The James Webb Space Telescope and stuff

[JoeSchmuckatelli]

4 hours ago, Gargamel said:

official NASA photo

I did not think about it when I first saw that photo - but I guess NASA sees 'the darkness of space' as a euphemism... Because JWST is clearly catching light from all over the place! 

[Gargamel]

16 minutes ago, JoeSchmuckatelli said:

I did not think about it when I first saw that photo - but I guess NASA sees 'the darkness of space' as a euphemism... Because JWST is clearly catching light from all over the place! 

Yeah... there's clearly a large star in the correct position that the sun shield is blocking, and then there's something reflecting light at us in the mirror... meaning it's really close and not in the aim of the telescope. 

So they plopped an infrared space telescope in a binary (or more) system... in the middle of a nebula.       I don't have high hope for these photos.

[JoeSchmuckatelli]

6 minutes ago, Gargamel said:

I don't have high hope for these photos.

Right!

And these are the same people who supposedly faked the moon landings?!?

Standards have clearly gone downhill

Edited January 26, 2022 by JoeSchmuckatelli

[HebaruSan]

On 12/18/2021 at 7:50 PM, HebaruSan said:

The standard science-communicator line is that JWST will stop operating after its stationkeeping fuel runs out. Since it's not going to be in Earth's shadow anyway, what would actually break? Couldn't they try to keep the comms dishes pointed at each other by carefully monitoring the drift away from L2? Is it a question of attitude control?

I was surprised to read this (emphasis mine):

https://www.theatlantic.com/science/archive/2022/01/nasa-james-webb-space-telescope-journey/621352/

Quote

When its tank gets low, engineers might command the observatory to push itself into a higher orbit, to make sure it doesn’t crash into any objects closer to home. If that happens, Webb could remain in orbit around the sun for hundreds, maybe thousands of years. It would no longer be yoked to the Earth in the same way, but its mirrors and scientific instruments could keep working, and Webb could still phone home, Yu said.

("Yu" is "Wayne Yu, a flight-dynamics engineer on Richon’s team at Goddard," and "Richon" is "Karen Richon, who leads the team at NASA’s Goddard Space Flight Center that created Webb’s trajectory.")

Now, this doesn't quite say that it could keep pointing at targets of interest and doing science, but it does muddy the waters a bit on exactly why and whether the propellant running out would be game-over. I guess once it drifts away from L2, it would get further and further from Earth along their nearly-shared orbit, maybe reaching the opposite side of the sun some of the time?

And I guess I don't know that much about what the post-L2 orbit might look like; if it turns out not to be circular, maybe the post-service-life JWST could drift radial-in, so its comms would not be able to point at Earth?

Edited January 26, 2022 by HebaruSan

[Codraroll]

22 hours ago, HebaruSan said:

Now, this doesn't quite say that it could keep pointing at targets of interest and doing science, but it does muddy the waters a bit on exactly why and whether the propellant running out would be game-over. I guess once it drifts away from L2, it would get further and further from Earth along their nearly-shared orbit, maybe reaching the opposite side of the sun some of the time?

Interesting. So they could potentially ask it to just photograph whatever it happens to be pointing at, and hope for it to be interesting. Chances are it will, given how Hubble took the Ultra-Deep Field photo by intentionally pointing into the darkest portion of the sky, and it still found lots of interesting stuff. Granted, they chose the darkest patch of sky not because it had nothing to look at but because it had the fewest obstructions, but chances still are that JWST would be able to find something science-worthy in every random direction if necessary.

23 hours ago, HebaruSan said:

And I guess I don't know that much about what the post-L2 orbit might look like; if it turns out not to be circular, maybe the post-service-life JWST could drift radial-in, so its comms would not be able to point at Earth?

Decades in the future, I hope we have enough relays to bounce the signal off of if it doesn't go straight towards Earth.

[JoeSchmuckatelli]

On 1/26/2022 at 9:38 AM, HebaruSan said:

And I guess I don't know that much about what the post-L2 orbit might look like; if it turns out not to be circular, maybe the post-service-life JWST could drift radial-in, so its comms would not be able to point at Earth?

I would have thought that so long as it has working solar that it could do work almost indefinitely, but apparently that's not the case.  I can't find the reference, but I once read that without some fuel reaction wheels eventually lose energy and then you've just got a drifting piece of junk.  I'd guess that a drifting Webb could still do work for at least as long as they have control authority to keep the sunshield oriented correctly, and the telescope pointed at a target.  So even if they don't have enough fuel for effective station-keeping and need to let it drift, that may not be EOS... but eventually control authority will be lost and then it's junk

[kerbiloid]

Oh, yeah... Space junk.

Spoiler

Imagine the feelings of the crew arriving to L2 several decades later and seeing the derelict JWST drifting in the abyss of the night.

[JoeSchmuckatelli]

Quote

HD 84406! That is the first star Webb will point at to gather engineering data to start the mirror alignment process. The team chose a bright star (magnitude 6.7 at a distance of about 260 light-years, as measured by Gaia). The star is a sun-like G star in the Ursa Major constellation, which can be seen by Webb at this time of the year. This is just the first step; HD 84406 will be too bright to study with Webb once the telescope starts to come into focus. But for now, it is the perfect target to begin our search for photons, a search that will lead us to the distant universe

 

https://blogs.nasa.gov/webb/

So - this is concerning news.  A bit over a decade ago I read something from Margaret Turnbull about Webb being able to take detailed looks at dim, sunlike stars for possible exoplanets in the respective habitable zones.  She specifically mentioned 18 Sco - which is about 42ly from here.  (18 Sco is a really cool system-a younger, higher metallicity solar twin that was a leading candidate for study some time ago... It's one of the things I've been looking forward to) 

If dim stars within our galaxy are too bright for Webb - that almost seems like an unfortunate limitation of the utility of the whole observatory. 

Yes, distant galaxies and things to dim for Hubble will be fantastic science - but c'mon. 

 

... 

Also of interest to KSP-ers is the mention of the DSN:

Quote

 

The team also turned on the High-Gain Antenna, enabling downlink to Earth through the Deep Space Network using the Ka radio band. The Ka-band provides a much higher data rate than the S-band that Webb has been using for communications up until now. The Ka-band and the High-Gain Antenna will eventually allow the observatory to send all of the science images and data down to the ground for astronomers around the world to analyze and make discoveries.

 

 

 

 

 

[Codraroll]

31 minutes ago, JoeSchmuckatelli said:

If dim stars within our galaxy are too bright for Webb - that almost seems like an unfortunate limitation of the utility of the whole observatory. 

Yes, distant galaxies and things to dim for Hubble will be fantastic science - but c'mon. 

At least it highlights the need for other telescopes to complement Webb. It's a good telescope, but not suitable for every use case, so preferably somebody should start work on another telescope for a slightly different use case pretty soon.

If Starship works as advertised, it might not even be prohibitively expensive either. I have often wondered how expensive it would be to build a reasonably capable telescope if mass wasn't (as much of) an issue and launches were really cheap.

[cubinator]

1 hour ago, Codraroll said:

If Starship works as advertised, it might not even be prohibitively expensive either. I have often wondered how expensive it would be to build a reasonably capable telescope if mass wasn't (as much of) an issue and launches were really cheap.

It would be at least as expensive as building a similarly capable telescope on a mountaintop.

[kerbiloid]

Quote

How Many People Have Smartphones Worldwide (Jan 2022)

https://www.bankmycell.com › ...

According to Statista, the current number of smartphone users in the world today is 6.648 billion, and this means 83.96% of the world's population owns

If a billion of people had pointed at a star with their smartphone cameras at once, ir would be an Extra Large Multicellular Camera Array, so we could see like the alphacentaurians are waving "hi!".

[Jacke]

6 hours ago, kerbiloid said:

If a billion of people had pointed at a star with their smartphone cameras at once, ir would be an Extra Large Multicellular Camera Array, so we could see like the alphacentaurians are waving "hi!".

Only with the added hardware and software providing the data to turn them into an astronomical interferometer.

[HebaruSan]

https://www.universetoday.com/154282/want-to-know-what-james-webb-looks-like-in-powerful-earth-telescopes-prepare-to-be-underwhelmed/

 

[Meecrob]

On 1/29/2022 at 7:43 AM, Jacke said:

Only with the added hardware and software providing the data to turn them into an astronomical interferometer.

True, but if every smartphone owner donated just one dollar, we would be two-thirds the way to a second JWST or similar.

Sorry its a bit off-topic, but @kerbiloid brings up a good point. Namely that space really isn't that expensive, it only is when one expects a handful of parties to foot the entire bill for something everyone on the planet benefits from.

 

5 hours ago, HebaruSan said:

https://www.universetoday.com/154282/want-to-know-what-james-webb-looks-like-in-powerful-earth-telescopes-prepare-to-be-underwhelmed/

I dunno, I'm impressed we can even see it so well. I imagine this was taken after the sunshield was deployed and we are seeing reflected Sun's rays?

[Entropian]

13 hours ago, HebaruSan said:

(post)

A couple people in my local astro club also managed to catch it as a smear in a long exposure with a 6" (I think) refractor.  I've been trying my luck with my 8" Dall-Kirkham but the weather's not been permitting for the past 2 weeks or so.

 

Edited February 1, 2022 by Entropian
grahmahrr

[Gargamel]

20 hours ago, HebaruSan said:

https://www.universetoday.com/154282/want-to-know-what-james-webb-looks-like-in-powerful-earth-telescopes-prepare-to-be-underwhelmed/

Most accurate URL ever. 

[JoeSchmuckatelli]

More info on why it will take so long before we see images from Webb:

Quote

 

While the MIRI instrument and some instrument components were powered on in the weeks after Webb’s Dec. 25 launch, the team didn’t finish turning on the remaining three instruments – NIRCam, NIRSpec, and FGS/NIRISS – until the past few days.

The mission operations team’s next major step is to turn off instrument heaters. The heaters were necessary to keep critical optics warm to prevent the risk of water and ice condensation. As the instruments meet pre-defined criteria for overall temperatures, the team is shutting off these heaters to allow the instruments to restart the months-long process of cooling to final temperatures.

When NIRCam reaches 120 kelvins (approximately -244 degrees Fahrenheit, or -153 degrees Celsius), Webb’s optics team will be ready to begin meticulously moving the 18 primary mirror segments to form a single mirror surface.

 

James Webb Space Telescope (nasa.gov)

I note that they do not mention 'Instrument coolers' so I'm presuming that being shielded from the sun, radiative cooling will take care of that.  Sadly my google-fu is failing me (I recently saw an explanation for how fast radiative cooling works to take something down to equalibrium with the cosmic background radiation) and I don't have the maths / education to try to work out the rate of cooling for a thing in shadow in space is... but apparently its 'months-long'.

[Gargamel]

I predict that after the decades of color corrected, slightly touched up, curated photos that Hubble released, there will be a collective “ahhh what?” From the general public when the first Webb photos get released.   

[JoeSchmuckatelli]

11 minutes ago, Gargamel said:

I predict that after the decades of color corrected, slightly touched up, curated photos that Hubble released, there will be a collective “ahhh what?” From the general public when the first Webb photos get released.   

Yeah - that's what I'm afraid of.  

[Gargamel]

7 minutes ago, JoeSchmuckatelli said:

Yeah - that's what I'm afraid of.  

I don’t think it’ll be a problem for us that understand the really purty picshures will come eventually, but still....   can’t be any worse than Hubble’s firsts pic though.  

[cubinator]

25 minutes ago, Gargamel said:

I predict that after the decades of color corrected, slightly touched up, curated photos that Hubble released, there will be a collective “ahhh what?” From the general public when the first Webb photos get released.   

"What do you mean you can't show us the real color?" 

Y-shaped diffraction spikes will also be a large point of conversation.

[JoeSchmuckatelli]

1 minute ago, Gargamel said:

I don’t think it’ll be a problem for us that understand the really purty picshures will come eventually, but still....   can’t be any worse than Hubble’s firsts pic though.  

Hope not.  Also hope the PR department is going to ask for false color given that they learned how much the public enjoys them!

[kerbiloid]

After Fallout 3 even a tinted green universe can't surprise very much.

(And the Chernobyl series.)

On the other hand, the world before 1960s was grayscale, and people got used to live there.

[VaPaL]

17 hours ago, JoeSchmuckatelli said:

I note that they do not mention 'Instrument coolers' so I'm presuming that being shielded from the sun, radiative cooling will take care of that.

There is at least one cooler for MIRI

https://sci.esa.int/web/jwst/-/46831-cryocooler-for-miri

This video explain how this cooler works

 

[VaPaL]

Amazing photo of JWST