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James Webb Space Telescope emerges successfully from final thermal vacuum test

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Re: James Webb Space Telescope emerges successfully from final thermal vacuum test

#111

Post by ethbro »

petschge wrote: post #44
sandworm101 wrote: post #28

Earlier quoted context omitted.

Hubble's cost structure is complicated. It is essentially a modified spy satellite and so much of its development costs were shrouded. We don't know how much was saved, or how much of Hubble's public budget was used on other projects. JWST is different. It is a unique object with no equivalent. Its cost structure is therefore not comparable to Hubble. (Or I am wrong. Maybe JWST is a modified version of a super-secret…

Part of the cost of Hubble was that the teams working on the keyhole satellites was not allowed to tell the Hubble designers about "lessons learned" and the Hubble team had to find them out the hard way.

Any links or references? Sounds like a fascinating backstory.

Re: James Webb Space Telescope emerges successfully from final thermal vacuum test

#112

Post by TrueDuality »

nn3 wrote: post #62
afpx wrote: post #14

Earlier quoted context omitted.

That's a bit cynical. There are many examples of NASA missions that had far exceeded the original expectations.

Let's assume expectations scale with budget. The original cost estimate was $0.5B [1]. Now it's roughly at $10B. So there was a 20x cost increase. So if we assume original expectations it would need to exceed original expectations by 20x just to make up for the cost growth. Of course we also need to consider all the other NASA telescopes that didn't get funded to feed this one. They all would likely have exceeded exp…

You're conflating expected value with investment cost.

Your argument has the same merit as "I need a car to get to a this new job which will cost $1000 and I'll make $100k more." If instead you purchase a car costing you $10k that doesn't mean it's no longer worth taking the job.

This project has advanced our ability to build complex devices, and refined various manufacturing processes that will all have meaningful impacts on our economy and that is before it has started it's mission. The data it will collect is potentially invaluable not to mention the personal inspiration that projects like these inspire in individuals.

Compare this to other ways that our government might have actually spent this $10B over the lifetime of this project and we're still getting a bargain.

Compared to other NASA projects we likely wouldn't have gotten the manufacturing processes or complex integration experience and even more likely we wouldn't have gotten the inspiration. Bigger and more expensive projects are expensive because they're hard. When we succeed in doing hard things and even make the same thing easier in the future we collectively absolutely get more value.

Re: James Webb Space Telescope emerges successfully from final thermal vacuum test

#113

Post by TremendousJudge »

NikolaeVarius wrote: post #69
rakoo wrote: post #56

Earlier quoted context omitted.

Minor nitpick, but the L2 point is selected so it doesn't need fuel to stay there. It's like a gravity well of the earth/sun system, any object getting a little further from it will get back to it.

They need to use fuel to station keep, there is a hard time limit to this.mission

Is it known how long it would last? Wikipedia doesn't say anything about this issue

Re: James Webb Space Telescope emerges successfully from final thermal vacuum test

#114

Post by the_jeremy »

btkramer9 wrote: post #101
AWildC182 wrote: post #66

Earlier quoted context omitted.

That's really weird... I made more than that as a jr engineer doing imaging satellite flight software. Most of us are over 100k in the Denver area.

Can you name companies?

I can! Denver: Northrop Grumman, Level 1 software engineer, 75k. Denver: Northrop Grumman, level 2 SWE, 82k. I talked to lots of colleagues at my level while there and they were all within 3k of those numbers at those levels.

Re: James Webb Space Telescope emerges successfully from final thermal vacuum test

#115

Post by gootdude »

TremendousJudge wrote: post #113
NikolaeVarius wrote: post #69

Earlier quoted context omitted.

They need to use fuel to station keep, there is a hard time limit to this.mission

Is it known how long it would last? Wikipedia doesn't say anything about this issue

The mission is minimum of 5 years with maximum 10 years based on the fuel.

https://jwst.nasa.gov/faq.html#howlong

Re: James Webb Space Telescope emerges successfully from final thermal vacuum test

#116

Post by snowwrestler »

ziotom78 wrote: post #89
CydeWeys wrote: post #75

Earlier quoted context omitted.

L2 is unstable. There are stable Lagrange points that would be much better for this purpose if that was the reason. The unique thing about L2 is that it's the only Lagrange point where the Sun is always blocked by the Earth. That's what they're going for here.

Not entirely true. Spacecrafts orbiting L2 do not stay still with respect to the Earth; rather, they follow a Lissajous orbit, which is quite efficient given the gravitational properties of the L2 point. Therefore, they will observe the Sun quite often. (The apparent size of the Sun from L2 is roughly the same as Earth's, so eclipsing the Sun would be too complicated.) And this is not bad, because otherwise solar pan…

The spacecraft would also keep the same distance from the Earth during the year in Earth orbit, so there has to be another reason they picked L2.

The real reason for L2 is that the sun, moon, and Earth are all the same direction from the telescope when it is at L2, so the sunshield can block them all simultaneously. Yes, the spacecraft will receive insolation at L2 (yay solar power), but it will always be from the same direction and therefore the instrument can be persistently shielded.

EDIT: from the the horse's mouth:

> To have the sunshield be effective protection (it gives the telescope the equivalent of SPF one million sunscreen) against the light and heat of the Sun/Earth/Moon, these bodies all have to be located in the same direction.

> This is why the telescope will be out at the second Lagrange point.

https://jwst.nasa.gov/orbit.html

Re: James Webb Space Telescope emerges successfully from final thermal vacuum test

#117

Post by HeadsUpHigh »

petschge wrote: post #95
Gravityloss wrote: post #94

Earlier quoted context omitted.

You can retire risk and accelerate progress by launching more smaller missions and accepting that some of them fail. The public must be enlightened enough to understand that occasional failure ia a much faster and better and even cheaper path to success.

The science done by a bunch of smaller IR telescope is different from what you can do with JWST. (Basically you are reducing resolution but get better time coverage of transients.)

You can combine multiple mirrors like they did with the black hole photo.

Re: James Webb Space Telescope emerges successfully from final thermal vacuum test

#118

Post by anchpop »

sigstoat wrote: post #104
afpx wrote: post #14

Earlier quoted context omitted.

That's a bit cynical. There are many examples of NASA missions that had far exceeded the original expectations.

> There are many examples of NASA missions that had far exceeded the original expectations. many of those concocted by NASA announcing artificially low public expectations, while ensuring the contractors know what the real (much higher) expectations are.

Citation?

Re: James Webb Space Telescope emerges successfully from final thermal vacuum test

#119

Post by tomr_stargazer »

HeadsUpHigh wrote: post #117
petschge wrote: post #95

Earlier quoted context omitted.

The science done by a bunch of smaller IR telescope is different from what you can do with JWST. (Basically you are reducing resolution but get better time coverage of transients.)

You can combine multiple mirrors like they did with the black hole photo.

In this case, the black hole image was created with radio interferometry, in which you can separately record electromagnetic waves from individual radio telescopes and then combine them electronically after-the-fact. Visible and infrared interferometry is much more technically challenging because the frequencies are orders of magnitude too high to record in the same way, and so it hasn't really been successfully applied in space. (See the Space Interferometry Mission[0] for one sort-of attempt at this kind of thing.)

[0] https://en.wikipedia.org/wiki/Space_Interferometry_Mission#I...

Re: James Webb Space Telescope emerges successfully from final thermal vacuum test

#120

Post by petschge »

HeadsUpHigh wrote: post #117
petschge wrote: post #95

Earlier quoted context omitted.

The science done by a bunch of smaller IR telescope is different from what you can do with JWST. (Basically you are reducing resolution but get better time coverage of transients.)

You can combine multiple mirrors like they did with the black hole photo.

This requires keeping the baseline constant to a fraction of the wave length. In other words you would have to position the satellites with a accuracy of 100 nm relative to each other. In other words: No we can not (, yet. For a decade at least).
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