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tech / sci.space.policy / Re: Merry Christmas from JWST

SubjectAuthor
* Merry Christmas from JWSTSnidely
+* Re: Merry Christmas from JWSTAlain Fournier
|`* Re: Merry Christmas from JWSTSnidely
| `* Re: Merry Christmas from JWSTSnidely
|  `* Re: Merry Christmas from JWSTAlain Fournier
|   +- Re: Merry Christmas from JWSTNiklas Holsti
|   `* Re: Merry Christmas from JWSTSnidely
|    `* Re: Merry Christmas from JWSTAlain Fournier
|     `* Re: Merry Christmas from JWSTSnidely
|      `* Re: Merry Christmas from JWSTAlain Fournier
|       `* Re: Merry Christmas from JWSTNiklas Holsti
|        `* Re: Merry Christmas from JWSTNiklas Holsti
|         `- Re: Merry Christmas from JWSTAlain Fournier
+* Re: Merry Christmas from JWSTJF Mezei
|+* Re: Merry Christmas from JWSTSnidely
||`* Re: Merry Christmas from JWSTJF Mezei
|| `* Re: Merry Christmas from JWSTSnidely
||  +* Re: Merry Christmas from JWSTNiklas Holsti
||  |`- Re: Merry Christmas from JWSTSnidely
||  `* Re: Merry Christmas from JWSTJF Mezei
||   `- Re: Merry Christmas from JWSTAlain Fournier
|`- Re: Merry Christmas from JWSTNiklas Holsti
+- Re: Merry Christmas from JWSTAlain Fournier
`* Re: Merry Christmas from JWSTAlain Fournier
 `- Re: Merry Christmas from JWSTSnidely

1
Subject: Merry Christmas from JWST
From: Snidely
Newsgroups: sci.space.policy
Organization: Dis One
Date: Sat, 25 Dec 2021 20:48 UTC
Path: i2pn2.org!i2pn.org!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: snidely....@gmail.com (Snidely)
Newsgroups: sci.space.policy
Subject: Merry Christmas from JWST
Date: Sat, 25 Dec 2021 12:48:28 -0800
Organization: Dis One
Lines: 6
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The easy part of the flight (flight!) has been successful!

/dps

--
Who, me?  And what lacuna?


Subject: Re: Merry Christmas from JWST
From: Alain Fournier
Newsgroups: sci.space.policy
Organization: A noiseless patient Spider
Date: Sun, 26 Dec 2021 20:51 UTC
References: 1
Path: i2pn2.org!i2pn.org!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: alain...@videotron.ca (Alain Fournier)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Sun, 26 Dec 2021 15:51:37 -0500
Organization: A noiseless patient Spider
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On Dec/25/2021 at 15:48, Snidely wrote :
The easy part of the flight (flight!) has been successful!

/dps


Yes! The flight is always interesting to see. But it is the images that we will (hopefully) get in about six months that should be exciting.


Alain Fournier


Subject: Re: Merry Christmas from JWST
From: Snidely
Newsgroups: sci.space.policy
Organization: Dis One
Date: Sun, 26 Dec 2021 22:39 UTC
References: 1 2
Path: i2pn2.org!i2pn.org!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: snidely....@gmail.com (Snidely)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Sun, 26 Dec 2021 14:39:59 -0800
Organization: Dis One
Lines: 17
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Watch this space, where Alain Fournier advised that...
On Dec/25/2021 at 15:48, Snidely wrote :
The easy part of the flight (flight!) has been successful!

/dps


Yes! The flight is always interesting to see. But it is the images that we will (hopefully) get in about six months that should be exciting.


Hey, it's FINALLY off the ground!

/dps

--
Who, me?  And what lacuna?


Subject: Re: Merry Christmas from JWST
From: Snidely
Newsgroups: sci.space.policy
Organization: Dis One
Date: Thu, 30 Dec 2021 05:40 UTC
References: 1 2 3
Path: i2pn2.org!i2pn.org!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: snidely....@gmail.com (Snidely)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Wed, 29 Dec 2021 21:40:49 -0800
Organization: Dis One
Lines: 40
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Just this Sunday, Snidely puzzled about:
Watch this space, where Alain Fournier advised that...
On Dec/25/2021 at 15:48, Snidely wrote :
The easy part of the flight (flight!) has been successful!

/dps


Yes! The flight is always interesting to see. But it is the images that we will (hopefully) get in about six months that should be exciting.


Hey, it's FINALLY off the ground!


L+ 04:17:16:27
Launch Elapsed

607175.3km From Earth
839156.3km To L2 Orbit
Distance Complete  41.9802%

Cruising Speed  0.8458km/s

Hot Side
Sunshield UPS  -6.67C
Spacecraft bus  9.44C

Cold Side
Mirrors  -57.22C
ISIM    -153.33C

URL:https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.html?units=metric

/dps

--
Rule #0: Don't be on fire.
 In case of fire, exit the building before tweeting about it.
(Sighting reported by Adam F)


Subject: Re: Merry Christmas from JWST
From: Alain Fournier
Newsgroups: sci.space.policy
Organization: A noiseless patient Spider
Date: Thu, 30 Dec 2021 15:49 UTC
References: 1 2 3 4
Path: i2pn2.org!i2pn.org!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: alain...@videotron.ca (Alain Fournier)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Thu, 30 Dec 2021 10:49:59 -0500
Organization: A noiseless patient Spider
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Le Dec/30/2021 à 00:40, Snidely a écrit :
Just this Sunday, Snidely puzzled about:
Watch this space, where Alain Fournier advised that...
On Dec/25/2021 at 15:48, Snidely wrote :
The easy part of the flight (flight!) has been successful!

/dps


Yes! The flight is always interesting to see. But it is the images that we will (hopefully) get in about six months that should be exciting.


Hey, it's FINALLY off the ground!


L+ 04:17:16:27
Launch Elapsed

607175.3km From Earth
839156.3km To L2 Orbit
Distance Complete  41.9802%

Cruising Speed  0.8458km/s

Hot Side
Sunshield UPS  -6.67C
Spacecraft bus  9.44C

Cold Side
Mirrors  -57.22C
ISIM    -153.33C

URL:https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.html?units=metric

About 10 hours later both the hot and cold sides have heated up. Why? The sunshield has started to deploy for a few days and deployment should be completed at launch +5.5 days (in a few hours). My guess is that it was launched with a limited stock of coolant that has boiled off and that the sunshield will take care of keeping it cool now.


L+05:03:18:52
Launch Elapsed

636971.6km From Earth
809360km To L2 Orbit
Distance Complete  44.0392%

Cruising Speed  0.8061km/s

Hot Side
Sunshield UPS  27.78C
Spacecraft bus  8.33C

Cold Side
Mirrors  -45.00C
ISIM    -145.00C


Alain Fournier


Subject: Re: Merry Christmas from JWST
From: Niklas Holsti
Newsgroups: sci.space.policy
Organization: Tidorum Ltd
Date: Thu, 30 Dec 2021 16:35 UTC
References: 1 2 3 4 5
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From: niklas.h...@tidorum.invalid (Niklas Holsti)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Thu, 30 Dec 2021 18:35:02 +0200
Organization: Tidorum Ltd
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On 2021-12-30 17:49, Alain Fournier wrote:
Le Dec/30/2021 à 00:40, Snidely a écrit :

    [snip]

(Earlier temperatures:)

Hot Side
Sunshield UPS  -6.67C
Spacecraft bus  9.44C

Cold Side
Mirrors  -57.22C
ISIM    -153.33C

URL:https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.html?units=metric


About 10 hours later both the hot and cold sides have heated up. Why?


See below for some guesses.


The sunshield has started to deploy for a few days and deployment should be completed at launch +5.5 days (in a few hours).


They have stated often that the deployment time-line is flexible, not to be relied on for precision. The first unrolling of the sunshield has a Nominal Event Time of launch + 6 days (but I don't know if this mean the start or the end of that step).


My guess is that it was launched with a limited stock of coolant that
has boiled off and that the sunshield will take care of keeping it
cool now.

I doubt that. It seems to be complication for no real benefit. And the telescope seems to have been ok at room temperatures before launch.

    [snip]

Hot Side
Sunshield UPS  27.78C


The aft UPS has deployed its "Aft Momentum Flap", which may be reflecting sunlight onto the temperature sensor.


Spacecraft bus  8.33C


That is actually cooler than the earlier value.


Cold Side
Mirrors  -45.00C
ISIM    -145.00C


The Deployable Tower Assembly has moved the telescope about 1.2 m away from its earlier contact with the sunshield. Perhaps some part of the telescope is now less shaded by the (still undeployed) sunshield.

Guesses only, of course...


Subject: Re: Merry Christmas from JWST
From: Snidely
Newsgroups: sci.space.policy
Organization: Dis One
Date: Fri, 31 Dec 2021 10:54 UTC
References: 1 2 3 4 5
Path: i2pn2.org!i2pn.org!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: snidely....@gmail.com (Snidely)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Fri, 31 Dec 2021 02:54:07 -0800
Organization: Dis One
Lines: 17
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Thus spake Alain Fournier:

About 10 hours later both the hot and cold sides have heated up. Why? The sunshield has started to deploy for a few days and deployment should be completed at launch +5.5 days (in a few hours). My guess is that it was launched with a limited stock of coolant that has boiled off and that the sunshield will take care of keeping it cool now.

The coolant is supposed to last for the 10 year mission.  And the limiting resource for the 10 year figure is propellant.

/dps

--
I have always been glad we weren't killed that night.  I do not know any particular reason, but I have always been glad.
  _Roughing It_, Mark Twain


Subject: Re: Merry Christmas from JWST
From: Alain Fournier
Newsgroups: sci.space.policy
Organization: A noiseless patient Spider
Date: Fri, 31 Dec 2021 17:36 UTC
References: 1 2 3 4 5 6
Path: i2pn2.org!i2pn.org!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: alain...@videotron.ca (Alain Fournier)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Fri, 31 Dec 2021 12:36:48 -0500
Organization: A noiseless patient Spider
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On Dec/31/2021 at 05:54, Snidely wrote :
Thus spake Alain Fournier:

About 10 hours later both the hot and cold sides have heated up. Why? The sunshield has started to deploy for a few days and deployment should be completed at launch +5.5 days (in a few hours). My guess is that it was launched with a limited stock of coolant that has boiled off and that the sunshield will take care of keeping it cool now.

The coolant is supposed to last for the 10 year mission.  And the limiting resource for the 10 year figure is propellant.

For the most part the telescope is passively cooled. The coolant is used only for the Mid-Infrared instrument (MIRI). And I doubt the MIRI is cooled yet. Its operating temperature is -266.5C or 6.7K, not in the same ball park than the -145C or 131K currently observed on the cold side of the JWST.

See: https://webb.nasa.gov/content/about/innovations/cryocooler.html


Alain Fournier


Subject: Re: Merry Christmas from JWST
From: Snidely
Newsgroups: sci.space.policy
Organization: Dis One
Date: Sat, 1 Jan 2022 02:40 UTC
References: 1 2 3 4 5 6 7
Path: i2pn2.org!i2pn.org!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: snidely....@gmail.com (Snidely)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Fri, 31 Dec 2021 18:40:17 -0800
Organization: Dis One
Lines: 31
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Alain Fournier wrote on 12/31/2021 :
On Dec/31/2021 at 05:54, Snidely wrote :
Thus spake Alain Fournier:

About 10 hours later both the hot and cold sides have heated up. Why? The sunshield has started to deploy for a few days and deployment should be completed at launch +5.5 days (in a few hours). My guess is that it was launched with a limited stock of coolant that has boiled off and that the sunshield will take care of keeping it cool now.

The coolant is supposed to last for the 10 year mission.  And the limiting resource for the 10 year figure is propellant.

For the most part the telescope is passively cooled. The coolant is used only for the Mid-Infrared instrument (MIRI). And I doubt the MIRI is cooled yet. Its operating temperature is -266.5C or 6.7K, not in the same ball park than the -145C or 131K currently observed on the cold side of the JWST.

See: https://webb.nasa.gov/content/about/innovations/cryocooler.html


But where would that "limited stock of coolant" be that boiled off?

/dps

--
"This is all very fine, but let us not be carried away be excitement, but ask calmly, how does this person feel about in in his cooler moments next day, with six or seven thousand feet of snow and stuff on top of him?"
  _Roughing It_, Mark Twain.


Subject: Re: Merry Christmas from JWST
From: Alain Fournier
Newsgroups: sci.space.policy
Organization: A noiseless patient Spider
Date: Sat, 1 Jan 2022 13:33 UTC
References: 1 2 3 4 5 6 7 8
Path: i2pn2.org!i2pn.org!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: alain...@videotron.ca (Alain Fournier)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Sat, 1 Jan 2022 08:33:17 -0500
Organization: A noiseless patient Spider
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On Dec/31/2021 at 21:40, Snidely wrote :
Alain Fournier wrote on 12/31/2021 :
On Dec/31/2021 at 05:54, Snidely wrote :
Thus spake Alain Fournier:

About 10 hours later both the hot and cold sides have heated up. Why? The sunshield has started to deploy for a few days and deployment should be completed at launch +5.5 days (in a few hours). My guess is that it was launched with a limited stock of coolant that has boiled off and that the sunshield will take care of keeping it cool now.

The coolant is supposed to last for the 10 year mission.  And the limiting resource for the 10 year figure is propellant.

For the most part the telescope is passively cooled. The coolant is used only for the Mid-Infrared instrument (MIRI). And I doubt the MIRI is cooled yet. Its operating temperature is -266.5C or 6.7K, not in the same ball park than the -145C or 131K currently observed on the cold side of the JWST.

See: https://webb.nasa.gov/content/about/innovations/cryocooler.html


But where would that "limited stock of coolant" be that boiled off?

I don't know, it probably never existed. That was just a guess on my part. Niklas Holsti and you have pretty much convinced me that it wasn't a good guess. I'm still not 100% sure there wasn't some short term coolant that boiled off. But I don't think that is very likely.

Anyway, the temperature seems to have stabilised, at least on the cold side.


Alain Fournier


Subject: Re: Merry Christmas from JWST
From: Niklas Holsti
Newsgroups: sci.space.policy
Organization: Tidorum Ltd
Date: Sat, 1 Jan 2022 16:31 UTC
References: 1 2 3 4 5 6 7 8 9
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From: niklas.h...@tidorum.invalid (Niklas Holsti)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Sat, 1 Jan 2022 18:31:25 +0200
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On 2022-01-01 15:33, Alain Fournier wrote:
On Dec/31/2021 at 21:40, Snidely wrote :
Alain Fournier wrote on 12/31/2021 :
On Dec/31/2021 at 05:54, Snidely wrote :
Thus spake Alain Fournier:

About 10 hours later both the hot and cold sides have heated up. Why? The sunshield has started to deploy for a few days and deployment should be completed at launch +5.5 days (in a few hours). My guess is that it was launched with a limited stock of coolant that has boiled off and that the sunshield will take care of keeping it cool now.

The coolant is supposed to last for the 10 year mission.  And the limiting resource for the 10 year figure is propellant.

For the most part the telescope is passively cooled. The coolant is used only for the Mid-Infrared instrument (MIRI). And I doubt the MIRI is cooled yet. Its operating temperature is -266.5C or 6.7K, not in the same ball park than the -145C or 131K currently observed on the cold side of the JWST.

See: https://webb.nasa.gov/content/about/innovations/cryocooler.html


But where would that "limited stock of coolant" be that boiled off?

I don't know, it probably never existed. That was just a guess on my part. Niklas Holsti and you have pretty much convinced me that it wasn't a good guess. I'm still not 100% sure there wasn't some short term coolant that boiled off. But I don't think that is very likely.

Anyway, the temperature seems to have stabilised, at least on the cold side.


But the cold side temperatures are a bit higher now than their first readings, by some 5 degrees C. With the sunshield unfurled this is surprising. However, the multiple layers of the sunshield have not yet been separated, and AIUI it this separation is very important for the shielding properties. Perhaps the unseparated shield is now entirely warming up, including its anti-Sun side, which then radiates some heat to the telescope.



Subject: Re: Merry Christmas from JWST
From: Niklas Holsti
Newsgroups: sci.space.policy
Organization: Tidorum Ltd
Date: Sat, 1 Jan 2022 19:11 UTC
References: 1 2 3 4 5 6 7 8 9 10
Path: i2pn2.org!i2pn.org!aioe.org!news.uzoreto.com!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail
From: niklas.h...@tidorum.invalid (Niklas Holsti)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Sat, 1 Jan 2022 21:11:17 +0200
Organization: Tidorum Ltd
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On 2022-01-01 18:31, Niklas Holsti wrote:
On 2022-01-01 15:33, Alain Fournier wrote:
On Dec/31/2021 at 21:40, Snidely wrote :
Alain Fournier wrote on 12/31/2021 :
On Dec/31/2021 at 05:54, Snidely wrote :
Thus spake Alain Fournier:

About 10 hours later both the hot and cold sides have heated up. Why? The sunshield has started to deploy for a few days and deployment should be completed at launch +5.5 days (in a few hours). My guess is that it was launched with a limited stock of coolant that has boiled off and that the sunshield will take care of keeping it cool now.

The coolant is supposed to last for the 10 year mission.  And the limiting resource for the 10 year figure is propellant.

For the most part the telescope is passively cooled. The coolant is used only for the Mid-Infrared instrument (MIRI). And I doubt the MIRI is cooled yet. Its operating temperature is -266.5C or 6.7K, not in the same ball park than the -145C or 131K currently observed on the cold side of the JWST.

See: https://webb.nasa.gov/content/about/innovations/cryocooler.html


But where would that "limited stock of coolant" be that boiled off?

I don't know, it probably never existed. That was just a guess on my part. Niklas Holsti and you have pretty much convinced me that it wasn't a good guess. I'm still not 100% sure there wasn't some short term coolant that boiled off. But I don't think that is very likely.

Anyway, the temperature seems to have stabilised, at least on the cold side.


But the cold side temperatures are a bit higher now than their first readings, by some 5 degrees C. With the sunshield unfurled this is surprising. However, the multiple layers of the sunshield have not yet been separated, and AIUI it this separation is very important for the shielding properties. Perhaps the unseparated shield is now entirely warming up, including its anti-Sun side, which then radiates some heat to the telescope.


.... but now the cold side is cooling down again, to clearly lower temperatures than before the sunshield was unfurled (-183 C on the radiator, -88 C on the main mirror) and I believe the shield layers are not yet separated -- per the JWST blog, tensioning the layers starts on Jan 2. So, reality seems more complex than simple guesses can explain.


Subject: Re: Merry Christmas from JWST
From: Alain Fournier
Newsgroups: sci.space.policy
Organization: A noiseless patient Spider
Date: Sat, 8 Jan 2022 22:06 UTC
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From: alain...@videotron.ca (Alain Fournier)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Sat, 8 Jan 2022 17:06:30 -0500
Organization: A noiseless patient Spider
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It is now fully deployed. For the next few months, it will be adjusted and calibrated. :-)


Alain Fournier


Subject: Re: Merry Christmas from JWST
From: JF Mezei
Newsgroups: sci.space.policy
Date: Mon, 10 Jan 2022 07:09 UTC
References: 1
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Subject: Re: Merry Christmas from JWST
Newsgroups: sci.space.policy
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On 2021-12-25 15:48, Snidely wrote:
The easy part of the flight (flight!) has been successful!


So I looked up the L2 orbit for JWST at
https://webb.nasa.gov/content/about/orbit.html
 and of course, I have some questions.

Is reaching L2 considered requiring escape velocity? Close to it, or not
even close?  (1.5 million kilometres is pretty far from Earth).


The site above says Arianne will get JWST on a direct route to L2
without first orbiting Earth.

Does Ariane first stage fall straight down back to Earth?  Does it's
second stage do the same?

Some of the NASA animations seem to depict a trajectory that is almost
straight up, as opposed to what one traditionally sees for ships going
to Mars.

Has wnyone got a link (or short explanation) of the orbital mechaniscs
involved in _reaching_ that point?  (I have seen explanations of why it
stays there once there).



At L2, with orbital period shorter than it should for that altitude, is
JWST in danger of wandering out into space if it strays too far from the
L2 sweet spot? (aka: more energy than needed to stay in orbit around sun
at that altitude)?

Or can one shoot straight up and avoid the pesky issue of Earth's orbit
because its gravity becomes too small at that altitude and it only adds
a bit to the Sun's which is why you need orbital speed that is higher
than if the Earth weren't between you and sun ? (hence 365.25 orbital
period around sun when at that altitude it would be greater)


Does the Earth provide a "gravity" assist to accelerate JWST
horizontally as it climbs up? or does JWST get all the energy needed
from its own engines  to travel a greater distance than the Earth does
in 365.25 days?

(I was under the impression it would be a Mars-like transfer with JWSt
accelerating forward, increasing altitude in sun orbit, which would
cause it to lag behind Earth, but once at 1.5m km altitude higher, would
nudge isrtelf forward to catch up with Earth and "snap into L2" once at
the right place, but apparently that isn't the case).

Once at L2, if it strays too far from the sweet spot, would JWST go
wander into space, hoping to be found by advanced civilization who would
build a great ship around it, and program it to return to Earth with a
mission to seek its Creator?


Another question with regards to the circular motion of JWST in a plane
perpendicular to radial line going to the sun with no mass in the middle
of that plane). Is this "required" because L2 sweet spot keeps moving,
or is that "orbit" unnecessary and all within L2 sweet spot, and done to
keep JWST "above the Earth's horizon" so its solar panels are not in
eternal shade?


Last question: I understand urgency of deploying solar panels and
antenna. But is there a reason they popped everything open before
arriving at L2? Wouldn't you want your fragile bits protected while
engines are still doing firings?

Wikipedia says it has 159 litres of hydrazine and 79.5l of oxydizer.
That may make it the world's most fuel efficient vehicle if it can climb
a hill 1.5m killometres long with only 159 litres of gasoline :-)  (and
that includes fiueld for station keeping for roughly 10 years, so that
is pretty amazing).







Subject: Re: Merry Christmas from JWST
From: Snidely
Newsgroups: sci.space.policy
Organization: Dis One
Date: Mon, 10 Jan 2022 07:44 UTC
References: 1 2
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From: snidely....@gmail.com (Snidely)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Sun, 09 Jan 2022 23:44:15 -0800
Organization: Dis One
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Remember when JF Mezei bragged outrageously?  That was Sunday:
On 2021-12-25 15:48, Snidely wrote:
The easy part of the flight (flight!) has been successful!


So I looked up the L2 orbit for JWST at
https://webb.nasa.gov/content/about/orbit.html
 and of course, I have some questions.

Is reaching L2 considered requiring escape velocity? Close to it, or not
even close?  (1.5 million kilometres is pretty far from Earth).


The site above says Arianne will get JWST on a direct route to L2
without first orbiting Earth.

Does Ariane first stage fall straight down back to Earth? 

Yes.

Does it's
second stage do the same?

For most launches, yes.  But for this one, like the Apollo lunar missions and their S-IVB stages, that stage is going to be Up There for about forever.

Some of the NASA animations seem to depict a trajectory that is almost
straight up, as opposed to what one traditionally sees for ships going
to Mars.

It's not going to Mars, it's only going out 30 days worth.  The L2 point is going to be 30 days ahead of where it was on launch day.

Has wnyone got a link (or short explanation) of the orbital mechaniscs
involved in _reaching_ that point?  (I have seen explanations of why it
stays there once there).

You can start with looking up a Hohmann transfer orbit.

At L2, with orbital period shorter than it should for that altitude, is
JWST in danger of wandering out into space if it strays too far from the
L2 sweet spot? (aka: more energy than needed to stay in orbit around sun
at that altitude)?

I don't think there will be anything dramatic for quite a while.  The initial perturbations will be small.  Wait long enough and they won't be small.


Last question: I understand urgency of deploying solar panels and
antenna. But is there a reason they popped everything open before
arriving at L2? Wouldn't you want your fragile bits protected while
engines are still doing firings?

The course corrections are unlikely to be any worse for the fragile bits than the station keeping firings.  The big nozzle has been done for almost all of the 15 2/3 days the telescope has been flying.

Meanwhile, you want to get the sun shade out ASAP because the longer you wait the longer it will take to get to the target instrument temperature, especially if part of it is being heated by exposure to the sun.


Wikipedia says it has 159 litres of hydrazine and 79.5l of oxydizer.
That may make it the world's most fuel efficient vehicle if it can climb
a hill 1.5m killometres long with only 159 litres of gasoline :-)  (and
that includes fiueld for station keeping for roughly 10 years, so that
is pretty amazing).

It's coasting up that hill.  Almost all that fuel is for station keeping, with just a little for course correction on the way there.

/dps

--
As a colleague once told me about an incoming manager,
"He does very well in a suck-up, kick-down culture."
   Bill in Vancouver


Subject: Re: Merry Christmas from JWST
From: Niklas Holsti
Newsgroups: sci.space.policy
Organization: Tidorum Ltd
Date: Mon, 10 Jan 2022 08:21 UTC
References: 1 2
Path: i2pn2.org!i2pn.org!aioe.org!news.uzoreto.com!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail
From: niklas.h...@tidorum.invalid (Niklas Holsti)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Mon, 10 Jan 2022 10:21:52 +0200
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On 2022-01-10 9:09, JF Mezei wrote:


Wikipedia says it has 159 litres of hydrazine and 79.5l of oxydizer.
That may make it the world's most fuel efficient vehicle if it can climb
a hill 1.5m killometres long with only 159 litres of gasoline :-)  (and
that includes fiueld for station keeping for roughly 10 years, so that
is pretty amazing).


At the post-deployment press conference, it was reported that thanks to the accurate performance of the Ariane 5, the JWST now has propellant for about 20 years of operation. The "about" was emphasized, presumably because it is hard to predict the actual rate of propellant expenditure for station-keeping.

It seems to me that one issue in that prediction may be the solar-sail effect of the sunshield. To observe a desired point on the sky, the whole craft is tilted -- the telescope cannot be pointed separately from the shield. When the sunshield tilts, the photon pressure force tilts too, because the sail is reflective. Possibly the sequence of observations, and thus the sequence of tilts, could be designed to provide part of the station-keeping forces, saving propellant.


Subject: Re: Merry Christmas from JWST
From: JF Mezei
Newsgroups: sci.space.policy
Date: Mon, 10 Jan 2022 21:58 UTC
References: 1 2 3
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Subject: Re: Merry Christmas from JWST
Newsgroups: sci.space.policy
References: <mn.cb007e5c1301711b.127094@snitoo>
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On 2022-01-10 02:44, Snidely wrote:

You can start with looking up a Hohmann transfer orbit.

This was mentioned as the usual method to goto Mars. And you just said
it wasn't going to Mars.

And in going to Mars, you raise your orbit around the sun with your
orbital speed matching your orbital altitude. Towarsds the end, Mars'
gravity gives you any assist needed to match its speed/altitude above
sun when it "invites" you to crash onto its surface.

JWST wants to raise its altitude around the sun, but have the wrong
speed for that altitude, unless you are at one specific altitude and
point with the earth between you and the sun.

So still not obvious to me how it gets there.  Is it really one firing
near Earth in the right direction with its new speed progressively
decresing as it is slowed by ever weaker Earth's gravity with the hopes
of its vertical speed reaching 0 at the L2 point?

Does this mean that its trajectory to destination will always keep the
earth between it and the sun? or is there some period where it might be
ahead of the earth which will catch up?


It's coasting up that hill.  Almost all that fuel is for station
keeping, with just a little for course correction on the way there.

Did stage 2 do all the heaby work? if so, conceptually, wouldn't it also
reach L2?  (I assume some burns created sufficient separation, but
generally, won't it have the energy to go to same altitude?)


Subject: Re: Merry Christmas from JWST
From: Snidely
Newsgroups: sci.space.policy
Organization: Dis One
Date: Tue, 11 Jan 2022 00:59 UTC
References: 1 2 3 4
Path: i2pn2.org!i2pn.org!paganini.bofh.team!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: snidely....@gmail.com (Snidely)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Mon, 10 Jan 2022 16:59:51 -0800
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JF Mezei was thinking very hard :
On 2022-01-10 02:44, Snidely wrote:

You can start with looking up a Hohmann transfer orbit.

This was mentioned as the usual method to goto Mars. And you just said
it wasn't going to Mars.

Correct.  Hohmann orbits can be used anywhere in the solar system (or within other star systems.   You may be able to use them between star systems, but I haven't check the math for that.

And in going to Mars, you raise your orbit around the sun with your
orbital speed matching your orbital altitude. Towarsds the end, Mars'
gravity gives you any assist needed to match its speed/altitude above
sun when it "invites" you to crash onto its surface.

yes, because otherwise, you keep transferring back to your starting point.  That's how Mars Cyclers work.

JWST wants to raise its altitude around the sun, but have the wrong
speed for that altitude, unless you are at one specific altitude and
point with the earth between you and the sun.

Part of station keeping will be doing the insertion burn.

So still not obvious to me how it gets there.  Is it really one firing
near Earth in the right direction with its new speed progressively
decresing as it is slowed by ever weaker Earth's gravity with the hopes
of its vertical speed reaching 0 at the L2 point?

Roughly speaking, yes.

Does this mean that its trajectory to destination will always keep the
earth between it and the sun? or is there some period where it might be
ahead of the earth which will catch up?

I haven't plotted the transfer orbit.  But no doubt some simulators around the web have.  Maybe you can even do it Kerbal.

I would expect that the angular speed would stay near that of Earth and that of L2.

It's coasting up that hill.  Almost all that fuel is for station keeping, with just a little for course correction on the way there.

Did stage 2 do all the heaby work? if so, conceptually, wouldn't it also
reach L2?  (I assume some burns created sufficient separation, but
generally, won't it have the energy to go to same altitude?)

Yes.  It likely won't reach the actual L2 sweet spot, as it won't be doing the course corrections, and it's likely to continue orbiting the Earth in a highly ellipitical orbit.  It is possible, though, that ESA did tweaks to it after separation to put it into a solar orbit.

/dps

--
"I am not given to exaggeration, and when I say a thing I mean it"
   _Roughing It_, Mark Twain


Subject: Re: Merry Christmas from JWST
From: Niklas Holsti
Newsgroups: sci.space.policy
Organization: Tidorum Ltd
Date: Tue, 11 Jan 2022 11:50 UTC
References: 1 2 3 4 5
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From: niklas.h...@tidorum.invalid (Niklas Holsti)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Tue, 11 Jan 2022 13:50:33 +0200
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On 2022-01-11 2:59, Snidely wrote:
JF Mezei was thinking very hard :
On 2022-01-10 02:44, Snidely wrote:

You can start with looking up a Hohmann transfer orbit.

This was mentioned as the usual method to goto Mars. And you just said
it wasn't going to Mars.

Correct.  Hohmann orbits can be used anywhere in the solar system (or within other star systems.   You may be able to use them between star systems, but I haven't check the math for that.


In principle, as long as the origin and destination stars are in the disk of the Milky Way, they orbit the same center and something like a Hohmann transfer orbit could be defined and used, but it is complicated by the fact that there is mass between the two orbits, not just in the system center as for the solar system.

In practice, the stars' orbital speeds are so low that a Hohmann transfer would take a very long time, on the order of 100 million years. And before starting on the transfer orbit you would have to wait for a similar or longer time (the synodic period) for the two stars to be placed suitably in their orbits.

So any practical interstellar travel will go in a straight line from star to star at much higher velocity.


And in going to Mars, you raise your orbit around the sun with your
orbital speed matching your orbital altitude. Towarsds the end, Mars'
gravity gives you any assist needed to match its speed/altitude above
sun when it "invites" you to crash onto its surface.

yes, because otherwise, you keep transferring back to your starting point.  That's how Mars Cyclers work.


Mars cyclers do not use Hohmann transfer orbits, because while those orbits do cycle between the Earth and Mars orbits, the planet would usually not be at the meeting point. See https://en.wikipedia.org/wiki/Mars_cycler


Subject: Re: Merry Christmas from JWST
From: JF Mezei
Newsgroups: sci.space.policy
Date: Tue, 11 Jan 2022 17:59 UTC
References: 1 2 3 4 5
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Subject: Re: Merry Christmas from JWST
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On 2022-01-10 19:59, Snidely wrote:

So still not obvious to me how it gets there.  Is it really one firing
near Earth in the right direction with its new speed progressively
decresing as it is slowed by ever weaker Earth's gravity with the hopes
of its vertical speed reaching 0 at the L2 point?

Roughly speaking, yes.

Earth Sun is 147.12m km   or 105,000 kmh to do 1 lap in 365.25 days
JWST  Sun is 148.7m km    or 106,000 kmh to do 1 lap in same time.

So is this just a case of throwing a ball straight up so it's apex is at
L2 altitude, and in doing so, also add 1000kmh horizontal speed so that
at apex/L2, its horizontal speed maintains angular speed around sun the
same as Earth's ?

I was taught that raising orbit is done by accelerating horizontally
which result in increase in altitude and decrease in horizontal speed.
Just trying to square the two methods and what happens to horizontal
speed when you are thrown up vertically.




Subject: Re: Merry Christmas from JWST
From: Alain Fournier
Newsgroups: sci.space.policy
Organization: A noiseless patient Spider
Date: Wed, 12 Jan 2022 00:42 UTC
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From: alain...@videotron.ca (Alain Fournier)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Tue, 11 Jan 2022 19:42:42 -0500
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On Jan/11/2022 at 12:59, JF Mezei wrote :
On 2022-01-10 19:59, Snidely wrote:

So still not obvious to me how it gets there.  Is it really one firing
near Earth in the right direction with its new speed progressively
decresing as it is slowed by ever weaker Earth's gravity with the hopes
of its vertical speed reaching 0 at the L2 point?

Roughly speaking, yes.

Earth Sun is 147.12m km   or 105,000 kmh to do 1 lap in 365.25 days
JWST  Sun is 148.7m km    or 106,000 kmh to do 1 lap in same time.

So is this just a case of throwing a ball straight up so it's apex is at
L2 altitude, and in doing so, also add 1000kmh horizontal speed so that
at apex/L2, its horizontal speed maintains angular speed around sun the
same as Earth's ?

I was taught that raising orbit is done by accelerating horizontally
which result in increase in altitude and decrease in horizontal speed.
Just trying to square the two methods and what happens to horizontal
speed when you are thrown up vertically.

If you have some horizontal speed and you accelerate vertically, you don't add to your horizontal speed. You will lose some horizontal speed as you approach apogee and then gain it again as you come down to perigee.

You really need to compute orbital trajectories to understand why. But there is one important difference between accelerating horizontally and vertically that might help you understand why accelerating horizontally will give you a vertical push up but accelerating vertically doesn't give you a horizontal push side way. While you are in orbit, the directions of vertical and horizontal are constantly changing. If you are in a circular orbit, your current direction of motion (horizontal) is 90 degrees of your direction of motion in a quarter orbit. So if you accelerate horizontally, you are accelerating in a direction that will be vertical up in a quarter orbit. Therefore, it isn't surprising that your excess speed over what is needed for circular orbit, will be used for going up. On the other hand, if you are in a circular orbit, then in one quarter orbit, you will be going in a direction that you are now considering to be vertical down. So if you accelerate vertical up, you are taking away from the speed you will have in a quarter orbit.

I hope this helps you. But as I said, you really need to compute orbital trajectories to really understand what is going on here.


Alain Fournier


Subject: Re: Merry Christmas from JWST
From: Snidely
Newsgroups: sci.space.policy
Organization: Dis One
Date: Wed, 12 Jan 2022 04:44 UTC
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From: snidely....@gmail.com (Snidely)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Tue, 11 Jan 2022 20:44:58 -0800
Organization: Dis One
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Niklas Holsti used thar keyboard to writen:
On 2022-01-11 2:59, Snidely wrote:
JF Mezei was thinking very hard :
On 2022-01-10 02:44, Snidely wrote:

You can start with looking up a Hohmann transfer orbit.

This was mentioned as the usual method to goto Mars. And you just said
it wasn't going to Mars.

Correct.  Hohmann orbits can be used anywhere in the solar system (or within other star systems.   You may be able to use them between star systems, but I haven't check the math for that.


In principle, as long as the origin and destination stars are in the disk of the Milky Way, they orbit the same center and something like a Hohmann transfer orbit could be defined and used, but it is complicated by the fact that there is mass between the two orbits, not just in the system center as for the solar system.

In practice, the stars' orbital speeds are so low that a Hohmann transfer would take a very long time, on the order of 100 million years. And before starting on the transfer orbit you would have to wait for a similar or longer time (the synodic period) for the two stars to be placed suitably in their orbits.

So any practical interstellar travel will go in a straight line from star to star at much higher velocity.


And in going to Mars, you raise your orbit around the sun with your
orbital speed matching your orbital altitude. Towarsds the end, Mars'
gravity gives you any assist needed to match its speed/altitude above
sun when it "invites" you to crash onto its surface.

yes, because otherwise, you keep transferring back to your starting point.  That's how Mars Cyclers work.


Mars cyclers do not use Hohmann transfer orbits, because while those orbits do cycle between the Earth and Mars orbits, the planet would usually not be at the meeting point. See https://en.wikipedia.org/wiki/Mars_cycler

Ah, that will teach me to skip the homework  :-(

The cycler actually shoots to point beyond the target, chosen to make the connection happen on either the outbound or inbound leg.  Just a little arithmetic required.

/dps

--
 Maybe C282Y is simply one of the hangers-on, a groupie following a future guitar god of the human genome: an allele with undiscovered virtuosity, currently soloing in obscurity in Mom's garage.
  Bradley Wertheim,  theAtlantic.com, Jan 10 2013


Subject: Re: Merry Christmas from JWST
From: Alain Fournier
Newsgroups: sci.space.policy
Organization: A noiseless patient Spider
Date: Thu, 17 Mar 2022 15:00 UTC
References: 1
Path: i2pn2.org!i2pn.org!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: alain...@videotron.ca (Alain Fournier)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Thu, 17 Mar 2022 11:00:21 -0400
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On Dec/25/2021 at 15:48, Snidely wrote :
The easy part of the flight (flight!) has been successful!

/dps


Adjustments and calibration of the mirrors seem to be going well.

https://www.newscientist.com/article/2312646-the-james-webb-space-telescope-has-sent-back-its-clearest-image-yet/

The JWST is cool, not only according to the thermometers.


Alain Fournier


Subject: Re: Merry Christmas from JWST
From: Alain Fournier
Newsgroups: sci.space.policy
Organization: A noiseless patient Spider
Date: Mon, 2 May 2022 23:45 UTC
References: 1
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From: alain...@videotron.ca (Alain Fournier)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Mon, 2 May 2022 19:45:50 -0400
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On Dec/25/2021 at 15:48, Snidely wrote :
The easy part of the flight (flight!) has been successful!

/dps


A harder part, the calibration and alignment has been successful also!!
https://www.universetoday.com/155686/now-we-can-finally-compare-webb-to-other-infrared-observatories/

:-)


Alain Fournier


Subject: Re: Merry Christmas from JWST
From: Snidely
Newsgroups: sci.space.policy
Organization: Dis One
Date: Tue, 3 May 2022 09:03 UTC
References: 1 2
Path: i2pn2.org!i2pn.org!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: snidely....@gmail.com (Snidely)
Newsgroups: sci.space.policy
Subject: Re: Merry Christmas from JWST
Date: Tue, 03 May 2022 02:03:46 -0700
Organization: Dis One
Lines: 30
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Alain Fournier used thar keyboard to writen:
On Dec/25/2021 at 15:48, Snidely wrote :
The easy part of the flight (flight!) has been successful!

/dps


A harder part, the calibration and alignment has been successful also!!
https://www.universetoday.com/155686/now-we-can-finally-compare-webb-to-other-infrared-observatories/

:-)


Alain Fournier

Lots of astronomers doing the Happy Dance, and some pretty pictures starting to percolate.


[I recently came across a post in a nearby group that mentioned that the first science observation had been picked ... that msg was in my backlog since 2017]

/dps

--
"What do you think of my cart, Miss Morland? A neat one, is not it? Well hung: curricle-hung in fact. Come sit by me and we'll test the springs."
(Speculative fiction by H.Lacedaemonian.)


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