# James Webb Space Telescope general discussion thread **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Tags:** science-math\ **Created:** [December 25, 2021, 1:18pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624 "2021-12-25T13:18:56Z")\ **Posts on this page:** 20\ **Page:** 18
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [January 24, 2022, 7:17pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/341 "2022-01-24T19:17:36Z")
From the Webb blog: > Today, at 2 p.m. EST, Webb fired its onboard thrusters for nearly five minutes (297 seconds) to complete the final postlaunch course correction to Webb’s trajectory. This mid-course correction burn inserted Webb toward its final orbit around the second Sun-Earth Lagrange point, or L2, nearly 1 million miles away from the Earth. > > The final mid-course burn added only about 3.6 miles per hour (1.6 meters per second) – a mere walking pace – to Webb’s speed, which was all that was needed to send it to its preferred “halo” orbit around the L2 point. > > “Webb, welcome home!” said NASA Administrator Bill Nelson. 🙂 ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [January 24, 2022, 7:30pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/342 "2022-01-24T19:30:59Z")
On the NASA channel there is a presentation, _What’s Next for Webb_ starting at 1pm EST, 2000 UTC. ---
**Author:** ![Euphonious\_Polemic](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/euphonious_polemic/32/3002_2.png) [@Euphonious\_Polemic](https://boards.straightdope.com/u/Euphonious_Polemic)\ **Post date:** [January 24, 2022, 8:01pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/343 "2022-01-24T20:01:24Z")
Status: Complete. Webb is in L2 Orbit! ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [January 24, 2022, 8:07pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/344 "2022-01-24T20:07:08Z")
> [@Senegoid](#): > > It passed through a space-time discontinuum at the L2-adjacent chronosynclastic infundibulum. > [@Dr.Strangelove](#): > > We just get some malevolent boy to pick up a piece of scrap metal, have him scrape and bend it whenever possible, maybe found a religion and start an interplanetary war, and after several years the piece will be an exact replacement for what has broken, and manage to be delivered directly to the JWST. (Bonus points for anyone who knows what we’re talking about here. 🙂 ) (ETA: Even more bonus points for anyone who knows what an “infundibulum” is. Yes, it’s a real thing.) ---
**Author:** ![squeegee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/squeegee/32/14537_2.png) [@squeegee](https://boards.straightdope.com/u/squeegee)\ **Post date:** [January 24, 2022, 8:14pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/345 "2022-01-24T20:14:02Z")
> [@Senegoid](#): > > (Bonus points for anyone who knows what we’re talking about here. 🙂 ) Zero points awarded on my end ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [January 24, 2022, 8:22pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/346 "2022-01-24T20:22:12Z")
Shades of Stony Stevenson and Schenectady! Tent rentals anyone? ---
**Author:** ![HMS\_Irruncible](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hms_irruncible/32/7394_2.png) [@HMS\_Irruncible](https://boards.straightdope.com/u/HMS_Irruncible)\ **Post date:** [January 24, 2022, 8:23pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/347 "2022-01-24T20:23:55Z")
So when is the glorious moment that we know for sure that this is an actual operating telescope and not 10-billion-dollar Lagrange-orbiting brick? ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [January 24, 2022, 8:24pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/348 "2022-01-24T20:24:37Z")
> [@HMS\_Irruncible](#): > > and not 10-billion-dollar Lagrange-orbiting brick? It can’t be a brick. It soared through space in exactly the same way that bricks don’t. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [January 24, 2022, 8:26pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/349 "2022-01-24T20:26:43Z")
> [@HMS\_Irruncible](#): > > So when is the glorious moment that we know for sure that this is an actual operating telescope and not 10-billion-dollar Lagrange-orbiting brick? If I may re-phrase this question a bit more specifically: We know that it will be several months of testing and calibrations before they start doing any “real science” with this telescope. But surely (?) that must include gathering images from afar and examining them for their calibration and testing work. Will any such images be made public during this time? ---
**Author:** ![squeegee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/squeegee/32/14537_2.png) [@squeegee](https://boards.straightdope.com/u/squeegee)\ **Post date:** [January 24, 2022, 8:33pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/350 "2022-01-24T20:33:20Z")
> [@Senegoid](#): > > But surely (?) that must include gathering images from afar and examining them for their calibration and testing work. Will any such images be made public during this time? I don’t know the answer, but @wolfpup 's [diagram](https://boards.straightdope.com/t/james-webb-space-telescope-successfully-launches/956624/335) has “first light” (usually an important milestone for a telescope) at L+59 and “observatory available for ISIM activities” (ISIM is the JWST instrument package) at L + 70, so _somebody_ is getting test images sooner than the L+180 we’ve been told when the 'scope is “fully commissioned”. ---
**Author:** ![HMS\_Irruncible](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hms_irruncible/32/7394_2.png) [@HMS\_Irruncible](https://boards.straightdope.com/u/HMS_Irruncible)\ **Post date:** [January 24, 2022, 8:35pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/351 "2022-01-24T20:35:49Z")
> [@Senegoid](#): > > If I may re-phrase this question a bit more specifically: We know that it will be several months of testing and calibrations before they start doing any “real science” with this telescope. Oh I understand there are still numerous setup chores remaining (so we’re told). Of course I’d love to see imagery as much as anyone else, but mainly I just want to know when we can relax about the prospect of suddenly finding out the thing isn’t going to work as advertised. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [January 24, 2022, 8:44pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/352 "2022-01-24T20:44:53Z")
I read a description somewhere describing a major part of that “calibration” work. I don’t recall if I saw this somewhere on the official Webb site, or earlier in this thread, or somewhere else. So they have these 18 separate mirrors that they’ve deployed with nanometer positioning precision. But they still need to get all 18 mirrors micro-positioned so, you know, they will all focus a distant star down to a _single_ point on the receptor instead of seeing 18 separate stars. So they will point the telescope at some known star, and then tweak the precise micro-positions of all 18 mirrors until they get all 18 images to coincide onto one point. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [January 24, 2022, 8:49pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/353 "2022-01-24T20:49:29Z")
What is the light-time distance from Earth to L2? That is, how much lag time will there be in any communications between Earth and the telescope? ETA: Okay, with a bit of Google-help, I immediately found an on-line light-time-distance calculator. 1000000 miles is about 5.368 light-seconds. More ETA: [Here’s the calculator site I used.](https://jumk.de/math-physics-formulary/speed-of-light.php) ---
**Author:** ![squeegee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/squeegee/32/14537_2.png) [@squeegee](https://boards.straightdope.com/u/squeegee)\ **Post date:** [January 24, 2022, 8:56pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/354 "2022-01-24T20:56:08Z")
> [@Senegoid](#): > > What is the light-time distance from Earth to L2? That is, how much lag time will there be in any communications between Earth and the telescope? Well, lessee. L2 is 1.5m km from Earth, and JWST is orbiting L2 at (using @wolfpup’s diagram) a diameter of 1.5m km (radius half that) so max distance is about 1.68m km or 5.6 light seconds @ 300km/sec lightspeed. Total napkin calculation, but I’d think close. ---
**Author:** ![Bootb](https://avatars.discourse-cdn.com/v4/letter/b/e19b73/32.png) [@Bootb](https://boards.straightdope.com/u/Bootb)\ **Post date:** [January 25, 2022, 12:19am UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/355 "2022-01-25T00:19:33Z")
I suspect that some people have already seen this; it’s an animation of the final orbit. https://www.youtube.com/embed/6cUe4oMk69E?feature=oembed&wmode=opaque&list=TLGG8tIphgpDAHkyNDAxMjAyMg ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [January 25, 2022, 4:44am UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/356 "2022-01-25T04:44:11Z")
One factoid I found interesting in the _What Now for Webb_ program I linked to above was that the orbit around the L2 point is about 180 days, very leisurely indeed. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [January 25, 2022, 3:05pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/357 "2022-01-25T15:05:52Z")
Not as leisurely as the Earth’s orbit around the sun. In fact, I would think that they are closely related. It would make sense for its orbit around L2 to be a fraction or a multiple of the Earth’s orbit. ---
**Author:** ![3AxisCtrl](https://avatars.discourse-cdn.com/v4/letter/3/ecd19e/32.png) [@3AxisCtrl](https://boards.straightdope.com/u/3AxisCtrl)\ **Post date:** [January 25, 2022, 3:14pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/358 "2022-01-25T15:14:05Z")
> [@k9bfriender](#): > > It would make sense for its orbit around L2 to be a fraction or a multiple of the Earth’s orbit. Wouldn’t its period be a function of its orbital radius? ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [January 25, 2022, 3:33pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/359 "2022-01-25T15:33:45Z")
Maybe? I don’t know orbital mechanics really well, but it’s not _actually_ orbiting around the L2 point, there’s no mass there for it to orbit, it’s orbiting around the sun, and doing so at an orbital velocity that would put it into a higher orbit were it not for the gravity of the Earth. Its orbit is inclined, so that, from the Earth, it seems to trace a circle in the sky, but that circle isn’t actually the route that it takes around the sun. The inclination of the orbit is what makes it seem to orbit a point, so I don’t think that the distance from that point (the amount of inclination of the orbit) would have any effect on how long it took to make that circle. Though, now I wonder why it is 180 days, rather than a whole year. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [January 25, 2022, 3:46pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/360 "2022-01-25T15:46:14Z")
> [@k9bfriender](#): > > Not as leisurely as the Earth’s orbit around the sun. > > In fact, I would think that they are closely related. They’re not related at all. The earth’s orbit, and its mass, determine _ **where** _ the second Lagrange point is located, that’s all. The JWST’s orbit is indeed really around L2, and the speed of its orbit is determined only by its radius from L2 at any given point and the gravitational balance at L2. JWST’s orbit is very slow both because it’s quite far from L2 (in a very elliptical orbit that takes it as far as about 1.5 million km) and because the effective gravitational balance at L2 is very weak. By happy coincidence, this is probably very helpful in minimizing the amount of tracking it has to do to maintain a fixed aim. Its orbit is basically perpendicular to the plane of the earth’s orbit (see the diagram I posted earlier) and is held within its own orbit by the usual orbital dynamics, and the orbital plane is held in place by the balance of the earth’s and sun’s gravity against the centrifugal force of moving with the same solar period as the earth while in a higher orbit. [Previous page](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624.md?page=17) [Next page](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624.md?page=19)