James Webb Telescope

[Puppycow]

Well I watched Bill Nelson's rambling "God bothering" statement live during the launch. First thought was "Who the hell is this idiot? Why is is saying all that crap?" I thought it was utterly cringeworthy.

What the hell were they thinking appointing this old fool as head of NASA - he's nearly 80 FFS. The NASA administrator needs to be someone younger with enthusiasm and fresh ideas.

Bring back Jim Bridenstine!!

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Oh I totally agree with you there. I was watching NASA's official feed too, and that was the low point. Absolute cringe-inducing drivel. Bill Nelson is a career politician. The reason he got the job of course is that as a former senator he was well-known to Joe Biden, also a long-time senator. We might also add that the president should also be someone younger with enthusiasm and fresh ideas. But unfortunately this is who voters chose.
(off-topic rant about Bill Nelson follows, please ignore)

Along with Joe Lieberman he's the reason why Americans still don't have affordable health care like every other first world country. He was a senator until 2019 before he became the NASA administrator and he helped to kill the "public option" from the ACA as a payoff for private insurance companies who profit from the lack of affordable healthcare.

[/rant]

 

[slyjoe]

I'm not reading this as a problem. I'm reading it as them having the luxury of doing something they prefer to do rather than something they urgently need to do. So, I'm reading this as the opposite of reactionary.

Two problems they worked:

They had to reset the solar panel so it would draw more power, and they repointed the telescope to limit sunlight on overheating motors.

Both problems were solved.

 

[RecoveringYuppy]

Two problems they worked:

They had to reset the solar panel so it would draw more power, and they repointed the telescope to limit sunlight on overheating motors.

Both problems were solved.

Not sure why you quoted me there, did something go wrong?

ETA: https://www.space.com/news/live/james-webb-space-telescope-updates

 

[smartcooky]

Not sure why you quoted me there, did something go wrong?

I think you need to read posts a bit more carefully. Sometimes, you don't seem to get that people quoting you are actually agreeing with you!

 

[RecoveringYuppy]

I think you need to read posts a bit more carefully. Sometimes, you don't seem to get that people quoting you are actually agreeing with you!

I'd love to hear that since the alternative is that something went wrong!

ETA: Oh, and I suppose I'm also demonstrating the same anxiousness Puppycow is expressing.

 

[Puppycow]

Glad to hear that regardless. So basically the only issue is that they needed to reorient the telescope a bit so the motors could cool down and the solar panel could draw more power.

IOW, just routine problems, not mission-threatening problems.

The blog also mentioned a conference call, which I haven’t had time to listen to yet, but plan to

 

[Puppycow]

Btw. I’m guessing that they will never be able to point this telescope at Earth or the moon. Because the sun shield won’t allow it.

 

[RecoveringYuppy]

Btw. I’m guessing that they will never be able to point this telescope at Earth or the moon. Because the sun shield won’t allow it.

I don't know about "able" but they certainly don't want to. And it won't be the sun shield that doesn't allow it, but rather the controller software.

Hubble can't be pointed at Earth or the Sun either, they are too bright and would damage the instrument (I think it may have a mode that allows it to be pointed at Earth but some instruments have to be put in a protective configuration but that's not an operating mode).

I suspect pointing JWST at either the Earth or Moon would destroy it since it would then also be pointing at the Sun. But even the brightness of the Moon or Earth without the Sun are definitely not what it is meant for. They might be damaging on their own.

 

[theprestige]

Btw. I’m guessing that they will never be able to point this telescope at Earth or the moon. Because the sun shield won’t allow it.

Why would they want to? We already have tons of task-optimized stuff looking at Earth.

 

[Blue Mountain]

Why would they want to? We already have tons of task-optimized stuff looking at Earth.

Indeed: although it's now known as NASA Earth Science, at one point it was poetically named the Mission to Planet Earth.

 

[Puppycow]

Why would they want to? We already have tons of task-optimized stuff looking at Earth.

I'm just curious what the Earth, Moon and Sun would look like in a photo from the L2 point, that's all. I don't think I've ever seen a photo where all three bodies are in one shot.

 

[smartcooky]

Btw. I’m guessing that they will never be able to point this telescope at Earth or the moon. Because the sun shield won’t allow it.

Correct. It can only get within 85° of pointing at earth.

 

[smartcooky]

I'd love to hear that since the alternative is that something went wrong!

ETA: Oh, and I suppose I'm also demonstrating the same anxiousness Puppycow is expressing.

I'd be beyond astonished if a mission as complex as this one went off without a single hitch.


So far, the only things that seem to have been sub-nominal are

A bad sensor reading on a non-explosive actuator - solved
A minor power issue - solved
Some minor overheating on a sunshield deployment motor - solved


Eta: Cold side temperatures continue to fall

Primary Mirror: -132°C (down from -116°C yesterday)
Instrument Radiator: -194°C (down from -192°C yesterday)

 

[Puppycow]

they are too bright and would damage the instrument

Yeah, you're right. The sun would be much too bright for the delicate instrument to look at without destroying it. We can't even look directly at it with our own eyes for more than half a second without damaging them. And you certainly wouldn't want to look at the sun through binoculars.

 

[RecoveringYuppy]

I'm just curious what the Earth, Moon and Sun would look like in a photo from the L2 point, that's all. I don't think I've ever seen a photo where all three bodies are in one shot.

The problems go beyond pointing the camera at Earth. The difference in brightness of those three objects would be daunting for a camera. And I think the field of view of the JWST is about 3 minutes of arc which mean you couldn't even get the entire sun in to the picture. Don't quote me on that last part.

 

[Puppycow]

The second and third layers of the sun shield have been tensioned now:

https://blogs.nasa.gov/webb/

 

[smartcooky]

The problems go beyond pointing the camera at Earth. The difference in brightness of those three objects would be daunting for a camera. And I think the field of view of the JWST is about 3 minutes of arc which mean you couldn't even get the entire sun in to the picture. Don't quote me on that last part.

Earth L2, is only 1% further away from the Sun than the earth itself, so the Sun's apparent diameter will be about the same as it is from earth - half a degree (30'), so yes, 10 times too big for Webb's FoV.

Even the Earth and the Moon are too big to fit in Webb's field of view (28' and 9' respectively)

 

[RecoveringYuppy]

Earth L2, is only 1% further away from the Sun than the earth itself, so the Sun's apparent diameter will be about the same as it is from earth - half a degree (30'), so yes, 10 times too big for Webb's FoV.

Even the Earth and the Moon are too big to fit in Webb's field of view (28' and 9' respectively)

Just to be clear: are you sure that 3 minutes of arc is the correct field of view for JWST? That was the part I was least certain of.

 

[smartcooky]

Just to be clear: are you sure that 3 minutes of arc is the correct field of view for JWST? That was the part I was least certain of.

Near-Infrared Camera (NIRCam):
Two modules, each observing a 2.2’ × 2.2’ area separated by ~44" and cover 9.7²' total.
https://jwst-docs.stsci.edu/jwst-near-infrared-camera/nircam-observing-modes/nircam-imaging

Mid Infrared Instrument (MIRI):
Its imaging FoV is 74" × 113" (arcseconds)
https://jwst-docs.stsci.edu/jwst-mid-infrared-instrument/miri-observing-modes/miri-imaging

Near Infrared Imager and Slitless Spectrograph (NIRISS):
Similar FoV to Nircam 2.2' x 2.2'
https://jwst-docs.stsci.edu/jwst-ne...rograph/niriss-observing-modes/niriss-imaging

Near-Infrared Spectrograph (NIRSpec):
Its 3' x 3' and is probably the one you are thinking of, but it does not have any imaging modes... its just a spectrograph.
https://jwst-docs.stsci.edu/jwst-ne...raredSpectrograph-Opticalelementsanddetectors

 

[theprestige]

I'm just curious what the Earth, Moon and Sun would look like in a photo from the L2 point, that's all. I don't think I've ever seen a photo where all three bodies are in one shot.

The Earth and the Moon wouldn't look like anything, not being illuminated by the sun.

Assuming you're properly at L2, the enshadowed disk of the moon would be invisible within the enshadowed disk of the earth, or vice versa. The larger disk would occlude some or all of the disk of the sun.

Getting all three in one shot would be a mild achievement in applied geometry, and an interesting happenstance of some other mission entirely. But it wouldn't look like much, and wouldn't be worth going out of our way for.