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Comment by claaams | Hacker News Reader

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.

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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.

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.

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.

I think that article is leaving out some of the other problems (which is understandable, it already covers plenty of downsides). The whole point of keeping the cold side cold is so that it doesn't emit any IR radiation (otherwise the JWST couldn't work). So by design it's "dark" to an IR or thermal camera in the same way it's dark to a visible light camera. Certainly you can build a camera to see it anyway (without extra lights), but the question then becomes how big that camera has to be, and I would assume it's way to big to be realistic.

That makes sense. Thanks. It was a question of mine just how much IR would be there to see.

First it’s possible to send up a camera that would be sensitive enough to use starlight to capture images on the dark side. However, those things aren’t light and would come at the cost of less propellant for minimal gain. Adding a tiny camera and a tiny light at the same time would also be possible but there really isn’t anything worth looking at via a single camera.

As to using infra red camera, they simply don’t work on objects the same temperature as the camera. NASA could have sent one up with a cooling system to look at the cold side of the sunshade, but again weight and pointlessness means it’s just wasteful.

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