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the james webb telescope


Hagbard Celine
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This thing is going to be awesome. And I'm not so much excited about the astronomy it's going to do (not to disparage that at all, it's just less my area of interest - it is going to teach us so much that Hubble couldn't, just due to having finer resolution), but I'm hugely excited by the space mission. The mission orbit L2 point is just effing badass. Getting there, then the hugely complex deployment, is an achievement that teaches a bunch for future missions elsewhere.

Details on the orbit, along with video.

https://webb.nasa.gov/content/about/orbit.html

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19 hours ago, Hagbard Celine said:

you should click the link *in the post just above yours*

There were lots of big words in that link.  But from what I gathered the Webb will actually orbit around L2, right? 

What I'm curious about it this: if you put a jelly bean at point L2 it will stay there in a stable relationship with the earth and the sun (or whatever 2 bodies).  How far away from that exact point can you put a jelly bean and still have it be in that stable spot?  I've heard of using the Lagrange points to store materials for future space stations.  So I'm thinking like a bundle of steel beams they insert into L2 and let it sit there until construction.  How precise do they have to place the materials so they don't drift away?  I'd guess the gravity of the object might be a factor, but I have no idea. 

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Dave Mohr

, 42 years working in and around NASA as a contractor,

Answered Aug 30, 2021 · Author has 1.1K answers and 2.6M answer views

With 344 “single points of failure”, what is the likelihood that the James Webb Telescope actually survives the trip to space and the deployment of all of its functions?

Hi Ian—As it happens, I got to participate in some of the earliest control system-structural interaction trade studies for James Webb. It had to do with a set of piezoelectric actuators that ‘flex’ to contour the mirror(s). That’s been a long time ago. I don’t even know if the sub-system that I helped conceived ‘made the cut’ to the actual flight vehicle.

I noticed you quoted 344 ‘single points of failure’. Frankly, I’m amazed that the number is that small. It may have been ‘massaged’ somewhat over the years to make it a bit less alarming……

On the other side of the argument, the telescope was built by Northrop Grumman—in particular the people that used to constitute the ‘TRW Space’ group. I’ve done a great deal of work for those people over the last 20 years or so. I know them very well.

The TRW Space people (or what is now Northrop Grumman Space) have a somewhat unique place in the history of the US space program. Some of our spacecraft (in particular some of the recon vehicles) have been larger that what will fit in the payload shroud of a launch vehicle. For this reason, these spacecraft have been built such that they ‘fold up’ for launch, and are ‘deployed’ after they reach orbit.

The quality of TRW’s engineering in this field was/is 2nd to NONE. In fact, as I think about it, I don’t believe that they ever had a failure that was related to a ‘deployable’ spacecraft ‘failing to deploy’.

I was a sub-contractor to them (for electrical power conversion systems) on a program called JIMO (‘Jupiter Icy Moons Orbiter’) that came about in the early 2000’s. This spacecraft was nuclear-powered, was ‘deployable’, and ‘deployed’ to a structure about the size of a football field (that’s not a mis-print!). I worked with the groups that decided how to ‘fold up’ the spacecraft (not because I know anything about ‘folding up’ a spacecraft. I don’t. But the power system had fluid lines and connections in it that had to traverse the parts that ‘folded up’). The experience and knowledge of those people was/is something that I can’t quite put into words.

All of that said, of course James Webb is risky. All space launches are. If you can’t accept and deal with a certain amount of risk, working in the space program is not something you’re likely to want to do. And, as the monetary value of the payload goes up, so does the risk. I only wish we were launching it on an American launch vehicle. Oh well…………

Thank you very much.

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On 12/17/2021 at 4:46 PM, miguelito said:

There were lots of big words in that link.  But from what I gathered the Webb will actually orbit around L2, right? 

What I'm curious about it this: if you put a jelly bean at point L2 it will stay there in a stable relationship with the earth and the sun (or whatever 2 bodies).  How far away from that exact point can you put a jelly bean and still have it be in that stable spot?  I've heard of using the Lagrange points to store materials for future space stations.  So I'm thinking like a bundle of steel beams they insert into L2 and let it sit there until construction.  How precise do they have to place the materials so they don't drift away?  I'd guess the gravity of the object might be a factor, but I have no idea. 

It probably is not that well-defined how big it is. Since L2 makes a stable equilibrium, if something gets pushed a little bit away from the exact point of L2, gravity will tend to pull the thing back. (That is what stable means.) So if your object is a little off center, then it is being pulled back in. For the unstable lagrange points, if your thing is a little off center, then gravity will tend to pull it farther away. So your things will not stay near the unstable lagrange point, but instead drift farther and farther away.

 

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I just knew I’d have some fellow space geeks here. I went to Northrop in 2018 to get a brief on this bad boy. And was able to see the testing and learn about it.  Super stoked for tomorrows launch. All of us are here in space weenie land are anxious and hoping it goes off.  Cheers 

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the ariane is a solid system

the decision to have the ariane be the esa contribution to the cost was made long before musk, and long before the delta IV heavy achieved it's record

the ariane has failed, on occasion

when the webb was only twice the cost of the launch system it didn't feel "risky" any moreso than any other high-profile launch

now that the device is 20 times more expensive than *the* launch system it does feel like just getting past maxQ is a big deal

but there are 130?+ other systems with one-and-done function that have to work on the way to L2 and at L2 so i will actually be surprised if this thing works as intended

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On 12/17/2021 at 4:46 PM, miguelito said:

There were lots of big words in that link.  But from what I gathered the Webb will actually orbit around L2, right? 

What I'm curious about it this: if you put a jelly bean at point L2 it will stay there in a stable relationship with the earth and the sun (or whatever 2 bodies).  How far away from that exact point can you put a jelly bean and still have it be in that stable spot?  I've heard of using the Lagrange points to store materials for future space stations.  So I'm thinking like a bundle of steel beams they insert into L2 and let it sit there until construction.  How precise do they have to place the materials so they don't drift away?  I'd guess the gravity of the object might be a factor, but I have no idea. 

The Lagrange points around celestial bodies is dependent upon the mass of the bodies. The L2 is roughly a million miles away on the far side of the earth in relation to the sun. A smaller body, such as Mars will have Lagrange points at different relative distances than the Earth, as gravity follows the inverse square law.. The properties of the L2 point from the Earth are that the Earth will act as a natural shield against solar radiation and heat, while also allowing for the radiative heat that needs to leave the James Webb in order for it to get down to operational temperatures. The five layers of heat shielding will further allow the instruments aboard to sink, thus costing less as far as necessary payload mass to cool the telescope to its nominal temperature. Idk how closely anyone else has followed this project through the years (decades) of development. I'm incredibly excited about this telescope finally going up and getting the data back that it will provide.

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