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James Webb is fully deployed

nasa.gov

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Re: James Webb is fully deployed

#241

Post by amelius »

JohnBooty wrote: post #208
daveslash wrote: post #204

Earlier quoted context omitted.

RE>> "I understand the reasons for not putting a camera on or near the JWST" What are the reasons? I'm sorry ~ I'm ignorant on the topic, but I'd love to learn more. Why/what are the reasons?

Great blog post from NASA themselves explaining it: https://blogs.nasa.gov/webb/2022/01/06/why-doesnt-webb-have-... the post is really not very long and I would suggest getting it straight from the horse's mouth, but for those not willing to devote a click here are arguably the most relevant bits! "deployment surveillance cameras would not add significant information of value for engineering teams commanding the spac…

Perhaps one day they could send a robot mechanic along with the mission, and then a camera could be of value.

Re: James Webb is fully deployed

#242

Post by sailingparrot »

BurningFrog wrote: post #233
sailingparrot wrote: post #179

Earlier quoted context omitted.

JWST was built to see in IR to help us get answers to a set of important questions. The best known one being trying to elucidate the question around the rate of expansion of the universe. We hope to get some answer by looking at objects much further away in space and time with the JWST and getting new estimates for the expansion rate. Something we cannot do today. You don't need two telescopes to do that, you just ne…

JWST is a general purpose telescope, and the by far most powerful ever built. It should, if working as intended, be able to observe anything in the sky, and get the most detailed pictures ever seen of them. In wavelengths not seen before. Without doing the math, there are probably billions of interesting things to point it at, most of which it will never get around to.

> be able to observe anything in the sky, and get the most detailed pictures ever seen of them

That's just not true. JWST is primarily infrared, with some limited ability to observe in visible light (essentially half of the spectrum, no blue or green). It has no capability in ultraviolet, x-rays, gamma-rays, microwaves or radio.

You just can't build a single instrument to "observe anything".

JWST can't do what Hubble can for the most part, and Hubble can't do what JWST will do.

WMAP, Spektr (Russian), Chandra and many other missions all do different things and help us answer different questions with very little overlap.

Re: James Webb is fully deployed

#243

Post by delecti »

wrycoder wrote: post #223
surfsvammel wrote: post #209

Earlier quoted context omitted.

Won't it be pretty close to earth in its final position at L2? If so, is there no chance that there will be future missions to do service to it? If so, maybe we can get a photo of if then?

Maybe Hubble could take a snapshot or two?

TLDR: Not really. At the distance of the JWST, a single pixel on the hubble's camera is about 700m across, or roughly 30 times the size of the JWST.

The L2 point is about 1.5 million km from earth [0]. The smallest size Hubble can resolve is about 1/20 arcsecond [1]. It's in a pretty low orbit, so is effectively "on earth" relative to the distance to the L2 point where JWST is. Calculating the size of an angular measure at a given distance [2], you get about 727m [3].

[0] https://en.wikipedia.org/wiki/Lagrange_point#L2_point

[1] https://illuminateduniverse.org/2019/04/11/angular-resolutio...

[2] https://astronomy.stackexchange.com/a/20728

[3] https://www.wolframalpha.com/input/?i=tan%28%281+arcsec%29%2...

Re: James Webb is fully deployed

#244

Post by stjohnswarts »

divbzero wrote: post #232
marcosdumay wrote: post #45

Earlier quoted context omitted.

AFAIK no single mirror segment failure would destroy the entire telescope, so the only one still on the future is the L2 insertion burn. As always, it's useful to post this link: https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html

Since L2 is an unstable equilibrium, won’t there also need to be routine adjustments throughout the mission?

Of course, nothing is perfect they will have to adjust position over time and have accounted for all of it with possible robotic missions in the future to extend and refuel as necessary, although that is a "hope" rather a surety.

Re: James Webb is fully deployed

#245

Post by [deleted] »

divbzero wrote: post #232
marcosdumay wrote: post #45

Earlier quoted context omitted.

AFAIK no single mirror segment failure would destroy the entire telescope, so the only one still on the future is the L2 insertion burn. As always, it's useful to post this link: https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html

Since L2 is an unstable equilibrium, won’t there also need to be routine adjustments throughout the mission?

[deleted]

Re: James Webb is fully deployed

#246

Post by stjohnswarts »

ducktective wrote: post #26
dgrin91 wrote: post #23

One of the big numbers that been thrown around is that JWST has 344 single points of failure in its mission. Now that deployment has been completed, is there somewhere that lists how many of those points we have passed?

>344 single points of failure How can a system have more that one single point of failure?

There are 344 individual items that can make the $10 billion satellite be a paper weight in orbit. Those are the very definition of single points of failure.

Re: James Webb is fully deployed

#247

Post by simonh »

dredmorbius wrote: post #239
divbzero wrote: post #232

Earlier quoted context omitted.

Since L2 is an unstable equilibrium, won’t there also need to be routine adjustments throughout the mission?

Yes. Those adjustments, as well as unloading of the reaction wheels used to position JWST, and the fuel burns reqiured for them, are the principle determinants of the JWAT's lifespan, estimated at 10 years. Nasa have lowballed such estimates for numerous missions in the past (Hubble and numerous Mars lander and rover missions come to mind), and it's possible JWST will exceed the planned lifetime, potentially by a wid…

Apparently the launch and mid course burn were precise enough that it should have enough remaining propellant for a bit more than 10 years of station keeping.

Re: James Webb is fully deployed

#248

Post by ddingus »

frosted-flakes wrote: post #234
wrycoder wrote: post #223

Earlier quoted context omitted.

Maybe Hubble could take a snapshot or two?

With Hubbles's highest resolution optics, the JWST will be about one-tenth the size of a pixel.

Scale. We are just a bit of noise in an impossible to understand large, complex system.

It is crazy to think about.

Re: James Webb is fully deployed

#249

Post by terramex »

joering2 wrote: post #168
_Microft wrote: post #114

Earlier quoted context omitted.

Why spend money on JWST 2 when you could as well spend it on ... LUVOIR ? ^^ https://en.wikipedia.org/wiki/Large_Ultraviolet_Optical_Infr...

JWST versus LUVOIR-A... just wow! Imagine difference in quality of pictures! https://en.wikipedia.org/wiki/Large_Ultraviolet_Optical_Infr...

Actually LUVOIR will most likely have smaller 6 meter mirror to reduce cost and use lessons from JWST construction. It will be simpler design than JWST as it will use only 2 or 3 layer sunshield and no cryocooler (creating equipment that can work at 5 Kelvin was massive issue for JWST). Its main science goal will be examining atmospheres of exoplanets, plus general observations like Hubble.

It will observe in UV/visible/near-IR so its resolution will be higher than JWST's as shorter wavelengths are easier to focus (diffraction limit is a function of wavelength) but it will not be able to see objects at the very end of observable universe as it cannot image in mid-IR or longer wavelengths. There is still plenty of interesting stuff closer to us and it will be "true" successor to Hubble.

Re: James Webb is fully deployed

#250

Post by bichiliad »

JohnBooty wrote: post #208
daveslash wrote: post #204

Earlier quoted context omitted.

RE>> "I understand the reasons for not putting a camera on or near the JWST" What are the reasons? I'm sorry ~ I'm ignorant on the topic, but I'd love to learn more. Why/what are the reasons?

Great blog post from NASA themselves explaining it: https://blogs.nasa.gov/webb/2022/01/06/why-doesnt-webb-have-... the post is really not very long and I would suggest getting it straight from the horse's mouth, but for those not willing to devote a click here are arguably the most relevant bits! "deployment surveillance cameras would not add significant information of value for engineering teams commanding the spac…

One thing they mentioned that kinda sends it home to me is that the telescope is aimed at the dark and away from the sun, and the other side is especially reflective[0]. In other words, one side is too dark to see, and the other is too bright to see.

[0]:https://twitter.com/NASAWebb/status/1479161991252131841

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