High cost astronomy

[Sonny Taylor]

I meant that to be a bit "tongue in cheek", but you're clarification is appropriate.

[Sonny Taylor]

I wonder how soon "first light" images will be available to the public? Maybe that should read "first heat" (being primarily an infrared telescope)

5 months 18 days if all goes well.

I presume you're referring to when scientific observations are scheduled to begin. What I meant was truly "first light" (i.e. telescope testing).

Like when in 1990 (dare I say it ) the early out of focus images were returned by Hubble.

[JagXKR]

Nice explanation here.
https://www.planetary.org/articles/jwst-first-images
One thing of note is the mirror actuators.

It will take the JWST team three months to very slowly and carefully align the 18 mirror segments. How slow? One of the telescope scientists described it to me this way: “the mirror segments move at the same rate that a blade of grass grows.” This delicate but time-consuming process brings the 18 separate images together to create one sharp image.

Another is the cooling, it's not cold enough yet!

It takes MIRI (the camera most sensitive to temperature) over three months to reach its final operating temperature.

[Sonny Taylor]

One thing of note is the mirror actuators.

It will take the JWST team three months to very slowly and carefully align the 18 mirror segments. How slow? One of the telescope scientists described it to me this way: “the mirror segments move at the same rate that a blade of grass grows.”

It's funny you should mention the actuators that power the alignment of the mirror segments.

I was seriously curious about that myself in a few days gone by and had found this detailed PDF file:
https://www.esmats.eu/amspapers/pastpap ... warden.pdf

It's titled "Cryogenic Nano-Actuator for JWST"

The paper is very detailed; if you don't have time then don't bother; but if ya really wanna know about this kinda stuff, this is cool reading.

To get straight to the mechanical details use search [ctrl-f] for "Actuator Mechanical Description". the description of the stepper motor and it's transmission is interesting.

I did read it all. Didn't fully grasp some parts of it (although perhaps most), but I did notice this:

All bearings and gears are coated with a Ball proprietary dry film lube to enable operation at 30K.

It kinda helps answer my cryogenic space lube question earlier.

[Jlabute]

Just over 100,000 mi to go. Exciting isn't it!

The mirrors can be adjusted in increments of 10nm.

At full speed, it takes about a day to move all the segments by just 1 millimeter. It’s about the same speed at which grass grows!

[Jlabute]

I guess we’ll be there today!
The next step, the wavefront process, will take threeeeeeee months.

[Sonny Taylor]

Being ever curious about JWST "First Light", I See that the 6th magnitude star HD 84406 in Ursa Major will be the initial target for mirror alignment.

HD 84406, is a star approximately 241 light-years away in the constellation of Ursa Major. HD 84406 will be the first star to be imaged by the James Webb Space Telescope in order to test the focus of the telescope. The star is a spectral type G star, similar to the sun and has a high proper motion.

https://en.wikipedia.org/wiki/HD_84406

I tried to find out more about this star but found less detail than I wanted here:
http://www.hygmap.space/index.php?selec ... t_center=1

And then more deep details that I can't fully comprehend:
https://simbad.u-strasbg.fr/simbad/sim-id?Ident=HD84406

My curiosity is why this star in particular? Is it because it's a class G star like the sun. Does that somehow aid in wavelength / wave front calibration (knowing our Sun's spectrum)? What about infrared calibration (or can it be implied that nanometer precision mirror focus at visible wavelengths will easily focus the longer infrared wavelengths)?

[Edit] I realize this is only the first test star. Surely there are other targets following this.

[Jlabute]

Being ever curious about JWST "First Light", I See that the 6th magnitude star HD 84406 in Ursa Major will be the initial target for mirror alignment.

HD 84406, is a star approximately 241 light-years away in the constellation of Ursa Major. HD 84406 will be the first star to be imaged by the James Webb Space Telescope in order to test the focus of the telescope. The star is a spectral type G star, similar to the sun and has a high proper motion.

https://en.wikipedia.org/wiki/HD_84406

I tried to find out more about this star but found less detail than I wanted here:
http://www.hygmap.space/index.php?selec ... t_center=1

And then more deep details that I can't fully comprehend:
https://simbad.u-strasbg.fr/simbad/sim-id?Ident=HD84406

My curiosity is why this star in particular? Is it because it's a class G star like the sun. Does that somehow aid in wavelength / wave front calibration (knowing our Sun's spectrum)? What about infrared calibration (or can it be implied that nanometer precision mirror focus at visible wavelengths will easily focus the longer infrared wavelengths)?

[Edit] I realize this is only the first test star. Surely there are other targets following this.

That's cool! So wiki will soon have a much better snapshot :-) I wonder of the amazing images to come. Their first task is wavefront alignment so, focusing. Maybe it doesn't matter so much for focusing so they picked an object they are well familiar with and not too faint? It isn't too far away, it is not a binary star, it is fairly constant.

[JagXKR]

A few things to consider.
One, you want to view a star that is away from the Galactic plane and even the Solar System plane. This will eliminate most of the dust and gas that may be in the way.
Two, you want the star to be away from the direction of the sun right now and that would be in the Ursa Major direction.
Three, as a class G star it's not too white, not too yellow, not too blue and not too red. It's just right.

how's that

ETA
my avatar is Messier 101, the Pinwheel Galaxy.
Guess what constellation......

[JagXKR]

Ursa Minor?
You cudda chose a avatar a little closer to home and not 19 million ly away.

How do you know that it's not my home?

[Sonny Taylor]

^^^ I'm missing the like button! That was a good exchange.

[JagXKR]

First light(s?) and a selfie!

[Jlabute]

^^^ Way cool. Alignment seems to be the most arduous chore. I see the cold side is much colder now.

[wewe88]

i am very curious about astronomy and stuff, if u do too check this artcle out, it is nice to read https://www.space.com/spaceflight-destr ... lood-cells

[Sonny Taylor]

i am very curious about astronomy and stuff, if u do too check this artcle out, it is nice to read https://www.space.com/spaceflight-destr ... lood-cells

Actually it was a bit disturbing to read, but quite interesting.

Artificial gravity on very long term manned space missions seems almost a necessity (for more reasons than just red blood cell loss). Too bad we're a long way from building a space station (or inter-planetary mission) with that capability.

Welcome to the forum wewe88.