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Thread: Instea of "Where's Wally?" here's Where's Webb

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    Default Instea of "Where's Wally?" here's Where's Webb

    was launched on Christmas day heading to an L2 orbit 1.5 million km above earth.
    I'm out of my mind, but feel free to leave a message...

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    Reading on about the orbit management, the lack of redundancy is disconcerting:

    Because the thrusters are located solely on the Sun-facing side of the observatory, all station-keeping operations are designed to slightly undershoot the required amount of thrust in order to avoid pushing the JWST beyond the semi-stable point, a situation which would be unrecoverable.
    Why the heck not have thrusters also on the opposite side incase this 'undershoot' strategy goes awry wrong?
    I would have put all the thrusters on all 4 'outside corners' in pairs pointing both towards and away from the sun.
    Too many times have I seen software/user errors occur but good old hardware comes along to save the day... or in this case an $8 Billion telescope !
    Last edited by Uncle Fester; 03-01-22 at 09:26 PM.
    Update: A deletion of features that work well and ain't broke but are deemed outdated in order to add things that are up to date and broken.
    Compatibility: A word soon to be deleted from our dictionaries as it is outdated.
    Humans: Entities that are not only outdated but broken... AI-self-learning-update-error...terminate...terminate...

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    I agree, however, I bet their "good" reasons were weigh!
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    According to The Goddard Spaceflight Center, Webb is now fully deployed. It is 3/4 of the way to it's destination.
    The fact that there's a highway to hell and a stairway to heaven says a lot about the anticipated traffic flow.

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    Quote Originally Posted by Uncle Fester View Post
    Why the heck not have thrusters also on the opposite side ....
    yep, first guess is always weight, but there are probably other reasons like contamination. You really do not want any gas in the cooled regions of the telescope else this becomes like frost in your freezer. Imagine having a thin layer of frost on your camera lens that builds up every time you maneuver.

    The explanation for how they deal with it does make sense though. I'm trying to think of a similar way to describe it. Ah, got an analgoue.
    If you're a scuba diver, do you err on the side of caution of positive or negative bouyancy? This is actually a real world problem. Divers are always in a semi-stable bouyancy. If they put no air in their BCD, they might float at the surface, but as soon as they get a bit of pressure, they start to sink faster and faster.
    This normally isn't a problem if you're diving where the bottom will stop you. In open water were the bottom is a long way down you could "theoretically" descend fast enough that you cannot inflate the BCD fast enough. though that is fat chance in reality with >100bar behind a generous regulator.

    The reverse situation is far more common. When at depth, if the diver does not dump gas from their BCD before or as they ascend they can easily get into a runaway scenario. The solution which they don't properly train recreational divers for is to stay negatively buoyant so you sink.
    This prevents the runaway but you have to swim up rather than float up.

    In the case of the JWST, it's the same thing. Gravity is pulling them towards the Earth and sun. So provided they stay on the down side of the L2 they can always use fuel to push up. Using fuel to push down is like the diver trying to swim against his buoyancy. It's much harder and uses more energy.

    The way I dive describes it quite well now I think of it. I dump gas and swim up to just below bouyance and dump more gas and swim up more.
    If I were to overshoot, it becomes a runaway situation and I have to dump gas fast or flip over and swim down fighting the buoyancy as it gets worse the longer I don't fight it. Never getting to buoyancy (the L2) means I have to use fuel, but I'm safe. I'll sink slowly rather than ascend fast.
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    Good analogy Trash.
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    The answer which a lot of engineering people ask is why not assemble and test it in low Earth orbit and then deliver it.
    I heard a response from one of the JWST engineers who said, this is one of our most asked questions.
    The Answer is that the telescope is much more rugged packed up. It can easily withstand the stress of launch etc.
    Had they assembled it and then tried to move it with any serious thrust, it would be too risky that might stress it and break it.

    Think of it like being on a wild side show ride. With your arms up in the air they are being pulled and shaken all over the place. But if they are tucked in by your side, they're much less likely to get damaged or break off

    For the JWST Small and compact was much safer than deployed and even only slightly shaken.
    Yes I am an agent of Satan, but my duties are largely ceremonial.

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    Webb is fully deployed and inserted into its L2 orbit (1,460,500km). My understanding is that there is a wait for it to cool to operating temperature....
    The fact that there's a highway to hell and a stairway to heaven says a lot about the anticipated traffic flow.

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    Cooling doesn't that that long. It's the calibration and commissioning that takes time.
    Everything needs to be tested and measured and measured again. Think about something as simple as pointing. This telescope is likely to have a sub milliarcsecond accuracy so just working out where it is pointing takes a bit of effort to get right. As a comparison, a 2.3m ground based telescope takes about 12 hours to re-calibrate pointing and this is with known parameters.
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    First Images released...........

    The fact that there's a highway to hell and a stairway to heaven says a lot about the anticipated traffic flow.

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    Quote Originally Posted by enf View Post
    First Images released...........

    I'm not a very technical person, don't know how this all works, but those photos are AWESOME!

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    I'd forgotten all about this thread, thanks for the piccies.
    I'm out of my mind, but feel free to leave a message...

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    Wow!! There's just as many dots in the background of all of these galaxies!!!

    Try zooming in, the shit just keeps going and going.. All those bright red galaxies are around 11 billion years old..

    That patch of sky is approximately the size of a grain of sand.. Really hard to comprehend.
    Bottom left corner definitely aliens. LOL
    Last edited by Johnno; 13-07-22 at 06:55 PM.

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    Quote Originally Posted by Johnno View Post
    That patch of sky is approximately the size of a grain of sand.. Really hard to comprehend.
    Good God, Mind Blowing stuff. Check this out....



    ZOOM OUT.

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    COMPARE

    Carina Nebula - NGC 3324 Hubble





    Carina Nebula - NGC 3324 Webb


    The fact that there's a highway to hell and a stairway to heaven says a lot about the anticipated traffic flow.

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    The fact that there's a highway to hell and a stairway to heaven says a lot about the anticipated traffic flow.

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