China's Space Program News Thread

[taxiya]

View attachment 71869
Just this image. I don't know where this slide come from. The FOV of Hubble is close to what I can find from Nasa's website. The angular resolution of Hubble is wrong though (unless they are not talking about visible light).

The figures above are FOVs of the lenses defined in unit of angle. It is 1.5/0.06=25.

I think the figure 300 is the ratio of area covered by the WFS sensors which is smaller than the lens would provide. A perfect spherical plane with 25 times radius would be 25*25=625 times in area. However, the sensors are not arranged in a circle, but a irregular shape, so the actual area of view of the main sensors is smaller. I think you have made that guess already.

 

[anzha]

I'm surprised at how little American telescopes I see in this picture. The native hawaiians do seem to have some impressive assets though.

There are other telescopes. However, the US builds them in Chile and Hawaii quite a bit.

 

[winword]

The figures above are FOVs of the lenses defined in unit of angle. It is 1.5/0.06=25.

I think the figure 300 is the ratio of area covered by the WFS sensors which is smaller than the lens would provide. A perfect spherical plane with 25 times radius would be 25*25=625 times in area. However, the sensors are not arranged in a circle, but a irregular shape, so the actual area of view of the main sensors is smaller. I think you have made that guess already.

That could be the reason, in the slide you posted it shows the center is 1.1*1.2 degrees. Using this number the result is close to 300.

But saying the resolution is the same as Hubble still seems a bit weird to me. According to this:

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"The high sensitivity to light of the 16 megapixel UVIS CCD, combined with a wide field of view (160x160 arcseconds), yields about a 35-times improvement in discovery power versus the ACS High Resolution Channel." But this indicates the resolution of Hubble is only 16 megapixels. That also agrees with 0.04" angular resolution (160/(16000000)^0.5) claimed by Nasa, so I'm probably using the correct numbers. I'm not very familiar with this topic but I feel like these new telescopes all have much higher resolutions than Hubble.

 

[Quickie]

Actually I was wrong, according to this link the FOV (1.5 degrees) is 25 times of the Hubble's FOV (0.06 degrees) (???), guess the 300 times means ~25*25 (but that would be 625)? I'm not sure how reliable it is and whether things have changed since then though. Hopefully there will be an official website soon cause these info seem a bit confusing to me.

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It also says the angular resolution is 0.15", the angular resolution of Hubble is 0.04" according to:

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It also says the angular resolution is 0.15", the angular resolution of Hubble is 0.04" according to:

That would mean about 4 times less angular resolution than the Hubble?
Hopefully, 0.15" is not the highest angular resolution that it can go.

 

[winword]

That would mean about 4 times less angular resolution than the Hubble?
Hopefully, 0.15" is not the highest angular resolution that it can go.

Looks like that's the case. The FOV is much larger though, it's using a different mirror design, I guess they can't have it both ways.

 

[Quickie]

Looks like that's the case. The FOV is much larger though, it's using a different mirror design, I guess they can't have it both ways.

I guess the experts would know better. I can imagine having a larger FOV would be advantageous in certain circumstances in its ability to collect more light energy per unit area of the image sensor.

 

[taxiya]

I think it is the meaning of FOV and resolution making the confusion.

I think when the chief designer said 300 times FOV, he meant 300 times of the space area of the sky the WFS system covers. The lower angular resolution makes any light dot on the sensor blurry than Hubble, instead of lighting up one pixel, it lights up 4 pixels (just say it). However, with a much wider optic lens and 2 times more pixels, the area it covers is 300 times. Hubble's WFC is 16M pixels while Xiuntian's WFS is 32M.

A close analog is comparing a mobile phone of 4K display, and a 8K TV of 100 inches. If one watch both of them in the same distance, the TV's FOV in size of area is certainly hundreds times bigger. Just reverse the displays to sensors and the viewers to stars, we would got the same conclusion.

 

[SilentObserver]

I'm surprised at how little American telescopes I see in this picture. The native hawaiians do seem to have some impressive assets though.

The ones you see in South America are mostly funded by the US. Having high altitude landmass is a strategic asset in astronomy. Thin atmosphere enables clearer images.

China has huge potential with Tibetan plateau, as the nickname implies it's the "roof of the world". It is the world's largest high altitude plateau that is accessible and distant from light and EM pollution. Practically speaking China doesn't have a space constraint for building high quality observatories and doesn't have to place assets in another nation for this purpose. It can even invite investment/cooperation from other nations.

On the map we can see that other than Tibetan plateau and Andes mountains earth doesn't have many very high elevation surfaces we can build structures on.

 

[siegecrossbow]

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Landing date tentatively set to the 17th.

 

[voyager1]

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Disturbances and aberrant phenomena in the firmament needed to be taken seriously as they might signal war, famine or pestilence. They might have also been seen as a message from the heavens that governing policies must change.

Keep this in mind as we ponder the remnants of China’s Long March 5B rocket, which streaked over the Mediterranean in the predawn hours of Sunday and splashed down around the Maldives.

SCMP journalism here, folks.

Enjoy this very high-quality article