OT - Where Is the James Webb Telescope and what is a Lagrange point?
We’ve had a couple of James Webb Telescope OP’s here and they have piqued my interest in this topic. I saw this article today:
…and read this:
This point is located approximately 930,000 miles away from the Earth in the exact opposite direction from the sun.
Emphasis mine, because I thought this was "L3" on the other side of the sun, right where the Alternate Universe Earth is! So, I looked up “what is a Lagrange Point?” and found this picture:
https://en.wikipedia.org/wiki/Lagrange_point
L2 is essentially twice the distance from the Earth to the Moon, but orbits the Sun. Because of this orbit, the satellite uses very little fuel. One of the comments in the article asks – why don’t they put it out by Neptune? Which is what I thought, thinking it could take better pictures, but the reasoning is that the “little” extra distance that provides in getting closer to a far away galaxy is negligible, based on the equipment on the telescope.
The next comment is: “It is currently sitting on a sound stage in Hollywood, right?” Well Akshully, it’s 23 days into it’s 29 day trip to L2.
January 18th, 2022 at 10:09 AM ^
Just as long as they don't pull it out of Uranus. Now that's something you don't want on a telescope.
January 18th, 2022 at 10:26 AM ^
So you are saying you don't need to....
January 18th, 2022 at 1:01 PM ^
It's THE Uranus. Many anuses (ani???) use THE as part of their official names.
January 18th, 2022 at 10:12 AM ^
Ray, pretend for a moment that I don't know anything about metallurgy, engineering, or physics, and just tell me what the hell is going on.
January 18th, 2022 at 10:19 AM ^
Of course we know all about this we just want to make sure you do
January 18th, 2022 at 10:50 AM ^
You never studied.
January 18th, 2022 at 1:34 PM ^
Sure, let me try...
Unlike Hubble, Webb is an infra-red telescope, which means it really measures heat signatures coming from very far places in the universe. This is great because it means it can see very far back in to the past without getting interference from the visible spectrum.
But this brings a different problem. For it to work well, it needs to be shielded from heat source. As you may know, sun is a rather large heat source. To work around this, they are placing it in the earth's shadow. With earth and its own heat shield (looks like a large tarp underneath the mirrors), you can have VERY VERY cold operating temperature, which is ideal.
But how do you make sure that the telescope stays in the earth's shadow all the time? By putting it in Lagrange point #2. This is a point in space where the gravity from sun and earth cancel each other out and any object can pretty much stay in place as long as you want (as it orbits the sun in the same velocity as the earth). This is where Webb is heading towards in several days, it has just enough momentum to get there and stop.
Once it is there, it will be ready to look back into moments just after the Big Bang, which is very very exciting.
January 18th, 2022 at 2:03 PM ^
Great explanation, except you parked it at the wrong LaGrange Point. It will be at L2, not L4. Therefore, you get a neg from me. Attention to detail, son!!! Nonetheless, a very good explanation!
January 18th, 2022 at 3:31 PM ^
Sorry! My BAD!
January 18th, 2022 at 2:07 PM ^
This is an interesting attempt at explaining, and I'm positive lostpatrol appreciates the effort. BUT I think he would probably appreciate the explanation MORE if you used a Twinkie to help the metaphor.
Basically, tell him about the Twinkie.
January 18th, 2022 at 3:16 PM ^
Wait.
Could someone first tell where in the world Carmen San Diego is before tackling Twinkies and Geometry?
January 18th, 2022 at 4:34 PM ^
BUT I think he would probably appreciate the explanation MORE if you used a Twinkie to help the metaphor.
Basically, tell him about the Twinkie.
What about the Twinkie?
January 18th, 2022 at 4:02 PM ^
I try not to correct people while blogging because there is almost no way to not come off like a condescending dick, so I apologize in advance.
JWST will never be in Earths shadow. Further, the JWST will never be eclipsed by the Earth or the Moon at any time because it will ride in a halo orbit. This is intentional for reasons I’m not 100% sure why.
January 18th, 2022 at 4:21 PM ^
The main reason is that it's solar powered.
January 18th, 2022 at 10:18 AM ^
I came across this video that explains LaGrange points. Science is cool.
January 18th, 2022 at 2:53 PM ^
This is a cool video! I don't totally get how the flat surface gets changed to a cone (gravity pulls a small object into the large object, not into a pit below it) but the scientist use it and it makes sense at some level.
January 18th, 2022 at 10:26 AM ^
Layman's explanation: Lagrange points are singular points in space where gravitational effects from multiple bodies (Sun, Earth, Moon mostly, but also sometimes Jupiter) are balanced out and the object appears to "not move" relative to the other bodies. It's a mathematical singularity though, so you never get to the perfect Lagrange point-- get close enough though and you basically stay in the same spot.
Useful for astronomical missions like looking at other stars / galaxies, or even the Sun since because you're in "the same spot" the whole time, you have constant lighting and viewing geometries, simplifying command and control and things like thermal control. The cons are they're all pretty far away from the Earth in relative terms to other spacecraft, hence you need more powerful rockets to get anything of subtantive mass out there. It's also a pretty harsh environment from a radiation exposure perspective, and the distance makes comms with Earth difficult as well.
January 18th, 2022 at 11:26 AM ^
This. There are, of course, exceptions to the rules of what they call "Lagrange points", but they are actually really cool. I'm not sure why, but I got into a really complex discussion with my cousins about this topic a couple of years ago.
January 18th, 2022 at 11:41 AM ^
So it’s like the tripod of the universe? Celestial steady cam?
January 19th, 2022 at 3:13 PM ^
Just curious, are you and DK81 the same person?
January 18th, 2022 at 10:55 AM ^
We are by definition 1 AU (astronomical unit) away from the sun which is 93,000,000 miles away. The telescope will be 930,000 miles away or 0.01 AU from Earth, or precisely 1%. In other words, the JWT will be a 1 percenter. Or, just mere coincidence?
January 18th, 2022 at 10:58 AM ^
The L2 point is quasi-stable - meaning it doesn't hold transient objects in the orbit, they pass through and move off. So JWST has thrusters that will push it back into the L2 point every so often, as the Sun's gravity is always pulling it back in. This is why it has a finite lifetime, it only has so much fuel. The lifetime is expect to be ~20 years, up from the estimated ~10 years because of the accuracy of the launch rocket trajectory and the two burns JWST itself did.
This page tells you exactly where it is and what's coming next. I can't wait for the science this thing will bring us!
January 18th, 2022 at 5:30 PM ^
Why not put it in L4 or L5 then? Combined with the above explanation that it's not ever in Earth's shadow, by design, it seems like a the stable orbits would work then too?
Or - just too far away (time), would take X years for it to get there and it'll be useless by then
Or - just too far away (momentum), and the fuel required to get to L4 or L5 significantly exceeds the fuel needed to keep it circling L2?
January 18th, 2022 at 6:42 PM ^
L4 and L5 are stable - so they keep all the debris they attract. Don't want your $10B telescope getting pummulled rocks hanging out in the same orbit and location!
January 18th, 2022 at 11:23 PM ^
Another excellent reason!
January 19th, 2022 at 12:08 AM ^
I think, and don't quote me on this, but L4 and L5 are closer to the sun than L2. The JWST relies on extremely cold temperatures on its mirrors and infra-red electronics to operate to design goals. In fact, it has multiple sun shields on board that shield the spacecraft from solar heat and keep the mirrors and infra-red electronics ultra cool, like -340F cold, i.e. cold AF. The additional solar radiation at L4 or L5 may have been too much to design for.
January 18th, 2022 at 11:02 AM ^
I found this online: "Discovered by the Germans in 1904, they named it a Lagrange Point, which of course in German means a whale's vagina."
January 18th, 2022 at 11:09 AM ^
...no, there's no way that's correct.
January 18th, 2022 at 11:11 AM ^
Agree to disagree...
January 18th, 2022 at 1:37 PM ^
Nice try but
"Joseph-Louis Lagrange was an Italian mathematician and astronomer, later naturalized French. He made significant contributions to the fields of analysis, number theory, and both classical and celestial mechanics."
https://en.wikipedia.org/wiki/Joseph-Louis_Lagrange#Lagrangian_mechanics
January 18th, 2022 at 2:11 PM ^
Hate to "well actually" everyone here, but it's actually named after a early 70's ZZ Top song about a rumor that was spreadin' around, in that Texas town, about a shack outside La Grange.
A haw, haw, haw, haw.
January 18th, 2022 at 6:39 PM ^
I hear there are a lot of nice girls there.
January 18th, 2022 at 11:12 AM ^
"Where Is the James Webb Telescope?" For those of us old enough to remember when this song written by JIMMY Webb and winner of six Grammy Awards in 1968 was a hit, the answer should be “Up, Up and Away”.
January 18th, 2022 at 11:23 AM ^
And as for the "Lagrange Point", ZZ Top has been explaining it for years:
January 18th, 2022 at 11:27 AM ^
Awesome song!
January 18th, 2022 at 11:32 AM ^
Heard they got a lot of nice girls.
And you know what I'm talkin about...
January 18th, 2022 at 2:13 PM ^
I made the same joke 2 hours late. I should have known my one true nemesis Robert F would have beat me to this low hanging fruit.
January 18th, 2022 at 2:33 PM ^
LOL.
2:50 late, to be exact.
January 18th, 2022 at 10:37 PM ^
rob f, I figured that I shouldn't be too greedy in posting song video clips with my comment, so I left that one for others.
January 18th, 2022 at 12:08 PM ^
The graphic is right for where L2 is. It's in "the opposite direction from the sun" in that if you drew a line from Earth to the sun, it's in the other direction (not farther along in the same direction, which is where L3 is).
You don't want it at L3, because then the sun is in the way when you try to send data back to Earth.
You don't want to put it out at Neptune, because it's much harder to phone home (farther away), much harder to get there, it has all the disadvantages of orbiting Earth in terms of thermal problems, and it's so far from the sun that your solar cells won't work very well.
January 18th, 2022 at 12:22 PM ^
You don't want it at L3 because the Alternate Universe Earth people might shoot it down!
January 18th, 2022 at 2:00 PM ^
[insert "Aliens!" meme here]
January 18th, 2022 at 3:58 PM ^
Space may be the final frontier but it's made in a Hollywood basement
And Cobain, can you hear the spheres singing songs off Station to Station?
And Alderaan's not far away, it's Californication
-RHCP
January 18th, 2022 at 4:33 PM ^
I HAVE QUESTIONS. SOOO MANY QUESTIONS. I have read a tone on JWST but haven't seen these answered.
1. At L2, does the Earth completely block out the sun? I assume not. I would think Earth would look small (at least, smaller than the sun), so it is not totally in the Earth's shadow?
2. What about light/heat from the Earth and Moon. I assume the sunshield reflects their heat too; however, the moon is at a different angle than the sun/earth (which are colinear, given L2), so does the shield have to rotate a bit to block off all light reflected from the Moon?
3. Can Elon's Starship get to L2? If so, that'll eventually allow us to service the dang thing. I wouldn't want to go out there and refuel it in person, however, but like change equipment on it.
By the way -- the reason this thing wasn't launched to Neptune is, the weight penalty. To get an object from Earth to that distance requires a LOT more fuel, and since our rockets have maximum weights they can launch, adding fuel = reducing size of the payload. The weight of JWST was already rigorously designed -- they actually would have preferred a larger mirror, but just couldn't add the weight -- so trying to move it any further from Earth on launch would have forced an even smaller satellite.
January 18th, 2022 at 5:09 PM ^
1) I don't believe so. The point allows one to always point the instruments away from the sun, earth, moon etc. Plus, L2 location is good b.c you can keep it there with minimal fuel to maintain position, as someone said above.
2) If you point it away, these aren't big issues.
3) Very likely not practical. There will be no manned missions to this tool if it fails. Back in the 90s 2-3 manned trips were made to Hubble to keep it viable as I recall. Hubble was in a pretty standard high Earth orbit
January 18th, 2022 at 5:25 PM ^
for 3, I have no clue how JWST is designed, but currently companies are already doing on orbit servicing/life extension, so presumably in 20 years you could send an unmanned life extension vehicle that latches onto JWST and becomes the engine, pushing it around to keep it active.