From: Georgi Guninski <guninski@guninski.com>

On Thu, Aug 04, 2016 at 02:22:05AM +0000, jim bell wrote:

>> http://www.dailymail.co.uk/sciencetech/article-3720772/China-launch-unbreakable-quantum-spy-satellite-say-one-day-lead-megascope-size-Earth-spot-license-plate-Jupiter-s-moons.html
>> [quote]
>> China to launch unbreakable quantum spy satellite - and it could one day lead to a megascope the size of Earth that could 'spot a license plate on Jupiter's moons'

>China (Austria is also involved) launched this on 16 August 2016:
>   https://en.wikipedia.org/wiki/Quantum_Experiments_at_Space_Scale
>Also in many news.

When I originally posted this, I briefly noted that I had a problem with this

 news item.  As I recall, one of the problems was that they referred to  this

'megascope', without explaining the connection.  It was as if two high-tech

articles collided, and bounced off each other, leaving a bit of detritus on 

the other.

What does this quantum link have to do with building a super telescope?  The

article was less than even unclear:  It was totally silent on that matter.

Currently, the largest single-lens telescope mirrors are made in a rotating

 furnace in Arizona, about 8.5 meters in diameter.  the purpose of the 

rotation is to make them very close to the idea curvature from the beginning,

rather than polishing them out of a flat blank of glass as was the previous process.

Other telescopes are going to use multiple-mirrors to increase the light-collecting

area.  That's important, but another factor is that the larger effective diameter 

of a telescope mirror, the smaller angular difference that can be imaged.  I 

recall a data point:  A 4.5 inch mirror has a resolution of about 1 second of arc.

(defined, I think, as a line/space pair, not merely a line.)

A telescope based on an 8.5 meter lens will have, ideally, a resolution of 0.0134

arc seconds.  Combine seven of them subtending a larger-diameter, and you'd

get perhaps 3 times the diameter, and one third the angular resolution:  About 

0.00448 arc seconds.  https://en.wikipedia.org/wiki/Giant_Magellan_Telescope

 Would it be possible to 'mount' three such 8.5 meter mirrors in an array where they

are millions of kilometers away from each other, and somehow combine their images 

and to produce and preserve the resolution of the larger diameter?  It wouldn't multiply

light-gathering ability, but it would increase the angular resolution immensely, perhaps by

a factor of 100 million to one billion.

I speculate that this is what is being alluded to in the article's reference to a 'super telescope'.  

It would not be sufficient to merely detect the images generated by each mirror; somehow

it would be necessary to combine the light signals to include phase information.  Perhaps this

could be done by some sort of quantum process.

          Jim Bell