China's Space Program Thread II

[FairAndUnbiased]

There is nothing unfortunate. The 2m diameter is NOT due to capability of making larger, it is because of the constraint of the spacecraft.

Hubble is 4.2m at its widest. Xuntian is 4.5m. Their sizes are limited by the payload fairing of CZ-5B (5.2m) or payload bay of Space Shuttle (4.6m). The reason that Xuntian's mirror is relatively smaller than Hubble is because Xuntian uses “off-axis three-mirror optical system”, this requires space on the side of the main 2m mirror. It works like following
View attachment 118978

Hubble uses coaxial system where all mirrors are set in the same axis, there is a hole in the main mirror, light in the center from object is blocked by a secondary mirror. Here is how does Hubble look.
View attachment 118980

Hubble has bigger mirror at the cost of lower performance. See the comparison of the two systems.
View attachment 118982

Depending on how big the hole in Hubble's central mirror, it could be that Xuntian has a bigger effective light collection size, as well as more advanced geometry.

 

[Temstar]

There is nothing unfortunate. The 2m diameter is NOT due to capability of making larger, it is because of the constraint of the spacecraft.

Hubble is 4.2m at its widest. Xuntian is 4.5m. Their sizes are limited by the payload fairing of CZ-5B (5.2m) or payload bay of Space Shuttle (4.6m). The reason that Xuntian's mirror is relatively smaller than Hubble is because Xuntian uses “off-axis three-mirror optical system”, this requires space on the side of the main 2m mirror. It works like following
View attachment 118978

Hubble uses coaxial system where all mirrors are set in the same axis, there is a hole in the main mirror, light in the center from object is blocked by a secondary mirror. Here is how does Hubble look.
View attachment 118980

Hubble has bigger mirror at the cost of lower performance. See the comparison of the two systems.
View attachment 118982

Oh no defraction spike, nice!

Those four or six light spikes that people immediately associate with stars is actually an artifact of telescope construction. In a reflecting telescope with a secondary mirror in the light path of the main mirror the little bars (telescope jargon: the spider) that hold the secondary in place causes those. If the spider has 3 arms you get six spikes, 4 arm spider result in 4 spikes in that classic cross shape.

If the secondary can be in the way but with no arms such as in a catadioptical telescope where the secondary is held in place by a lens with hole in the middle then you get very pleasing perfectly round stars with no spikes.

Offsetting those mirrors with none of them in the way if each other should give even better image.

 

[Temstar]

Here's a image from Hubble showing many deep sky objects like galaxies with a few stars sprinkled in, including a bright one with large spikes. This cross pattern defraction spike tells you it was taken by a telescope with a secondary that's held in place in front of the primary mirror with a 4 arm spider.

These spikes besides being ugly in my opinion also gets in the way of professional astronomers by blocking objects they are interested in from time to time. They will then have to request the image be take again and hopefully the spikes are in a different orientation on the second image.

 

[broadsword]

View attachment 118987
Here's a image from Hubble showing many deep sky objects like galaxies with a few stars sprinkled in, including a bright one with large spikes. This cross pattern defraction spike tells you it was taken by a telescope with a secondary that's held in place in front of the primary mirror with a 4 arm spider.

These spikes besides being ugly in my opinion also gets in the way of professional astronomers by blocking objects they are interested in from time to time. They will then have to request the image be take again and hopefully the spikes are in a different orientation on the second image.

I used to think it was the result of a filter that gave it the starry romantic look.

 

[Michael90]

South Africa has joined the Chinese lunar base project:

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Is South Africa the only member so far?

 

[anzha]

Is South Africa the only member so far?

Russia may be.

Venezuela says an astronaut (taikonaut?) of theirs will go:

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[by78]

The specs for Zhongke's Lijian-3 rocket appears to have been downgraded (2nd image) from an earlier presentation (1st image). The diameter has been cut from 3.6m to 3.35m. Take-off mass has been halved, thrust has been more than halved, and payload capacity has been significantly reduced.

I believe a correction is in order. The second image in the quoted post should be the Lijian-2 rocket, not Lijian-3 as previously stated.

 

[by78]

A medium frequency antenna developed for the

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has been erected at a CETC test facility, where it will undergo testing and verification.

 

[Jiang ZeminFanboy]

First failure for Ceres-1

https://twitter.com/i/web/status/1704861976810467459

 

[Dante80]

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That is unfortunate. Best wishes for completing the root cause analysis, and a quick return to flight.