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Another hitch with JWST


Swoop1
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just watched an explanation on YouTube which looked to be a honest appraisal of the event and situation. The key issue is that all the monitoring sensors were disconnected when the mounting clamp band deployed so the engineers don't have any hard data on how severe the bang was to the telescope main bus area.

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15 hours ago, tomato said:

Still aiming for a December launch, so I understand. A Christmas mission, just like Apollo 8.

Yeah, the 22nd I believe 🤞

Suppose they have to be 100% satisfied with it...once it's up they can't go and fix it 😬

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I guess the instrumentation on the receiving end of the scope is fairly tried and tested technology, as is putting it in the desired orbit, but having it all deploy and accurately align, that must be ground breaking stuff. Let's hope nothing get's stuck. 

I think on the website it is described as 30 days of terror.

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You never know about things like this......The kid in the middle of this 1970 image of our local astronomy club went on to become a project manager on the Webb telescope project.  Unfortunately he passed away from cancer before he got to see the WST get launched.  His name was William Whiddon.   Bill and I always had sort of a friendly competition for whoever had the largest and best telescope.......I guess Bill wins. (^8

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Edited by CCD-Freak
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I remember reading about this telescope back in secondary school, really looking forward to it actually being launched. However the thing I don't understand is why build a 13 billion dollar telescope that only has a 10 year lifespan? Surely some kind of automated mission to refuel it to keep it in position must be possible?  

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2 minutes ago, callisto said:

The Hubble was only give a 15 year lifespan...30 years later and still going 😃

I get that and expect it will last way longer but Hubble was serviced several times and why not just build it with maintenance for many decades to come factored in?   

Edited by AbsolutelyN
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27 minutes ago, AbsolutelyN said:

I get that and expect it will last way longer but Hubble was serviced several times and why not just build it with maintenance for many decades to come factored in?   

I recall the JWST will be in a very different location making getting there harder than the shuttle would ever manage.

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4 minutes ago, UKDiver said:

I recall the JWST will be in a very different location making getting there harder than the shuttle would ever manage.

Yes it’s about 1.5 million miles away. If it’s not possible to refuel via some kind of automated mission why not some kind of nuclear power source that will last multiple decades? I’m sure there is a good reason.

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41 minutes ago, AbsolutelyN said:

Yes it’s about 1.5 million miles away. If it’s not possible to refuel via some kind of automated mission why not some kind of nuclear power source that will last multiple decades? I’m sure there is a good reason.

 I understand it's the fuel and oxidant for the motors that's the issue, Hydrazine and N2O4 respectively. 

Yes, a A Nuclear power source  could have been fitted, but in its orbit around the Earth/Sun L2 point it would be easy to get a comparable amount of energy from Solar Panels, but it's the propellant that's the issue.

The key need is for something with enough momentum to provide adequate thrust, and although there are ion engines that don't need the same weight of propellant, I don't think we have ones yet that can provide the level of thrust needed to maintain station and control. 

Edited by Gfamily
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  • 2 weeks later...

I do love how we think we know better than hundreds of professional scientists working for years on end, on something that’s never been done before, and is not exactly easy!

There are engineering compromises all over the place I’m sure; actually getting it in a rocket for a start which drove the complex folding design. The L2 position was driven by the need to be in the shadow of the Earth for cooling purposes, and that means orbiting the L2 position whilst orbiting the sun, not just orbiting the sun. So, that needs fuel, which means a certain lifetime.

When the project started, all sorts of things were not possible, and possibly not even conceived yet so it’s hard to blame them for where we are now. Decisions on rocket type had to be made way before SpaceX was a thing I’m sure.

10 years is enough time for a huge amount of science, so the most important thing is just that it gets up there safely, and works correctly for its rated life at least 🤞🤞

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I’ve just read the Wikipedia article on JWST. A review in 2018 revealed 344 single-point failures, any one of which could doom the whole. Which means that if they are all independent, each one has to be reduced to an average 0.2% chance of failure (1 in 500) just to achieve a 50% chance of none of them failing.

Looked at another way, if each one has a 99% chance of success, 1 in 100 of failure, the chance of none of them failing reduces to a bit over 3%.

On that view, I have to say I’m more pessimistic 😟 . I sincerely hope they’ve mitigated them all 🤞.

Edited by Captain Magenta
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