data? China's flagship space telescope: 350 times larger than hubble field of view

China Youth Network published an interview with the Sky Survey Telescope on the common orbital flight of the Tiangong Space Station online, which involved multiple parameters about the telescope, although many data can not be understood, but there is a description that everyone must know:

The telescope of the Chinese space station, which is expected to launch in 2023, is very imposing, the size of a large bus, standing up three stories high. Its aperture of two meters is comparable to that of the U.S. Hubble Space Telescope, and the field of view is 350 times larger than that of hubble.

Sky Survey Optical Segment: What is the real data?

The original design concept of the Chinese space station telescope is a module of the Tiangong space station, which is integrated with the space station to facilitate daily management and maintenance, but this mode has advantages and disadvantages, the advantage is that the maintenance is very convenient, and the astronauts can overhaul and maintain it when they leave the capsule!

The disadvantage is that the sky survey optical module needs to be aimed at a target for a long time or temporarily adjust the observation angle to observe the sudden celestial body, and the optical telescope observation needs to be "absolutely quiet", the work and "walking" of the astronauts on the space station, as well as the docking of the spacecraft, extravehicular walking, etc. will cause a lot of vibration, affecting the work of the space telescope.

So later the sky survey optical module became an independent module running in common orbit with the space station, if necessary, the space station can be close to its maintenance, normal work is not affected by each other, I have to say that it is really a great idea, the current Hubble telescope has a serious problem of maintenance difficulties, because it is not in orbit with the space station, only the space shuttle can berthed for maintenance, and the space shuttle has long been retired in 2011, and the Hubble telescope can only walk a day to count a day.

Sky Survey Telescope, how good is it?

About the sky survey optical module Chinese introduction materials are relatively small, many are to charge, the author flipped to two materials, one is the Baidu library "China Space Station Multi-functional Optical Platform High Spatial Resolution Ability Multi-color Deep Survey" Chinese version of the data, the other is the Chinese Academy of Sciences National Astronomical Observatories researcher Zhan Hu on November 5, 2019 in Beijing space mission of the weak gravitational lensing research conference report, the two data have some differences, the following to understand:

Data by Zhan Hu, a researcher at the National Astronomical Observatory

One is the introduction of the instruments and equipment loaded by CSST (Chinese Space Telescope):

These include: measurement camera (SC), terahertz receiver (THz), multi-channel imager (MCI), integral field spectrometer (IFS), cold planetary imaging corona instrument (CPIC), etc., and below it is the optical path structure and the position of the optical chamber where the equipment is located.

This page is an introduction to optical performance, the aperture is 2 meters, the focal length is 28 meters, the optical limit resolution is 0.13 arcseconds, other such as pointing accuracy is not introduced, we look at the key optical parameters, and the other is the information that can be found on Baidu:

The above figure is Chinese data, it seems to be an early data in the early stage of design, because the parameters are required, and its limit resolution requirement is 0.1 arcsecond, which is very close to the 0.13 '' in the PPT of Zhan Hu researcher, of course, based on the data of Zhan Hu researcher, one is closer in time, and the second is that Zhan Hu is a researcher at the National Astronomical Observatory of the Chinese Academy of Sciences, and its credibility is very high.

Zhan Hu (Researcher, National Astronomical Observatories, Chinese Academy of Sciences)

Is it really better than the performance of the Hubble Space Telescope?

Compared with the two telescopes, the optical parameters are undoubtedly the first, and the optical performance parameters of hubble are as follows, which are screenshotted from NASA's Hubble handbook:

Hubble has a caliber of 2.4 meters, which is obviously larger than the CSST, which means that its light collection is better than the CSSST, simply put, shooting a dark object, Hubble's time is shorter.

The other is the ultimate resolution, Hubble is 0.1 arcseconds, which is similar to the 0.13 arcsecond of CSSST, because arcseconds are also called arcseconds, and the two are the same thing, so as introduced in the text, the resolution of the Chinese space telescope and Hubble is almost the same, and there is really no big problem, because it is indeed similar.

Hubble or CSST, which is stronger?

Optical resolution is almost indistinguishable, so the performance of the two is similar? In fact, it is not, in the ZHAN Hu researcher's CSST PPT, there is also a data that the field of view for survey observation is 1.1 °, so the maximum area of a single image is 0.95 square degrees.

I can't find the overall field of view data of hubble telescope, only the field of view of a few cameras, but find a NGRST (Nancy Grace Roman Telescope) field of view is 100 times the data of Hubble, and the field of view of NGRST is 0.281 square degrees, then the difference between the two is multiples of 3.38, and then multiplied by 100, then it is almost 338 times.

Therefore, the data given in many data is 350 times, or 300 times should be reliable, but from different fields of view, such as the FOV of a camera CCD or the overall field of view.

200 times the PPT data

Of course, in addition to the resolution and field of view, its equipped WITH CCD and optical filters, etc. have a qualitative leap, of which the CCD resolution has been improved by an order of magnitude, which is also the key reason why the high resolution is still guaranteed under the large field of view, CSST can be used to survey the sky, you can also gaze at a deep space target observation, the future efficiency will be greatly improved than Hubble.

CSST will be a very useful complement to the study of cosmology, and its ability to acquire images, rapid sky surveys, etc. will be greatly enhanced.