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#40
by
Hobbes-22
on 18 Jan, 2023 07:01
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If JWST had failed in some major way, it might have been much harder to advocate for a next-gen observatory. Also, lessons learned during JWST development and deployment can be applied to the observatory. But I too wish the aperture was larger.
This video is an interview with Lee Feinberg, Optical Telescope Element Manager for JWST. He addresses the plans for HWO incl. why they chose this size. Summary: the technology isn't there yet for a visible-wavelength telescope larger than JWST.
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#41
by
redliox
on 19 Jan, 2023 01:24
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I'll grant that exoplanet detection very hard, but I'd like to see options for something better than Webb's size, moreso if either New Glenn or Starship launchers have fairings far wider than 7 meters. Might as well maximize the size if we have to wait another 20 years.
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#42
by
VSECOTSPE
on 19 Jan, 2023 04:40
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Collecting area is just one design factor in research telescopes, and it doesn’t make sense to pay billions for collecting area that’s not needed to achieve the research goals of a particular telescope.
In the case of HWO, the primary challenge is the picometer-level precision needed to control photons in the visible and ultraviolet wavelengths. JWST only needs nanometer-level precision to control infrared photons. If the HWO team can’t make that three orders of magnitude improvement in wavefront sensing and control, it doesn’t matter how much collecting area HWO has. The imagery output will be out-of-phase, nonsensical, unintelligible garbage, regardless.
The second challenge for HWO is coronagraph contrast. The Roman Space Telescope, which is obviously still in development and yet to fly, is supposed to demonstrate a contrast of 10^7 to 10^8. To suppress light from the parent star and get data on potentially habitable planets, HWO will need a contrast of 10^10 or so from its coronagraph. Again, if the HWO team can’t achieve this two to three orders of magnitude improvement, HWO literally won’t be able to do the job in its name, regardless of the size of its collecting area.
After that, collecting area and other factors play into the design. This is mostly a rocket website, and it’s understandable that rocket folks would look to big telescopes with big collectors to help justify SLS, Starship, or whatever their favorite big rocket is. But collecting area is not the first or even second technical challenge to the next steps in space telescope design after JWST. It’s just not where the science and technology are at.
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#43
by
Blackstar
on 08 Jun, 2023 21:43
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Interesting thing came up in today's Space Studies Board meeting--NASA is now considering a monolithic (single mirror) approach to the HWO instead of a multi-segmented mirror. They did not explain why.
For those who do not know the background, while a single big mirror might seem like it would be easier to manufacture than a multi-segmented mirror like JWST, that is not inherently true. The big problem is that the mirror is manufactured in gravity and has to be shaped to accommodate the sagging that occurs in gravity. It has to be designed so that it un-sags properly in microgravity. This is very hard to simulate, and there is the risk that the telescope could be launched and then not un-sag into the proper shape.
It will be interesting to see how this progresses.
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#44
by
redliox
on 10 Jun, 2023 10:44
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For those who do not know the background, while a single big mirror might seem like it would be easier to manufacture than a multi-segmented mirror like JWST, that is not inherently true. The big problem is that the mirror is manufactured in gravity and has to be shaped to accommodate the sagging that occurs in gravity. It has to be designed so that it un-sags properly in microgravity. This is very hard to simulate, and there is the risk that the telescope could be launched and then not un-sag into the proper shape.
It will be interesting to see how this progresses.
Aren't there ways to adjust the telescope post launch? Adaptive optics, ect? The Hubble got corrective optics added in and Webb can adjust the individual mirrors by microns; built-in ways to adjust the secondary mirror and within the instruments themselves seem plausible. Not as much a show-stopper as it was in Hubble's prime.
Likewise interested to see how this progresses.
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#45
by
Blackstar
on 10 Jun, 2023 11:54
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Aren't there ways to adjust the telescope post launch? Adaptive optics, ect? The Hubble got corrective optics added in and Webb
All I know is that this was discussed as a problem back when we were doing the decadal survey in 2020, so I assume that the ways of adjusting are either insufficient, or not applicable. I'm not saying that this stuff cannot be overcome, just that we now have significant experience with large multi-mirror telescopes and we don't have experience with monolithic space mirrors greater than 2.4 meters in diameter.
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#46
by
ttle2
on 13 Jun, 2023 20:38
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I thought HWO was always planned to use an unobstructed (off-axis) monolithic mirror because that gives the cleanest PSF, which is what you really want for high-contrast coronagraphy.
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#47
by
jbenton
on 14 Jun, 2023 04:32
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I thought HWO was always planned to use an unobstructed (off-axis) monolithic mirror because that gives the cleanest PSF, which is what you really want for high-contrast coronagraphy.
IIRC, that was suggested for the HabEx proposal, but the decadal-proposed fusion of LUVIOR and HabEx (which became HWO) was envisioned being unobstructed, but segmented. Apparently, a segmented mirror doesn't hurt contrast requirements nearly as much as obstruction:
One definitely would prefer a monolithic mirror for exoplanet imaging. Segmented mirrors have (small) gaps between their edges. The diffraction effects of the segments are adverse for very high contrast applications (where the main challenge is the suppression of starlight).
That's exactly what I thought, too, but the report differs. Here's the figure below - it shows no difference from segmenting, as long as the telescope is unobscured. My guess at the reasoning behind this is that starlight suppression involves mostly suppressing the low order mirror deformations. Segmentation introduces almost exclusively high-order edges, so it's not a problem. Obscuration, on the other hand, unavoidably introduces low-order terms, by its high-area blockage in one spot.
(this quote is from the
2020 Astrophysics Decadal thread in this forum)
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#48
by
Blackstar
on 01 Feb, 2024 15:42
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A couple of slides on what HWO could do in terms of planetary astronomy.
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#49
by
StraumliBlight
on 21 May, 2024 17:07
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#50
by
deadman1204
on 21 May, 2024 17:55
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A couple of slides on what HWO could do in terms of planetary astronomy.
Question for you Blackstar. That right image of what HWO could potentially do with Pluto. It mentions that hwo could do years long imaging of pluto. Does that mean multi-year image integration to acheive that view?
Can we even do a multiyear image integration?
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#51
by
Blackstar
on 21 May, 2024 18:53
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Question for you Blackstar. That right image of what HWO could potentially do with Pluto. It mentions that hwo could do years long imaging of pluto. Does that mean multi-year image integration to acheive that view?
Can we even do a multiyear image integration?
I really don't know. I was going to speculate, but I'm not a planetary astronomy expert.
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#52
by
redliox
on 22 May, 2024 02:45
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I'd like to see how Eris looks in the future; compare "dwarf planets" to compare and contrast and maybe rename them planets.
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#53
by
gongora
on 22 May, 2024 02:52
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#54
by
Star One
on 22 May, 2024 10:18
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The video I posted in the Roman space telescope thread yesterday talks about how the coronagraph for that mission is a technical pathfinder for this mission.
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#55
by
deadman1204
on 22 May, 2024 14:10
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I'd like to see how Eris looks in the future; compare "dwarf planets" to compare and contrast and maybe rename them planets.
rename the dwarf planets?
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#56
by
meekGee
on 22 May, 2024 20:04
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I'd like to see how Eris looks in the future; compare "dwarf planets" to compare and contrast and maybe rename them planets.
rename the dwarf planets?
Sneezy becomes Squeaky etc.
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#57
by
redliox
on 23 May, 2024 13:10
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I'd like to see how Eris looks in the future; compare "dwarf planets" to compare and contrast and maybe rename them planets.
rename the dwarf planets?
Sneezy becomes Squeaky etc.
I meant to imply giving Eris and Pluto planet status, provided we get more data on Eris to boot it's case (by way of the HWO or bigger scopes).
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#58
by
Blackstar
on 23 May, 2024 15:22
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I'd like to see how Eris looks in the future; compare "dwarf planets" to compare and contrast and maybe rename them planets.
rename the dwarf planets?
Sneezy becomes Squeaky etc.
I meant to imply giving Eris and Pluto planet status, provided we get more data on Eris to boot it's case (by way of the HWO or bigger scopes).
There was a joke that sailed over your head.
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#59
by
redliox
on 23 May, 2024 23:02
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There was a joke that sailed over your head.
I'll leave the jokes at that and let the thread be about HWO again
