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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

#111

Post by ultramegachurch »

BurningFrog wrote: post #105
ultramegachurch wrote: post #69

Earlier quoted context omitted.

I suspect the deployed structure cannot handle the acceleration required for escape velocity. That also may require much more propellant. Then on top of that, we don’t have the capability for humans to service satellites other than the ISS. So this is all a moot point.

We had the capability in 1993, and could of course develop it again. A broken JWT could wait a few years in orbit.

That may be true, but designing a mission based off that hypothetical is a bad idea. The reality is we currently don’t have the capability for humans to service satellites, and developing that capability would probably take years and cost >$100 million. And NASA can’t just decide to take on that endeavor, it would require congress and months of political bickering. JWST was designed for what is currently feasible and practical.

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

#112

Post by usrusr »

twistedpair wrote: post #99
eterm wrote: post #77

Earlier quoted context omitted.

How feasible is a repair mission without the shuttle?

L2 is very far from earth, well beyond the Moon. The Shuttle could never leave Low Earth Orbit, so it's a non-factor in repair missions once JWST is on station.

I believe what was GP was getting at is that even in a "convenience orbit", a repair mission would be very unlikely.

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

#113

Post by myself248 »

rrss wrote: post #51
mrtksn wrote: post #41

Earlier quoted context omitted.

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.

They did though. It was delayed, they chose to delay it from October to December 18 to December 22 to Christmas instead of like the first week of January or whatever. It’s not like this thing is launching to Mars and they’d have to wait a couple years if they miss this week - it could launch on 210 days of each year. https://jwst.nasa.gov/content/about/faqs/faq.html#launchWind... I don’t mind at all, I just think it’…

what's funny about it? You think there's anyone working on this project who isn't super excited to see it go up on Christmas?

No better gift than a successful launch. The folks working on preparations overnight surely see themselves as Santa's Elves in some fashion.

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

#114

Post by bendhoefs »

CyanBird wrote: post #71
Symmetry wrote: post #67

Earlier quoted context omitted.

It doesn't have enough fuel onboard to go from LEO to the Lagrange point itself.

It wouldn't need to, you could park it there a secondary liquid fuel booster attached, and then after the origami shenanigans if it unfolds correctly the second booster could send it away to its final position I saw some interviews of engineers of the jwst and few of them had similar ideas, or at least to assemble them in leo then slingshot them to their final positions/orbits

What booster would you use?

Another booster up in the fairing? That would need to be quite heavy. It would be a totally custom thing for this specific mission. You would need a suitable storable propellant.

Leave the booster from the Ariane attached? The lh2 and lox would boil off after a few days.

What do you do if the deployment fails? SpaceX's dragon can't do space-walks on its own, it doesn't have an airlock. There would be no way to fix it short of developing a whole new space craft for that task.

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

#115

Post by ufmace »

BurningFrog wrote: post #65

We're told that since JWT will travel very far away before it unfolds and activates all its systems, there is no practical way to service it if something would go wrong. Why can't it unfold etc in Earth orbit, where a repair mission can be sent if needed, and then travel to its Lagrange point?

Absent all of the other practical considerations, even in LEO, a repair mission would probably be so expensive that it would be cheaper to build and launch a new one instead.

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

#116

Post by GekkePrutser »

throw0101a wrote: post #60
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…

> 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? There is no room for redundancy in many aspects of the design, unlike, say a Boeing 777 or Airbus A350. How can you have a redundant heat shield, or primary mirror (two parts of which swing)? I'm sure some computer…

Does this have a heat shield? It won't re-enter right? It's far too far away for that.

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

#117

Post by GekkePrutser »

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…

Every kilo launched costs a proverbial and probably nearly literal tonne of fuel so things are not as simple as that.

It's also has to fit on the rocket hence the once off folding mechanism. And after deploying it has to be perfectly aligned (remember the Hubble with its slightly off mirror)

I think having redundancy for everything would just not make for a launchable spacecraft.

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

#118

Post by justin66 »

BurningFrog wrote: post #65

We're told that since JWT will travel very far away before it unfolds and activates all its systems, there is no practical way to service it if something would go wrong. Why can't it unfold etc in Earth orbit, where a repair mission can be sent if needed, and then travel to its Lagrange point?

> Why can't it unfold etc in Earth orbit, where a repair mission can be sent if needed, and then travel to its Lagrange point?

Another comment mentioned that it's not designed to accelerate while it's fully deployed, and that's true enough. You'd wreck it.

The other essential thing is that there's no way to give it and its instruments anything like their designed operating parameters (pretty hot on one side of the sunshade, something like 40 kelvin on the other side) in Earth orbit.

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

#119

Post by samwillis »

bendhoefs wrote: post #114
CyanBird wrote: post #71

Earlier quoted context omitted.

It wouldn't need to, you could park it there a secondary liquid fuel booster attached, and then after the origami shenanigans if it unfolds correctly the second booster could send it away to its final position I saw some interviews of engineers of the jwst and few of them had similar ideas, or at least to assemble them in leo then slingshot them to their final positions/orbits

What booster would you use? Another booster up in the fairing? That would need to be quite heavy. It would be a totally custom thing for this specific mission. You would need a suitable storable propellant. Leave the booster from the Ariane attached? The lh2 and lox would boil off after a few days. What do you do if the deployment fails? SpaceX's dragon can't do space-walks on its own, it doesn't have an airlock. The…

For space walk accessibility maybe they should have docked it to the ISS for initial setup before then boosting it to its final point?

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

#120

Post by BurningFrog »

ultramegachurch wrote: post #111
BurningFrog wrote: post #105

Earlier quoted context omitted.

We had the capability in 1993, and could of course develop it again. A broken JWT could wait a few years in orbit.

That may be true, but designing a mission based off that hypothetical is a bad idea. The reality is we currently don’t have the capability for humans to service satellites, and developing that capability would probably take years and cost >$100 million. And NASA can’t just decide to take on that endeavor, it would require congress and months of political bickering. JWST was designed for what is currently feasible and…

$100M is 1% of what JWST cost.

Looks like a reasonable repair cost (and only if) it turns out to be broken.

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