James Webb Telescope

So, if I get this right, they launched it knowing the actuators in two (I think) of the mirrors weren't working properly, but they had a workaround and it would have been too time consuming to switch them out?
 
3point14 said:
So, if I get this right, they launched it knowing the actuators in two (I think) of the mirrors weren't working properly, but they had a workaround and it would have been too time consuming to switch them out?
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Not sure what you mean. Two of the actuator assemblies are of a different design (A3 and A6).
 
slyjoe said:
Not sure what you mean. Two of the actuator assemblies are of a different design (A3 and A6).
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Nope. 3point14 has it right. A3 and A6 are the same design as the other segments, but they have a fault which means their data has to be read differently

Warning 4.4mb pdf

https://authors.library.caltech.edu/91565/1/1069808.pdf

Section 1.2 Describes the operation
Section 2:4:2 Para 2 Describes the problem.

Essentially, there are a couple of defective linear variable differential transformers (LVDT) on the position sensors of mirror segments A3 and A6. Each LVDT has two coils to cancel out differential thermal effects. On A3 and A6, one of the two coils on each LVDT is faulty.

The engineers had to work out a way of getting accurate readouts using only one coil in each LVDT. So they developed a different readout procedure that could use only the one good coil in each LVDT."

Even though this was discovered back in 2018, it would have put a huge delay on the whole mission because the mirror would have to be disassembled to get the the components to be replaced (remember in 2018 they were very close to what they thought was their launch date).
 
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Wow. Here I had thought it was a design choice or design constraint. I guess they determined that it wasn't a mission-critical problem and could be worked around. I hope they're right.
 
Puppycow said:
Wow. Here I had thought it was a design choice or design constraint. I guess they determined that it wasn't a mission-critical problem and could be worked around. I hope they're right.
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I thought the same thing; I hadn't heard there were actually issues with the actuators.

And thanks for the post smartcooky.
 
smartcooky said:
Nope. 3point14 has it right. A3 and A6 are the same design as the other segments, but they have a fault which means their data has to be read differently

Warning 4.4mb pdf

https://authors.library.caltech.edu/91565/1/1069808.pdf

Section 1.2 Describes the operation
Section 2:4:2 Para 2 Describes the problem.

Essentially, there are a couple of defective linear variable differential transformers (LVDT) on the position sensors of mirror segments A3 and A6. Each LVDT has two coils to cancel out differential thermal effects. On A3 and A6, one of the two coils on each LVDT is faulty.

The engineers had to work out a way of getting accurate readouts using only one coil in each LVDT. So they developed a different readout procedure that could use only the one good coil in each LVDT."

Even though this was discovered back in 2018, it would have put a huge delay on the whole mission because the mirror would have to be disassembled to get the the components to be replaced (remember in 2018 they were very close to what they thought was their launch date).
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Thank you :)
 
Two days to MCC2; mid-course correction 2 - the insertion burn.

Webb has just passed 97% of the distance to its final destination.

Primary mirror temperature -209°C
Instrument radiator -202°C
 
Puppycow said:
https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html?units=metric

99.7% there. The remaining distance is less than the distance from New York to London, or from Auckland to Perth.

I hope those NASA engineers remembered to wax their slide rules!
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Ziggurat said:
Is that a euphemism? ;)
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More of an anachronism, I think. I still have a lovely bamboo one. It's self lubricating and runs so smooth. I'd go to exams with two of them, the bamboo for most things and a plastic one for scales it didn't have.
 
JWST has arrived at L2, the orbital insertion burn was successfully completed, the telescope is in its halo orbit, ready a to align the mirrors and finish cooling down to operating temperature. All going well, it will be reading in six months time to start doing some science.:wave1
 
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My gf asks, Why 6 months? I explained patiently that the astronomers have to go out to the parking lot and duke to see who gets viewing time.

She thought I was joking, of course. Women!
 
I think the actual answer is because NASA wants to play with their new toy first, before handing it over to the astronomers. (I'm only half joking.) ;)

But they did say, if memory serves, six months before we get science images. Not necessarily six months before it is fully operational.
 
Puppycow said:
I think the actual answer is because NASA wants to play with their new toy first, before handing it over to the astronomers. (I'm only half joking.) ;)

But they did say, if memory serves, six months before we get science images. Not necessarily six months before it is fully operational.
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Please don't **** on NASA with this crap. First access to data and first publication rights are well understood and properly agreed by the funding agencies well ahead of time.
 
theprestige said:
Please don't **** on NASA with this crap. First access to data and first publication rights are well understood and properly agreed by the funding agencies well ahead of time.
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A slightly more serious possibility is that six months is a conservative estimate, which leaves room for the working out of unanticipated issues that might come up. If such issues do not materialize and everything goes smoothly, maybe it will be ready before six months.

E.g., like how it turned out that they actually have enough fuel for significantly more than 10 years of service. They lowballed the estimate on the theory that if there are going to be any surprises, it would be nice if they are on the up-side rather than the down-side.
 
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