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James Webb is fully deployed

nasa.gov

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Re: James Webb is fully deployed

#261

Post by ehsankia »

wolverine876 wrote: post #255

Something I am wondering about the L2 orbit ... per NASA: > Webb's orbit [~ around L2] ... is actually similar in size to the Moon's orbit around the Earth! This orbit (which takes Webb about 6 months to complete once) keeps the telescope out of the shadows of both the Earth and Moon. Unlike Hubble, which goes in and out of Earth shadow every 90 minutes, Webb will have an unimpeded view that will allow science operat…

> with Earth providing an extra sunshield

Maybe it needs the sun for its solar power?

> And "an unimpeded view" of what?

If hubble is looking at sometihng not perpendicular to its orbit, during half the 90 minutes the target will be "behind" the earth, right? So it can only look at things that are to the left or right of its orbit.

Re: James Webb is fully deployed

#262

Post by simonh »

BurningFrog wrote: post #137
sailingparrot wrote: post #102

Earlier quoted context omitted.

Because it's a wrong assumption. Significant cost come from the assembly and testing of all the components itself, that you would have to redo entirely. Also if you were to build just 2 or 3 of them, you can't expect any economy of scale. On top of that, the operational cost of JWST is expected to be around 1B$ for it's lifetime, you could expect that to be similar for every single replica you have. And finally, you…

> the benefits of a second one would be marginal compared to the benefits of the first one. This can't be true. The benefit of the JWST is the observations it can make Two JWSTs can make twice as many observations as one, so it provides twice the benefit. In some sense there is a diminishing return in that the most important observations will be attempted first, and and over time the average observation will be less…

There is a list of specific questions JWST was built to answer.

* What were the first stars and galaxies like?

* How do stars come to form deep within a dusty nebula?

* What are the atmospheres of Earth-sized worlds like, and do they contain signatures of life?

* How far away do we need to look to see the pristine, pre-stellar Universe?

* How did the early stars and galaxies assemble to give rise to what we have today?

Once these questions have been answered, answering them again with exact copies of the same instruments at the same fidelity does offer diminishing returns. Sure it will provide valuable data for its whole lifespan, but there are diminishing returns. Better to invest the marginal cost of another JWST in a different instrument that gives us measurements the JWST can’t. There will be successors to the JWST, and that’s where the investment should go.

Re: James Webb is fully deployed

#263

Post by jazzyjackson »

amelius wrote: post #241
JohnBooty wrote: post #208

Earlier quoted context omitted.

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.

I’m sure if we ever have sufficient technology to build a city on the moon, the first museum exhibit will be a captured JWST

Re: James Webb is fully deployed

#264

Post by BurningFrog »

sailingparrot wrote: post #242
BurningFrog wrote: post #233

Earlier quoted context omitted.

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…

You seem to argue against something I didn't say.

I understand it observes a different frequency range than Hubble, but it can still "observe anything in the sky, and get the most detailed pictures ever seen of them".

Re: James Webb is fully deployed

#265

Post by BurningFrog »

simonh wrote: post #262
BurningFrog wrote: post #137

Earlier quoted context omitted.

> the benefits of a second one would be marginal compared to the benefits of the first one. This can't be true. The benefit of the JWST is the observations it can make Two JWSTs can make twice as many observations as one, so it provides twice the benefit. In some sense there is a diminishing return in that the most important observations will be attempted first, and and over time the average observation will be less…

There is a list of specific questions JWST was built to answer. * What were the first stars and galaxies like? * How do stars come to form deep within a dusty nebula? * What are the atmospheres of Earth-sized worlds like, and do they contain signatures of life? * How far away do we need to look to see the pristine, pre-stellar Universe? * How did the early stars and galaxies assemble to give rise to what we have toda…

I know NASA has a reputation for bureaucracy, but I don't think it will be forbidden to use JWST for other purposes than those 5 questions?

It is capable of being aimed at any point of the sky and show us things we've never seen before, is it not?

Re: James Webb is fully deployed

#266

Post by idealmedtech »

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.

How can it make out galaxies at billions of light years away, but not a truck sized craft at a few million miles?

I haven't done the math myself, so I'm certain one side of that equation is wrong, but that seems hard to believe!

Re: James Webb is fully deployed

#267

Post by andrewflnr »

Dayshine wrote: post #259
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?

Does anybody know exactly how unstable L2 is? I've seen lots of people talk about how some Lagrange points are stable and others are unstable, but I've never been able to find a source for how much this matters. How long would it take for Webb to move so far off L2 that we can't communicate with it anymore, or for it to be at risk of being completely thrown out of orbit to the point that it would impact earth or the…

It matters enough that "over ten years" of fuel left (as we supposedly have now) is a really great outcome, as opposed to just five we might have form. Scott Manley on YouTube has a pretty good video on Lagrange points (and it's a topic where the video medium is actually pretty helpful).

Re: James Webb is fully deployed

#269

Post by Rebelgecko »

wolverine876 wrote: post #255

Something I am wondering about the L2 orbit ... per NASA: > Webb's orbit [~ around L2] ... is actually similar in size to the Moon's orbit around the Earth! This orbit (which takes Webb about 6 months to complete once) keeps the telescope out of the shadows of both the Earth and Moon. Unlike Hubble, which goes in and out of Earth shadow every 90 minutes, Webb will have an unimpeded view that will allow science operat…

The advantage of L2 is that the sun and earth will always be in the same direction (more or less) so it's easy to cancel it out. I don't think there's an orbit that would stay in Earth's shadow constantly that would have the same properties (without needing a ton of fuel)

Re: James Webb is fully deployed

#270

Post by yholio »

wruza wrote: post #251

Do we see anything up there yet?

A months long alignment period will follow, where the hexagonal segments are bent and turned by thousands of actuators until they are all focused to wavelength precision.

The first images will follow, but not before the dark side cools enough to not flood any interesting target into locally generated infrared.

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