James Webb Space Telescope

[molesworth]

What is the Scottish-built instrument?

It's the "Mid InfraRed Instrument" or MIRI, which has been built and tested at the UK Astronomy Technology Centre at the University of Edinburgh :

https://www.technologysi.stfc.ac.uk/Pages/MIRI.aspx

I got a look at it during development a few years back during a tour of the facility as part of a conference at the Royal Observatory Edinburgh.  It promises to deliver some very high quality results.

[bknight]

I just saw this this morning.  Another delay with scheduled launch 31/10/2021.

https://knpr.org/npr/2020-07/nasa-pushes-back-launch-date-webb-space-telescope-citing-covid-19?gclid=Cj0KCQiA4L2BBhCvARIsAO0SBdY4myIgNVGugvh4htu4HgxYggUY0ZGdNtU4fRibiYm6XAOY_PMy7xAaArwJEALw_wcB

Uggggg

[apollo16uvc]

At this point I am afraid that materials are ageing that were never meant to be in earth atmosphere for so long.

What about the plating on the mirrors? the filters, the optical system, the sensors.


If this fails to properly deploy we won't have anything of this scale for the next 50 years.


Do you think that having several smaller space telescopes in sync will be the future for large aperture space telescopes, instead of building a single massive one?

[raven]

Yeah, I was thinking earlier we might have a Galileo high gain antenna situation on our hands, only it's the whole bloody mirror and/or the sun shield. Damn, I really hope not;  not only would that would be absolute mud in NASA's eye, I really want this beauty to work. Being able to fold up mirrors is going to be a boon for future space telescopes.

[bknight]

The scope unfolded for the last(?) time prior to shipment and launch now scheduled for 31 Oct (?).  We'll see if that date holds.

https://www.spacedaily.com/reports/NASAs_giant_Webb_telescope_succeeds_in_key_pre-launch_test_999.html

[bknight]

Covers removed and ready to start the testing prior to launch in 018.  The one aspect that disappoints me is the launch by ESA.
http://www.nasa.gov/feature/goddard/2016/james-webb-space-telescopes-golden-mirror-unveiled

This was one of my concerns, and now this.
https://www.universetoday.com/151191/concerns-about-james-webbs-ariane-5-rocket-might-push-the-launch-back/

As we reported yesterday, the usually reliable Ariane 5 has experienced problems on two previous launches where unexpected vehicle accelerations occurred when the fairing separated from the rocket. The fairing is the nose cone used to protect a spacecraft payload during launch and acceleration through Earth’s atmosphere.

The Ariane 5 has been grounded for several months while the European Space Agency and Arianespace investigate the issue. In both anomalies, the payloads were successfully placed in orbit, however. There are two Ariane launches on the manifest before the JWST launch, and those launches are now expected no earlier than June and August 2021, respectively.

My misgivings are resurfacing again.

I do hope this happens without further delay and has no issues.

[cjameshuff]

At this point I am afraid that materials are ageing that were never meant to be in earth atmosphere for so long.

What about the plating on the mirrors? the filters, the optical system, the sensors.


If this fails to properly deploy we won't have anything of this scale for the next 50 years.


Do you think that having several smaller space telescopes in sync will be the future for large aperture space telescopes, instead of building a single massive one?

For radio it might be possible (though costly), but you can't feasibly combine multiple smaller orbital telescopes for optical observations. You'd need them to be positioned within a fraction of a wavelength, which at optical wavelengths means within tens of nanometers, and you need to somehow collect the optical signals from all the nodes together in one place. This isn't something that can be done electronically, optical sensors don't preserve the needed information. A modular telescope assembled in orbit would be more feasible, but at that point you may as well just make a big segmented mirror.

The problem with JWST isn't that it's big, the problem (apart from its basic management issues) is that it can't reasonably fit in its launch vehicle. The same telescope built for a larger vehicle would be far cheaper and less delicate, because it wouldn't have to be optimized down to razor-thin margins. If they'd done a half-sized vehicle to prove out the new technologies, they would have been able to use the experience to plan the mass and volume budgets better for the full-scale JWST and we'd now be looking at years of data from something slightly less ambitious and far less expensive and delayed.

[smartcooky]

For radio it might be possible (though costly), but you can't feasibly combine multiple smaller orbital telescopes for optical observations. You'd need them to be positioned within a fraction of a wavelength, which at optical wavelengths means within tens of nanometers, and you need to somehow collect the optical signals from all the nodes together in one place. This isn't something that can be done electronically, optical sensors don't preserve the needed information. A modular telescope assembled in orbit would be more feasible, but at that point you may as well just make a big segmented mirror

Why would it not be feasible to do this electronically? Ultimately, the optical signals from telescopes like Hubble and Chandra are converted into digital signals for transmission to earth, so why couldn't each element convert the signals and send them back to earth for later processing

These guys seem to think its possible...

https://www.nature.com/articles/ncomms7852

"Highest resolution imaging in astronomy is achieved by interferometry, connecting telescopes over increasingly longer distances and at successively shorter wavelengths. Here, we present the first diffraction-limited images in visual light, produced by an array of independent optical telescopes, connected electronically only, with no optical links between them." 

Now, I have not read the whole paper, and I do not claim or pretend to understand all of it, but the principle seems sound to me.

[cjameshuff]

For radio it might be possible (though costly), but you can't feasibly combine multiple smaller orbital telescopes for optical observations. You'd need them to be positioned within a fraction of a wavelength, which at optical wavelengths means within tens of nanometers, and you need to somehow collect the optical signals from all the nodes together in one place. This isn't something that can be done electronically, optical sensors don't preserve the needed information. A modular telescope assembled in orbit would be more feasible, but at that point you may as well just make a big segmented mirror

Why would it not be feasible to do this electronically? Ultimately, the optical signals from telescopes like Hubble and Chandra are converted into digital signals for transmission to earth, so why couldn't each element convert the signals and send them back to earth for later processing

These guys seem to think its possible...

https://www.nature.com/articles/ncomms7852

"Highest resolution imaging in astronomy is achieved by interferometry, connecting telescopes over increasingly longer distances and at successively shorter wavelengths. Here, we present the first diffraction-limited images in visual light, produced by an array of independent optical telescopes, connected electronically only, with no optical links between them." 

Now, I have not read the whole paper, and I do not claim or pretend to understand all of it, but the principle seems sound to me.

Hubble and Chandra do not "convert the optical signal to a digital form", they take measurements of integrated intensity over a period of time. The original optical signal is completely lost. Current sensor technologies just can't capture that information past a couple terahertz.

The process described in the paper, as far as I understand it, requires a completely different approach involving very precisely timed photon detections. It is apparently only physically possible with small telescopes, which limits it to very hot and bright sources. It is also poorly suited to imaging, note that their reconstructions involved knowledge of the target being reconstructed. It seems mainly useful for measuring the sizes of particularly hot and nearby stars, when the number of stars is known, and when they're separated enough that you can gather the data needed without them moving too much during the observations.

[bknight]

Well we have a delay again.

https://spacenews.com/jwst-launch-slips-to-november/

Maybe this year.  I do hope ESA gets the faring issue solved, this must be making NASA nervous.

[apollo16uvc]

I don't think astronomy could recover if the JWST failed. We likely won't see a space telescope of that scale and expanse for a generation of astronomers. Its failure could literally set back research by decades.

Imagine if repairs to the Hubble weren't possible... and how profoundly set-back the field would be would we not have been able to use that telescope for decades. If the Hubble failed, nothing on its scale would have been attempted since and astronomy would have been nothing like we know it as today.


But if it succeeds, it could change astronomy forever and take photos that define this century.