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Other Conspiracy Theories / Re: COVID-19
« Last post by Glom on Today at 03:23:04 PM »
With the surge vaxxing in Bolton, I bet it delays me getting mine. They probably think, now that the oldies are done, it's best to prioritise by hotspot. The South-West ain't a hotspot do back of the queue probably.
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Other Conspiracy Theories / Re: COVID-19
« Last post by gillianren on Today at 10:19:15 AM »
BAUT holds to the belief that we should be able to discuss the pandemic without politics entering into the discussion.  There are some very simple issues at hand with anti-maskers and why the CDC decision was a bad one, but we can't have the conversation there.
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General Discussion / Re: James Webb Space Telescope
« Last post by cjameshuff on May 17, 2021, 04:22:54 PM »
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.
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General Discussion / Re: James Webb Space Telescope
« Last post by smartcooky on May 17, 2021, 06:45:10 AM »
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.
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General Discussion / Re: James Webb Space Telescope
« Last post by cjameshuff on May 15, 2021, 10:37:58 AM »
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.
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General Discussion / Re: James Webb Space Telescope
« Last post by bknight on May 14, 2021, 04:00:28 PM »
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/
Quote
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.
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General Discussion / Re: James Webb Space Telescope
« Last post by bknight on May 12, 2021, 09:46:57 AM »
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

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Rocket exhaust contains ionised gases doesn't it? Would that affect the signals in some way?

Yes, but I can't see how it would affect the cameras inside the hole. If you've ever see one of those beautiful videos of taken from inside a Falcon 9 payload fairing as it re-enters the earth's atmosphere, you would see that the ionization doesn't affect the video.

I am also pretty sure the downlink antennae are exterior.   


ETA: Here you go.... enjoy


Wow! What spectacular images!

Do you mind me asking, though: were those images broadcast, or recovered from the Go-Pro once the fairing was picked up?

That I don't know

I doubt they were broadcast intentionally but they could have been downlinked via telemetry.

This Scott Manley video tells about some clever people tapping into SpaceX's downlinks and grabbing video from the engineering cameras, video that doesn't appear on the live youtube channel during launches, for example, the cameras inside the fuel tanks.

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General Discussion / Re: Kids say the darnedest things...
« Last post by Peter B on May 09, 2021, 10:25:14 AM »
When it's early...

= = = =

10YOS shuffles into the family room, Friday morning just after 7am.

Me: Good morning!

10YOS: What?

Me: I said, good morning!

10YOS: Oh, okay.
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Other Conspiracy Theories / Re: COVID-19
« Last post by Bryanpoprobson on May 09, 2021, 03:03:43 AM »
Second Pfizer due on Tuesday 11th May.
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