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One thing they mentioned that kinda sends it home to me is that the telescope is aimed at the dark and away from the sun, and the other side is especially refle

One thing they mentioned that kinda sends it home to me is that the telescope is aimed at the dark and away from the sun, and the other side is especially reflective[0]. In other words, one side is too dark to see, and the other is too bright to see. [0]:https://twitter.com/NASAWebb/status/1479161991252131841 https://twitter.com/NASAWebb/status/1479161991252131841

newman8r 5y ago
Couldn't they just use an image intensifier tube for night vision? I think they should just stick with the excuse of it being costly and unnecessary.
- Sebb767 5y ago
  We're talking about "see the faintest light from stars millions of lightyears away"-dark (for that reason you also can't shine a light on it), with our sun in the background. To see something on that side, you'd basically need the vision capabilities the telescope itself has and that's obviously not going to happen.
  - newman8r 5y ago
    > to see something on that side, you'd basically need the vision capabilities the telescope itself I'm not sure if that's correct - there's a lot of photons hitting the telescope (the night sky), and night vision systems can work off of a relatively small number of photons
  - dTal 5y ago
    It obviously needs a selfie mirror.
    - nullc 5y ago
      It has a selfie 'lens': NIRcam has extra optics that can be swung in that allows the camera to focus on the primary mirror instead of out in the great infinity. So in this sense webb is already a camera which can photograph itself! This capability exists for mirror alignment: They'll point webb at an isolated star, switch to focusing on the primary mirror, swap in optics that cause small phase differences to result in diffraction patterns, and then they can use the resulting images to fine tune the positioning of the mirror segments to a small fraction of the wavelength of light that they're using.
      - dTal 5y ago
        That's amazing. I was wondering how they did that. Every new thing I learn about this machine blows me away.
deleted 5y ago
[deleted]
freeflight 5y ago
> the telescope is aimed at the dark and away from the sun To be more specific; It's "parked" in an orbit [0] that constantly puts Earth between the sun and James Webb. So it's not only aimed away from the sun, Earth is also acting as a planetary scale sunscreen for it. [0] https://en.wikipedia.org/wiki/Lagrange_point https://en.wikipedia.org/wiki/Lagrange_point
- willis936 5y ago
  Actually JWST orbits around L2 at appreciable altitude. The unique aspect of the orbit is that it is never in the shadow of the Earth or moon. It guarantees consistent solar power and thermal load. https://jwst-docs.stsci.edu/jwst-observatory-characteristics/jwst-orbit https://jwst-docs.stsci.edu/jwst-observatory-characteristics...
  - tomr_stargazer 5y ago
    Wow. I’m an astronomer and somehow I never learned this! Thank you for the link! Of course a solar powered satellite can’t be parked in the shade. Can’t believe I never thought about that.
    - baq 5y ago
      It can, it has batteries, but you don’t want to mess with thermals on that thing.
    - JohnBooty 5y ago
      My first thought is, "Why didn't they eschew solar power entirely and 'simply' park it in the shade?" Surely they considered that, and the wins would have been massive -- no sunshields needed. So I'm sure the downsides must have been massive as well. Not enough plutonium fuel, or perhaps it just wouldn't provide enough power over the life of the mission. And of course the radioactive fuel would generate its own heat as well. Now I need to find out more about that decision.... edit: Another commenter mentioned, "The earth's shadow never reaches L2 anyhow - it's only penumbra at that distance since the angular size of the earth is smaller then the angular size of the Sun." If that's correct, then there was never truly an option of "parking it in the shade" anyway.
bmitc 5y ago
It seems to me that that isn't quite right. "Dark" just means no visible light, but an infrared or thermal camera could see stuff. The article above mentions this possibility and the problems, which are harnessing and operating at cryogenic temperatures.
- claaams 5y ago
  The point of the telescope is to capture IR light from space, if the telescope itself were generating IR light itself it would disrupt the sensor and data that it collects. Part of why its going to take so long for it to begin operating is that it needs to cool down to ultra cold temperatures before beginning operation.
  - bmitc 5y ago
    Who said anything about generating infrared light? And I don't know what your last sentence is in reference to. Yes, it needs to cool down. Why is that relevant to this discussion other than what's already mentioned about that being a downside to operating cameras? From the article so people can just debate NASA's own reporting: > Although infrared or thermal-imaging cameras on the cold side could obviate the need for illumination, they would still present the same harnessing disadvantages. Furthermore, cameras on the cold side would have to work at very cold cryogenic temperatures.
    - ilstormcloud 5y ago
      The JWST has an extremely sensitive IR camera. And it is going to cool down to near absolute zero so that the IR sensors don't get flooded with radiation from the rest of the telescope. Because it will get so cold, it is not going to be emitting much IR (I think this is what the GP said when they said "generating"). Your typical deployment observation IR camera's won't be of much help in that case.
      - bmitc 5y ago
        That makes sense, and I got thrown off (by maybe misreading the comment) thinking they meant the camera or something else would generate additional IR to illuminate the telescope, which I got confused by. It makes sense now that the comment was meaning that the cool down was to reduce as much telescope generated IR noise as possible.

newman8r 5y ago

Couldn't they just use an image intensifier tube for night vision? I think they should just stick with the excuse of it being costly and unnecessary.

Sebb767 5y ago
We're talking about "see the faintest light from stars millions of lightyears away"-dark (for that reason you also can't shine a light on it), with our sun in the background. To see something on that side, you'd basically need the vision capabilities the telescope itself has and that's obviously not going to happen.
- newman8r 5y ago
  > to see something on that side, you'd basically need the vision capabilities the telescope itself I'm not sure if that's correct - there's a lot of photons hitting the telescope (the night sky), and night vision systems can work off of a relatively small number of photons
- dTal 5y ago
  It obviously needs a selfie mirror.
  - nullc 5y ago
    It has a selfie 'lens': NIRcam has extra optics that can be swung in that allows the camera to focus on the primary mirror instead of out in the great infinity. So in this sense webb is already a camera which can photograph itself! This capability exists for mirror alignment: They'll point webb at an isolated star, switch to focusing on the primary mirror, swap in optics that cause small phase differences to result in diffraction patterns, and then they can use the resulting images to fine tune the positioning of the mirror segments to a small fraction of the wavelength of light that they're using.
    - dTal 5y ago
      That's amazing. I was wondering how they did that. Every new thing I learn about this machine blows me away.

deleted 5y ago

[deleted]

freeflight 5y ago

> the telescope is aimed at the dark and away from the sun To be more specific; It's "parked" in an orbit [0] that constantly puts Earth between the sun and James Webb. So it's not only aimed away from the sun, Earth is also acting as a planetary scale sunscreen for it. [0] https://en.wikipedia.org/wiki/Lagrange_point https://en.wikipedia.org/wiki/Lagrange_point

willis936 5y ago
Actually JWST orbits around L2 at appreciable altitude. The unique aspect of the orbit is that it is never in the shadow of the Earth or moon. It guarantees consistent solar power and thermal load. https://jwst-docs.stsci.edu/jwst-observatory-characteristics/jwst-orbit https://jwst-docs.stsci.edu/jwst-observatory-characteristics...
- tomr_stargazer 5y ago
  Wow. I’m an astronomer and somehow I never learned this! Thank you for the link! Of course a solar powered satellite can’t be parked in the shade. Can’t believe I never thought about that.
  - baq 5y ago
    It can, it has batteries, but you don’t want to mess with thermals on that thing.
  - JohnBooty 5y ago
    My first thought is, "Why didn't they eschew solar power entirely and 'simply' park it in the shade?" Surely they considered that, and the wins would have been massive -- no sunshields needed. So I'm sure the downsides must have been massive as well. Not enough plutonium fuel, or perhaps it just wouldn't provide enough power over the life of the mission. And of course the radioactive fuel would generate its own heat as well. Now I need to find out more about that decision.... edit: Another commenter mentioned, "The earth's shadow never reaches L2 anyhow - it's only penumbra at that distance since the angular size of the earth is smaller then the angular size of the Sun." If that's correct, then there was never truly an option of "parking it in the shade" anyway.

bmitc 5y ago

It seems to me that that isn't quite right. "Dark" just means no visible light, but an infrared or thermal camera could see stuff. The article above mentions this possibility and the problems, which are harnessing and operating at cryogenic temperatures.

claaams 5y ago
The point of the telescope is to capture IR light from space, if the telescope itself were generating IR light itself it would disrupt the sensor and data that it collects. Part of why its going to take so long for it to begin operating is that it needs to cool down to ultra cold temperatures before beginning operation.
- bmitc 5y ago
  Who said anything about generating infrared light? And I don't know what your last sentence is in reference to. Yes, it needs to cool down. Why is that relevant to this discussion other than what's already mentioned about that being a downside to operating cameras? From the article so people can just debate NASA's own reporting: > Although infrared or thermal-imaging cameras on the cold side could obviate the need for illumination, they would still present the same harnessing disadvantages. Furthermore, cameras on the cold side would have to work at very cold cryogenic temperatures.
  - ilstormcloud 5y ago
    The JWST has an extremely sensitive IR camera. And it is going to cool down to near absolute zero so that the IR sensors don't get flooded with radiation from the rest of the telescope. Because it will get so cold, it is not going to be emitting much IR (I think this is what the GP said when they said "generating"). Your typical deployment observation IR camera's won't be of much help in that case.
    - bmitc 5y ago
      That makes sense, and I got thrown off (by maybe misreading the comment) thinking they meant the camera or something else would generate additional IR to illuminate the telescope, which I got confused by. It makes sense now that the comment was meaning that the cool down was to reduce as much telescope generated IR noise as possible.