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Old 29th December 2021, 10:50 AM   #281
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Interesting that they have temperature data in both F and C, but not Kelvin, which would be the most useful.

Currently -153 C on the cold side, which is 120 K, if my math is correct. Seems that the heat shield is already working, even though it isn't even deployed yet.
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Old 29th December 2021, 10:54 AM   #282
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Quote:
After a successful launch of NASA’s James Webb Space Telescope Dec. 25, and completion of two mid-course correction maneuvers, the Webb team has analyzed its initial trajectory and determined the observatory should have enough propellant to allow support of science operations in orbit for significantly more than a 10-year science lifetime. (The minimum baseline for the mission is five years.)
Something told me they were lowballing it. This is great news though. But still a lot of things left to do before we pop the champange.
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Old 29th December 2021, 10:59 AM   #283
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Originally Posted by Puppycow View Post
Currently -153 C on the cold side, which is 120 K, if my math is correct. Seems that the heat shield is already working, even though it isn't even deployed yet.
-153 C isn't particularly cold for the dark side of an object in this region of space. Night time temperatures on the Moon can get colder than that.
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Old 29th December 2021, 11:05 AM   #284
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Originally Posted by RecoveringYuppy View Post
-153 C isn't particularly cold for the dark side of an object in this region of space. Night time temperatures on the Moon can get colder than that.
yes, but on a stellar body, heat can be transferred through other means than just radiation - James Webb can only cool itself via radiation.
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Old 29th December 2021, 11:12 AM   #285
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Originally Posted by The Great Zaganza View Post
yes, but on a stellar body, heat can be transferred through other means than just radiation - James Webb can only cool itself via radiation.
Huh? How many stars do you think there are near Earth? I only know of the one. And how do stars cool themselves besides radiation? I wouldn't think the solar wind is doing much of the cooling of the Sun.
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Old 29th December 2021, 11:30 AM   #286
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Originally Posted by RecoveringYuppy View Post
Huh? How many stars do you think there are near Earth? I only know of the one. And how do stars cool themselves besides radiation? I wouldn't think the solar wind is doing much of the cooling of the Sun.
any mass in space can transmit heat via thermal conduction, thermal convection and thermal radiation. Colder patches on the Moon (or relatively colder patches on the Sun) can act as heat sinks.
the Heat shield of James Webb, on the other hand, can only remove the heat of photon absorption via radiation. it does that by cleverly letting the infrared radiation reflect until it is bounced out at the side.
people say that space is cold, but it would be more accurate to say that it has no temperature.
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Old 29th December 2021, 11:56 AM   #287
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Still confused by what you are saying. I was talking about the night side of the Moon. There would be no convection there and conduction would be from other parts of the Moon which would make it a warming mechanism, not a cooling mechanism.

And what stellar object were you referring to?
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Old 29th December 2021, 12:47 PM   #288
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Deleted. Missed some posts.
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Old 29th December 2021, 01:12 PM   #289
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Originally Posted by RecoveringYuppy View Post
Still confused by what you are saying. I was talking about the night side of the Moon. There would be no convection there and conduction would be from other parts of the Moon which would make it a warming mechanism, not a cooling mechanism.

And what stellar object were you referring to?
only the top layer of the Moon gets exposed to photons (even the dark side is catching some) that heat is conducted deeper into the ground, which acts as a heat sink.
Webb can't do that.
therefore, your comparison of Moon and Webb was not appropriate.
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Old 29th December 2021, 01:29 PM   #290
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Originally Posted by The Great Zaganza View Post
only the top layer of the Moon gets exposed to photons (even the dark side is catching some) that heat is conducted deeper into the ground, which acts as a heat sink.
Webb can't do that.
therefore, your comparison of Moon and Webb was not appropriate.
Uh, no. The Moon's surface would be a heat source on the night side. And besides, my statement is true for astronauts floating in space and for the ISS. The cold side temperature of Webb right now is not unusual. It's not unusually cold for an object that isn't explicitly trying to be cold.
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Old 29th December 2021, 01:39 PM   #291
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Originally Posted by Puppycow View Post
Interesting that they have temperature data in both F and C, but not Kelvin, which would be the most useful.

Currently -153 C on the cold side, whicJWSTh is 120 K, if my math is correct. Seems that the heat shield is already working, even though it isn't even deployed yet.
Originally Posted by RecoveringYuppy View Post
-153 C isn't particularly cold for the dark side of an object in this region of space. Night time temperatures on the Moon can get colder than that.
Originally Posted by The Great Zaganza View Post
yes, but on a stellar body, heat can be transferred through other means than just radiation - James Webb can only cool itself via radiation.
It is expected that JWST will take many weeks too cool down to its operational temperature of 40K. The instruments must be cooled slowly to avoid outgassing, so they have begun cooling and will continue to do so throughout the telescope commissioning.

MIRI (Mid-Infrared Instrument) is the most sensitive to temperature of all the instruments on board, and it will take at least three months to reach its final operating temperature.
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Old 29th December 2021, 05:09 PM   #292
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The Deployable Tower Assembly (the structure that holds the mirrors and the instrument housing) has now been deployed. It has been extended "up" about two metres to give clearance for the sun shield to deploy.
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Old 29th December 2021, 05:20 PM   #293
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Looks like they used less fuel than they expected on the course correction burns, leaving more fuel and therefore a longer potential operations life.

https://blogs.nasa.gov/webb/2021/12/...-expectations/
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Old 29th December 2021, 05:31 PM   #294
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Originally Posted by slyjoe View Post
And NASA says the launch was very good and the corrections used much less propellant than expected, possibly giving the telescope a longer mission life.
The launch was unvelievably accurate:

Originally Posted by 3point14 View Post
There's nominal and then there's nominal.

https://i.redd.it/9uynjtjms2881.jpg
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Old 30th December 2021, 04:06 AM   #295
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Originally Posted by 3point14 View Post
There's nominal and then there's nominal.

https://i.redd.it/9uynjtjms2881.jpg
Jesus, I can't even hang wallpaper that accurately!!!
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Old 30th December 2021, 05:49 AM   #296
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Originally Posted by Puppycow View Post
https://www.youtube.com/watch?v=QeiQEG450gc

How James Webb's Deployments MUST Work (Launch Pad Astronomy)
That was really interesting, thanks.
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Old 30th December 2021, 12:12 PM   #297
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The Aft Momentum Flap has been deployed (this used to minimize the effect of solar pressure that would otherwise push the telescope out of its orbit)

The sun shield covers have been opened, so they are getting ready to extend, first the port then the starboard sun shield - nervous times!
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Old 30th December 2021, 12:21 PM   #298
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Originally Posted by 3point14 View Post
There's nominal and then there's nominal.

https://i.redd.it/9uynjtjms2881.jpg
Well it's not brain surgery.
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Old 30th December 2021, 12:37 PM   #299
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Originally Posted by wobs View Post
Well it's not brain surgery.
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That is a great skit.
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Old 30th December 2021, 01:46 PM   #300
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Originally Posted by smartcooky View Post
The sun shield covers have been opened, so they are getting ready to extend, first the port then the starboard sun shield - nervous times!
Port and starboard sound like terms ripe for confusion.
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Old 30th December 2021, 01:49 PM   #301
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NASA reports Webb has fuel for "decade-plus" of operation.

Quote:
NASA announced Wednesday morning, Webb may get to peer deep into the universe for even longer than expected: Webb used less of its limited supply of propellant during two course-correction thruster burns after launch than expected, and the space agency says it should have enough left over to enable operations “significantly” longer than the expected 10-year mission.

That’s particularly important for Webb, which will operate too far from Earth to be serviced or refueled like the aging Hubble telescope. If all continues to go well with Webb’s deployment and testing over the coming months, today’s fuel savings will mean several tomorrows’ stunning images of the most distant galaxies in our universe.
https://blogs.nasa.gov/webb/2021/12/...-expectations/
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Old 30th December 2021, 01:55 PM   #302
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Originally Posted by RecoveringYuppy View Post
Port and starboard sound like terms ripe for confusion.
Let's just hope it doesn't turn turtle.
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Old 30th December 2021, 10:09 PM   #303
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Originally Posted by RecoveringYuppy View Post
Port and starboard sound like terms ripe for confusion.
Little known fact. All distances will be computed in fathoms.
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Old 30th December 2021, 10:28 PM   #304
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Having thought about this for a bit. All the cables, pulleys, and assorted machines necessary to deploy the heat shield. Yeah, the nautical reference is entirely appropriate.
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Old 31st December 2021, 02:05 AM   #305
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Originally Posted by RecoveringYuppy View Post
Port and starboard sound like terms ripe for confusion.
Not at all.

Spacecraft have been using nautical terminology since the 1950s and 60s.

The rear bulkhead on the Apollo CM (the bulkhead at the blunt end) was referred to as the "aft bulkhead". The heat shield at that end was called the "aft heat shield", but what many people don't know is that there was also a heat shield at the pointy end called, of course, the "foreward heat shield" and the crew compartments were also referred to as "fore" and "aft"



Directions in Skylab were referred to as fore/aft/port/starboard/overhead/deck. So too was the Space Shuttle and so is the ISS



Why not use nomenclature that is already well understood?

By any measure you would like to name, the JWST is a spacecraft. The telescope mirror points "forward", so "port" is on the left, "starboard" is on the right. How simple is that?
.
.
.
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Old 31st December 2021, 02:06 AM   #306
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I prefer sherry.
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Old 31st December 2021, 02:09 AM   #307
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Originally Posted by The Great Zaganza View Post
I prefer sherry.
Philistine!
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Old 31st December 2021, 02:15 AM   #308
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I think the words should be adopted for vehicles of all sorts. Cars, for example.

Because left and right are relative directions, but port and starboard are always unambiguous.
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Old 31st December 2021, 07:44 AM   #309
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Originally Posted by smartcooky View Post
The telescope mirror points "forward", so "port" is on the left, "starboard" is on the right. How simple is that?
Which way is left and right? For that matter up and down/front and back aren't clear either. Port and starboard are defined by function on boats and boats have a well defined front and back. Not seeing either of those here. You've even defined "forward" in terms of thing that moves. What reference point that is asymmetric is actually being used here?

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Old 31st December 2021, 07:50 AM   #310
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As I recall Mad Magazine explaining it, first, "port" and "left" both have four letters, so port is left. Then starboard remains to be defined, so starboard is left.
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Old 31st December 2021, 08:04 AM   #311
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Originally Posted by RecoveringYuppy View Post
Which way is left and right? For that matter up and down/front and back aren't clear either. Port and starboard are defined by function on boats and boats have a well defined front and back. Not seeing either of those here. You've even defined "forward" in terms of thing that moves. What reference point that is asymmetric is actually being used here?
Which is port and which is starboard isprobably very well understood by those that need to know. Whatever term you choose is going to be based on an arbitrary choice on which side is which.
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Old 31st December 2021, 08:08 AM   #312
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Originally Posted by Puppycow View Post
Because left and right are relative directions, but port and starboard are always unambiguous.
Yeah. That's the problem but note that Smartcooky's post above defines starboard and port in terms of left and right.

There seems to be a lot of ambiguity to me, hopefully the controllers are using something unambiguous to define this. Something easier to keep straight than feet or meters, for example.

Even the assignment of the axe's seem ambiguous. I can see myself thinking of the telescope/bus asymmetry as either defining forward/backward (during travel in space), up/down (during launch), or left/right (during it's assembly).

And smartcooky used the direction the telescope is pointing to define forward. Doesn't that change during operation?

ETA: The last question I asked above prompted me to look in to JWST's pointing mechanism. Seems it has less pointing capability than I expected but I'm not sure I've found a good description yet.

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Old 31st December 2021, 01:09 PM   #313
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Originally Posted by RecoveringYuppy View Post
And smartcooky used the direction the telescope is pointing to define forward. Doesn't that change during operation?.
Nope. The telescope mirror, assembly remains fixed. The whole spacecraft is rotated to the direction it needs to be pointed using reaction wheels so fore, aft, port, starboard, overhead and deck remain the same regardless of where it is pointed (as it was for Apollo, Skylab, IRAS, Spitzer, and the shuttle orbiters, and as it still is for Chandra, , WFIRST, Hubble and the ISS)

ETA: Here is a great description, once again by Scott Manley, explaining the telescope pointing and its limitations. The link is time coded to the point you would be interested in here, but the whole 17 minute video is worth watching.

https://youtu.be/cp_7AJseYYc?t=377
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Old 31st December 2021, 01:39 PM   #314
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Sunshield deployment has just commenced.
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Old 31st December 2021, 01:45 PM   #315
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Thanks. I found most of what I was looking for at Wikipedia but Scott Manley is always good to watch and I'll check that out later. Much less pointing ability than I had thought and it looks to me like it there will be very limited opportunities to take really long exposures though I'm not sure that's really a problem for doing science since we expect the universe to be homogeneous.

https://en.wikipedia.org/wiki/Optical_Telescope_Element (and other related articles).
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Old 31st December 2021, 04:24 PM   #316
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Originally Posted by smartcooky View Post
Sunshield deployment has just commenced.
Where do you go to learn this? I'm watching the "Where is Webb" link at NASA, but it still says "Sunshield Cover Release" like it did yesterday. The cold side telemetry is finally starting to move down though. Is this because there's a partial shield deployment??
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Old 31st December 2021, 06:34 PM   #317
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Originally Posted by miatasport99 View Post
Where do you go to learn this? I'm watching the "Where is Webb" link at NASA, but it still says "Sunshield Cover Release" like it did yesterday. The cold side telemetry is finally starting to move down though. Is this because there's a partial shield deployment??

From the "Launchpad Astronomy" YouTube channel live updates

https://www.youtube.com/channel/UCNq...fqimqHkgbWMNYA

"Where is Webb" is only updated when the deployment has been completed. Currently, it says that the Port Sunshield Boom has deployed.
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Old 31st December 2021, 09:07 PM   #318
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The Starboard Sunshield Boom has deployed

All 107 "non-explosive" release devices associated with the sunshield deployment successfully released. The two mid-boom arms are locked in their final position, and over the next few days the the membranes will separate into the five layers and will be tensioned.
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Old 31st December 2021, 09:43 PM   #319
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Originally Posted by smartcooky View Post
The Starboard Sunshield Boom has deployed

All 107 "non-explosive" release devices associated with the sunshield deployment successfully released. The two mid-boom arms are locked in their final position, and over the next few days the the membranes will separate into the five layers and will be tensioned.
Yay!

That's a significant fraction of the mechanisms that needed to actuate properly, isn't it? I seem to recall there were something over 300 in total.

I'm starting to think this may actually work. Still a lot more things need to go right though.
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Old 31st December 2021, 11:51 PM   #320
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Originally Posted by Puppycow View Post
Yay!

That's a significant fraction of the mechanisms that needed to actuate properly, isn't it? I seem to recall there were something over 300 in total.

I'm starting to think this may actually work. Still a lot more things need to go right though.

Not quite that many. There are 178 of these types of "non-explosive actuators", and the sunshield has 140 of them, as well as 70 hinge assemblies, 400 pulleys, 90 cables and eight deployment motors, all of which have to work properly for the five layers to deploy as planned.

Other actuators were/are involved in the release of the solar array, the antenna, the fore and aft pallets, the mirror tower, the momentum flap, the secondary mirror support, the aft radiator, and the primary mirror "wings".




but there are many other "single point of failure" actions
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