James Webb Information Thread!

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Huxter

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For comparison - live web cam of my yard:

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boomtube-mk2

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It's moving at the "Speed of grass".
If they had built it to move at the "Speed of Kudzu", we'd already be getting pictures from it.
 

Funkworks

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Just over 97% of Distance complete as of 1010 January 21, 2022.

Almost there ...
tumblr_n386ioTEGC1s2wio8o1_500.gif


 

TigerHawk

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Just over 97% of Distance complete as of 1010 January 21, 2022.
Looks like NASA updated the Distance complete for Webb, as earlier today they were showing just over 97% and now it’s showing just under 96%.
 

Marc_G

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Until the insertion burn completes, and it approaches nominal distance, it's all kinda academic at this point, right? It's mostly out there, and "there" isn't so much a point but a region of space.
 

Funkworks

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Until the insertion burn completes, and it approaches nominal distance, it's all kinda academic at this point, right? It's mostly out there, and "there" isn't so much a point but a region of space.

The probe will actually be orbiting the L2 point.
webbs-orbit.png

So it seems like its trajectory will be like that of:
- a red dot,
- on a slipping wheel (wheel not spinning as fast as it "should"),
- of a bicycle running around a track.

Edit: removed stuff after looking up stuff.
 
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neil_w

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I suspect the reason for this is that reaching the L2 point exactly would require perfect accuracy, but in practice, that is not realistic and anywhere near is good enough. The size of the orbit will represent how accurate they can be, or care to be.
The orbit ensures that the JWST won't be permanently in Earth's shadow. Needs sunshine to supply its vitamin D.
 

Funkworks

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The orbit ensures that the JWST won't be permanently in Earth's shadow. Needs sunshine to supply its vitamin D.

Curious about its radius and how much of the Sun the Earth hides from L2. Will do some searches.
 
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OverTheTop

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Looks like NASA updated the Distance complete for Webb, as earlier today they were showing just over 97% and now it’s showing just under 96%.
Eddies in the space-time continum.

How can something "Orbit" nothing?
It is orbiting a virtual point in space that is made possible due to the orbit and gravitational effect of the earth. The orbit will be somewhat rectilinear and not circular. So the spacecraft only approximately orbits the point, but very little fuel is needed to ensure it keeps station over the long duration of an Earth orbit around the sun. Temporal effects on the orbit are caused by changing distances of the Earth-Sun system.
 

Jeff Lassahn

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Current speed according to the "Where is Webb" website is .1322 mi/sec.
That's 476 mph.
Subsonic relative to the earth!
This got me to thinking what the speed of sound actually is in that region of space. It's a lot faster than what we normally think of as the speed of sound, probably at least 20K mph but it's tricky to pin down the exact number:
 

Blast it Tom!

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This got me to thinking what the speed of sound actually is in that region of space. It's a lot faster than what we normally think of as the speed of sound, probably at least 20K mph but it's tricky to pin down the exact number:
In space, no one can hear you scream... :eek:
 

Funkworks

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This got me to thinking what the speed of sound actually is in that region of space.

Sound is atoms pushing and pulling other atoms (or molecules).
But let's simplifiy this and look only at the pushing part.

Imagine line of dominos.
The closer they are to each other, the faster the wave (the "knock over wave") will travel.

Same with sound:
The speed of sound in normal air is 343 m/s.
The speed of sound in water is 1433 m/s.
The speed of sound in solids like metals is even faster.

Inversely, if you you spread the atoms, molecule, or dominos apart, they will not even touch or influence each other. No wave will travel, so there won't be any such thing as sound. A speaker will move nothing and nothing will move a mic.
 

Jeff Lassahn

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Well, kind of.
The speed of sound in solids and liquids depends on chemical binding forces that don't really apply for gasses, so they're not really comparable.
The speed of sound in gas is not very dependent on the density, instead it depends on the temperature. Basically the speed of sound is related to the speed at which the gas molecules move. Instead of acting like a line of dominoes, they act like billiards balls and the faster the balls are moving the faster they transmit the wave from one place to another.

In some sense, lower gas density does make it harder for sound to travel. The key measure here is the mean free path, basically how far a molecule travels before it hits another molecule. This puts a limit on how small the sound waves will be. Lower densities mean longer waves and lower frequencies. In interplanetary space the mean free paths can be millions of miles but things get complicated because the solar wind is a plasma and ions in a plasma interact by EM fields so sound waves can propagate in a plasma that couldn't propagate in neutral gas.

None of this means little high frequency sounds like your pitiful mortal screaming can be heard in space, but there is still a meaningful notion of supersonic vs subsonic, and large objects traveling at supersonic speeds (like the earth) produce shock waves in the interplanetary medium.
 
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