Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Posted: Sun Dec 26, 2021 6:12 am
by AVAO
Hey JWST - Welcome to the Universe!
...but if everything goes well, in summer 22 there is a lot of work waiting for you.
In Cycle 1 the following missions are scheduled:
70 Exoplanets & Discs
75 Galaxies
3 Intergalactic Medium and the Circumgalactic Medium
9 Large Scale Structure of the Universe
22 Solar System Astronomy
42 Stellar Physics and Stellar Types
36 Stellar Populations and the Interstellar Medium
29 Supermassive Black Holes and AGN
286 Total (6,000 hours)
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Posted: Sun Dec 26, 2021 8:48 am
by DL MARTIN
Having been around as an observer since SPUTNIK, I simply want to say this Webb thing is absolutely amazing. Congratulations.
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Posted: Sun Dec 26, 2021 8:52 am
by johnlcarswell@bellsouth.net
Where was the camera that took photo taken?
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Posted: Sun Dec 26, 2021 11:38 am
by rstevenson
johnlcarswell@bellsouth.net wrote: ↑Sun Dec 26, 2021 8:52 am
Where was the camera that took photo taken?
It was on the upper stage of the rocket. A lot of people asking the same question wherever this pic appears.
Rob
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Posted: Sun Dec 26, 2021 1:03 pm
by orin stepanek
DL MARTIN wrote: ↑Sun Dec 26, 2021 8:48 am
Having been around as an observer since SPUTNIK, I simply want to say this Webb thing is absolutely amazing. Congratulations.
Amazing indeed! There is nothing People can't accomplish given enough time!
e: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
The Gimbaled Antenna Assembly (GAA) holds Webb's high rate antenna. It is rotated to its parked position pointed back to the Earth. This is an 'automatic' deployment as well as the solar panel which preceded it. All other deployments will be controlled by commands from the ground.
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Posted: Sun Dec 26, 2021 8:19 pm
by Supernovice
After more than 50 years involved in the biological health sciences, retirement is allowing me to explore some subjects that have always fascinated me. I check the APOD photo daily and always read the “discussion” to see what you brainy people think. Please excuse this rather amateur posting but I would love to know the answer to two questions I have about the JWST. 1. Is the L2 point on the same three dimensional plane as the earth and sun? 2. I realize that the telescope has some pretty sophisticated sun shields and am wondering how much of the sun will be blocked by earth? Thanks. Happy New Year.
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Posted: Sun Dec 26, 2021 8:41 pm
by Chris Peterson
Supernovice wrote: ↑Sun Dec 26, 2021 8:19 pm
After more than 50 years involved in the biological health sciences, retirement is allowing me to explore some subjects that have always fascinated me. I check the APOD photo daily and always read the “discussion” to see what you brainy people think. Please excuse this rather amateur posting but I would love to know the answer to two questions I have about the JWST. 1. Is the L2 point on the same three dimensional plane as the earth and sun? 2. I realize that the telescope has some pretty sophisticated sun shields and am wondering how much of the sun will be blocked by earth? Thanks. Happy New Year.
Three points define a plane! And two points define an infinite number of planes. I assume you're asking if the L2 point lies on the plane of Earth's orbit around the Sun. Yes, it does.
If the JWST actually sat at the L2 point, most of the Sun would be blocked by the Earth, since the Earth subtends just a few hundredths of a degree less than the Sun at that point. However, JWST doesn't sit at the L2 point, it orbits it in a complex way that is designed to avoid the shadow of both the Earth and the Moon. A major reason it does this is because it results in a very constant thermal environment, which is much easier to manage than one where the radiation is always changing as the shadowing varies.
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Posted: Sun Dec 26, 2021 10:02 pm
by johnnydeep
So psyched that JWST is doing great so far!
PS - minor quibble: is the launch vehicle ever officially referred to as the "Ariane V" as it is in the text? Yes, "V" is the Roman numeral for 5, but I believe the official name of the rocket is Ariane 5. And the next one will be Ariane 6, not Ariane VI.
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Supernovice wrote: ↑Sun Dec 26, 2021 8:19 pm
After more than 50 years involved in the biological health sciences, retirement is allowing me to explore some subjects that have always fascinated me. I check the APOD photo daily and always read the “discussion” to see what you brainy people think. Please excuse this rather amateur posting but I would love to know the answer to two questions I have about the JWST. 1. Is the L2 point on the same three dimensional plane as the earth and sun? 2. I realize that the telescope has some pretty sophisticated sun shields and am wondering how much of the sun will be blocked by earth? Thanks. Happy New Year.
Three points define a plane! And two points define an infinite number of planes. I assume you're asking if the L2 point lies on the plane of Earth's orbit around the Sun. Yes, it does.
If the JWST actually sat at the L2 point, most of the Sun would be blocked by the Earth, since the Earth subtends just a few hundredths of a degree less than the Sun at that point. However, JWST doesn't sit at the L2 point, it orbits it in a complex way that is designed to avoid the shadow of both the Earth and the Moon. A major reason it does this is because it results in a very constant thermal environment, which is much easier to manage than one where the radiation is always changing as the shadowing varies.
Very cool. Better to be in constant sun with the known effect of a constant sun shield than in inconstant shadows. I was wondering what the purpose of that complex orbit was!
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Supernovice wrote: ↑Sun Dec 26, 2021 8:19 pm
After more than 50 years involved in the biological health sciences, retirement is allowing me to explore some subjects that have always fascinated me. I check the APOD photo daily and always read the “discussion” to see what you brainy people think. Please excuse this rather amateur posting but I would love to know the answer to two questions I have about the JWST. 1. Is the L2 point on the same three dimensional plane as the earth and sun? 2. I realize that the telescope has some pretty sophisticated sun shields and am wondering how much of the sun will be blocked by earth? Thanks. Happy New Year.
Three points define a plane! And two points define an infinite number of planes. I assume you're asking if the L2 point lies on the plane of Earth's orbit around the Sun. Yes, it does.
If the JWST actually sat at the L2 point, most of the Sun would be blocked by the Earth, since the Earth subtends just a few hundredths of a degree less than the Sun at that point. However, JWST doesn't sit at the L2 point, it orbits it in a complex way that is designed to avoid the shadow of both the Earth and the Moon. A major reason it does this is because it results in a very constant thermal environment, which is much easier to manage than one where the radiation is always changing as the shadowing varies.
Very clear. Thank you.
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Posted: Mon Dec 27, 2021 4:30 am
by MarkBour
I was thrilled when I saw this image during the launch coverage. A few seconds before this view, it was out of focus and glitching in the 2nd stage camera image. A few seconds later, it was overexposed and looked like a fuzzy blob of light as the 2nd stage maneuvered to avoid hitting it and then it went out of the field of view of that camera. (As the announcer noted, perhaps never to be seen by human eyes or cameras again.)
But for a brief moment, it glittered like a huge piece of diamond jewelry. (And it probably cost as much to build as it would have, if it were just made of diamonds.)
I assume this perfect shot of it glistening was not specifically planned to have turned out that way. When it was launched in the early morning hours, the Ariane rocket initially pitched right toward the Sun (aiming East). But when the second stage released Webb, it had gone one-quarter of the way around the world and was perhaps at noon "local" time. And at the angle between the camera and its subject, just after release, Webb was perhaps almost in opposition; and many of its reflective surfaces appeared to light on fire.
And the DDO, Jean Luc Voyer, was saying: "Go, Webb. Go Webb!"
According to the animations, this separation took place above the east coast of Africa. I think the geographical feature you can see on the Earth is the Gulf of Aden.
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
DL MARTIN wrote: ↑Sun Dec 26, 2021 8:48 am
Having been around as an observer since SPUTNIK, I simply want to say this Webb thing is absolutely amazing. Congratulations.
Amazing indeed! There is nothing People can't accomplish given enough time!
Except make an artificial sweetener that tastes good!
Eric
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Posted: Mon Dec 27, 2021 11:47 am
by XgeoX
The Earth in the photo reminds very much of the Earth in 2001 with it’s dreamy washed out colors…
Eric
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Posted: Mon Dec 27, 2021 3:44 pm
by johnnydeep
A question I had: it seems odd to me that they would jettison the protective fairing covering the scope so soon. The announcer said that then required them to keep "shimmying" or rotating the vehicle a little to keep the exposed mirror segments out of the sun. So, was the reason for jettisoning the fairing mainly (or solely) to save weight?
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Posted: Mon Dec 27, 2021 4:08 pm
by neufer
johnnydeep wrote: ↑Mon Dec 27, 2021 3:44 pm
it seems odd to me that they would jettison the protective fairing covering the scope so soon. The announcer said that then required them to keep "shimmying" or rotating the vehicle a little to keep the exposed mirror segments out of the sun.
So, was the reason for jettisoning the fairing mainly (or solely) to save weight?
Probably. The fairing was to protect JWST from Earth's atmosphere...not that of Space.
<<On Friday 17 December, the Ariane 5 rocket fairing was closed around the James Webb Space Telescope. This protective fairing, or ‘nose cone’, will shield the telescope during liftoff and its journey through the atmosphere. The fairing is equipped with specialised environmental controls that keep the observatory in a perfectly controlled temperature and humidity range during its final few days on Earth.>>
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
<<This burn fine-tunes Webb's trajectory after launch. The duration of the burn will depend on Ariane 5 launcher performance.
There are three mid-course correction (MCC) maneuvers: MCC-1a, MCC-1b, and MCC-2. This is the second. The first burn, MCC-1a, is the most important and the only other time-critical operation aside from solar array deployment during Webb’s commissioning period.
The second, MCC-1b, is a shorter burn performed before the sunshield deployment is scheduled to start. The final maneuver, MCC-2, performed 29 days after launch, is designed to insert Webb into the optimum orbit around L2.>>
------------------------------------------------------------------------------------------- This step begins the Sunshield deployment phase.
Nominal Event Time: Launch + 3 days
<<The UPS supports and carries the five folded sunshield membranes. Prior to this, the spacecraft is maneuvered to provide warmer temperatures on the forward UPS and various heaters are activitated to warm key deployment components. Key release devices are activated. Various electronics and software are configured prior to support the UPS motions, which are driven by a motor. This step represents the start of the Sunshield deployment phase and the start of all major deployments.>>
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Supernovice wrote: ↑Sun Dec 26, 2021 8:19 pm
After more than 50 years involved in the biological health sciences, retirement is allowing me to explore some subjects that have always fascinated me. I check the APOD photo daily and always read the “discussion” to see what you brainy people think. Please excuse this rather amateur posting but I would love to know the answer to two questions I have about the JWST. 1. Is the L2 point on the same three dimensional plane as the earth and sun? 2. I realize that the telescope has some pretty sophisticated sun shields and am wondering how much of the sun will be blocked by earth? Thanks. Happy New Year.
Three points define a plane! And two points define an infinite number of planes. I assume you're asking if the L2 point lies on the plane of Earth's orbit around the Sun. Yes, it does.
If the JWST actually sat at the L2 point, most of the Sun would be blocked by the Earth, since the Earth subtends just a few hundredths of a degree less than the Sun at that point. However, JWST doesn't sit at the L2 point, it orbits it in a complex way that is designed to avoid the shadow of both the Earth and the Moon. A major reason it does this is because it results in a very constant thermal environment, which is much easier to manage than one where the radiation is always changing as the shadowing varies.
Very cool. Better to be in constant sun with the known effect of a constant sun shield than in inconstant shadows. I was wondering what the purpose of that complex orbit was!
So what about the orbit do you think is complex? Are referring to the halo orbit around L2?
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Three points define a plane! And two points define an infinite number of planes. I assume you're asking if the L2 point lies on the plane of Earth's orbit around the Sun. Yes, it does.
If the JWST actually sat at the L2 point, most of the Sun would be blocked by the Earth, since the Earth subtends just a few hundredths of a degree less than the Sun at that point. However, JWST doesn't sit at the L2 point, it orbits it in a complex way that is designed to avoid the shadow of both the Earth and the Moon. A major reason it does this is because it results in a very constant thermal environment, which is much easier to manage than one where the radiation is always changing as the shadowing varies.
Very cool. Better to be in constant sun with the known effect of a constant sun shield than in inconstant shadows. I was wondering what the purpose of that complex orbit was!
So what about the orbit do you think is complex? Are referring to the halo orbit around L2?
Yes. But that isn't actually an orbit, because there's nothing at L2 that can be orbited. So it's actually a complex pattern of station keeping that keeps the telescope in the vicinity of L2.
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Very cool. Better to be in constant sun with the known effect of a constant sun shield than in inconstant shadows. I was wondering what the purpose of that complex orbit was!
So what about the orbit do you think is complex? Are referring to the halo orbit around L2?
Yes. But that isn't actually an orbit, because there's nothing at L2 that can be orbited. So it's actually a complex pattern of station keeping that keeps the telescope in the vicinity of L2.
Yes, and my response is tailored to him answering yes as you did.
I interpreted his reply as saying the "orbital" complexity was mostly, if not solely, driven by the complications regarding shadow avoidance and minimizing thermal fluctuations. I disagree. For other reasons, a halo orbit is complex anyway, regardless of mission. As you know, L1, L2 & L3 Lagrange points are dynamically unstable, and a series of orbital thrust maneuvers are required insert it into orbit and to maintain that orbit (station keeping). In detail, halo-orbit designs can vary, but in general, their primary focus is dealing with orbital instabilities, and thrust-controlled loops appear to be a common way to do this. So, when I look at halo orbits for SOHO (L1) and JWST (L2), I can't see any difference in fundamental shapes, and I can't assign any mission-dependent orbital planning just by looking at those halo orbits (maybe JWST's loops are larger to assure 10 years of shadow avoidance?). I don't have doubt that JWST is the most sophisticated and technically demanding telescope mission - managing shadow avoidance (Earth and moon) over 10-year lifetime and the uncertainty of thrust / fuel demands for orbital corrections are critical. I think this sophistication and the new activities for operation at L2 are where most risks and complexities lie. Considered separately, I'd say the halo-orbit design for JWST is relatively straight forward, and fundamentally the same as other halo-orbits.
JWST Orbit wrote:Orbit maintenance
The L2 orbit has an orbit period of 6 months. While orbits about the L2 point are inherently unstable, the orbit size is large and the orbital velocity is low (~1 km/s), so the orbit "decays" slowly. However, JWST's large sun shield, roughly the size of a tennis court, is subject to significant solar radiation pressure which results in both a force and a torque. The direction of solar force varies as the observatory's attitude changes from observation to observation. The solar torque is balanced by reaction wheels, but periodically, the accumulated momentum is dumped by firing thrusters. Because JWST operations are event-driven, the observatory attitude profile and momentum dumping cannot be accurately predicted months in advance.These 2 perturbations increase the acceleration of JWST from its orbit about L2, and necessitates more frequent orbit maintenance (station keeping) maneuvers than other Lagrange orbit missions (which are typically 3–4 times per year). Accurate orbit determination will require daily tracking measurements over a period of 19 days, so station keeping will be performed every 21 days.
Orbit perturbations along the Sun-L2 axis have the greatest impact on orbit stability. Thrusters are mounted on the spacecraft bus (located on the side of the sun shield facing the Sun); those used for orbit correction are oriented as far away from the sun shield as possible. The sun shield can support a larger sun-pitch angle† for orbit correction than that allowed for science operations. This architecture allows thruster firing at angles up to 90° from the Sun consistent with Sun avoidance restrictions, which is sufficient to provide orbit correction in all cases.
The orbit will be biased to compensate for mean outward forces associated with gravitation of the planets and radiation pressure on the sun shield.
Again, said simply, I think the complexities of L1,L2 & L3 halo orbits are mostly driven by the common, intrinsic dynamic instabilities, not so much the mission criteria.
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
alter-ego wrote: ↑Tue Dec 28, 2021 11:07 pm
So what about the orbit do you think is complex? Are referring to the halo orbit around L2?
Yes. But that isn't actually an orbit, because there's nothing at L2 that can be orbited. So it's actually a complex pattern of station keeping that keeps the telescope in the vicinity of L2.
Yes, and my response is tailored to him answering yes as you did.
I interpreted his reply as saying the "orbital" complexity was mostly, if not solely, driven by the complications regarding shadow avoidance and minimizing thermal fluctuations.
Yes, I think that is the case. There are a large number of possible halo orbits that could have been chosen. Certainly, some such path is a requirement for a metastable existence near L2. But this orbit was carefully designed because the mission is only possible if the probe is in constant sunlight. This particular orbit was designed specifically for that purpose.
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
Yes. But that isn't actually an orbit, because there's nothing at L2 that can be orbited. So it's actually a complex pattern of station keeping that keeps the telescope in the vicinity of L2.
Yes, and my response is tailored to him answering yes as you did.
I interpreted his reply as saying the "orbital" complexity was mostly, if not solely, driven by the complications regarding shadow avoidance and minimizing thermal fluctuations.
Yes, I think that is the case. There are a large number of possible halo orbits that could have been chosen. Certainly, some such path is a requirement for a metastable existence near L2. But this orbit was carefully designed because the mission is only possible if the probe is in constant sunlight. This particular orbit was designed specifically for that purpose.
In detail, I have to agree. I just don't appreciate the specific differences between one that works and one that doesn't. On the surface, it looks like a basic halo orbit. I guess every halo orbit is different and appreciating the differences in complexity means understanding those design details.
Interesting - I'd like a top-10 list of mission orbit designs, 1 being the most difficult / complex. Maybe use code optimization complexity? One thing for sure, computer evolution has impacted the design capability.
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
alter-ego wrote: ↑Wed Dec 29, 2021 3:05 am
Yes, and my response is tailored to him answering yes as you did.
I interpreted his reply as saying the "orbital" complexity was mostly, if not solely, driven by the complications regarding shadow avoidance and minimizing thermal fluctuations.
Yes, I think that is the case. There are a large number of possible halo orbits that could have been chosen. Certainly, some such path is a requirement for a metastable existence near L2. But this orbit was carefully designed because the mission is only possible if the probe is in constant sunlight. This particular orbit was designed specifically for that purpose.
In detail, I have to agree. I just don't appreciate the specific differences between one that works and one that doesn't. On the surface, it looks like a basic halo orbit. I guess every halo orbit is different and appreciating the differences in complexity means understanding those design details.
Interesting - I'd like a top-10 list of mission orbit designs, 1 being the most difficult / complex. Maybe use code optimization complexity? One thing for sure, computer evolution has impacted the design capability.
If I were to guess, I'd say that #1 was the requirement of an orbit that kept it unshadowed from the Earth and Moon, and #2 was such an orbit that minimized thruster-based station keeping (which also involves optimization of reaction wheel station keeping, since the two interact).
Re: APOD: James Webb Space Telescope over Earth (2021 Dec 26)
-------------------------------------------------------------------------------------------
The Aft Unitized Pallet Structure (UPS)
Nominal Event Time: Launch + 3 days
<<The UPS supports and carries the five folded sunshield membranes. Prior to this, the spacecraft will have been maneuvered to provide warmer temperatures on the forward UPS and various heaters have been activitated to warm key deployment components. Key release devices have been activated. Various electronics and software have also been configured prior to support the UPS motions, which are driven by a motor.>>
James Webb Space Telescope over Earth
