<p>Wikipedia's <a href="https://en.wikipedia.org/wiki/NEOSTEL" rel="nofollow noreferrer">NEOSTEL</a> says:</p>
<blockquote>
<p>The Near Earth Object Survey TELescope (NEOSTEL - also known as &quot;Flyeye&quot;) is an astronomical survey and early-warning system for detecting near-Earth objects sized 40 metres (130 feet) and above a few weeks before they impact Earth.</p>
</blockquote>
<p>and</p>
<blockquote>
<p>The fly eye aspect of the telescope refers to the use of compound optics, as opposed to the single set of optics used in a conventional telescope. Classically, telescopes were designed around a single human observer looking through an eye piece. Astrographs were developed in the 19th century where a photographic plate, or later a CCD, records the image, which a human observer can then view. With the human eye no longer directly observing the image there is no longer a restriction on a single viewing point, and asteroid detection software has become fully automated, so a human observer need not view the majority of images at all.</p>
<p>Light enters the NEOSTEL telescope through the aperture and is reflected off the primary mirror onto a secondary, consisting of 16 mirrors <strong>arranged on a hexadecagonal pyramid</strong>. The split beam then passes into 16 separate aspheric lenses and on to 16 corresponding CCD image sensors. NEOSTEL uses the 16 CCD cameras to view 45 square degrees of light entering the telescope aperture. The pixel scale is 1.5 arc seconds per pixel across the whole field of view.</p>
</blockquote>
<p><strong>Question:</strong></p>
<p>I understand the nontraditional secondary is <em>multifaceted</em> but its been hard for me to find details on the optical design. Are these beam splitters very close to the primary focus so that they cut up the field of view fairly cleanly, or are they far from the focus so that there's quite a lot of overlap and sharing of field between adjacently viewing cameras?</p>
<p>Are the faces flat or curved? What shape are they (e.g. rectangular, hexagonal, etc.)</p>
<p>And <em>just how aspheric</em> are each of the lenses used to correct individual fields? They must be pretty unusually shaped!</p>
<hr />
<p>Potentially helpful but paywalled:</p>
<ul>
<li><a href="https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11445/114453B/About-the-development-of-the-first-fly-eye-telescope/10.1117/12.2562227.short?SSO=1" rel="nofollow noreferrer">About the development of the first fly-eye telescope</a></li>
<li><a href="https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9908/99085T/The-Flys-Eye-camera-system--new-results-with-an/10.1117/12.2233586.short" rel="nofollow noreferrer">The Fly's Eye camera system: new results with an autonomously observing telescope</a></li>
</ul>
<hr />
<p>From <a href="https://conference.sdo.esoc.esa.int/proceedings/neosst1/paper/481/NEOSST1-paper481.pdf" rel="nofollow noreferrer">The Fly-Eye Telescope, Development and First Factory Tests Results</a> Proc. 1st NEO and Debris Detection Conference, Darmstadt, Germany, 22-24 January 2019, published by the ESA Space Safety Programme Office
Ed. T. Flohrer, R. Jehn, F. Schmitz (<a href="http://neo-sst-conference.sdo.esoc.esa.int" rel="nofollow noreferrer">http://neo-sst-conference.sdo.esoc.esa.int</a>, January 2019):</p>
<p><a href="https://i.sstatic.net/ZJze2.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/ZJze2m.jpg" alt="Figure 3. NEOSTEL Opto-mechanical assembly" /></a> <a href="https://i.sstatic.net/zB7iD.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/zB7iDm.jpg" alt="Figure 4. Fly Eye optical architecture concept" /></a></p>
<p>click figures for full size</p>
<p><a href="https://i.sstatic.net/nCwQs.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/nCwQsm.jpg" alt="Screenshots from the ESA video &quot;Asteroid Day: GV'S ESA'S FlyEye Telescope, OHBITALIA, Milan, Italy&quot;" /></a> <a href="https://i.sstatic.net/RvBf4.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/RvBf4m.jpg" alt="Screenshots from the ESA video &quot;Asteroid Day: GV'S ESA'S FlyEye Telescope, OHBITALIA, Milan, Italy&quot;" /></a></p>
<p>Screenshots from the ESA video <a href="https://www.esa.int/esatv/Videos/2018/06/Asteroid_Day/GV_s_ESA_s_Flyeye_Telescope_OHBItalia_Milan_Italy" rel="nofollow noreferrer">Asteroid Day: GV'S ESA'S FlyEye Telescope, OHBITALIA, Milan, Italy</a> found <a href="http://www.brera.mi.astro.it/sormano/telescope/advancedtelescopes.html" rel="nofollow noreferrer">here</a>. Click figures for full size</p>

CC BY-SA 4.0
2021-10-06T18:21:34.227Z
Good question. I found [this video](https://www.esa.int/ESA_Multimedia/Videos/2018/07/Flyeye_the_bug-eyed_telescope_monitoring_our_skies) from ESA about the telescope which gives some interesting shots, but, after some digging, I couldn't find anything useful in terms of actual details that wasn't resolutely behind a paywall. This may be a tricky one to answer, unless someone has access to get behind the paywall.
zephyr
CC BY-SA 4.0
2021-10-06T19:18:18.533Z
@zephyr thanks! Most days I'll have a chance to do so. I can take a look but won't answer my own question for a while in case someone else wants to. I think it's going to be an interesting looking secondary array!
uhoh
CC BY-SA 4.0
2022-01-29T10:18:07.283Z
This probably doesn't add much, and doesn't answer your main question really, but the faces are flat. Consider the faces of a traditional four sided pyramid. Then imagine you cut the four corners off to form an octagon - now you have 8 flat faces, 16 when you cut those 8 corners off. I admit the word facet is a bit of a problem, because it means both the flat faces of e.g. a pyramid, but also means the parts of a compound eye, which are not flat of course. If you happen to find the answer to your question, please feel free to update the Wikipedia article (remembering to cite your sources).
Raffles
CC BY-SA 4.0
2022-01-29T11:44:05.963Z
@Raffles I'm kinda slow, it's taken me more than half a decade to get used to Stack Exchange, I don't think I'll ever venture into the world of Wikipedia editing.
uhoh
CC BY-SA 4.0
2022-01-29T11:53:19.800Z
@uhoh OK well if you post it here (with references) and I spot it, I'll update the article :)
Raffles
CC BY-SA 4.0
2022-01-29T11:59:25.123Z
@Raffles okay that's great! Thank you.
uhoh
<observational-astronomy><telescope><optics><observatory><near-earth-object>
How exactly does NEOSTEL's fly's eye telescope's secondary mirror array split the primary beam among sixteen cameras?
uhoh
# How exactly does NEOSTEL's fly's eye telescope's secondary mirror array split the primary beam among sixteen cameras?

(Asked by: username_0 on 2021-09-30)

Wikipedia's [NEOSTEL](https://en.wikipedia.org/wiki/NEOSTEL) says:

> The Near Earth Object Survey TELescope (NEOSTEL - also known as "Flyeye") is an astronomical survey and early-warning system for detecting near-Earth objects sized 40 metres (130 feet) and above a few weeks before they impact Earth.

and

> The fly eye aspect of the telescope refers to the use of compound optics, as opposed to the single set of optics used in a conventional telescope. Classically, telescopes were designed around a single human observer looking through an eye piece. Astrographs were developed in the 19th century where a photographic plate, or later a CCD, records the image, which a human observer can then view. With the human eye no longer directly observing the image there is no longer a restriction on a single viewing point, and asteroid detection software has become fully automated, so a human observer need not view the majority of images at all.
>
> Light enters the NEOSTEL telescope through the aperture and is reflected off the primary mirror onto a secondary, consisting of 16 mirrors **arranged on a hexadecagonal pyramid**. The split beam then passes into 16 separate aspheric lenses and on to 16 corresponding CCD image sensors. NEOSTEL uses the 16 CCD cameras to view 45 square degrees of light entering the telescope aperture. The pixel scale is 1.5 arc seconds per pixel across the whole field of view.

**Question:**

I understand the nontraditional secondary is *multifaceted* but its been hard for me to find details on the optical design. Are these beam splitters very close to the primary focus so that they cut up the field of view fairly cleanly, or are they far from the focus so that there's quite a lot of overlap and sharing of field between adjacently viewing cameras?

Are the faces flat or curved? What shape are they (e.g. rectangular, hexagonal, etc.)

And *just how aspheric* are each of the lenses used to correct individual fields? They must be pretty unusually shaped!

---

Potentially helpful but paywalled:

* [About the development of the first fly-eye telescope](https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11445/114453B/About-the-development-of-the-first-fly-eye-telescope/10.1117/12.2562227.short?SSO=1)
* [The Fly's Eye camera system: new results with an autonomously observing telescope](https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9908/99085T/The-Flys-Eye-camera-system--new-results-with-an/10.1117/12.2233586.short)

---

From [The Fly-Eye Telescope, Development and First Factory Tests Results](https://conference.sdo.esoc.esa.int/proceedings/neosst1/paper/481/NEOSST1-paper481.pdf) Proc. 1st NEO and Debris Detection Conference, Darmstadt, Germany, 22-24 January 2019, published by the ESA Space Safety Programme Office
Ed. T. Flohrer, R. Jehn, F. Schmitz (<http://neo-sst-conference.sdo.esoc.esa.int>, January 2019):

[![Figure 3. NEOSTEL Opto-mechanical assembly](https://i.sstatic.net/ZJze2m.jpg)](https://i.sstatic.net/ZJze2.jpg) [![Figure 4. Fly Eye optical architecture concept](https://i.sstatic.net/zB7iDm.jpg)](https://i.sstatic.net/zB7iD.jpg)

click figures for full size

[![Screenshots from the ESA video ](https://i.sstatic.net/nCwQsm.jpg)](https://i.sstatic.net/nCwQs.jpg) [![Screenshots from the ESA video ](https://i.sstatic.net/RvBf4m.jpg)](https://i.sstatic.net/RvBf4.jpg)

Screenshots from the ESA video [Asteroid Day: GV'S ESA'S FlyEye Telescope, OHBITALIA, Milan, Italy](https://www.esa.int/esatv/Videos/2018/06/Asteroid_Day/GV_s_ESA_s_Flyeye_Telescope_OHBItalia_Milan_Italy) found [here](http://www.brera.mi.astro.it/sormano/telescope/advancedtelescopes.html). Click figures for full size

**Tags:** observational-astronomy, telescope, optics, observatory, near-earth-object
> **Comments:**
> **username_1**: Good question. I found [this video](https://www.esa.int/ESA_Multimedia/Videos/2018/07/Flyeye_the_bug-eyed_telescope_monitoring_our_skies) from ESA about the telescope which gives some interesting shots, but, after some digging, I couldn't find anything useful in terms of actual details that wasn't resolutely behind a paywall. This may be a tricky one to answer, unless someone has access to get behind the paywall.  
> **username_0**: @zephyr thanks! Most days I'll have a chance to do so. I can take a look but won't answer my own question for a while in case someone else wants to. I think it's going to be an interesting looking secondary array!  
> **username_2**: This probably doesn't add much, and doesn't answer your main question really, but the faces are flat. Consider the faces of a traditional four sided pyramid. Then imagine you cut the four corners off to form an octagon - now you have 8 flat faces, 16 when you cut those 8 corners off. I admit the word facet is a bit of a problem, because it means both the flat faces of e.g. a pyramid, but also means the parts of a compound eye, which are not flat of course. If you happen to find the answer to your question, please feel free to update the Wikipedia article (remembering to cite your sources).  
> **username_0**: @Raffles I'm kinda slow, it's taken me more than half a decade to get used to Stack Exchange, I don't think I'll ever venture into the world of Wikipedia editing.  
> **username_2**: @uhoh OK well if you post it here (with references) and I spot it, I'll update the article :)  
> **username_0**: @Raffles okay that's great! Thank you.  

---

## 0 answers

