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James Webb is fully deployed

nasa.gov

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Re: James Webb is fully deployed

#171

Post by WalterBright »

mlyle wrote: post #164
WalterBright wrote: post #152

Earlier quoted context omitted.

I remember having manuals printed in the 1980s. The first manual cost $1000 to print, the second one $1. This was with camera-ready copy. Never mind all the cost of writing the manual, proofing it, and formatting it. When I worked at Boeing, the first forging of a part cost $250,000. The next, just a handful of dollars. At Boeing, the first airplane gets a ton of testing, as the design is being tested. Airplanes #2 a…

You still don't choose forging as a process to make quantity 2 (unless you absolutely need forged parts for strength). Instead, you're milling two parts from billet. Milling 2 parts from billet is cheaper per unit than milling 1 (some shared setup and programming costs), but it's the same amount of raw material and basically the same amount of operator time.

You're right that a one-off forging is so expensive that a hogout will be used instead. My point was how expensive one-offs can be compared to multiple ones, and I used extreme examples as illustrative.

Even in custom machine work, the cost is in the setup. A machinist can make two identical cuts on two parts for not much more cost than one cut on one part.

Re: James Webb is fully deployed

#172

Post by godelski »

sailingparrot wrote: post #102
WalterBright wrote: post #75

Since 90% of the cost is probably in R+D of the telescope, one could build and deploy another for another 10%. Why isn't this done? Why is every space telescope completely unique?

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…

Honestly that doesn't sound like much money. Especially since these projects aren't solely funded by one country, even if one foots most of the bill. Also, $1bn over it's lifetime is really cheap even just for the US alone.

Re: James Webb is fully deployed

#173

Post by nitrogen »

ascar wrote: post #148
ianai wrote: post #130

Earlier quoted context omitted.

Agree. A replica wouldn’t have to be sent to L2 for that matter. Pretty sure a lot of science could be done with even a slow trajectory leaving the solar system, if orbiting something else is infeasible.

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.

Re: James Webb is fully deployed

#175

Post by yongjik »

WalterBright wrote: post #155
henrydark wrote: post #138

Earlier quoted context omitted.

Reminds me of the line in Contact: "why build one when you can have two at twice the price?"

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 greenhouse effect), the seasonal changes on Mars (windblown dust) and the reddish haze of Titan (complex organic molecules).

> For his work, Dr. Sagan received the NASA Medals for Exceptional Scientific Achievement and for Distinguished Public Service twice, as well as the NASA Apollo Achievement Award.

https://www.planetary.org/profiles/carl-sagan

Re: James Webb is fully deployed

#176

Post by taftster »

dylan604 wrote: post #66
fotta wrote: post #13

Earlier quoted context omitted.

It'll take a few weeks after L2 insertion to cool the components and another 5 months to calibrate the instruments.

I'm hoping that the 5 months of calibration time is one of those where the engineers were asked "how long", so they thought about it and then padded the shit out of it, then the PMs took that number and padded it yet again. After all that, it only takes a few weeks. It'll be the first milestone JWST would meet early, so not too likely. We've only waited decades, so a few more months isn't that bad. At least it is off…

I can tell, you're an engineer. Of some variety.

Re: James Webb is fully deployed

#177

Post by rcxdude »

WalterBright wrote: post #72

What puzzles me is the maneuvering fuel. When that fuel runs out, the telescope can no longer orient itself. This ended the life of the Kepler telescope. But aren't there other ways to orient in space? 1. use pressure from the solar wind 2. have 3 electric motors on 3 axis. Wouldn't spinning those motors rotate the craft? Electric power to do it would come from solar panels, giving it plenty of fuel.

As far as I can tell it only really needs the fuel to maintain an L2 orbit, which is important because if it's too far away we can't really communicate with it effectively (i.e. actually download much of the data it's generating). For orientation it uses reaction wheels as you mention, and then there's a general plan to desaturate these momentum wheels by managing the average orientation of the telescope (it's effectively like an inverted pendulum: the solar wind will push it further away from having its back to the sun), but this might intefere with some observations so they may burn some fuel to maintain orientation in certain circumstances.

https://space.stackexchange.com/questions/35399/how-will-jws...

Kepler used a similar strategy (though I don't know what its desaturation strategy was): it only ran out of fuel very quickly after its reaction wheels failed.

Re: James Webb is fully deployed

#178

Post by MegaDeKay »

micromacrofoot wrote: post #16
elefanten wrote: post #10

For those not up on the project, what are some of the earliest novel types of information we expect to receive from it?

One of the more interesting things that we'll get is data about what's in the atmosphere of exoplanets https://jwst.nasa.gov/content/science/origins.html Note that the next 5 months or so will consist of mirror cooling and calibration, so nothing until summer.

Would you happen to know if they can make intermediate observations while this is in process e.g. observe a relatively nearby object before the telescope is fully cooled and aligned? I'm wondering if they would be able to prove out the optics early on - this is no slam dunk as the Hubble proved.

Re: James Webb is fully deployed

#179

Post by sailingparrot »

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…

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 need one with a specific set of IR capabilities.

Sure, having twice the imaging power is better, but it's definitely far from doubling the benefits. The lifetime of the JWST is expected to be 10+ years, that's a lot of data that will come to us already, and everything the astronomer community deems important will have time on the telescope.

Just like we only needed 1 LHC to confirm the existence of the Higgs boson and the robustness of the standard model. Building two of those would have been a massive waste of money, it was much better to build one, run experiments, assess the results and then use the money that was saved by building a single one to build new tools with new capabilities to answer the new questions.

Of course the reality of government budgeting is a little bit more complicated than my rosy picture but the point stands.

Re: James Webb is fully deployed

#180

Post by rcxdude »

WalterBright wrote: post #141
irdc wrote: post #135

Earlier quoted context omitted.

It worked for 9 years and 7 months, whilst being planned to operate for 3,5 years, so beyond it's expected lifetime then.

And it would have worked for longer if it didn't depend on the fuel! BTW, I doubt there's enough experience with space hardware to accurately predict it's life, especially since each machine is a one-off.

It would have lasted a lot longer if its reaction wheels hadn't failed. That was the main failure which shortened its remaining operation.
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