Hubble in trouble

"In the second, third and fourth months: Initial optics checkouts, and telescope alignment. Using the Fine Guidance Sensor, we will point Webb at a single bright star and demonstrate that the observatory can acquire and lock onto targets, and we will take data mainly with NIRCam. But because the primary mirror segments have yet to be aligned to work as a single mirror, there will be up to 18 distorted images of the same single target star. We will then embark on the long process of aligning all the telescope optics, beginning with identifying which primary mirror segment goes with which image by moving each segment one at a time and ending a few months later with all the segments aligned as one and the secondary mirror aligned optimally. Cooldown will effectively end and the cryocooler will start running at its lowest temperature and MIRI can start taking good data too."

https://www.webb.nasa.gov/content/about/orbit.html
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Non-jinxing has worked so well that I an reluctant to change course.

 

I'd like to see two 'Webbs' doing donuts around L2 and inferometric analyses. But NASA has other plans.

Nancy Grace Roman:
Roman Space Telescope/NASA

Subsequent wish list is long:
https://skyandtelescope.org/astronomy-news/2020-decadal-survey-future-astronomy/

Overall it seems L2 is the place to be

 

polar inferiority eh? Glerble.

This may well be the decade (or two) when L2 gets loaded up with with shiny gadgets. It is quite spacious though. If I read right, JWST donut will be earth-moon-distance diameter, and it will take 6 months (?) to make its loop.

 

The other two observatories at L2 are GAIA (astrometry) and Spektr-RG (x-ray), which won't combine with JWST for interferometry. I don't think JWST will work for interferometry either, it seems to take purpose-built systems.

If you mean using different L-points for interferometry, that would be just a radio-astronomy project for the foreseeable future. Their separations are vastly greater than we could consider for optical work now or anytime soon.

 

I remember when the first Very Long Baseline Interferometry reached baselines comparable to Earth's diameter. I think (but don't quote me) that they were using the 21 cm hydrogen wavelength, recorded separately on videotape, with separate local clocks. Analysis was all in post-processing after the recordings were brought together at a central location, and accuracy was limited by the relative stability of the separate clocks. Since then, they have pushed this to much shorter radio wavelengths (higher frequencies). These methods work with orbiting satellites too, though the data link is no longer by videotape.

The optical interferometry that I've read about doesn't involve separate individual clocks, or down-conversion and recording, at each receiver. Instead, the signals are physically piped together to a central location, and put into an optical combiner in real time. This limits the baseline, and is where the existing engineering crashes when applied to satellites. It seems that it will be a while until the existing radio methods can be pushed all the ways up to optical frequencies.

 

Temperatures of 50 and 49 Kelvin today, respectively, getting closer to the target of 40 K.

And the first star image is in too, a Big Dipper star split into 18 pieces. And they've already identified which piece belongs to each mirror, a necessary step before starting the long series of adjustments:

 

Let another post the 'selfie' as it is surprisingly 'fuzzy'

For mosaic posted above I'd feel better if each segment's aberration pointed at the center 'of mass'. Only those in Mission Control know if this portends anything at all.

Segment A4 is really out there. Tilt better, you hunk of beryllium.

 

From the team's posting, it seemed that they were pleased the image pieces were as close as they are. The test field covered a much larger area, in case some were much farther out.

As for the shape and direction of the image pieces, that would definitely be a concern if the mirror segment adjustments had only 3 mounting points, or degrees of freedom. But with 6 adjustable mounting points each, plus a separate curvature adjustment, it seems too early to be concerned. I also wonder if they deliberately applied different small aberration shapes and orientations to different mirrors as part of the identification process.

 

Darn clever thoughts from a fella now suffering COVID aberrations.

 

It is too early to spot any potential long-covid symptoms. Though a very short drive to an appointment this morning revealed that I ought not be driving that soon after waking up.

 

Try some wordles? Don't drive at night?

 

Isn't Wordle addictive? Just what I need, more electronic addictions.

I've already cut back night driving due to cataract development, and am not expecting to be ready for surgery for a few more years.

 

Now the image pieces have been moved into a close array matching their mirror positions:



It is encouraging to be seeing interference fringes now, a sign that the process is progressing.

The next step will be focusing each individual image. Later, they will be stacked together, followed by fine phasing adjustment.

 

Two more steps of major progress posted today!

First is a successful Segment Alignment, in which all the mirrors are individually focused,. Notice the 18 mostly beautiful Airy disks, nice tight circles surrounded by a diffraction ring or two:




Then they were all stacked into a single image:




The many interference bars in the hex spikes show that the mirrors are still out of phase, they have different heights. The next step is Coarse Phasing, which will bring the mirrors much closer to matched heights. That is followed by Fine Phasing, which ought to make this stacked image more like a bright version of one of the images in the first frame, a nice tight circle with one or two visible diffraction rings.

 

I think that is a diffraction artifact caused by the hexagonal mirror configuration. It should shrink sharply with the Coarse and Fine Phasing, but may never go completely away. Even if it does vanish, there will still be a 3-pointed star caused by diffraction around the Secondary Mirror supports.