James Webb Space Telescope

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

  1. geordief Valued Senior Member

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    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 .

    Fasten your seatbelts please

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    Last edited: Jan 24, 2022
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  3. exchemist Valued Senior Member

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    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.
     
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  5. geordief Valued Senior Member

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    So there is no actual massive object at L2 but some sort of a centre of gravity?
     
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  7. exchemist Valued Senior Member

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    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. billvon Valued Senior Member

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    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. geordief Valued Senior Member

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  10. arfa brane call me arf Valued Senior Member

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    Thanks for flying with NASA. Please exit the vehicle in an orderly manner.
     
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  11. Michael 345 New year. PRESENT is 72 years oldl Valued Senior Member

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  12. sculptor Valued Senior Member

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    OK
    So, now the James Webb circles around L2 ?
     
  13. Michael 345 New year. PRESENT is 72 years oldl Valued Senior Member

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    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

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  14. Janus58 Valued Senior Member

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    https://en.wikipedia.org/wiki/Home_on_Lagrange_(The_L5_Song)
     
  15. Michael 345 New year. PRESENT is 72 years oldl Valued Senior Member

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    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

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    PS never even linked Lagrange as a rhyme with Range

    As Cheshire Cat would remark curiouser and curiouser

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    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. geordief Valued Senior Member

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    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. exchemist Valued Senior Member

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    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. billvon Valued Senior Member

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    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. DaveC426913 Valued Senior Member

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  20. Janus58 Valued Senior Member

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    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.
     
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  21. Michael 345 New year. PRESENT is 72 years oldl Valued Senior Member

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    Sweet as

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  22. geordief Valued Senior Member

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  23. foghorn Valued Senior Member

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    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: ↓

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    Quote and picture from:
    https://webb.nasa.gov/content/about/orbit.html
     
    Last edited: Jan 26, 2022

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