James Webb Space Telescope News

[lexluthermiester]

What part of the orbit do you mean? The path of L2 around the Sun specifically? The L2 point can catch slower dust particles from comets etc. in a temporary orbit but it doesn't necessarily reduce their speed relative to JWST, and it affects faster ones even less, so I don't see how if could reduce the danger of something hitting the telescope at high speed.

There is nowhere in the solar system that is immune to risk of impact. However, L2's favorable gravimetric qualities make it very much less prone to such impact risks, which ends up being a Win/Win location for the JWT.

 

[Wirko]

There is nowhere in the solar system that is immune to risk of impact. However, L2's favorable gravimetric qualities make it very much less prone to such impact risks, which ends up being a Win/Win location for the JWT.

That's what I'm trying to understand. What are those gravimetric qualities that matter here?

A planet has cleared its neighbourhood around its orbit of smaller bodies, and that's part of the definition of a planet. As Wikipedia describes, a large body will tend to cause small bodies either to accrete with it, or to be disturbed to another orbit, or to be captured either as a satellite or into a resonant orbit. L1, L2 and L3 do not have the ability to do that ... or do they? Or does the orbit-clearing effect of the Earth extend to L2?

 

[lexluthermiester]

What are those gravimetric qualities that matter here?

It's a place where gravity is in a careful balance that will allow the JWT to just "hover" in orbit with little or no adjustment needed. The region surrounding the L2 has gravity pulling in a way that has the effect of deflecting objects and debris away from the area. Other Lagrange points in orbit share similar characteristics but lack the benefit of being in the shadow of the Earth most of the time. L2 is an ideal location for the JWT.

Or does the orbit-clearing effect of the Earth extend to L2?

It's actually much more complicated, but yes, that is the general effect.

 

[Wirko]

It's a place where gravity is in a careful balance that will allow the JWT to just "hover" in orbit with little or no adjustment needed. The region surrounding the L2 has gravity pulling in a way that has the effect of deflecting objects and debris away from the area. Other Lagrange points in orbit share similar characteristics but lack the benefit of being in the shadow of the Earth most of the time. L2 is an ideal location for the JWT.

It's actually much more complicated, but yes, that is the general effect.

Thanks!

A small correction, though - the JWST won't be anywhere close to Earth's shadow, its orbit around the L2 will be giant compared to the size of Earth. I found some nice drawings at Stack Exchange.

 

[lexluthermiester]

Thanks!

A small correction, though - the JWST won't be anywhere close to Earth's shadow, its orbit around the L2 will be giant compared to the size of Earth. I found some nice drawings at Stack Exchange.

Maybe I misread an article. Thought I read somewhere that the shadow of earth would be a factor of the cooling effect of JWT...

Yup, I misunderstood.

Orbit - NASA Science

webb.nasa.gov

 

[ARF]

The cruising speed is decreasing, it will eventually get there but very slowly.
Now less than 0.5 km/s and declines.

Where Is Webb? NASA/Webb

 

[Wirko]

I find it funny that the space vessel has a port side and a starboard side (these terms were used in the description of deployment of sunshield). Does an average Joe from UK or USA, with no experience in navigation, know what they mean?

 

[WonkoTheSaneUK]

At 16:20 Central European Time today, the boom supporting the secondary mirror will begin unfolding.

https://twitter.com/i/web/status/1478729739137425413

 

[ARF]

The temperature difference between the cold and the warm side can be used to generate electricity Naturally and for free

That's how the Peltier element works
Thermoelectric generator - Wikipedia
A thermoelectric generator (TEG), also called a Seebeck generator, is a solid state device that converts heat flux (temperature differences) directly into electrical energy through a phenomenon called the Seebeck effect [1](a form of thermoelectric effect). Thermoelectric generators function like heat engines, but are less bulky and have no moving parts. However, TEGs are typically more expensive and less efficient.[2]

Thermoelectric generators could be used in power plants to convert waste heat into additional electrical power and in automobiles as automotive thermoelectric generators (ATGs) to increase fuel efficiency. Radioisotope thermoelectric generators use radioisotopes to generate the required heat difference to power space probes.[2]

Orbit - Webb/NASA

 

[Wirko]

The temperature difference between the cold and the warm side can be used to generate electricity Naturally and for free

The cold side of the Peltier element would become warm. The infrared telescope would be not amused.

 

[ARF]

The cold side of the Peltier element would become warm. The infrared telescope would be not amused.

Very weak argument for a so expensive, innovative piece of equipment.
It is like saying that we can't build cars running on hydrogen, because we cannot produce hydrogen safely lol

 

[lexluthermiester]

I find it funny that the space vessel has a port side and a starboard side (these terms were used in the description of deployment of sunshield). Does an average Joe from UK or USA, with no experience in navigation, know what they mean?

When looking "forward", port is to the left and starboard is to the right.

Why do ships use 'port' and 'starboard' instead of 'left' and 'right?'

Unlike left and right, port and starboard refer to fixed locations on a vessel.

oceanservice.noaa.gov

Very weak argument for a so expensive, innovative piece of equipment.
It is like saying that we can't build cars running on hydrogen, because we cannot produce hydrogen safely lol

You are missing some context. There are thermal limits to how effective a Peltier type thermo-electric circuit will be. At the extreme low temps that are needed by the JWT, such a system would introduce heat to an area that needs an absence of heat.

Folks, John made a very informative video.

 

[Bones]

Very weak argument for a so expensive, innovative piece of equipment.
It is like saying that we can't build cars running on hydrogen, because we cannot produce hydrogen safely lol

With this I guess we blow up a few people a week, maybe a few buildings/facilities a year to get them made because the tech is just "So New" it's worth it.
That's gonna work out really well..... Not.

But hey - At least we're making hydrogen (Bombs?).

You are missing some context. There are thermal limits to how effective a Peltier type thermo-electric circuit will be. At the extreme low temps that are needed by the JWT, such a system would introduce heat to an area that needs an absence of heat.

This means the entire purpose of the craft is diminished to the point of it's findings are not reliable or even useful, defeating the entire purpose of why it even exists or was launched if heat is introduced to that arrea of it.
If it's not gonna work that way, it's not gonna work that way.

It requires a very cold region around these instruments to operate as designed and intended to.

 

[Space Lynx]

Since there is no resistance in outer space, can someone please explain to me why the JWST keeps slowing down? every day it seems to be getting slower? is that an active device on the JWST slowing it down for its orbit insertion in 10 days or so, so it doesn't overshoot it?

 

[the54thvoid]

Gravity. It's still being affected by that of the Earth and the Sun. Orbits keep things mostly stable but in a linear path there is no (as such) centrifugal pull. And yes, centrifugal isn't the right term but it describes what I mean.

 

[ARF]

You are missing some context. There are thermal limits to how effective a Peltier type thermo-electric circuit will be. At the extreme low temps that are needed by the JWT, such a system would introduce heat to an area that needs an absence of heat.

The introduced heat will be very negligible and it can be isolated from the instruments that need to work at close to 0K.
I am quite sure that you are not a specialist in the area, nor it has been attempted.

Since there is no resistance in outer space, can someone please explain to me why the JWST keeps slowing down? every day it seems to be getting slower? is that an active device on the JWST slowing it down for its orbit insertion in 10 days or so, so it doesn't overshoot it?

There should be at least partial resistance since it isn't perfect vacuum, and also the telescope itself is so large that it introduces resistance.

 

[the54thvoid]

There should be at least partial resistance since it isn't perfect vacuum, and also the telescope itself is so large that it introduces resistance.

Found this to explain.

Photons Are a Drag

Any object in motion feels a bit of friction as it moves through the sea of radiation that is constantly emitted by its surroundings.

physics.aps.org

Their calculations show that a lone object in motion experiences friction. It comes from the sea of real photons emitted by everything around it. Night vision goggles prove that any warm body emits infrared light, but even frigid intergalactic space is awash in microwave photons that would gradually slow a drifting space traveler. The friction occurs because the moving object absorbs more photons at its front surface than at its rear. The object slows from the flow of photons, just as a cyclist is slowed by the wind she feels in her face.

 

[Divide Overflow]

In thermal related news from actual spacecraft engineers:

Webb’s Specialized Heat Radiator Deployed Successfully​

At about 8:48 a.m. EST, a specialized radiator assembly necessary for Webb’s science instruments to reach their required low and stable operating temperatures deployed successfully. The Aft Deployable Instrument Radiator, or ADIR, is a large, rectangular, 4 by 8-foot panel, consisting of high-purity aluminum subpanels covered in painted honeycomb cells to create an ultra-black surface. The ADIR, which swings away from the backside of the telescope like a trap door on hinges, is connected to the instruments via flexible straps made of high-purity aluminum foil. The radiator draws heat out of the instruments and dumps it overboard to the extreme cold background of deep space.

The deployment of the ADIR – a process that released a lock to allow the panel to spring into position – took about 15 minutes.

Webb’s final series of major deployments is planned to start tomorrow, Jan. 7, with the rotation into position of the first of two primary mirror wings. The second primary mirror wing – Webb’s final major spacecraft deployment – is planned for Saturday, Jan. 8.

 

[authorized]

Found this to explain.

Photons Are a Drag

Any object in motion feels a bit of friction as it moves through the sea of radiation that is constantly emitted by its surroundings.

physics.aps.org

Although the radiation emitted by the sun, pushing outward, dwarfs any such effect from all the other directions combined.

 

[_Flare]

sailing in the solar wind, all the cosmos to larboard and starboard

 

[WonkoTheSaneUK]

The introduced heat will be very negligible and it can be isolated from the instruments that need to work at close to 0K.
I am quite sure that you are not a specialist in the area, nor it has been attempted.

The people who built JWST are experts in the area, and decided against using a peltier system.

 

[lexluthermiester]

The introduced heat will be very negligible and it can be isolated from the instruments that need to work at close to 0K.

Incorrect. You clearly do not understand how thermoelectric coupling functions. There is no way to isolate a Peltier type system from a certain amount of heat. Don't argue with me, Argue with the laws of physics.

I am quite sure that you are not a specialist in the area

And that is where you are incorrect again. I worked with thermoelectric systems, including Peltier types, for a number of years professionally. Such a system has practical applications in many areas of industry and technology. However, such is a poor choice in the design of a satellites as the power requirements are unacceptably high and in the case of JWT, the thermal performance would not get the parts needing to be cooled anywhere near the ideal operation range.

This is not an argument you can win. The overwhelming amount of science surrounding thermoelectric systems is against you. Let it go.

 

[Wirko]

View attachment 231274

All temperatures were accurate to 0.01 C or F two days ago when you took the screenshot but changed to whole degrees soon after. That's strange. And NASA would better switch to Kelvins now, it's the only scale that makes sense from now on.

 

[Divide Overflow]

Primary Mirror Wings Deployed, All Major Deployments Complete​

Today, at 1:17 p.m. EST, NASA’s James Webb Space Telescope completed all of its large-scale deployments with the extension and latching of its starboard primary mirror wing. Now that the telescope is structurally fully deployed – with the secondary mirror tripod and both primary mirror wings in place – the three-month process of aligning all of Webb’s telescope optics into a precise system can now commence. Learn more.

 

[lexluthermiester]

Primary Mirror Wings Deployed, All Major Deployments Complete​

Today, at 1:17 p.m. EST, NASA’s James Webb Space Telescope completed all of its large-scale deployments with the extension and latching of its starboard primary mirror wing. Now that the telescope is structurally fully deployed – with the secondary mirror tripod and both primary mirror wings in place – the three-month process of aligning all of Webb’s telescope optics into a precise system can now commence. Learn more.

Now begins the process of alignment and calibration of the mirror assembly. THAT is going to take a long time.