[HN Gopher] Thin Flat Lenses Could Unleash a Revolution in Space...
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Thin Flat Lenses Could Unleash a Revolution in Space Telescopes
Author : giuliomagnifico
Score : 7 points
Date : 2023-07-21 20:58 UTC (2 hours ago)
(HTM) web link (www.universetoday.com)
(TXT) w3m dump (www.universetoday.com)
| dredmorbius wrote:
| The proposed application for these lenses is for a
| _spectrographic_ telescope, looking for exoplanet atmospheric
| biosignatures. See the white paper "Nautilus: A Very Large-
| Aperture, Ultralight Space Telescope for Exoplanet Exploration,
| Time-domain Astrophysics, and Faint Objects" (2019)
|
| <http://nautilus-array.space/wp-content/uploads/2019/07/Nauti...>
| (PDF)
|
| As such, the disadvantages of Fresnel lenses (or for Nautilus, a
| "multi-order diffractive engineered material lens" or MODE lens)
| for _imaging_ of objects are largely mooted, as the challenge
| instead is to gather sufficient quantities of light, in
| sufficiently short exposure periods, to gather useful
| spectroscopic data, that is, the light _spectrum_ showing
| specific absorption lines experienced during planetary transits
| of their star.
|
| From the white paper above:
|
| _The driver of the design of the Nautilus is to maximize the
| ratio of sensitivity (light-collecting area and throughput) to
| cost. The Nautilus combines a simple, non-cryogenic instrument
| (imager and slitless spectrograph) with a new, lightweight, and
| low-cost optical element instead of primary mirrors.... Nautilus
| will use an 8.5m-diameter multi-order diffractive engineered
| material lens (MODE lens) instead of a primary mirror. These
| diffractive lenses have ~100x lower areal density than
| traditional mirrors, are 100-1,000x less sensitive to
| misalignments (drastically reducing fabrication and integration
| costs), and can be cost-effectively replicated (via pressure
| molding).... Nautilus will use a single instrument, the Nautilus
| visual /near-infrared imaging spectrograph (NAVIIS). At this
| point no optical design exists yet for NAVIIS, but in the
| following we describe the preliminary concept for this
| instrument. NAVIIS will utilize a dichroic mirror to split the
| incoming light into the visible light (NAVIIS-VIS, 0.5-0.95 mm)
| and near-infrared (NAVIIS-NIR, 0.95-1.7 mm) channels._
| onetimeuse92304 wrote:
| Pure BS.
|
| The main problem with making optics for telescopes, and
| especially for large and/or space telescopes is precision.
|
| It is hard enough to grind something to a precise shape when that
| shape is a smooth surface. Forget about making precise fresnel
| lens that has extremely complex shape that relies on very precise
| smooth surfaces right next to very sharp discontinuities, that is
| not going to happen.
|
| Another problem is that you don't really ever want lenses for a
| high power telescope. Lenses cause optical aberration -- and once
| light rays of different colors go each their own way it is pretty
| much impossible to put them back precisely enough for the kind of
| telescope you would want to shoot into space.
|
| The article sounds like a third grader got interested in
| astronomy and suddenly discovered fresnel. Do you think NASA
| somehow overlooked an obvious solution to all their problems that
| has been known for hundreds of years to everybody else?
| ithkuil wrote:
| Have you read
| https://iopscience.iop.org/article/10.3847/1538-3881/ab2631 and
| are making a critique of their work or are you talking about
| the journalist that wrote a piece perhaps dumbing down the
| concepts a bit too much?
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(page generated 2023-07-21 23:01 UTC)