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James Webb Space Telescope

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James Webb Space Telescope

Old 01-08-22, 09:35 PM
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Re: James Webb Space Telescope

So what issues did they have earlier? I couldn't find any info on it.
Old 01-08-22, 10:14 PM
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Re: James Webb Space Telescope

Probably the biggest problem dealt with current draw from the solar array. I don't understand the nature of the problem or how it was resolved. I *think* it had to do with temperature differentials early in the deployments. Some things were hotter than expected. Other things were much colder, and they had to run some heaters at full, all of which put a strain on the solar array or battery charging. Really not sure though.

A star tracker suddenly reset itself. AIUI, later, that same one and another star tracker reset again. The observatory was in a sun pointing mode, so it didn't affect anything. There was thought it could have been because the moon was in the star tracker's sight. Or that cosmic rays corrupted memory. RAM on spacecraft can correct single bit errors, and can detect, but not correct multi-bit errors. In the case of a multi-bit error being detected, the response of many devices is to reset.

For all of the things that deploy, there are microswitches that indicate whether that mechanism is deployed. Some of the switches still indicate stowed, even though they are deployed. The engineers on the ground know these things are deployed from secondary effects -- attitude disturbances and temperature changes.

Some of the temperature sensors seem to occasionally drop-out, giving an erroneous value. The sensors may be bad or there may be something else going on. Under investigation.

Last edited by Kevin Phillips; 01-08-22 at 11:00 PM.
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Old 01-08-22, 10:56 PM
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Re: James Webb Space Telescope

Originally Posted by Sdallnct View Post
That’s awesome….was reading that thing is traveling at 900 MPH……I realize their is no friction in space, but still hard to wrap my head around the fact it can do all those delicate movements while traveling 900 MPH.
You've bumped into Special Relativity. It's going 900 mph in reference to what? The Earth? The Sun? The galactic core? The nominal center of our local cluster? On top of that, its local environment is the solar wind, which goes one million miles per hour, so relative to that it's barely moving at all! It's traveling different speeds depending where you measure from. But from the perspective of the telescope, none of that matters. It can be treated as if it were standing still.

Then there cosmic rays, which are moving at almost the speed of light. They are going so fast that they punch right through the thing, sometimes altering a random bit in the programming.

Things get weird in space.

Last edited by Nick Danger; 01-08-22 at 11:02 PM.
Old 01-09-22, 05:48 PM
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Re: James Webb Space Telescope

Originally Posted by Sdallnct View Post
Just saw they r revising that. Evidently launch was so “perfect” they have had to do very little course corrections. Meaning more fuel for science. So should be well over 10 years
Or 20...

On Friday, NASA mission systems engineer Mike Menzel shared that thanks to the accuracy of the telescope's launch and deployment, Webb should have enough propellant, roughly speaking, to operate “around 20 years.” After that, JWST will likely run out of fuel and slowly drift off course.
Old 01-14-22, 07:23 PM
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Re: James Webb Space Telescope

It's been about a week, so I thought I'd post an update.

They're currently moving the mirrors from their stowed/launch position to be close to their expected final position. It's a slow and meticulous process. There are six motors behind each mirror for aiming/pointing. They move all of the mirrors' motors a little bit, check the results, move them a little bit, check the results, lather, rinse, repeat... (Before anyone says, "but I heard there are seven motors"... Yes, there is a seventh motor. The seventh motor is is for altering the mirror's radius of curvature and doesn't have anywhere near the range of motion of the other motors).

The mirror moves got a late start because of fun with the star tracker (see post #77). So... once the flight operations team were done with the deployments last week, they put the observatory into what is called a "normal" attitude mode. That mode uses the star tracker. Shortly after going into normal mode, the star tracker indicated a fault and the entire observatory was put into safe mode. It took about a full day to recover after that. After talking with the star tracker manufacturer, their (the manufacturer's) opinion is the fault was relatively innocuous and going into safe was not necessary.
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Old 01-18-22, 12:46 AM
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Re: James Webb Space Telescope

I wonder if they had to wait on hold for 3 hours just to talk to "John" with a thick Indian accent who was clearly just reading off of a script to deal with their setup issue.
Old 01-20-22, 08:43 AM
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Re: James Webb Space Telescope



All of the vendors are proud to have their hardware on JWST. So I'm sure that when JWST calls, they'll do whatever they can to help.

They have finished moving all of the mirrors from their launch position. That is a total movement of about 12mm per motor. The first eight or so days was moving 16 of the primary mirrors and the secondary mirror into position. The last few days was moving the two remaining primary mirrors. Those two were done separately because they each have a motor with a flaky position sensor. The bad sensors were known before launch. I'm sure they decided to launch as-is because replacing the sensors wasn't realistic; it would be risking a lot more problems than solving. The motors are working fine; the sensors just provide a level of verification.

Something silly that people say: The mirror motors move slower than grass grows. Yeah, their AVERAGE speed is slow, because they spend the bulk of their time NOT MOVING. It's like driving a car for 1-mile at 60mph, letting it sit for a week, and saying the car's average speed is slower than grass growing. In theory, the mirror motors *can* be driven super-slowly - but they don't do that, because it would be a stupid waste of time.

Right now, they're doing calibration of the HGA (high-gain antenna). Science instrument power-on will be next week.

EDIT: Correction, NIRSpec, one of the four science instruments, will be powered-on tonight.

Last edited by Kevin Phillips; 01-20-22 at 02:51 PM.
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Old 01-20-22, 11:03 PM
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Re: James Webb Space Telescope

The speed at which the mirror motors move on such a highly sensitive and precise instrument is a very odd thing to comment on. It's like why is that neurosurgeon cutting out that brain tumor so slowly.
Old 01-21-22, 07:03 AM
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Re: James Webb Space Telescope

Its the false dramatics of "The mirror motors move slower than grass grows!" and annoys me because its not true. I think Including idle time when calculating the average speed of a motor is misleading. Anyway I'm running the risk of making more of this than I meant to; it's really just a peeve.
Old 01-21-22, 01:48 PM
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Re: James Webb Space Telescope

I assumed that it was a stepping motor that clicked once an hour (or whatever) because the mirrors had to be moved gently.
Old 01-22-22, 09:01 AM
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Re: James Webb Space Telescope

Motor moves are very short -- each move is less than ten seconds. The motors' slowest speed is about 1.5 steps/second. I *think* they run the motors at around 100+ steps/second. There are two types of motor moves: coarse and fine. Coarse moves, which is what they were doing last week, are about 4,000x larger than fine motor moves.

Thursday night, a few hours after I posted, the platform went into safe-haven again -- an automatic protective measure when the onboard computers detect a problem. They're investigating and are also executing steps to bring it back to a normal operating configuration. Since they're coming up on MCC-2 (Mid-course correction #2), they'll probably delay all instruments' power-on.
Old 01-24-22, 02:37 PM
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Re: James Webb Space Telescope

They just finished MCC #2. The burn results still have to be checked, but assuming everything went as planned JWST is now at L2.
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Old 01-28-22, 05:52 PM
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Re: James Webb Space Telescope

All of the science instruments are powered-on. Three of them are initialized; the fourth is on hold while some data is being checked. I think the next few days is Solar Torquer checkout. After that...? I think they're going to start mirror commissioning.
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Old 01-29-22, 03:19 PM
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Re: James Webb Space Telescope

I keep reading we could get “first images” soon with a huge warning that that will be very blurry images. And these blurry images will help focus the mirrors that will take a while.

Old 01-30-22, 07:29 AM
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Re: James Webb Space Telescope

When they moved the mirrors from their launch/stowed position, they moved them to positions a little bit away from their expected final position. Since each mirror is off center, they will be reflecting what they see onto a different part of the instrument's detectors. So when they point the telescope to at a single bright object (star or galaxy), what the detectors will see is 18 separate versions of the object scattered on its field of view -- one instance from each mirror. The objects will be faint, because each one is only 1/18 of the light gathering capability of the telescope. Using that, the scientists can determine each mirror's actual position (versus expected). Then they can start centering them. They'll move them into center and back out and center them again a couple of times. That process will probably start very soon.

I didn't mention in my last post they did two the first two images using MIRI on Friday. I think the first one was a just a test pattern, so not a real image. The 2nd set was "darks", where you don't have anything bright in the field-of-view. Also, its detectors were still very warm relative to their final temperature, so it will look overexposed.

Until yesterday, they had been using heaters to keep the science-instruments' detectors from getting too cold. This was for a couple of reasons. First, there was water vapor and other possible contaminants outgassing. By keeping the detectors warm relative to the rest of the satellite, any water vapor or contaminants will condense on the colder parts of the satellite, where it won't hurt anything. In post #69, tanman had a blurb about the programmable ASICs. They're used on three of the instruments. Although the ASICs can run at very cold temperatures, they have to be powered-on and initialized while still relatively warm, and that's what they were doing on Thursday and Friday. The other instrument, MIRI, doesn't use ASICs; it's detectors are going to be actively cooled to something like 6-8K (can't remember the actual number), and the ASICs won't operate that cold.

Yesterday, they finished initializing the last science instrument. And since all of the science instruments were up and running, they turned off the heaters on the detectors, allowing them to start cooling to their final temperatures. Sometime around next weekend, they should be at, or close, to their temperature. Once they get there, low-power "trim" heaters will be used to keep the detector temperatures steady.



Last edited by Kevin Phillips; 01-30-22 at 09:59 AM.
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Old 01-30-22, 10:22 PM
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Re: James Webb Space Telescope

Originally Posted by Kevin Phillips View Post
When they moved the mirrors from their launch/stowed position, they moved them to positions a little bit away from their expected final position. Since each mirror is off center, they will be reflecting what they see onto a different part of the instrument's detectors. So when they point the telescope to at a single bright object (star or galaxy), what the detectors will see is 18 separate versions of the object scattered on its field of view -- one instance from each mirror. The objects will be faint, because each one is only 1/18 of the light gathering capability of the telescope. Using that, the scientists can determine each mirror's actual position (versus expected). Then they can start centering them. They'll move them into center and back out and center them again a couple of times. That process will probably start very soon.

I didn't mention in my last post they did two the first two images using MIRI on Friday. I think the first one was a just a test pattern, so not a real image. The 2nd set was "darks", where you don't have anything bright in the field-of-view. Also, its detectors were still very warm relative to their final temperature, so it will look overexposed.

Until yesterday, they had been using heaters to keep the science-instruments' detectors from getting too cold. This was for a couple of reasons. First, there was water vapor and other possible contaminants outgassing. By keeping the detectors warm relative to the rest of the satellite, any water vapor or contaminants will condense on the colder parts of the satellite, where it won't hurt anything. In post #69, tanman had a blurb about the programmable ASICs. They're used on three of the instruments. Although the ASICs can run at very cold temperatures, they have to be powered-on and initialized while still relatively warm, and that's what they were doing on Thursday and Friday. The other instrument, MIRI, doesn't use ASICs; it's detectors are going to be actively cooled to something like 6-8K (can't remember the actual number), and the ASICs won't operate that cold.

Yesterday, they finished initializing the last science instrument. And since all of the science instruments were up and running, they turned off the heaters on the detectors, allowing them to start cooling to their final temperatures. Sometime around next weekend, they should be at, or close, to their temperature. Once they get there, low-power "trim" heaters will be used to keep the detector temperatures steady.
Interesting. With terrestrial based astro cameras, a hot detector results in more noise, rather than overexposure. I'm not familiar with the particular detectors on the JWST, so I'm wondering why overexposure would be the result?

So the JWST will be collimated by ensuring a particular point of light is at the same area on the sensor, from each mirror? (Is it still called collimation with multiple mirror segments?) How do they ignore data from the other mirrors, while checking one? Intentionally cripple all the others by misaligning them?

What is your role, at this point?

This is really getting exciting!
Old 01-30-22, 10:39 PM
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Re: James Webb Space Telescope

Originally Posted by andicus View Post
Interesting. With terrestrial based astro cameras, a hot detector results in more noise, rather than overexposure. I'm not familiar with the particular detectors on the JWST, so I'm wondering why overexposure would be the result?
I was trying to make it more understandable, and probably phrased it badly (I have a pure CompSci background, with no astronomy or engineering, and only 1st year physics in college), so I am probably not always explaining/understanding correctly. When warm, the vast majority of the pixel readout values are close to their max values, even with short integration times.

How the scientists know how to align the mirrors is beyond me

My role? Now that JWST has launched, I'm just an ops monkey, working shifts, monitoring my subsystem's telemetry in case something goes out of whack.

Last edited by Kevin Phillips; 01-30-22 at 11:20 PM.
Old 01-30-22, 11:42 PM
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Re: James Webb Space Telescope

Originally Posted by Kevin Phillips View Post
I was trying to make it more understandable, and probably phrased it badly (I have a pure CompSci background, with no astronomy or engineering, and only 1st year physics in college), so I am probably not always explaining/understanding correctly. When warm, the vast majority of the pixel readout values are close to their max values, even with short integration times.

How the scientists know how to align the mirrors is beyond me

My role? Now that JWST has launched, I'm just an ops monkey, working shifts, monitoring my subsystem's telemetry in case something goes out of whack.
Damn! That's my background, but I don't get to work on the scope. I only know what I know about it because from my astrophotography is a hobby of mine.

I know you said you'd rather move onto another project, at this point, but it's still got to be cool to be involved, and I know we at DVDT appreciate the insight and updates.
Old 01-31-22, 11:44 PM
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Re: James Webb Space Telescope

Originally Posted by Kevin Phillips View Post
My role? Now that JWST has launched, I'm just an ops monkey, working shifts, monitoring my subsystem's telemetry in case something goes out of whack.
That's interesting. So in a typical day is that really exciting or really boring? What's your shift like? Seems like a really boring aspect of a really exciting mission if that makes sense.

Originally Posted by andicus View Post
Damn! That's my background, but I don't get to work on the scope. I only know what I know about it because from my astrophotography is a hobby of mine.

I know you said you'd rather move onto another project, at this point, but it's still got to be cool to be involved, and I know we at DVDT appreciate the insight and updates.
That's cool. I've been interested in astrophotography but haven't really dived in. I've taken pics of the solar eclipse a few years back and a mercury solar transit by hobbling together a welder's lens taped onto my cheap kit zoom lens. (this was before I made custom solar lens caps for the eclipse).

What kind of equipment do you have? What's a good place for a newbie to start to learn?
Old 02-01-22, 01:35 AM
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Re: James Webb Space Telescope

Originally Posted by tanman View Post
That's interesting. So in a typical day is that really exciting or really boring? What's your shift like? Seems like a really boring aspect of a really exciting mission if that makes sense.
I am doing the 2nd of four graveyard shifts this week. It is very, very boring. The only thing going on right now is monitoring temperatures as the detectors cool. I record temperature and electrical values in a spreadsheet and make a couple of shift-log entries.

Tomorrow may be more interesting, as they may start doing exposures for real for mirror commissioning. But even then, I will just be watching the observations happen.
Old 02-01-22, 05:27 AM
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Re: James Webb Space Telescope

Originally Posted by Kevin Phillips View Post
I am doing the 2nd of four graveyard shifts this week. It is very, very boring. The only thing going on right now is monitoring temperatures as the detectors cool. I record temperature and electrical values in a spreadsheet and make a couple of shift-log entries.

Tomorrow may be more interesting, as they may start doing exposures for real for mirror commissioning. But even then, I will just be watching the observations happen.
Wow, so it is that boring. That's funny because it seems like something like that could be automated. Can you at least work from home? Seems like the ideal shift to work from home on. Like if everything hit the fan could you be called upon to do something about it? Or answer questions or something like that? Or is it really just watching numbers on a screen and transferring that to a spreadsheet?
Old 02-01-22, 02:43 PM
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Re: James Webb Space Telescope

Yeah, some of the work can be automated. But I think the point of it is that it is make-work, to give us something to do and "keep us engaged."

I could do everything remotely -- as long as nothing goes wrong. However, the remote interface is slow and borders on being illegible. It also tends to get bogged down when a lot of people are using it. So we always have to have people on site in case something does go wrong.
Old 02-01-22, 03:32 PM
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Re: James Webb Space Telescope

Originally Posted by Kevin Phillips View Post
Yeah, some of the work can be automated. But I think the point of it is that it is make-work, to give us something to do and "keep us engaged."

I could do everything remotely -- as long as nothing goes wrong. However, the remote interface is slow and borders on being illegible. It also tends to get bogged down when a lot of people are using it. So we always have to have people on site in case something does go wrong.
I've done that. I worked every Thanksgiving for years so I could monitor the equipment. But I could save product if something went wrong. Could you save anything from a million miles away?
Old 02-01-22, 04:56 PM
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Re: James Webb Space Telescope

Originally Posted by tanman View Post
That's interesting. So in a typical day is that really exciting or really boring? What's your shift like? Seems like a really boring aspect of a really exciting mission if that makes sense.



That's cool. I've been interested in astrophotography but haven't really dived in. I've taken pics of the solar eclipse a few years back and a mercury solar transit by hobbling together a welder's lens taped onto my cheap kit zoom lens. (this was before I made custom solar lens caps for the eclipse).

What kind of equipment do you have? What's a good place for a newbie to start to learn?
Off topic:
Spoiler:
It's a fun, but often frustrating hobby. Like the 'golf ruins a nice walk' idea, astrophotography can ruin an evening with a scope. There's just so much that can go wrong, as opposed to just looking through a scope.

Regardless, as I said, it is fun. I currently have an 8" Celestron Edge HD scope. That's on my list to upgrade, though that's only because I want something a bit bigger (with more light gathering power). It's mounted on a Paramount MYT, which is a fantastic piece of hardware, but quite expensive (currently $7295 US). I use a Canon 7dMkII DSLR for imaging, though I'm also considering moving to a dedicated astro camera. I also have a Pegasus Astro stepper motor focuser, so I can do all my imaging remotely from the warm/mosquito-less/skunkless house.

It's very difficult to recommend equipment for someone new to the hobby, but I would suggest reading threads on Cloudynights.com. There are also many helpful folks on the site. There are a ton of discussions on equipment for just about any level, as well as a lot of imaging threads, so you can get an idea of what sort of images you can expect to acquire with the equipment you're considering. This is very helpful to set realistic expectations. There is so much to consider, like do you want to do solar or planetary imaging, or deep space objects? Different equipment is better suited for different needs.

The most difficult thing to start into the hobby, is that you don't want something so cheap that you're just frustrated with it, but you also don't want to dive in with expensive equipment, on the off chance that you decide it's not for you.

My equipment is pretty much my third iteration, and it really is night and day from what I have now, to either of my other setups. The second setup still wasn't cheap (scope and mount are currently slightly over $3k US), but it was unreliable. Knowing what I know, now, I would've bought my current setup instead of my 2nd one.

Having said that, you can (and should) start out with something much cheaper, unless you have a lot of spare cash.





Old 02-01-22, 05:32 PM
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Re: James Webb Space Telescope

The first pictures the JWST will take is a sun like star that resides in the big dipper.


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