# James Webb Space Telescope

Discussion in 'Astronomy, Exobiology, & Cosmology' started by geordief, Dec 24, 2021.

1. ### geordiefValued Senior Member

Messages:
1,789
Cruising speed (.1255 ml/s hasn't changed in quite a while)

I wonder do they do some kind of a course correction quite soon to get into the right orbit ?

Must be in the next few hours I'd say.

Distance to L2 less than Rome to Moscow .

Please Register or Log in to view the hidden image!

Last edited: Jan 24, 2022

to hide all adverts.
3. ### exchemistValued Senior Member

Messages:
11,152
I imagine it will have a velocity < L2 escape velocity by the time it gets there, but I gather it needs to orbit perpendicular to the plane of the ecliptic, so so the principal correction will presumably be to give it orbital motion out of the plane, and to make the orbit more circular.

to hide all adverts.
5. ### geordiefValued Senior Member

Messages:
1,789
So there is no actual massive object at L2 but some sort of a centre of gravity?

to hide all adverts.
7. ### exchemistValued Senior Member

Messages:
11,152
Yes, posts 41-44 describe it a bit. A gravity well, surrounded by a ring doughnut of lower gravity, such that the object tends to stay in the centre, though it still tends to fall out along the axis of the doughnut. At least that is what I think.

Janus will know more, I have no doubt.

8. ### billvonValued Senior Member

Messages:
20,574
Sort of. It is a mathematical construct but a useful one - things at L2 tend to stay there. It works like this:

1) If the Earth wasn't there, then things orbiting where the Earth is now, going the same speed, would stay in orbit around the Sun (obviously.) Things farther out would orbit more slowly; things closer in to the sun would orbit more rapidly. Basic orbital dynamics. Another way of saying that is that if something farther from the Earth's orbit were going the same speed as the Earth in its orbit, it would tend to move away from the Sun due to it having higher than orbital speed.

2) Since the Earth is there it exerts a gravitational force on things near it. If something is at the L2 location orbiting at the same speed as the Earth, then ordinarily they would move away from the Sun. But at L2 the gravitational attraction of the Earth exactly cancels that tendency out.

It is worth noting that there are five Lagrangian points - L1 through L5. L4 and L5 are stable. Things there tend to stay there, and if you try to nudge them out of that location, they tend to either return or orbit the point. Thus you can often find asteroids in the L4 and L5 points around Earth (and Jupiter, and Saturn etc.)

L1, L2 and L3 are only partially stable. They are only stable in one axis. On the other two axes, things will tend to drift away if nudged. Hence the need for an engine to prevent tiny nudges (from light pressure or micrometeoroid impacts) from moving the telescope out of position.

9. ### geordiefValued Senior Member

Messages:
1,789
Michael 345 likes this.
10. ### arfa branecall me arfValued Senior Member

Messages:
7,640
Thanks for flying with NASA. Please exit the vehicle in an orderly manner.

sculptor likes this.

Messages:
12,118
12. ### sculptorValued Senior Member

Messages:
8,264
OK
So, now the James Webb circles around L2 ?

13. ### Michael 345New year. PRESENT is 72 years oldlValued Senior Member

Messages:
12,118
Ode to James Webb

Oh give me a home
Where I'm free to roam
And look at far distant
Stars all the day
Where never is heard
A disparaging word
As I walz around
On my merry ol' way

Home home at L2
Where some space debris lay
An no sky ever gets in the way

Home home at L2
I'm here forever to stay
I can't look away
I can only decay
Until there's no longer today

Please Register or Log in to view the hidden image!

Please Register or Log in to view the hidden image!

sculptor likes this.
14. ### Janus58Valued Senior Member

Messages:
2,285
https://en.wikipedia.org/wiki/Home_on_Lagrange_(The_L5_Song)

15. ### Michael 345New year. PRESENT is 72 years oldlValued Senior Member

Messages:
12,118
Thank you for the link

I had no idea The L5 Song existed

I don't recall even ever hearing the L5 Song or about it

No idea why it popped into my head to write a poem about the James Webb Telescope based on Home on the Range

The older I get the more weird the world becomes

Thanks again

Please Register or Log in to view the hidden image!

PS never even linked Lagrange as a rhyme with Range

As Cheshire Cat would remark curiouser and curiouser

Please Register or Log in to view the hidden image!

https://en.m.wikipedia.org/wiki/Cheshire_Cat

Did some foraging. Wasn't the cat it was Alice who said curiouser and curiouser

Weirder and Weirder said Michael 345

Last edited: Jan 25, 2022
16. ### geordiefValued Senior Member

Messages:
1,789
Do the Lagrange points actually attract objects a la Sargasso Sea?

Maybe,if they do we might come across some jetsam from an ancient voyage from a Star far far away.

17. ### exchemistValued Senior Member

Messages:
11,152
I somehow doubt it. I'd have thought any object from outside the solar system would have already been accelerated, in its fall towards the sun, too fast to be captured by something as feeble as a Lagrange point.

18. ### billvonValued Senior Member

Messages:
20,574
No. But - if asteroids do have an orbit that passes near L4 or L5, then there's a good chance they will eventually be captured by it. Random collisions and sunlight pressure slowly change orbits, and once inside the "potential well" around L4 or L5 they will tend to stay there.

Think of like flypaper. It doesn't pull flies in - but once they get there they don't leave.

19. ### DaveC426913Valued Senior Member

Messages:
16,488
sculptor likes this.
20. ### Janus58Valued Senior Member

Messages:
2,285
I've got a copy of of "The Endless Frontier" (edited by Jerry Pournelle), which has all the lyrics.
The first verse goes:

Oh give me a locus where the gravitons focus,
Where the three-body problem is solved,
Where microwaves play down at 3 degrees K
And the cold virus never evolved.

Michael 345 likes this.
21. ### Michael 345New year. PRESENT is 72 years oldlValued Senior Member

Messages:
12,118
Sweet as

Please Register or Log in to view the hidden image!

Messages:
1,789
23. ### foghornRegistered Senior Member

Messages:
966
If I'm understanding correctly I think the cold side will cool to -233C ( -388F ) according to the picture below
Yet, on that same page you get: ↓

Please Register or Log in to view the hidden image!

Quote and picture from: