<p>By offsetting the SCA columns, the Field of View layout follows the natural annular curve of an off-axis TMA optimized field.
Short answer:  Yes, off axis aberration magic.</p>
<p>Longer answer: The <a href="https://doi.org/10.1117/12.2325859" rel="nofollow noreferrer">following journal article</a>, &quot;Optical design and predicted performance of the WFIRST phase-b imaging optics assembly and wide field instrument&quot; (Bert et al., 2018) includes this statement that answer this question:</p>
<blockquote>
<p>By offsetting the SCA columns, the Field of View layout follows the
natural annular curve of an off-axis TMA optimized field.</p>
</blockquote>
<p>Unpacking the jargon a bit –
SCA == sensor chip assembly, these are the detector array assemblies, 4k x 4k pixels 10um each, Near IR
<strong>TMA == three mirror anastigmat</strong>, a telescope design form that minimizes aberrations over a wide field</p>

CC BY-SA 4.0
2021-10-14T13:27:06.197Z
*Sweet!* Thank you for the speedy, concise, clear and well-sourced answer, and welcome to Stack Exchange!
uhoh
CC BY-SA 4.0
2021-10-14T13:03:34.470Z
2021-10-14T14:22:38.473Z
2021-10-14T14:22:38.473Z
Dave Content
<p>The Curious Droid YouTube video <a href="https://youtu.be/PNO_ofQijbY?t=115" rel="nofollow noreferrer">NASA's Mega Hubble - The Roman Space Telescope</a> illustrates the shape of the telescope's field of view and the outline has a smile or frown shape. For whatever reason it reminds me of a PacMan &quot;ghost&quot;.</p>
<p>Why does the field of view have this curved shape, I'd naively expect it to be rectangular. Is there some off-axis aberration correction magic going on? Something to do with its adaptive optics system?</p>
<hr />
<p><a href="https://i.sstatic.net/SQzPp.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/SQzPp.jpg" alt="screenshot from Curious Droid YouTube video &quot;NASA's Mega Hubble - The Roman Space Telescope&quot; https://youtu.be/PNO_ofQijbY" /></a></p>
<p>From <a href="https://science.nasa.gov/science-pink/s3fs-public/atoms/files/Kruk_WFIRST_APAC_April2018.pdf" rel="nofollow noreferrer">WFIRST Update; Jeffrey Kruk, WFIRST Project Scientist</a>  (<a href="https://web.archive.org/web/20211010211555/https://science.nasa.gov/science-pink/s3fs-public/atoms/files/Kruk_WFIRST_APAC_April2018.pdf" rel="nofollow noreferrer">Archived</a>)</p>
<p><a href="https://i.sstatic.net/Gl335.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Gl335.jpg" alt="from &quot;WFIRST Update; Jeffrey Kruk, WFIRST Project Scientist&quot; https://science.nasa.gov/science-pink/s3fs-public/atoms/files/Kruk_WFIRST_APAC_April2018.pdf Archived https://web.archive.org/web/20211010211555/https://science.nasa.gov/science-pink/s3fs-public/atoms/files/Kruk_WFIRST_APAC_April2018.pdf" /></a></p>
<p>Screenshot from Google Doodle <a href="https://www.google.com/logos/2010/pacman10-i.html" rel="nofollow noreferrer">pacman10-i</a> <strong>note:</strong> it starts playing as soon as you click, adjust your device volume first, then enjoy!</p>
<p><a href="https://i.sstatic.net/bEmk1.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/bEmk1.png" alt="Screenshot from Google Doodle https://www.google.com/logos/2010/pacman10-i.html note: it starts playing as soon as you click, adjust your device volume first, then enjoy!" /></a></p>

CC BY-SA 4.0
2021-10-13T08:22:58.887Z
“Something to do with its adaptive optics system?” It’s a space telescope, so it doesn’t need or have adaptive optics…
Peter Erwin
CC BY-SA 4.0
2021-10-13T08:32:02.857Z
@PeterErwin and yet, *it most certainly does!* In order for the (really amazing) coronagraph to work sufficiently to allow imaging of exoplanetary systems, the wavefront has to be correct to tens of picometers, in order to allow for deep nulling of the bright light from the primary. [See sections starting below figure 37](https://directory.eoportal.org/web/eoportal/satellite-missions/r/rst) There's no way to build something like that on the ground, launch it into space and maintain it in a space environment to such optical tolerances passively.
uhoh
CC BY-SA 4.0
2021-10-13T08:44:45.180Z
DM1 and DM2 in Figure 37 are *deformable mirrors*. Unlike ground systems that work at close to kHz, the figure shows their actuation bandwidth is about 5 milli-Hertz, consistent with a very slow (sub picometer per second) thermal drift of a well built space telescope optical system.
uhoh
<observational-astronomy><optics><space-telescope><adaptive-optics><nancy-grace-roman-telescope>
Why is the Nancy Grace Roman Space Telescope's field of view shaped like a PacMan "ghost"?
uhoh
# Why is the Nancy Grace Roman Space Telescope's field of view shaped like a PacMan "ghost"?

(Asked by: username_0 on 2021-10-12)

The Curious Droid YouTube video [NASA's Mega Hubble - The Roman Space Telescope](https://youtu.be/PNO_ofQijbY?t=115) illustrates the shape of the telescope's field of view and the outline has a smile or frown shape. For whatever reason it reminds me of a PacMan "ghost".

Why does the field of view have this curved shape, I'd naively expect it to be rectangular. Is there some off-axis aberration correction magic going on? Something to do with its adaptive optics system?

---

[![screenshot from Curious Droid YouTube video ](https://i.sstatic.net/SQzPp.jpg)](https://i.sstatic.net/SQzPp.jpg)

From [WFIRST Update; Jeffrey Kruk, WFIRST Project Scientist](https://science.nasa.gov/science-pink/s3fs-public/atoms/files/Kruk_WFIRST_APAC_April2018.pdf) ([Archived](https://web.archive.org/web/20211010211555/https://science.nasa.gov/science-pink/s3fs-public/atoms/files/Kruk_WFIRST_APAC_April2018.pdf))

[![from ](https://i.sstatic.net/Gl335.jpg)](https://i.sstatic.net/Gl335.jpg)

Screenshot from Google Doodle [pacman10-i](https://www.google.com/logos/2010/pacman10-i.html) **note:** it starts playing as soon as you click, adjust your device volume first, then enjoy!

[![Screenshot from Google Doodle https://www.google.com/logos/2010/pacman10-i.html note: it starts playing as soon as you click, adjust your device volume first, then enjoy!](https://i.sstatic.net/bEmk1.png)](https://i.sstatic.net/bEmk1.png)

**Tags:** observational-astronomy, optics, space-telescope, adaptive-optics, nancy-grace-roman-telescope
> **Comments:**
> **username_1**: “Something to do with its adaptive optics system?” It’s a space telescope, so it doesn’t need or have adaptive optics…  
> **username_0**: @PeterErwin and yet, *it most certainly does!* In order for the (really amazing) coronagraph to work sufficiently to allow imaging of exoplanetary systems, the wavefront has to be correct to tens of picometers, in order to allow for deep nulling of the bright light from the primary. [See sections starting below figure 37](https://directory.eoportal.org/web/eoportal/satellite-missions/r/rst) There's no way to build something like that on the ground, launch it into space and maintain it in a space environment to such optical tolerances passively.  
> **username_0**: DM1 and DM2 in Figure 37 are *deformable mirrors*. Unlike ground systems that work at close to kHz, the figure shows their actuation bandwidth is about 5 milli-Hertz, consistent with a very slow (sub picometer per second) thermal drift of a well built space telescope optical system.  

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## 1 answers

### Answer by username_2 on 2021-10-14. Score: 4 | Accepted answer

By offsetting the SCA columns, the Field of View layout follows the natural annular curve of an off-axis TMA optimized field.
Short answer: Yes, off axis aberration magic.

Longer answer: The [following journal article](https://doi.org/10.1117/12.2325859), "Optical design and predicted performance of the WFIRST phase-b imaging optics assembly and wide field instrument" (Bert et al., 2018) includes this statement that answer this question:

> By offsetting the SCA columns, the Field of View layout follows the
> natural annular curve of an off-axis TMA optimized field.

Unpacking the jargon a bit –
SCA == sensor chip assembly, these are the detector array assemblies, 4k x 4k pixels 10um each, Near IR
**TMA == three mirror anastigmat**, a telescope design form that minimizes aberrations over a wide field

> **Comments:**
> **username_0**: *Sweet!* Thank you for the speedy, concise, clear and well-sourced answer, and welcome to Stack Exchange!  

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