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Hubble Telescope Back Up!

07/18/2021 8:35 PM

"NASA has returned the science instruments on the Hubble Space Telescope to operational status, and the collection of science data will now resume. This will be the first science data collected since the payload computer experienced a problem on June 13, which placed the instruments in a safe configuration and suspended science operations."

https://www.nasa.gov/feature/goddard/2021/operations-underway-to-restore-payload-computer-on-nasas-hubble-space-telescope

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#1

Re: Hubble Telescope back up!

07/18/2021 9:03 PM

This is excellent news.

I recently heard they think terrestrial telescopes can obtain images similar to or better than this pioneering optical orbital telescope. Thus this telescope may be the only one of its kind. I still think an optical observatory on the moon would be a good idea.

I hope the James Webb telescope is half as successful as the Hubble telescope has been.

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#2
In reply to #1

Re: Hubble Telescope back up!

07/19/2021 7:05 AM

<...hope the James Webb telescope is half as successful as the Hubble telescope...>

What an of odd thing to <...hope...> for.

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#3
In reply to #2

Re: Hubble Telescope back up!

07/19/2021 7:56 AM

Yeah, I forgot to include the critical and intended "... at least half as successful as the Hubble telescope."

Still, since the James Webb telescope will be out of reach of any repair service and Hubble had multiple service visits reaching half the success without any repairs won't be bad.

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#4
In reply to #1

Re: Hubble Telescope back up!

07/19/2021 10:45 AM

Adaptive optics (AO) allows a ground-based telescope to remove the distortion from the atmosphere. A laser beam creates a guide star which is used as a reference for the adaptive optics system.

A deformable mirror is adjusted by the AO to linearize the wavefront from the artificial star, thus removing the atmospheric distortion.

Introduction to Adaptive Optics and Deformable Mirrors (edmundoptics.com)

A space-based telescope is still needed for wavelengths filtered out by the atmosphere.

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#5
In reply to #4

Re: Hubble Telescope back up!

07/19/2021 10:55 PM

Yes! Adaptive Optics is precisely the mechanism that can ultimately obsolete the Hubble telescope's apparent advantage over terrestrial telescopes. I think the paper I found paid deliberate tribute to Isaac Asimov for this idea by starting with one of his most famous quotes and avoiding his first short story and its much later sequel involving an "anoptic imager". Asimov may not have initially contemplated adjustments of part of the field of view for distortions a terrestrial telescope will observe but he did plant that seed of an idea in the sequel to his first short story.

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#6
In reply to #4

Re: Hubble Telescope back up!

07/19/2021 11:49 PM

I assume that the laser creating the "guide star" is in essentially the same location as the telescope, so there is no mirror to reflect the laser light back to the telescope. Does the sensor detect the light reflected by dust and other particles in the atmosphere?

If it is a pulsed laser, then precise timing could presumably detect different distortions caused by different layers of the atmosphere.

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#7
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Re: Hubble Telescope back up!

07/20/2021 8:38 AM

The laser(s) are mounted on and aligned with the telescope. One type is tuned to sodium emission which is only present in the upper atmosphere. The other type is pulsed and employs Rayleigh scattering, and the receiver is gated to ignore low atmosphere dust reflections.

Laser guide star - Wikipedia

"There are two main types of laser guide star system, known as sodium and Rayleigh beacon guide stars.

Sodium beacons are created by using a laser tuned to 589.2 nanometers to energize atoms in the sodium layer of the mesosphere at an altitude of around 90 km (56 mi). The sodium atoms then re-emit the laser light, producing a glowing artificial star. The same atomic transition of sodium is used in sodium-vapor lamps for street lighting.

Rayleigh beacons rely on the scattering of light by the molecules in the lower atmosphere. In contrast to sodium beacons, Rayleigh beacons are much simpler and less costly, but do not provide as good a wavefront reference, since the artificial beacon is generated much lower in the atmosphere. The lasers are often pulsed, with measurement of the atmosphere being time-gated (taking place several microseconds after the pulse has been launched, so that scattered light at ground level is ignored and only light that has traveled for several microseconds high up into the atmosphere and back is actually detected)."

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

A far distant point source should have a flat wavefront, i.e., all light rays should be perfectly parallel. The wavefront sensor has a 2-dimensional array of lenslets, each of which casts an image on a common sensor. The position of the star images on the sensor indicates the correction that needs to be made to linearize the wavefront.

Introduction to Adaptive Optics and Deformable Mirrors (edmundoptics.com)

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#9
In reply to #7

Re: Hubble Telescope back up!

07/20/2021 11:36 AM

Thanks! I was unaware of a "sodium layer" in the upper atmosphere.

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#8

Re: Hubble Telescope Back Up!

07/20/2021 9:43 AM

I always thought it would be nice if we could retrieve the Hubble, once it finally dies, and put it in the Smithsonian. Maybe now with all these billionaires going into space one of them could take on the project. Or better yet, a collaboration. They could use it as a marketing event.

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#10

Re: Hubble Telescope Back Up!

07/20/2021 4:33 PM

Real picture of a Black Hole....

https://www.cnet.com/news/after-capturing-first-photo-of-a-black-hole-event-horizon-telescope-zooms-in-on-a-second/

These images, from a program led by Julianne Dalcanton of the University of Washington in Seattle, demonstrate Hubble's return to full science operations. [Left] ARP-MADORE2115-273 is a rarely observed example of a pair of interacting galaxies in the southern hemisphere. [Right] ARP-MADORE0002-503 is a large spiral galaxy with unusual, extended spiral arms. While most disk galaxies have an even number of spiral arms, this one has three. Credit: Science: NASA, ESA, STScI, Julianne Dalcanton (UW) Image processing: Alyssa Pagan (STScI)

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