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James Webb is fully deployed

nasa.gov

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Re: James Webb is fully deployed

#501

Post by [deleted] »

JohnBooty wrote: post #486
dev_tty01 wrote: post #394

Earlier quoted context omitted.

NASA has often added video or image capability with low scientific value to increase public engagement, despite the associated risk and cost. They made a call not to do it this time. My only point is that it would have been a nice PR opportunity if they could have found a way to make it work within their mission parameters. I apologize if making such a simple and obvious point has offended you in some way.

As the aforelinked blog post explains, the extreme environment of the JWST makes this more challenging than it would be for missions like the Mars rovers. The dark side of the JWST (where all the instruments are) will be operating very close to absolute zero and in near-absolute darkness which, of course, is the entire point of the mission. A selfie camera there would need to function in that environment, while also…

[deleted]

Re: James Webb is fully deployed

#502

Post by WalterBright »

sailingparrot wrote: post #475
WalterBright wrote: post #435

Earlier quoted context omitted.

Is it unfair? In Spring 2020, in this forum, the vaccine experts here told me in no uncertain terms that a vaccine would take 18 months to develop. I said it could be done in 6 if all the slack was removed, and things done serially were done concurrently. I was told that was all completely unreasonable and impossible. 6 months later, the vaccine was released. The JWST has what, 390 single points of failure, and cost…

What I am saying is unfair is your insistence on trying to think of astronomy as a problem that can be resolved by scale. > that a vaccine would take 18 months to develop. I said it could be done in 6 Cool anecdote. I was also part of those who thought it would be done earlier, we agreed on this. This is not comparable at all. > so $10B was spent to ensure it would not fail. And it worked! But suppose for $1B one cou…

Apparently NASA and the Soviet Union used to build duplicates:

https://flyingbarron.medium.com/the-james-webb-space-telesco...

so it's not such a ridiculous idea after all.

Intelligence has nothing to do with it. All you have to do is look at the space shuttle design. It was a seriously flawed concept. I did not understand how that concept could have been pushed forward. So I emailed Homer Hickam about it, wondering what I missed. He said I was right, and that he'd also thought the concept was completely wrong. Events later showed both of us were right in every aspect. (I had not expected a reply from him, but he was very nice to do so!)

The Fukushima reactor and the Deepwater Horizon drilling rig were also designed and built by experienced, intelligent people, but they both could have used experience from the airline people. Both had multiple single points of failure, which failed, and none of those points had to be there. I see this again in the auto industry, in particular Toyota's onboard computer.

The software industry is also full of the smartest people I know. Yet I've been able to bring in ideas from airliner design that are of significant benefit. For example, "defensive programming" comes from a talk I gave in the 1990s.

I recommend James Burke's "Connections" series. It is a history of technology, on the theme of how outsiders repeatedly spark advances and innovation by seeing things that the insiders don't see.

I'm an outsider as far as space probes go. I know little about the details. But that also means I am not immersed in the conventional wisdom that develops around the insiders of every profession, and sometimes and outsider can see things the insiders don't.

I don't claim I'm always right. But all I ask is to keep an open mind. Sometimes an outsider with experience in another industry can make a connection.

Re: James Webb is fully deployed

#503

Post by kragen »

WalterBright wrote: post #429
kragen wrote: post #220

Earlier quoted context omitted.

A lot of times when you make one of something, there's stuff you would make tooling for if you were going to do more than one, but which instead you do by hand. Sometimes this is even true in software, but not very often, because the advantages of being able to recompile something from source code are so huge.

Even when doing things by hand, making a duplicate alongside the original is not much more time. That happens to me every time I do something by hand.

This is true for things like motor mounts and pipe flanges, but not for things like optical surfaces and lathe ways. Even in cases where it is true, if you didn't make the duplicate alongside the original, you have to do the setup again to make a duplicate.

Re: James Webb is fully deployed

#504

Post by idealmedtech »

frosted-flakes wrote: post #287
idealmedtech wrote: post #266

Earlier quoted context omitted.

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!

Here's the math[1]. Seems believable to me. The Web telescope is miniscule conpared to faraway galaxies, and it doesn't emit much light. [1]: https://mobile.twitter.com/gfish/status/1479339620785524736

I did a little math of my own, and found that while the ratio of these distances is on the order of 10^15, the ratio of the sizes of these objects is on the order of 10^19.

In other words, Webb is only one TEN THOUSANDTH the apparent size of a galaxy that's a _billion light years away_

That's just mind numbing to consider!

Re: James Webb is fully deployed

#505

Post by idealmedtech »

kadoban wrote: post #495
Sebb767 wrote: post #326

Earlier quoted context omitted.

To be fair, for someone who is not well-versed in either optics or space physics, calculating the answer is not that straight-forward.

You can do pretty well just comparing the ratios of the size to the distance, right? Or is it more than that?

That's a start, for sure, but to do a super accurate calculation (the kind I feel unqualified to carry out), you need to take into account apparent size, redshift, whether or not there's gravitational lensing, interstellar dust in the way, etc etc.

But I want to reiterate that what's meaningful about this discussion is in part how unintuitive things at the far edges of our scales of perception really are. It's a muscle that, left untrained, will lead you to make incorrect characterizations like the one I made.

Re: James Webb is fully deployed

#506

Post by dTal »

nullc wrote: post #397
dTal wrote: post #324

Earlier quoted context omitted.

It obviously needs a selfie mirror.

It has a selfie 'lens': NIRcam has extra optics that can be swung in that allows the camera to focus on the primary mirror instead of out in the great infinity. So in this sense webb is already a camera which can photograph itself! This capability exists for mirror alignment: They'll point webb at an isolated star, switch to focusing on the primary mirror, swap in optics that cause small phase differences to result i…

That's amazing. I was wondering how they did that. Every new thing I learn about this machine blows me away.

Re: James Webb is fully deployed

#507

Post by bigiain »

z3t4 wrote: post #461
bigiain wrote: post #388

Earlier quoted context omitted.

How much electrical power do you want to devote to this feel-good PR selfie camera? According to the mission director SmarterEveryDay interviewed on his YouTube channel recently, the James Webb Space Telescope is so sensitive it could detect the heat signature of a bumblebee at the distance of the moon. I’m pretty sure if you asked the astronomers if you could put a 5 Watt webcam on the dark side of their sun shield…

If it could see a bumblebee on the moon could it detect a while on Jupiters moons ? Can anyone do the calculations ?

It’s designed to see things very very far away, which are all severely redshifted. It’s mostly an infrared camera. In the human visual range of light frequencies, is camera sensors only go up to orange.

So no, it can’t detect a blue whale… ;-)

Re: James Webb is fully deployed

#508

Post by joshvm »

JohnBooty wrote: post #482
joshvm wrote: post #451

Earlier quoted context omitted.

It's probably not practical for JWST, but starlight is actually fairly bright. If you travel to somewhere with essentially zero light pollution, like a desert, if it's a clear sky you can see with starlight. At the South Pole on a clear night we would walk out to the dark sector (where the telescopes are) with our headlamps off because it just wasn't necessary. The only illumination sources outside were red safety li…

If you travel to somewhere with essentially zero light pollution, like a desert, if it's a clear sky you can see with starlight This reminds me... I need to experience this firsthand at some point. Thank you! Question: how much (if any) of that light is due to atmospheric scattering? ie, the sun's light hitting the daytime side of the earth, being scattered in our atmosphere, and faintly illuminating the night side o…

Plenty of places around the world offer dark enough conditions (but make sure it’s a new moon) - in the US you just need to get out to Arizona or Joshua Tree (or similar empty places). In Europe and elsewhere look for International Dark Sky Reserves. In general go visit places where telescopes are built.

Possible that some of it is from scattering and then if course you wouldn't get that in space as there's no atmosphere to scatter from! Scattering is incredibly faint though, even compared to starlight.

See also gegenschein and the Zodiacal light - both are backscatter effects.

Re: James Webb is fully deployed

#509

Post by joshvm »

joshvm wrote: post #451
bmitc wrote: post #411

Earlier quoted context omitted.

It seems to me that that isn't quite right. "Dark" just means no visible light, but an infrared or thermal camera could see stuff. The article above mentions this possibility and the problems, which are harnessing and operating at cryogenic temperatures.

It's probably not practical for JWST, but starlight is actually fairly bright. If you travel to somewhere with essentially zero light pollution, like a desert, if it's a clear sky you can see with starlight. At the South Pole on a clear night we would walk out to the dark sector (where the telescopes are) with our headlamps off because it just wasn't necessary. The only illumination sources outside were red safety li…

Slight addendum - actually you often want satellites to be reflective. Dark means good radiator, but also good absorber and a black spacecraft is about as bad as you can get for thermal management if you point it in the wrong direction. For an Earth orbiting craft that means it’ll overheat in sunlight and then dump everything in shadow - lots of thermal stress and not good for instruments that like a constant temperature. That’s why you often see sats covered in polymide foil.

Re: James Webb is fully deployed

#510

Post by yreg »

JohnBooty wrote: post #484
yreg wrote: post #467

Earlier quoted context omitted.

I doubt adding a tiny camera is adding a significant complexity.

I see you haven't read NASA's aforelinked blog post where they explicitly detail the sorts of complexity it would add. Since you've indicated an unwillingness to read the blog post I'll summarize briefly: A camera on the "light" side of JWST would need its own heat shielding and wouldn't show us any of the instruments. A camera on the "dark" side of JWST would need to function at temperatures close to absolute zero.…

There is no reason to use the camera while the telescope is telescoping. From what is being requested in this subthread it doesn’t even need to survive past the initial unfolding, just get a pic or two and be done with it.

I’ve read the article and I’m not criticising NASA’s decision. I’m just pointing out that a cam wouldn’t need to bring significant complexity, not in the insane context of this project.

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