Webb telescope completes curvature test...

[Smithysteve]

Engineers and technicians working on the James Webb Space Telescope successfully completed the first important optical measurement of Webb's fully assembled primary mirror, called a Center of Curvature test. 

Taking a "before" optical measurement of the telescope's deployed mirror is crucial before the telescope goes into several stages of rigorous mechanical testing to simulate the violent sound and vibration environment the telescope will experience inside its rocket on its way out into space... then it will be tested again... It has taken a couple of years to work out how to best carry out the curvature test - a fascinating read...

 

http://phys.org/news/2016-11-nasa-webb-telescope-center-curvature.html

 

[Tweedledee]

That is fascinating stuff. I suppose they can't afford to over engineer it structurally as a heavy payload would vastly bump up the launch costs, but they need to strike a balance and make sure it cannot be permanently damaged by the stresses and vibrations of the launch. It is amazing that the mirror vibrations caused by people talking can be detected.

 

I also wonder how the mirror surface deforms after the transition to zero gravity. I don't think there is a method to test that on earth, so I can only assume they have to accurately calculate and allow for the deformation. I would think that there must be a considerable change in the mirror surface going from 1g to 0g when the whole surface needs to be accurate to a fraction of the wavelength of light. 

[Smithysteve]

54 minutes ago, Tweedledee said:

That is fascinating stuff. I suppose they can't afford to over engineer it structurally as a heavy payload would vastly bump up the launch costs, but they need to strike a balance and make sure it cannot be permanently damaged by the stresses and vibrations of the launch. It is amazing that the mirror vibrations caused by people talking can be detected.

 

I also wonder how the mirror surface deforms after the transition to zero gravity. I don't think there is a method to test that on earth, so I can only assume they have to accurately calculate and allow for the deformation. I would think that there must be a considerable change in the mirror surface going from 1g to 0g when the whole surface needs to be accurate to a fraction of the wavelength of light. 

I also thought along the same lines as you, so they must have taken that and plenty more into account, also the temperature will be much much lower in space...how will that effect the shape and size of the mirrors, they have carried out cryogenic tests already... like I mentioned they have spent two years developing the tests - it's amazing the depth they go to! Brilliant stuff!

[BAZ]

It's going to be a nail biter this one, once they light the blue touch paper, that's it. It is a wonderful piece of engineering, there are so many moving and locking components. 

[Big Al]

On 11/14/2016 at 18:05, Smithysteve said:

It has taken a couple of years to work out how to best carry out the curvature test

 

 

Not surprising, I can't imagine for a moment that they might be just a teensy-weensy bit paranoid about  this