James Webb Telescope

[JoeMorgue]

NASA reports Webb has fuel for "decade-plus" of operation.

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...l-likely-to-extend-its-lifetime-expectations/

 

[Matthew Best]

Port and starboard sound like terms ripe for confusion.

Let's just hope it doesn't turn turtle.

 

[Fidelio]

Port and starboard sound like terms ripe for confusion.

Little known fact. All distances will be computed in fathoms.

 

[Fidelio]

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.

 

[smartcooky]

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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[The Great Zaganza]

I prefer sherry.

 

[smartcooky]

I prefer sherry.

Philistine!

 

[Puppycow]

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.

 

[RecoveringYuppy]

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?

 

[shemp]

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.

 

[3point14]

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.

 

[RecoveringYuppy]

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.

 

[smartcooky]

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

 

[smartcooky]

Sunshield deployment has just commenced.

 

[RecoveringYuppy]

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).

 

[miatasport99]

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??

 

[smartcooky]

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/UCNqNkZ7kKfqimqHkgbWMNYA

"Where is Webb" is only updated when the deployment has been completed. Currently, it says that the Port Sunshield Boom has deployed.

 

[smartcooky]

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.

 

[Puppycow]

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.

 

[smartcooky]

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