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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

#151

Post by onphonenow »

wslack wrote: post #82
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 suggest the book "Failure is not an option" by Gene Kranz, an Apollo flight director (played by Ed Harris in Apollo 13). He describes how the primary work of flight controllers in all missions is risk management. You are constantly balancing mission needs, fuel needs, mass needs, temperature needs, and etc etc. I don't think that a raw metric of the number of SPOF is the right way to measure the risk of this spacec…

What I don't understand is for $11 billion - can't we do 3 $3B space telescopes that work reasonably well? Spread risk? More science?

Let's say a Falcon 9 launch is $90M. Falcon heavy let's say $200M.

So you take your 3x $3B. Put $200M/instrument into launch, have $2.8B per telescope leftover.

There just seems to be something wrong that it costs THIS much to build a telescope.

That said, the Thirty Meter Telescope is also a sort of "forever" job, the delays have stretched on and on.

I wonder if you did something like bid out and paid just on performance instead of this forever cost reimbursement thing. Right now if you can get onto one of these mega projects, and can stretch it out with delays, it basically can cover your career (ie, 20 year projects).

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

#152

Post by desmosxxx »

rrss wrote: post #127
soperj wrote: post #96

Earlier quoted context omitted.

If you worked on something since 1996, do you think you would give two flying figs what day it launches on?

my personal preference is irrelevant. my comment was regarding whether it is tractable to plan around Christmas, or unreasonable because there are too many holidays of comparable significance.

Too many holidays might be a factor but I really doubt it's a large one. The bigger reason is you just don't delay a 20 year $10billion project for any holiday.

Some of the grunts might be disappointed but having worked on way less important things that were launched on holidays, I can guarantee anyone significantly involved in the project is just happy to see it get off the ground no matter what day. You have a good window for launch, you take it

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

#153

Post by krisoft »

GekkePrutser wrote: post #116
throw0101a wrote: post #60

Earlier quoted context omitted.

> 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.

Not the kind of heat shield you would use to re-enter.

The telescope is designed to image very faint sources of infrared light. The problem is that everything (including the telescope itself) glows in infrared. The hotter things are the more infrared they emit. Because of this you want to keep the instrument as cold as possible. (You do this because you don’t want to drown the faint sources by the glow of the telescope itself.)

Now of course there are parts which has to be “hot”. At least relatively to the very cold instruments. The solar panels are heated by the sun, the transmission electronics and the processing turns electricity into heat. The positioning thrusters burn chemicals which makes them hot.

Because of this they designed the spacecraft with two sides, a cold one for the instrument and a hot one for everything else. They even choose the orbit cleverly so they can keep the sun and the earth and the moon always on the hot side of the vehicle.

And then you have this problem that you have to make sure that the hot side won’t warm up your cold side. This is where the heat shield comes into play. Sometimes it is also called a sun shield since the sun is the main source of heat for it to shield against of course, but it also shields the instrument from the heat of the hot side equipments.

Structurally it is a 5 layer lassagne. They just replaced the pasta with metalized kapton tape and the sauce with the vacuum of space. It is about the size of a tennis court, launches folded up and will un-fold in space. Hopefully. :)

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

#155

Post by azalemeth »

onphonenow wrote: post #151
wslack wrote: post #82

Earlier quoted context omitted.

I suggest the book "Failure is not an option" by Gene Kranz, an Apollo flight director (played by Ed Harris in Apollo 13). He describes how the primary work of flight controllers in all missions is risk management. You are constantly balancing mission needs, fuel needs, mass needs, temperature needs, and etc etc. I don't think that a raw metric of the number of SPOF is the right way to measure the risk of this spacec…

What I don't understand is for $11 billion - can't we do 3 $3B space telescopes that work reasonably well? Spread risk? More science? Let's say a Falcon 9 launch is $90M. Falcon heavy let's say $200M. So you take your 3x $3B. Put $200M/instrument into launch, have $2.8B per telescope leftover. There just seems to be something wrong that it costs THIS much to build a telescope. That said, the Thirty Meter Telescope is…

I'd bet that the vast majority of that cost isn't going to be materials -- it'll be staff time to design and optimise the telescope and make something that can work, including where necessary how to make new materials or processes to make that telescope. I'm not saying the actual hardware is cheap by any stretch of the imagination, but making three different telescopes isn't a linear function of that budget. They're literally pushing the envelope of what's possible here. If something terrible happens to the rocket, lots of forms will be written and people will be sad but fundamentally I think they'll build something a bit better on a few years and nail it. A bit like New Horizons (awesome Mars rover) vs Beagle 2 (awesome Mars rover that died on arrival to Mars).

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

#156

Post by rtsil »

onphonenow wrote: post #151
wslack wrote: post #82

Earlier quoted context omitted.

I suggest the book "Failure is not an option" by Gene Kranz, an Apollo flight director (played by Ed Harris in Apollo 13). He describes how the primary work of flight controllers in all missions is risk management. You are constantly balancing mission needs, fuel needs, mass needs, temperature needs, and etc etc. I don't think that a raw metric of the number of SPOF is the right way to measure the risk of this spacec…

What I don't understand is for $11 billion - can't we do 3 $3B space telescopes that work reasonably well? Spread risk? More science? Let's say a Falcon 9 launch is $90M. Falcon heavy let's say $200M. So you take your 3x $3B. Put $200M/instrument into launch, have $2.8B per telescope leftover. There just seems to be something wrong that it costs THIS much to build a telescope. That said, the Thirty Meter Telescope is…

JWST was (re)launched in 2005, the very idea of cheap spaceflight didn't exist back then, so you'd have ended up with three expensive flights. Also consider that the expected cost back then was $4.5 billion.

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

#157

Post by mongol »

onphonenow wrote: post #151
wslack wrote: post #82

Earlier quoted context omitted.

I suggest the book "Failure is not an option" by Gene Kranz, an Apollo flight director (played by Ed Harris in Apollo 13). He describes how the primary work of flight controllers in all missions is risk management. You are constantly balancing mission needs, fuel needs, mass needs, temperature needs, and etc etc. I don't think that a raw metric of the number of SPOF is the right way to measure the risk of this spacec…

What I don't understand is for $11 billion - can't we do 3 $3B space telescopes that work reasonably well? Spread risk? More science? Let's say a Falcon 9 launch is $90M. Falcon heavy let's say $200M. So you take your 3x $3B. Put $200M/instrument into launch, have $2.8B per telescope leftover. There just seems to be something wrong that it costs THIS much to build a telescope. That said, the Thirty Meter Telescope is…

Perhaps that is what will happen from now on. But when JWST was initiated, the options looked different.

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

#158

Post by harshreality »

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 think all the SPOF talk is expectation management in case it fails. It's part space telescope mission, part engineering challenge. Even if the space telescope part fails, the engineering effort that's gone into it means something.

They must've calculated that the overall chance of success, and they have a target, and they met their target. Unfortunately, tests and theoretical modelling have a tendency to not exactly replicate a space environment (or any true production environment), nobody's perfect at anticipating everything, and management has ways of manipulating engineering estimates.

The Space Review [1] quotes NASA as saying there are 344 SPOF. They talk mainly about the sun shield, so that's probably the biggest risk, but consider all of them as about equal...

If each SPOF has a 0.1% chance of failure, net success rate is only 71%. Presumably most of the estimated failure probabilities are less than that, and the sun shield—which probably comprises many of the SPOFs—averages (far?) more than 0.1% per SPOF, because everyone seems to be particularly worried about that working.

I wonder what that figure is. Has it been published anywhere? Dear NASA and ESA, what do your engineers say about overall chance of failure?

[1] https://www.thespacereview.com/article/4303/1

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

#159

Post by alserio »

ultramegachurch wrote: post #69
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?

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.

What about an unmanned mission to fix it? And maybe to refuel it.

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

#160

Post by lamontcg »

onphonenow wrote: post #151
wslack wrote: post #82

Earlier quoted context omitted.

I suggest the book "Failure is not an option" by Gene Kranz, an Apollo flight director (played by Ed Harris in Apollo 13). He describes how the primary work of flight controllers in all missions is risk management. You are constantly balancing mission needs, fuel needs, mass needs, temperature needs, and etc etc. I don't think that a raw metric of the number of SPOF is the right way to measure the risk of this spacec…

What I don't understand is for $11 billion - can't we do 3 $3B space telescopes that work reasonably well? Spread risk? More science? Let's say a Falcon 9 launch is $90M. Falcon heavy let's say $200M. So you take your 3x $3B. Put $200M/instrument into launch, have $2.8B per telescope leftover. There just seems to be something wrong that it costs THIS much to build a telescope. That said, the Thirty Meter Telescope is…

JWST is driven by the size of the mirror, the need for an IR instrument and the temperature you need to keep the instrument at to do the observations. Spamming a bunch of hubble-sized instruments up into orbit won't accomplish the same thing. And I don't think you can do space VLBI in the optical/IR or it would have been done already (but I don't know why?).

It is kind of like asking why 5 Ford Rangers can't replace one Lamborghini or something.

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