The James Webb Telescope

[Muse]

so 5 more months before it can start sending images?

A lot of work setting up and calibrating, but I think the major reason is the need for the craft and components to cool down enough so that the infrared readings make sense and are accurate.

 

[[DHT]Osiris]

so 5 more months before it can start sending images?

It takes an exceedingly long time for things to cool down in a vacuum, especially to near absolute zero.

 

[spacejamz]

It takes an exceedingly long time for things to cool down in a vacuum, especially to near absolute zero.

Didn't Kahn confirm that it was cold in space? LOL

 

[Red Squirrel]

Come to think of it, where does heat go in space? Like, in a non vacuum, the air will conduct heat away, but in a vacuum, how does that happen? I know they have special radiator panels but how do those work exactly?

 

[Spacehead]

It takes an exceedingly long time for things to cool down in a vacuum, especially to near absolute zero.

Do we know how cold it needs to be to work? Currently the cold side is at -332 & -347F. Hot side is at 55 & 129F.
https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html

 

[Fenixgoon]

Come to think of it, where does heat go in space? Like, in a non vacuum, the air will conduct heat away, but in a vacuum, how does that happen? I know they have special radiator panels but how do those work exactly?

heat is radiated in the form of electromagnetic radiation - specifically, infrared light (the same kind of light Webb is trying to collect, and the whole reason the thing needs to be protected so well from the sun's radiation)

Do we know how cold it needs to be to work? Currently the cold side is at -332 & -347F. Hot side is at 55 & 129F.

the MIRI detector needs to be at 7K (-267C) or less. -448.6F for those heathen imperial unit users

the other three other detectors "only" need an operating temperature of 37K

edit: handy nasa link! - https://webb.nasa.gov/content/about/innovations/cryocooler.html

 

[Muse]

Are they constantly using fuel to keep the Webb in the halo orbit?

Edit: Ya know, I don't think anyone saw this coming 100 years ago.

 

[[DHT]Osiris]

Are they constantly using fuel to keep the Webb in the halo orbit?

Edit: Ya know, I don't think anyone saw this coming 100 years ago.

The magic of Lagrange points: no fuel necessary to maintain orbital dynamics.

 

[[DHT]Osiris]

Come to think of it, where does heat go in space? Like, in a non vacuum, the air will conduct heat away, but in a vacuum, how does that happen? I know they have special radiator panels but how do those work exactly?

Black body radiation primarily, though some does 'radiate' to atomic hydrogen in the soup we call a vacuum.

 

[Fritzo]

Do we know how cold it needs to be to work? Currently the cold side is at -332 & -347F. Hot side is at 55 & 129F.
https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html

Luckily NASA was able to use McDLT technology to keep the hot side hot and the cold side cold.

 

[skyking]

The magic of Lagrange points: no fuel necessary to maintain orbital dynamics.

Not true for L1, L2 and L3. Those are unstable and will require a bit of fuel to keep station. They planned on having 10 years of fuel on arrival but they did so well with the insertion burns that they have 20 years of station keeping fuel.
L4 and L5 are stable and have captured some objects.

 

[Muse]

The magic of Lagrange points: no fuel necessary to maintain orbital dynamics.

Did you watch the video of the halo orbit?

Those loops, I figure, don't happen by themselves but are jet propelled. No?

 

[SKORPI0]

Not true for L1, L2 and L3. Those are unstable and will require a bit of fuel to keep station. They planned on having 10 years of fuel on arrival but they did so well with the insertion burns that they have 20 years of station keeping fuel.
L4 and L5 are stable and have captured some objects.

I was wondering why NASA didn't choose to use L4 or L5.

Sun–Earth L2 is a good spot for space-based observatories. Because an object around L2 will maintain the same relative position with respect to the Sun and Earth, shielding and calibration are much simpler. It is, however, slightly beyond the reach of Earth's umbra,[24] so solar radiation is not completely blocked at L2. Spacecraft generally orbit around L2, avoiding partial eclipses of the Sun to maintain a constant temperature. From locations near L2, the Sun, Earth and Moon are relatively close together in the sky; this means that a large sunshade with the telescope on the dark-side can allow the telescope to cool passively to around 50 K – this is especially helpful for infrared astronomy and observations of the cosmic microwave background. The James Webb Space Telescope was positioned in a halo orbit about L2 on January 24, 2022.

Lagrange point - Wikipedia

en.wikipedia.org

NASA’s James Webb telescope ready to arrive at its final destination, L2

NASA’s James Webb telescope is set to arrive at its final destination, L2 or the second Lagrange point. The Webb team will fire the telescope’s thrusters to

www.businessinsider.in

 

[skyking]

Cold, it was all about hiding from the sun behind the earth. L4 and L5 are going to be relatively warmer, and also present more complex shading problems.
I'd love to see the day when they travel out to L2 and top off Webb's fuel like it was no thing at all.

 

[Muse]

Cold, it was all about hiding from the sun behind the earth. L4 and L5 are going to be relatively warmer, and also present more complex shading problems.
I'd love to see the day when they travel out to L2 and top off Webb's fuel like it was no thing at all.

Ah, that makes sense. The sunlight is a big problem. So, they're going to keep it basically in the earth's shadow all the time?

I was wondering a couple hours ago about this. Wondering if they made a provision for this like the thing on your car where you fill up at a gas station. Obviously, not something so primitive, but something that could be used to add fuel if and when they develop a vehicle that could refuel the JWST. Don't know how long it would be operational but they're saying it's the fuel running out that will be the end.

 

[ISAslot]

Ah, that makes sense. The sunlight is a big problem. So, they're going to keep it basically in the earth's shadow all the time?

I was wondering a couple hours ago about this. Wondering if they made a provision for this like the thing on your car where you fill up at a gas station. Obviously, not something so primitive, but something that could be used to add fuel if and when they develop a vehicle that could refuel the JWST. Don't know how long it would be operational but they're saying it's the fuel running out that will be the end.

It won't directly be in the shadow since it needs sunlight for power.

 

[Red Squirrel]

The orbit it's in is really interesting really, I never realized such orbit was possible.

This explains it:

Orbit - Webb/NASA

The James Webb Space Telescope (sometimes called Webb or JWST) is a large infrared telescope with a 6.5-meter primary mirror. Webb is the premier observatory of the next decade, serving thousands of astronomers worldwide. It studies every phase in the history of our Universe, ranging from the...

jwst.nasa.gov

I still don't understand it 100% especially how it's orbiting around L2, which is not an actual object. But my guess is that what is happening is it's influenced by earth but the centrifugal force of also being around the sun pulls it back at that position. So it's almost like it wants to orbit earth but the orbit is pulled further from it. At least that's how I'm interpreting what's going on.

I can see why they will need fuel to keep this orbit stable though as it's probably near impossible to get it dead on.

 

[JEDI]

edit:
Q about L4/L5 answered above

 

[balloonshark]

"Photons Received: Webb Sees Its First Star – 18 Times"

Photons Received: Webb Sees Its First Star – 18 Times – James Webb Space Telescope

blogs.nasa.gov

 

[ArizonaSteve]

And now they have the 18 images in an aesthetically pleasing hexagonal array.

Webb Team Brings 18 Dots of Starlight Into Hexagonal Formation – James Webb Space Telescope (nasa.gov)

 

[ArizonaSteve]

And now it's all fully aligned.

NASA’s Webb Reaches Alignment Milestone, Optics Working Successfully | NASA

 

[trungma]

I am so impressed at the engineering. Everything has been flawless so let's hope it continues!

 

[Red Squirrel]

First image! This is with a special camera used for alignment purposes and not the main camera. So what's to come is going to be even better.

Crazy to think that a lot of those dots are a galaxy.

 

[Charmonium]

A lot of work setting up and calibrating, but I think the major reason is the need for the craft and components to cool down enough so that the infrared readings make sense and are accurate.

I'm probably going to answer my own question here but I thought we were long past needing near AZ temps to get good signal/noise response. Of course with the cosmic background only being about 5F above AZ, the signals probably clean up much, much, much more nicely.

 

[BoomerD]

It takes an exceedingly long time for things to cool down in a vacuum, especially to near absolute zero.

Nonsense...the solar wind cools things off quickly...