James Webb is fully deployed • Hacker News Board

Re: James Webb is fully deployed

#191

Post by bumby » Sat, Jan 08, 2022, 10:39 PM UTC

WalterBright wrote: post #165

bumby wrote: post #146

Earlier quoted context omitted.

> Making two adds little cost. I think you are overextending your experience in a production environment here. I’ve worked in both, and the type of builds in these aerospace applications still have huge costs in subsequent runs. Hell, even rebuilding an existing component can be prohibitively expensive. Much of the GSE was likely existing so that’s probably a non-issue.

> huge costs in subsequent runs Often that's because they have to rebuild and reset the tooling. Within the run, though, the incremental cost should be minimal. The huge costs may be huge, but not huge compared to the cost of the prototype.

IMO your logic fits with large production runs.

In space applications costs can be exaggerated compared to actual production environments because the risks aren’t mitigated by something like the FAA, meaning they are often mitigated by some downstream process. Besides, a lot of the the designs already include critical spares, so there’s more than a single run, even in a one-off design

Re: James Webb is fully deployed

#192

Post by jl6 » Sat, Jan 08, 2022, 10:40 PM UTC

More great news. Congratulations to all who have worked on the project.

I understand the reasons for not putting a camera on or near the JWST, but I’m still a little sad that we’ll probably never get to see the thing in situ in all its operational glory.

Maybe one day when it finally expires, we can launch a “sample return” mission to tow it back.

Re: James Webb is fully deployed

#193

Post by thiagotomei » Sat, Jan 08, 2022, 10:40 PM UTC

sailingparrot wrote: post #179

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…

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…

A small nitpick: yes, we only needed 1 LHC to confirm the existence of the Higgs boson, BUT we made sure to have two experiments (ATLAS and CMS) looking for it. As far as I know, every modern high energy physics accelerator has had two (or more) sister experiments to cross-check each others!

Of course, it is not a perfect analogy, since the two experiments are not replicas. They try to address the same physics cases, but they were designed, built and are operated in a completely independent way.

Re: James Webb is fully deployed

#194

Post by WalterBright » Sat, Jan 08, 2022, 10:40 PM UTC

ramesh31 wrote: post #185

WalterBright wrote: post #119

Earlier quoted context omitted.

Assuming your figures are correct, you'll get double the data for another 30% cost. If you wait a month before launching #2, if problems appear in #1 (like the telescope mirror was ground improperly) it can be fixed in #2. The operational cost will not double. The same ground facility, equipment, and staff can manage both. If you're buying two identical launches, you can get a quantity discount. > the benefits of a s…

>I do have some experience with this. I worked for 3 years on the design of the 757. Thousands of engineers spending maybe 5 years on it. Just wanted to say that's really awesome. The 757 is by far my favorite Boeing jet of all time. They are so overpowered it feels like taking off in a fighter jet. Delta still flies them from LAX to HNL, and it's always so much better than cramming into a 737.

I am always pleased to be boarding a 757! I was sad when the front page of the Seattle Times showed one being cut up for scrap.

Re: James Webb is fully deployed

#195

Post by ThinkBeat » Sat, Jan 08, 2022, 10:41 PM UTC

It says it will arrive in 14 days or so at L2.

Right now, it is moving 0.3933km/s which according to Google is 1415.88km/h. That is pretty fast.

What speed does it need to be at for insertion and steady state? How long will it be breaking? (If at all, or of it is not already doing it).

Re: James Webb is fully deployed

#196

Post by davesque » Sat, Jan 08, 2022, 10:44 PM UTC

gitgrump wrote: post #121

davesque wrote: post #86

This feels perhaps like a silly comment, but I have this intuition that the data collected by JWST could prove to be some of the most important ever collected.

I keep telling people that, no matter what, we're going to learn something cool about the universe. I'm so excited to see these images. I mean, imagine humans 10,000 years ago, just surviving, maybe figuring out agriculture, and thinking about their place in the world. They looked up at the stars in wonder. Now, we've progressed to the point where we can polish gold down to the nanometer, and we're sending a giant hu…

I suppose I meant it felt silly in the sense that it would probably come across as seeming vague. And I may as well say a few more words. If I had anything specific in mind, it was the possibility that the JWST could find evidence of compounds in the atmospheres of distant planets that made it seem likely that there is life on those planets. Even if that doesn't happen, the fact that it feels like it's even on the table is amazing.

I'm also thinking back to when the Hubble came online and they started releasing the deep field images. And there was this moment where we all realized, "Wow, those things up in the sky that we all casually assumed were stars...many of them are actually galaxies. And all those black spaces in between are full of...more galaxies." Maybe astronomers already knew this; I don't know. But the average person didn't and it was hard to deny once we started seeing those images.

Not sure if it's justified, but I expect similar kinds of moments when the JWST starts collecting its first images.

Re: James Webb is fully deployed

#197

Post by baq » Sat, Jan 08, 2022, 10:44 PM UTC

ThinkBeat wrote: post #195

It says it will arrive in 14 days or so at L2. Right now, it is moving 0.3933km/s which according to Google is 1415.88km/h. That is pretty fast. What speed does it need to be at for insertion and steady state? How long will it be breaking? (If at all, or of it is not already doing it).

About 0. It’s climbing a hill and has just enough energy to get to the top. A small burn then will be all it takes to put it in an orbit around L2.

Re: James Webb is fully deployed

#198

Post by WalterBright » Sat, Jan 08, 2022, 10:45 PM UTC

yongjik wrote: post #175

WalterBright wrote: post #155

Earlier quoted context omitted.

Contact was written by a scientist who had no experience whatsoever in building things.

That doesn't sound right... > Carl Sagan played a leading role in the American space program since its inception. He was a consultant and adviser to NASA beginning in the 1950s, he briefed the Apollo astronauts before their flights to the Moon, and was an experimenter on the Mariner, Viking, Voyager, and Galileo expeditions to the planets. He helped solve the mysteries of the high temperature of Venus (a massive gree…

I've met Sagan (he came by our dorm for conversation and dinner with the students). He was a great man. He was wonderful to talk to. He has made great contributions to science. He deserves all the credit and accolades you mentioned.

But I doubt he ever set foot in a machine shop. Making things is an entirely different skill.

Re: James Webb is fully deployed

#199

Post by ascar » Sat, Jan 08, 2022, 10:46 PM UTC

nitrogen wrote: post #173

ascar wrote: post #148

Earlier quoted context omitted.

As I understood the engineering of the JWST requires it to be at L2 so it's in permanent shadow of the sun and can keep the very low temperatures necessary for good infrared image quality.

It has solar panels, so it can't be in shadow. IIUC the advantage of earth-sun L2 is it's away from the light and shadow of the earth and moon, while being reachable by radio year round.

I didn't check for sources again earlier, but this NASA article [1] explains it.

Yea shadow was the wrong word and doesn't actually apply because of the relative size of the sun and earth. However the L2 point is by definition in a straight line Sun -> Earth -> L2, so if the sun would be a single point light source that would block the sun and place the JWST in the permanent shadow thrown by the earth. The point is actually that the sunscreen is always facing earth and sun at the same time to block/reflect a maximum of heat.

[1] https://jwst.nasa.gov/content/about/orbit.html

Re: James Webb is fully deployed

#200

Post by lazide » Sat, Jan 08, 2022, 10:46 PM UTC

WalterBright wrote: post #123

lazide wrote: post #88

Earlier quoted context omitted.

When it takes so long to build, it’s already obsolete by the time it gets launched. If you made a new one every year, it wouldn’t be so bad of course, but a decade+? Oof. It was so bad they kept redesigning it mid way through to upgrade things as new discoveries were made, which caused even more delays.

> redesigning it mid way through And that doesn't have to be redone when making a copy.

Except it will because no one wants an exact copy, because if you do it at the same time that’s twice the rework, and if you do it later, you’re building something you know is obsolete. No one can resist throwing in some upgrades.