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Photons incoming: Webb team begins aligning the telescope
- divbzero 5y agoIt’s incredibly exciting to watch Webb deploy. I was too young to remember Hubble but will definitely remember this.
- guerrilla 5y agoIt makes me feel like a kid again.
- fsckboy 5y agoHubble deployed only to discover they had screwed up and it was blurry. https://www.nasa.gov/content/hubbles-mirror-flaw https://www.nasa.gov/content/hubbles-mirror-flaw
- deleted 5y ago[deleted]
- jacquesm 5y agoWhich was then fixed in space by astronauts during 5 consecutive EVAs.
- lisper 5y agoOnly the first of those missions was to fix the flaw. The others were to install various upgrades. And all this was only possible because Hubble was in LEO. If JWST fails it’s game over.
- jacquesm 5y ago> Only the first of those missions was to fix the flaw. First mission five space walks. https://en.wikipedia.org/wiki/STS-61 https://en.wikipedia.org/wiki/STS-61 > The others were to install various upgrades. Those were completely different missions, not different spacewalks. > If JWST fails it’s game over. Yes, let's hope that it doesn't.
- lisper 5y ago> First mission five space walks. I stand corrected.
- jacquesm 5y agoNP, just wanted to make sure that was accurate. We transmitted STS-82 live so I remember that one pretty clearly, but STS-61 really was the one that made all the difference. Unfortunately we didn't have our software ready at that time, that only happened in 95 and then NASA and NetNitco talked to us just in time to have it all ready to go for STS-82. Thinking about it: that's actually scary how quick the time has passed, it's like yesterday. I don't think I left the office from about an hour before countdown until it was back on the ground. Here is a shot from STS-82: https://twitter.com/jmattheij/status/1474767067236777991 https://twitter.com/jmattheij/status/1474767067236777991
- deleted 5y ago[deleted]
- virgildotcodes 5y agoTotally naive question here - can all this not be done automatically? It seems to me as if this is a largely manual process, and that's why it's going to take 3 months, no?
- dylan604 5y agoif you automated it, then what are all of these people going to do? all you automation people wanting to take away the jobs of all these people! this is why unions exist! ;-)
- BurningFrog 5y agoThat may be overly cynical. But what I always think when a NASA control room erupts in joy after a landing, is that those people just learned they have a job for years.
- mikepurvis 5y agoI don't think that's really the case, is it? Usually there's a handoff between the flight/EDL team and the surface operations team.
- BurningFrog 5y agoThat sounds like it's probably true. I have to make an orderly retreat to my next cynical line: everyone in that room is aware that their reaction wis filmed and will be shown across the world.
- dylan604 5y agoYou're just a right fun chap, aren't you? Your team spent years researching something that had never been done before. Survived many rounds of "should we just cancel this project", continued to be funded after coming in no where near your proposed budget, delay after delay, to finally see the thing lift off. You wouldn't have the slightest bit of non-robotic emotion for yourself and fellow team members? Hope I never have to work with someone as dull as that.
- dghughes 5y agoWhen you get some new device and it says leave plugged in for 12 hours to charge first before using, but you don't. I have to wonder with JWST I bet there is a desire to try to have a sneak peek. But I guess calibration is automated so no way to bypass rules. And way too much to lose if something goes wrong ~30 years and $10B.
- RosanaAnaDana 5y agoI think its much more than the sunk cost we would lose. There would never be another.
- dmitryminkovsky 5y agoWhy not? You mean JWST specifically or some reason there can’t be a similar telescope?
- sohkamyung 5y agoThe Nancy Grace Roman Space Telescope is upcoming. It's mirror is 'only' the size of the Hubble's [1] [1] https://roman.gsfc.nasa.gov/ https://roman.gsfc.nasa.gov/
- dmitryminkovsky 5y agoSo JWST is so massive that it’s unlikely anything like it will happen again in our lifetimes?
- mwint 5y agoIf Starship happens, I’m guessing JWST-class telescopes become much more approachable.
- rich_sasha 5y agoI’d imagine launch cost is a fraction of the cost. JWST is immensely complex.
- rswail 5y agoWatching the Webb unfold has been both heart-stopping and amazing. Just the heatshield itself is astounding and bodes well for future human travel.
- A_No_Name_Mouse 5y ago> Although Image Stacking puts all the light in one place on the detector, the segments are still acting as 18 small telescopes rather than one big one. The segments need to be lined up with each other with an accuracy smaller than the wavelength of the light. Why is this necessary? Phase difference shouldn't matter unless the light is coherent, which I wouldn't expect in starlight. Which assumption is wrong?
- sbierwagen 5y agoYou can get interference patterns off of white light: https://www.quora.com/Can-white-light-produce-interference-pattern-What-is-its-nature https://www.quora.com/Can-white-light-produce-interference-p... After all, physicists were producing interference fringes in the 18th century, and they sure didn't have lasers back then: https://en.wikipedia.org/wiki/Young%27s_interference_experiment https://en.wikipedia.org/wiki/Young%27s_interference_experim...
- A_No_Name_Mouse 5y agoFor interference the light needs to be able to take two separate paths with different length, which is the case in the oil film example or with two slits. In a telescope, each photon can only take a single path. So what would it interfere with? If it's a different photon then coherence seems to be required
- Sharlin 5y agoHm? Oil slick iridescence and the original double slit experiment demonstrate entirely classical wave behavior. No QM needed. Same thing with Webb. Light arriving from the same source but in slightly different phases absolutely causes interference patterns explainable in purely classical terms.
- cwillu 5y agoThat's a classical-world blunder: single photons can and do interfere with themselves. Making a measurement of which path a photon took, is forcing the photon to have taken one path. If you don't make the measurement (read, if you don't interact with the photon somewhere along some path it could take), you can get interference between the paths, despite it being a single photon.
- radium3d 5y agoShow us the photons! :)
- tomas789 5y agoI would be interested in reading something more in-depth. Especially how the algorithms behind the alignment work.
- qwertox 5y agoThere's a relatively new video on YouTube by Launch Pad Astronomy named "How James Webb Orbits 'Nothing'" [0] which left me baffled on how they are capable of orbiting "around" L2, which I had been thinking about for some weeks now and never could find a solution to it. I think Webb is not the first one to do this, but the video makes it clear how crazy the planning of the orbit insertion and staying in orbit must be. I hope that the NASA could release some details on this. [0] https://www.youtube.com/watch?v=ybn8-_QV8Tg https://www.youtube.com/watch?v=ybn8-_QV8Tg
- sandworm101 5y agoSome would say it really isnt an orbit. Orbit presumes a single attractive force (gravity or magnetic) from one body while another moving body is held away by momentum. The circular path around an L point is more a confluance of attractive forces from two bodies. The object is not held up by momentum rather than by balanced pulls of multiple attractive forces. If there is no minimum required velocity to maintain altitude, it isnt really an orbit imho.
- mannykannot 5y agoFrom a physics point of view, an orbit around a celestial body is just a special case of a more general phenomenon. The explanation is the same, only the numbers giving the spatial distribution of the gravitational potential within the gravity well are different. > If there is no minimum required velocity to maintain altitude, it isnt really an orbit imho. If you put, into a gravity well, a body that is initially stationary with respect to the location of the well's minimum potential, but offset from it, it will begin to move on an orbit, under the influence of that gravitational potential. The JWST orbit is more complicated, because L2 is a potential saddle, not a well, and it is affected by the moon's gravity, but I think one needs to be aware of the points I made above before one can begin to deal with those complications.
- sandworm101 5y agoThat goes down the road of saying that every circular path is an orbit. I'm reminded of the concept that the sun "orbits" around in the milky way. I don't really consider that an orbit either because the dynamics are totally different. I try to use "orbit" in relation to objects moving around a larger mass and/or a barycenter, which is conceptually a location of average mass. A third tiny object is rather in an orbit around one of the the bodies but that which is constrained by the gravity of the second.
- ColinWright 5y agoContext for the level of accuracy. Quoting from the article: To work together as a single mirror, the telescope’s 18 primary mirror segments need to match each other to a fraction of a wavelength of light – approximately 50 nanometers. To put this in perspective, if the Webb primary mirror were the size of the United States, each segment would be the size of Texas, and the team would need to line the height of those Texas-sized segments up with each other to an accuracy of about 1.5 inches.
- dwaltrip 5y agoDoes this mean that they have some sort of actuator that can move with nanometer precision? I didn’t realize that was possible… wow.
- GuB-42 5y agoThe best part is that you may already have one. Modern hard disks have a track pitch in tens of nanometers, and the read head has to move with matching precision, it also flies 3 nanometers above the surface.
- dwaltrip 5y agoWow, that's really cool. Thanks for sharing the knowledge. I didn't realize how physically precise modern hard drives were! I suppose if it makes sense if you think about how much information they are storing in a small space.