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Old 12-31-2021, 09:46 AM   #21
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Old 12-31-2021, 10:19 AM   #22
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If you want to better understand where this telescope is headed (like I did) I posted a video with a fantastic explanation the science thread:


I just hope they don’t zoom in on Pluto. Nothing to see here…
Thats fascinating. To think that scientists and mathematicians were coming up with these theories and models hundreds of years ago absolutely blows my mind.
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Old 01-04-2022, 04:01 AM   #23
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The Webb team has completed tensioning for the first three layers of the observatory’s kite-shaped sunshield, 47 feet across and 70 feet long.

The first layer – pulled fully taut into its final configuration – was completed mid-afternoon.

The team began the second layer at 4:09 pm EST today, and the process took 74 minutes. The third layer began at 5:48 pm EST, and the process took 71 minutes. In all, the tensioning process from the first steps this morning until the third layer achieved tension took just over five and a half hours.

These three layers are the ones closest to the Sun. Tensioning of the final two layers is planned for tomorrow.

“The membrane tensioning phase of sunshield deployment is especially challenging because there are complex interactions between the structures, the tensioning mechanisms, the cables and the membranes,” said James Cooper, NASA’s Webb sunshield manager, based at Goddard Space Flight Center. “This was the hardest part to test on the ground, so it feels awesome to have everything go so well today. The Northrop and NASA team is doing great work, and we look forward to tensioning the remaining layers.”
https://blogs.nasa.gov/webb/

So far so good for 3/5 of the sunshield tensioning processes....
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Old 01-04-2022, 06:57 AM   #24
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Man, working through that must have been....tense.
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Old 01-04-2022, 08:57 AM   #25
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The finally added the ability to toggle Time or Distance on the Where is Webb page - drove me bonkers before.
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Old 01-04-2022, 09:29 AM   #26
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Difference between hot and cold side is stunning. Looks like they are gradually slowing down the craft I assume to minimize gravitational force as much as possible.
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Old 01-04-2022, 09:33 AM   #27
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Difference between hot and cold side is stunning. Looks like they are gradually slowing down the craft I assume to minimize gravitational force as much as possible.
I am pretty sure it has been, and will be, gradually slowing down since they completed the last burn.

You don’t want to burn there, then burn to stop. You calculate the burn to get you there with gravity stopping you as much as possible at the destination.
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Old 01-04-2022, 09:35 AM   #28
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You calculate the burn to get you there with gravity stopping you as much as possible at the destination.
Gravity from what?
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Old 01-04-2022, 09:40 AM   #29
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Gravity from what?
Even once in L2 it will be experiencing slight pull from earth and the sun. More from those bodies before reaching L2
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Old 01-04-2022, 10:02 AM   #30
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Gravity from what?
You aren’t free from gravity in space.

L2 is a “stable” point where things can remain in a constant relative position to the earth and Sun.

So the gravity from the Sun and the earth is what holds it there.

Though it’s more like a ball at the top of a hill - move a little too far to the side, and gravity will pull you away.
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Old 01-04-2022, 10:21 AM   #31
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Gravity from what?
The Sun and the Earth at L2 are pulling the object back toward it.

The satellite is moving perpendicular to the sun and the earth.

The Lagrange 2 point is such that the gravitation pull from the earth and the sun match the centrifugal force of the satellite. Since these forces are equal the satellite stays put.

What is unique about the Lagrange points is that the angular velocity required to create the matching centrifugal force matches the angular velocity of the earth so that the gravitational pull of the sun and earth remains constant throughout the orbit.
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Old 01-04-2022, 10:26 AM   #32
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Gravity from what?
There is no point where the earths gravity stops. everything that has ever been on earth will continue to accelerate towards earth, it's just something might gain an equal or greater acceleration in different directions.

I believe that L2 the basically put it in an orbit around the sun that would normally be unsustainable, but the earths gravity pulls it along.

So JWST will forever be accelerating towards the sun at 274 m/s2 and towards earth at 9.81 m/s2 and will have an angular momentum just a little bit faster than earths. Right now the Sun and the Earth are still slowing it down, the goal is it's go the exact speed and momentum as it falls into that pocket that those 3 numbers balance out, and keep it basically at a fixed distance from earth with a fixed speed around the sun, sans fuel.
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Old 01-04-2022, 10:37 AM   #33
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There is no point where the earths gravity stops. everything that has ever been on earth will continue to accelerate towards earth, it's just something might gain an equal or greater acceleration in different directions.

I believe that L2 the basically put it in an orbit around the sun that would normally be unsustainable, but the earths gravity pulls it along.

So JWST will forever be accelerating towards the sun at 274 m/s2 and towards earth at 9.81 m/s2 and will have an angular momentum just a little bit faster than earths. Right now the Sun and the Earth are still slowing it down, the goal is it's go the exact speed and momentum as it falls into that pocket that those 3 numbers balance out, and keep it basically at a fixed distance from earth with a fixed speed around the sun, sans fuel.
You've got those numbers wrong. Acceleration due to gravity on the surface of the Earth is 9.81, but gravity is calculated g = G*M/R^2, where R is distance between objects. So it decreases the further from Earth you are. It is nowhere near 9.81 for JWST, but you could do the math easily.
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Old 01-04-2022, 10:42 AM   #34
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I'm out of my depth but quick math says there is not nearly enough gravitational pull to slow the spacecraft before it reaches destination.
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Old 01-04-2022, 10:45 AM   #35
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I'm out of my depth but quick math says there is not nearly enough gravitational pull to slow the spacecraft before it reaches destination.
It’s not slowing to zero, if that’s what you based your calculation on.
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Old 01-04-2022, 10:50 AM   #36
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That video I posted explains a bit about keeping the telescope in L2. Every now and then, the telescope will need to do a burn to correct it's positioning within L2 orbit. That's why it has a defined lifespan, as it only has enough fuel to self correct it's positioning for 10 years or so.
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Old 01-04-2022, 10:50 AM   #37
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I'm out of my depth but quick math says there is not nearly enough gravitational pull to slow the spacecraft before it reaches destination.
Maybe it would be better to understand what you think is happening.

They burn to eject earth orbit (which doesn’t mean it doesn’t feel the effects of earths gravity), with enough steam to carry the to their location (with correction burns factored in). It’s part of what takes so long. They can’t cruise there burnin the whole way and then burn retro to stop (the telescope can’t turn around, that would take a ton of extra fuel, also would likely need addition front facing boosters to complete, etc…). They utilize as much gravity slowing as they can.
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Old 01-04-2022, 11:02 AM   #38
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That video I posted explains a bit about keeping the telescope in L2. Every now and then, the telescope will need to do a burn to correct it's positioning within L2 orbit. That's why it has a defined lifespan, as it only has enough fuel to self correct it's positioning for 10 years or so.
They have already announced that they saved a bunch of fuel from burns that have already happened, so they should have enough fuel for longer than 10 years.
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Old 01-04-2022, 11:10 AM   #39
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Old 01-04-2022, 11:37 AM   #40
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Difference between hot and cold side is stunning.
Meh, McDonalds already perfected this technology with the McDLT back in the 1990s.
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