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Space

The James Webb Space Telescope Arrives At Its Final Orbit (engadget.com) 98

Posted by BeauHD from the going-according-to-plan dept.
NASA has confirmed that the James Webb Space Telescope has successfully entered its final orbit around the second Sun-Earth Lagrange point after one last course correction burn. Engadget reports: The telescope's primary mirror segments and secondary mirror have already been deployed, but you'll have to wait until the summer for the first imagery. NASA will spend the next several months readying the JWST for service, including a three-month optics alignment process. The L2 orbit is crucial to the telescope's mission. It provides a largely unobstructed view of space while giving the spacecraft a cold, interference-free position that helps its instruments live up to their full potential. The JWST is expected to study the early Universe using infrared light, providing data that wouldn't be available from an Earth orbit telescope like Hubble.
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The James Webb Space Telescope Arrives At Its Final Orbit More

The James Webb Space Telescope Arrives At Its Final Orbit

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  • I mean really (Score:4, Funny)

    by eclectro ( 227083 ) on Tuesday January 25, 2022 @06:03AM (#62205221)

    Slashdot was started not long after the JWST. Who here ever thought they'd actually see this day arrive???

    • I cannot for the life of me understand how an orbit around the La Grange point works. It all seems to me the wrong way around and that anything put at that point will move away from it. Is there a simple explanation of the gravity well at that place?

      • Re:How does the orbit work? (Score:5, Informative)

        by necro81 ( 917438 ) on Tuesday January 25, 2022 @09:01AM (#62205457) Journal
        Here is a recent Youtube video that may help explain: What Makes Lagrange Points Special Locations In Space [youtu.be]

        With the exception of L1, which most people could grasp pretty readily as being the balance point between two massive bodies, the other Lagrange points exist because the whole multi-body setup is rotating. That is: L2-L5 for the Sun-Earth system are stable points that are more-or-less fixed w.r.t. the Earth, but the Earth is itself orbiting the sun. That rotation introduces additional forces.

        The other thing to note is that the stability of the Lagrange points depends on the whole three-body setup being fairly orderly. That is: you want the primary body to be overwhelmingly more massive than the second body, which is itself much more massive than the third body in the Lagrange point. The stability also depends on there not being many other perturbations, like from other gravitating bodies.

      • Re:How does the orbit work? (Score:5, Informative)

        by Burdell ( 228580 ) on Tuesday January 25, 2022 @10:12AM (#62205647)

        First, don't think of "orbit" in the usual sense. Normally, orbit is used to describe body 1 going in a circle(-ish) around body 2. That's not the case here.

        JWST is at the L2 Lagrange point. Technically speaking, it is in an orbit around the Sun... but at a million miles further out than the Earth, it should have a different orbital period. However, the L2 point is a spot where the gravity of the Earth (trying to pull it in a long orbit around the Earth) and the gravity of the Sun line up, so the L2 point moves around the Sun at the same (angular) speed as the Earth. So JWST will always be (nearly) at the point opposite the Sun, getting a nice big amount of shade from the Earth.

        But... it's then more complicated. The L2 point is not a stable point (because we're not talking about uniform spherical cows in a vacuum). You can't just park something at L2 and have it stay - it'll gradually drift off, so it takes constant energy (read: thrusters) to stay there. However, it turns out you can go to the area near L2 and effectively "orbit" around the L2 point for very little energy (read: much less thruster use).

        It's not an orbit in the traditional sense of one body going around another, but it's kind of like an orbit in that JWST will be going around a particular point in space for as long as it has thruster fuel (which could be close to 20 years, since everything worked nearly perfect during launch and the trip).

        • I know this was a typo, but "Uniformed Spherical Cows in a Vacuum" has all sorts of possibilities for humorous mental imagery...

        • Re: (Score:2)

          by bws111 ( 1216812 )

          The JWST is in an orbit such that the sun is NEVER eclipsed by the earth. This is required for thermal stability and power generation. See the post titled 'Webbs journey to L2 is nearly complete'. https://blogs.nasa.gov/webb/ [nasa.gov]

          • It is to far away to be in "constant shadow" anyway.
            Who ever saw a lunar eclipse knows that. The sun is just to big. It shines left and right around the earth into L2.

        • Re: (Score:2)

          by necro81 ( 917438 )

          it'll gradually drift off, so it takes constant energy (read: thrusters) to stay there

          I'd rephrase that slightly, and say that it takes "continual adjustment" (using thrusters) to stay there. "Constant" suggests that there's always a rocket firing, which is not the case. You'll do just fine with small corrections applied every couple of weeks. What you're doing is maintaining a balance by small nudges, rather than continually "pushing uphill"

          • You are correct that parking any satellite in the L2 would require almost continuous adjustment via power burns.

            The JWST doesn't much care about tiny wobbles at L2. It's in orbit around L2 and fluctuations will be minimal.

            NOTE: I find it ironic that we are reintroducing Ptolemy's epicycles.

            • Re: (Score:3)

              by necro81 ( 917438 )

              I'd rephrase that slightly, and say that it takes "continual adjustment" (using thrusters) to stay there.

              You are correct that parking any satellite in the L2 would require almost continuous adjustment via power burns.

              Be careful about word usage: continuous is not quite the same as continual. The former means "happening all the time (without pause)", while the latter means "happening over and over (at intervals, with gaps between events". Both of these are slightly different than "constant", as the GP us

        • getting a nice big amount of shade from the Earth.

          That part is not correct, the JWST orbits L2 outside the earths shadow so that it can get power from its solar panels.

        • So JWST will always be (nearly) at the point opposite the Sun, getting a nice big amount of shade from the Earth.

          No.

          If that were true, the solar panels would be useless. "The James Webb Space Telescope (JWST) is in a halo orbit around L2, at a sufficient radius around the Lagrange point that it is in perpetual sunlight."

          If the Earth provided a "... nice big amount of shade ..." we wouldn't need such a complex heat shield.

        • You can't just park something at L2 and have it stay - it'll gradually drift off, so it takes constant energy (read: thrusters) to stay there.
          That is not really true.

          However, it turns out you can go to the area near L2 and effectively "orbit" around the L2 point for very little energy (read: much less thruster use).
          Mostly true. It is called an "halo orbit", it is perpendicular to the plane of earth and sun. The axis of that orbit points to the sun.

          Assume we had put it behind the moon. In the L2 of earth and

      • Re: (Score:2)

        by ceoyoyo ( 59147 )

        Anything placed at any of the Lagrange points does move away from them. Webb requires station keeping. That's what limits its life.

        If you look at the orbit around the L1 point in the rotating frame it's just an orbit around the sun that bobs up and down above and below the Earth's orbit.

      • So basically, L2 is just a special, mathematically significant point in space that moves around the sun in conjunction with the Earth.

        If you consider only the sun's gravitational pull, then to orbit the sun at a given distance, you have to be at a specific angular speed. At that speed, your inertia offsets the sun's gravitational pull on you. Closer to the sun = faster, further = slower. If you are too fast for the distance you're at, you head away from the sun. Too slow, you get pulled closer.

        So L2 is

  • As of now, most, if not all, space telescopes are within the orbital plane. At what point do we start sending probes/telescopes/whatever "above" and "below" the plane? We are limiting our exploration to certain segments of the universe. Looking up and down might reveal new discoveries.

    • Re: (Score:1)

      by io333 ( 574963 )

      Khan!

    • Re:Next exploration? (Score:5, Informative)

      by ShanghaiBill ( 739463 ) on Tuesday January 25, 2022 @08:27AM (#62205387)

      As of now, most, if not all, space telescopes are within the orbital plane.

      Why do you think that matters?

      Looking up and down might reveal new discoveries.

      JWST can look straight up and straight down with reference to the orbital plane.

      If zero degrees is directly away from the sun, JSWT can pivot up to 95 degrees in any direction.

      It can observe 100% of the sky over the course of a year.

      JWST field of view [stsci.edu]

      • Out of the plane? Why not? [Re:Next exploration?] (Score:5, Interesting)

        by XXongo ( 3986865 ) on Tuesday January 25, 2022 @12:13PM (#62205967) Homepage

        As of now, most, if not all, space telescopes are within the orbital plane.

        Up until now, all of the space telescopes except for a few observing the sun have been in Earth orbit.

        Why do you think that matters?

        A good question.

        Looking up and down might reveal new discoveries.

        JWST can look straight up and straight down with reference to the orbital plane. If zero degrees is directly away from the sun, JSWT can pivot up to 95 degrees in any direction. It can observe 100% of the sky over the course of a year. JWST field of view [stsci.edu]

        Someone else has already moderated this "informative," so I don't have to.

        Getting out of the ecliptic plane is tremendously difficult. You have to cancel out the Earth's orbital velocity. The easiest way to do this is with a Jupiter gravity assist, but that takes years of travel time, a lot of delta-V... and puts the telescope into an orbit hundreds of million miles away (which gives the communications links a much lower bit-rate).

        However, it turns out that there is actually is one good reason to get out of the ecliptic plane: Zodiacal light. We don't usually notice it, but the Earth orbits inside a very diffuse dust cloud in the plane of the planets. This dust cloud produces a background glow that slightly obscures the faintest measurements (it's just barely visible to a dark-adapted eye at a very clear observing location), and so getting out of the ecliptic would in fact allow us to make better observations.

        But... not enough better to make it worth the difficulty.

        • Up until now, all of the space telescopes except for a few observing the sun have been in Earth orbit.

          If I understand the mechanics correctly, this space telescope is also in an earth orbit. One that requires exactly one year for each orbit of the earth.

      • JWST can look straight up and straight down with reference to the orbital plane.
        Yes. But not into the solar system.
        To have an early asteroid warning system you need probes in a polar orbit versus the sun, and hopefully in an orbit as big as the distance Sun - Mars.

    • To make the only observation we can't currently do, you'd need to launch a telescope thousands of lightyears out of the plane of the Milky Way, so we can see what's behind the galactic center.

    • Re: (Score:3)

      by necro81 ( 917438 )
      As it turns out, the are portions of the sky near the ecliptic poles - up and down, as you say - that are visible 100% of the time for JWST. Portions of the sky along the ecliptic are visible only for a few dozen days at a time, because the telescope must stay oriented away from the sun. [ref [stsci.edu]]

      As a practical matter, orbital inclination changes are really expensive in terms of delta-V. In vector space, you need to provide an acceleration to move a velocity vector from pointing in one direction to pointi

    • At what point do we start sending probes/telescopes/whatever "above" and "below" the plane?

      To what end?

      Looking up and down might reveal new discoveries.

      Telescopes in the plane can point anywhere except right at the sun. That direction changes as they orbit.

      And it takes a shitload of delta-v to change the plane of the orbit.

      • Telescopes in the plane can point anywhere except right at the sun.
        Exactly. And if you had a telescope in a polar orbit you would see asteroids comming from "behind the sun".

        And it takes a shitload of delta-v to change the plane of the orbit.
        No it does not. It takes simply a single gravity assist.

        • Exactly. And if you had a telescope in a polar orbit you would see asteroids comming from "behind the sun".

          This reminds me of maybe the best line from Blades of Glory: "They laughed at Louis Armstrong when he said he was gonna go to the moon Now he's up there, laughing at them." There is so much wrong that every time I start trying to compose a reply, I think I need to address a different point first.

          In no particular order:

          JWST and other deep field astronomical observatories aren't generally looking for ast

          • JWST and other deep field astronomical observatories aren't generally looking for asteroids.
            Well known.

            Polar orbits let you observe all of the earth: the object they are orbiting.
            Parent and me where talking about a polar orbit over the sun, not earth.

            The satellite is not fixed in the firmament. All this shit is moving all the time, so "behind" the sun changes constantly. The only way an asteroid would remain hidden is in if were in a perfectly matched orbit opposite the telescope.
            And that is the case if you

            • > Parent and me where talking about a polar orbit over the sun, not earth.

              Yes that's the point. Polar orbits are useful for earth observation because they let you observe all points on the earth. A polar sun orbit is useful for observing all points on the surface of the sun. But these telescopes aren't observing the sun.

              > No, you don't.

              Yes you do. You really really do. Changing orbital planes require huge changes in velocity.

              > You only need a random planet or moon to gravity assist it into a differ

              • Yes that's the point. Polar orbits are useful for earth observation because they let you observe all points on the earth. A polar sun orbit is useful for observing all points on the surface of the sun. But these telescopes aren't observing the sun.

                Yes. They are not observing the sun. And that is not the point. The point is to look from above onto the planetary plane. He jumped topic. And you did not grasp that. That is all. We did not talk about the James Webb telescope looking into the wrong direction. We

                • he didn't say anything about looking onto the planetary plane from above, he talked about looking up and down to see different bits of the universe.

                  But tell me what precisely do you expect to see on the plane that won't come into view sober or later?

                  As for Latin, tell you what you represent vectors as scalars in Latin, and me, the fine people at NASA and the rest of the engineering and science world will treat velocity as a vector.

                  Either way you don't seem to believe that changing inclinationinclination req

                  • he didn't say anything about looking onto the planetary plane from above,
                    Correct. He did not.

                    And that is why I explained it to you.

                    And now you make a dozen posts with gibberish instead of saying: "Ah, ha! Good idea!"

                    You are deeply confused about physics.
                    Unlikely, as I have a degree in physics. But perhaps I'm senile and forgot everything ...

                    I can back up my claims with links to elementary sources.

                    No, you can't. Because your "thoughts" are wrong. good luck.

                    orbital velocity vector
                    The key word is 'vector' -

                    • And that is why I explained it to you.

                      No this is you trying to turn it into a scenario where you think you're right.

                      Unlikely, as I have a degree in physics. But perhaps I'm senile and forgot everything ...

                      You do appear to have.

                      The key word is 'vector'

                      And velocity is taken to be a vector in physics and engineering.

                      Here's what wikipedia says:

                      "The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time. Velocity is equivalent to a specificati

                    • The one who is nitpicking is you.

                      The parent was "what about a telescope in polar orbit"

                      He was not about: why is JWT not in a polar orbit.

                      So I explained it to you.

                      And velocity is taken to be a vector in physics and engineering.
                      That is wrong.

                      Velocity is just another fancy word for speed
                      the two vectors (delta-V) is zero.
                      Delta-v is: difference in speed - delta is the greek letter used to describe a difference. V is velocity, aka speed.

                      Have a good day with your non existing knowledge about physics.

                    • You are so desperate to be right that you've invented a position for the original poster out of whole cloth.

                      The original poster talked about "looking up and down" and that we were missing whole areas of the universe. A polar orbit doesn't help that. Telescopes can already loo up and down.

                      It doesn't matter how many times you explain an alternative position that exists only in your head, the Ops question is there in black and white.

                      And as for velocity, no, you are wrong.

                      Or maybe me, Wikipedia, Purdue physics

                    • Well, I told you how i interpreted the parents post.
                      That is all.

                      Your luck up down makes no sense ...

                    • Well, I told you how i interpreted the parents post.
                      That is all.

                      No that's not all. You told me how I should and had some choice words for me for disagreeing with you.

                      Your luck up down makes no sense ...

                      Yeah no shit, Sherlock. That's my whole point. This is literally what the original poster said, that I responded to:

                      "Looking up and down might reveal new discoveries." -- original poster

                      And he made that in response to an article about the JWST, which can, in fact, look up and down.

                    • "Looking up and down might reveal new discoveries." -- original poster

                      Correct. But that is not your interpretation of looking up and down. Your interpretation is that an earth based telescope can "look up and down". Which it cant. It can only look "outside" from the plane of earth orbit.

                      Are you really that daft or do you try to see if you can make me angry?

                      A probe in a polar orbit can "look down" onto the solar system as soon as it is significantly "north".
                      A probe in a polar orbit can "look up" onto the sol

                    • Correct. But that is not your interpretation of looking up and down. Your interpretation is that an earth based telescope can "look up and down". Which it cant. It can only look "outside" from the plane of earth orbit.

                      This is some stupid shit right there. Let's look at what the actual OP said, right?

                      "At what point do we start sending probes/telescopes/whatever "above" and "below" the plane? We are limiting our exploration to certain segments of the universe. Looking up and down might reveal new discoveries.

                    • Well,
                      if we both argue about what the OP said, and he is not contributing. Then it probably makes no sense to discuss about what the OP said.

                      Have a nice week.

                    • Ultimately it doesn't matter what the OP meant because a polar orbit isn't useful for looking outside the solar system, and it's not especially useful for looking inside either.

                      With even vaguely practical orbits you can only substantially "look down" on the ecliptic from about the distance of Mars inwards.

                      TL;DR regardless of the OP's reasoning, people don't use a lot of polar solar orbits because you get essentially no advantage and a lot of disadvantages.

                      Either that or me and most of the national space age

                    • Ultimately it doesn't matter what the OP meant because a polar orbit isn't useful for looking outside
                      Exactly.
                      the solar system, and it's not especially useful for looking inside either.
                      Yes it is. And that is why we want/need one.
                      Or how do you detect an asteroid coming straight earth from behind the sun?

                      TL;DR regardless of the OP's reasoning, people don't use a lot of polar solar orbits because you get essentially no advantage and a lot of disadvantages.
                      Either that or me and most of the national space agenci

                    • Or how do you detect an asteroid coming straight earth from behind the sun? :facepalm:

                      I love the idea that an asteroid is going to lurk behind the sun until the very last minute, then pop out and hurtle towards the Earth. For the asteroid to stay hidden from the Earth at all times, it pretty much has to be at L3, having the same orbital period, at which point, well, it's not heading for the Earth. To hit the Earth, it's going to have to be orbiting differently, so it is not always going to be behind the sun

                    • For the asteroid to stay hidden from the Earth at all times, it pretty much has to be at L3,
                      And how do you come to that braindead idea?

                      having the same orbital period, at which point, well, it's not heading for the Earth.
                      Obviously. So what is your point?

                      Or you could spend a shitload of delta-v on getting a stable polar orbit fo
                      Sorry. You are bad in reading comprehension.
                      I explained it already to you.

                      I explain it again. You do not need any fucking delta-v to sent a probe into a polar orbit around the sun.

                      Yo

                    • And how do you come to that braindead idea?

                      Well how the hell else does it stay hidden at all times?

                      I explained it already to you.

                      You can state your wrong opinions as often as you like, it doesn't make them right.

                      [blah de blah de blah]

                      So... you just point the satellite at the moon and it gets there all by itself? No dV involved? Jut like magic eh. And now you're in a very elliptical orbit around the sun that pretty much intersects the Earth, so it'll last for about 1 year before it's wildly destabilised. So

                    • So... you just point the satellite at the moon and it gets there all by itself? No dV involved?
                      Exactly.

                      I suggest to get a class in physics, or stay out of discussions about physics.

                      Good luck in your "physic less" life :P I hope you get not electrocuted or something by your utterly lack of knowledge about physics.

                      NEO surveyor is not in a polar orbit, so no idea why you bring it up as argument ...

                    • And you still haven't explained how the polar orbit is superior to a normal heliocentric one, or having several satellites.
                       Because a polar orbit, when high enough above or low enough below the orbital plane: sees everything? And everything else is blocked by the light of the sun.

                      Sorry, you should not only get a physics class but get out more.

                      Look at the sky, do you see the sun? Do you see what is behind it? Oh? You do? Then make yourself knowledgable and get a contract as "sun glarer - the guy who can look

                    • NEO surveyor is not in a polar orbit, so no idea why you bring it up as argument ...

                      Gee... why would I bring up a counter example to your claim to show why your claim might be bogus?

                      You are claiming that it's free and also the best place for looking for potential earth impactors.

                      NASA have funding for such a satellite, yet they chose to put it at L1, not a polar orbit. I reckon it's because NASA is like all morons and you're super-duper smart. Did they turn you down after interview because your kung-fu was t

    • Re: (Score:2)

      by ceoyoyo ( 59147 )

      Damn. We might discover the little dipper. Or Draco even!

  • And in other news (Score:5, Funny)

    by MightyMartian ( 840721 ) on Tuesday January 25, 2022 @08:13AM (#62205357) Journal

    In other news Elon Musk has launched the FlashlightX, which will orbit 30 yards off the JWT.

    • In other news Elon Musk has launched the FlashlightX, which will orbit 30 yards off the JWT.

      Unfortunately, due to supply chain issues, the ‘a’ could not be sourced in time for launch. Instead an ‘e’ has been substituted, given the most general use case of these satellites.

  • Since no one else is saying it... (Score:5, Insightful)

    by JoeRobe ( 207552 ) on Tuesday January 25, 2022 @08:36AM (#62205417) Homepage

    This is awesome news, and congrats to everyone involved to make such a sophisticated spacecraft!

    I'm extremely excited to see first light on JWST, other than whatever object they look at for mirror alignment. Has NASA said what star they're using for mirror alignment? I assume they have a list of first targets, maybe to benchmark against Hubble? Is that list public?

    There was a time on /. when this comment section would be full of excitement and discussion of the science ahead and engineering behind JWST. Sorry to see that's not the case anymore.

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