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Webb flies Ariane 5: watch the launch live on 25 December

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Re: Webb flies Ariane 5: watch the launch live on 25 December

#41

Post by mrtksn »

rrss wrote: post #34
daenney wrote: post #27

Earlier quoted context omitted.

“They” didn’t find anything. It wasn’t originally planned for tomorrow. The weather found a way. There’s only so much wiggle room and launch windows.

> It wasn’t originally planned for tomorrow Right, it was originally planned for 2007. It is sorta funny that after 14 years of delays they picked the week of Christmas.

They didn’t pick that either, it was supposed to launch earlier but a clamp broke down when attaching the telescope to the rocket sending vibrations all over it and and as a result they had to inspect for damages, further delaying the launch. Then the weather wasn’t good and delayed once more.

Re: Webb flies Ariane 5: watch the launch live on 25 December

#42

Post by dimtion »

I do have a question about JWST that I wasn't able to find a fine answer in other forums.

A lot of people and engineers are saying that the JWST is a marvel of engineering, with truly inovative technical solutions and a giant step up compared to Hubble Telescope. And it does seems like so!

However, I'm always baffled how everyone seems proud that the telescope has something like 200 SPOF during deployment, and if even one of them fails the whole mission could fail.

I know that each step has probably been throughoutly tested, and that the acceptable probability of failure of each one of those steps has been deemed acceptable. But I'm still surprised that people are proudly conflating excellent engineering with a design that has a large number of spofs.

In my domain this would be considered as a terrible design (aka "hope is not a strategy"), even given the constraints of mass and volume that such project incur: 200 hundred low probability events, chained, can get in the realm of possible.

I can't imagine JSWT team doing "bad engineering", so I'm sure I'm missing a piece. Is it only PR that underline this aspect? Is JWST as brittle as the news want to make us think? Or are there technical reasons or acceptable failure modes that gives confidence that those steps are not as critical as the news let us people know?

Re: Webb flies Ariane 5: watch the launch live on 25 December

#44

Post by rrss »

jacquesm wrote: post #37
foobarian wrote: post #3

Decades of meticulous planning and they couldn't give their teams a day off on Christmas? Of course it could be that consensus was this beats any other kind of activity that day in which case fair enough. :-)

If you start planning your rocket launches around religious holidays then that is going to be a bit of a problem, there are just too many of them: https://nationaltoday.com/religious-holidays/

How about planning around the single most celebrated holiday in the US, religious or not: https://en.m.wikipedia.org/wiki/Public_holidays_in_the_Unite...

Re: Webb flies Ariane 5: watch the launch live on 25 December

#46

Post by darknavi »

dimtion wrote: post #42

I do have a question about JWST that I wasn't able to find a fine answer in other forums. A lot of people and engineers are saying that the JWST is a marvel of engineering, with truly inovative technical solutions and a giant step up compared to Hubble Telescope. And it does seems like so! However, I'm always baffled how everyone seems proud that the telescope has something like 200 SPOF during deployment, and if eve…

> However, I'm always baffled how everyone seems proud that the telescope has something like 200 SPOF during deployment, and if even one of them fails the whole mission could fail.

I'm not sure I've seen anyone who is _proud_ of it, lots of people are just setting expectations. Probably due to the similarities with Hubble (although JWST can self-align it's mirrors!).

It also might be posturing to show how well the thing is built. Space is hard, like really hard, and these agencies keep knocking it out of the park.

Re: Webb flies Ariane 5: watch the launch live on 25 December

#47

Post by jpgvm »

ajross wrote: post #30
mortenjorck wrote: post #21

Earlier quoted context omitted.

True, though it’s also worth considering that Webb is going far beyond “orbit“ as we generally think of it. I don’t know how much has been launched all the way out to L2 before, but it’s probably an order of magnitude less than what’s in Earth orbit.

Meh, but there's nothing to hit in space. The energy required to reach a routine geosynchronous orbit is already ~85% of escape velocity. The added boost is minimally more dangerous and the trip is just empty hours. "Time" does kill spacecraft, but not often. The Webb self-assembly is absolutely where the scary bits lurk.

Yeah valid. Though the whole "hurtling upwards on top of a bomb" part is still definitely scary in it's own right.

Re: Webb flies Ariane 5: watch the launch live on 25 December

#48

Post by nharada »

dimtion wrote: post #42

I do have a question about JWST that I wasn't able to find a fine answer in other forums. A lot of people and engineers are saying that the JWST is a marvel of engineering, with truly inovative technical solutions and a giant step up compared to Hubble Telescope. And it does seems like so! However, I'm always baffled how everyone seems proud that the telescope has something like 200 SPOF during deployment, and if eve…

I'm guessing it's a case where all the various extreme requirements simply do not allow for redundancy in the places the engineers would prefer to have it. The options are likely (1) okay performance with a lower chance of failure or (2) extreme performance with a higher chance of failure.

Re: Webb flies Ariane 5: watch the launch live on 25 December

#50

Post by jacquesm »

rrss wrote: post #44
jacquesm wrote: post #37

Earlier quoted context omitted.

If you start planning your rocket launches around religious holidays then that is going to be a bit of a problem, there are just too many of them: https://nationaltoday.com/religious-holidays/

How about planning around the single most celebrated holiday in the US, religious or not: https://en.m.wikipedia.org/wiki/Public_holidays_in_the_Unite...

Ariane 5 is a European effort, not a US effort, it will launch from French Guyana, not from the US.

https://en.wikipedia.org/wiki/Ariane_5

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