• Merry Christmas from JWST

    From Snidely@21:1/5 to All on Sat Dec 25 12:48:28 2021
    The easy part of the flight (flight!) has been successful!

    /dps

    --
    Who, me? And what lacuna?

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  • From Alain Fournier@21:1/5 to Snidely on Sun Dec 26 15:51:37 2021
    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

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  • From Snidely@21:1/5 to All on Sun Dec 26 14:39:59 2021
    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?

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  • From Snidely@21:1/5 to All on Wed Dec 29 21:40:49 2021
    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)

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  • From Alain Fournier@21:1/5 to All on Thu Dec 30 10:49:59 2021
    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

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  • From Niklas Holsti@21:1/5 to Alain Fournier on Thu Dec 30 18:35:02 2021
    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...

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  • From Snidely@21:1/5 to All on Fri Dec 31 02:54:07 2021
    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

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  • From Alain Fournier@21:1/5 to Snidely on Fri Dec 31 12:36:48 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


    Alain Fournier

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  • From Snidely@21:1/5 to Alain Fournier on Fri Dec 31 18:40:17 2021
    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.

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  • From Alain Fournier@21:1/5 to Snidely on Sat Jan 1 08:33:17 2022
    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

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  • From Niklas Holsti@21:1/5 to Alain Fournier on Sat Jan 1 18:31:25 2022
    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.

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  • From Niklas Holsti@21:1/5 to Niklas Holsti on Sat Jan 1 21:11:17 2022
    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.

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  • From Alain Fournier@21:1/5 to All on Sat Jan 8 17:06:30 2022
    It is now fully deployed. For the next few months, it will be adjusted
    and calibrated. :-)


    Alain Fournier

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  • From JF Mezei@21:1/5 to Snidely on Mon Jan 10 02:09:14 2022
    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).

    --- SoupGate-Win32 v1.05
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  • From Snidely@21:1/5 to All on Sun Jan 9 23:44:15 2022
    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

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  • From Niklas Holsti@21:1/5 to JF Mezei on Mon Jan 10 10:21:52 2022
    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.

    --- SoupGate-Win32 v1.05
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  • From JF Mezei@21:1/5 to Snidely on Mon Jan 10 16:58:28 2022
    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?)

    --- SoupGate-Win32 v1.05
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  • From Snidely@21:1/5 to All on Mon Jan 10 16:59:51 2022
    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

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  • From Niklas Holsti@21:1/5 to Snidely on Tue Jan 11 13:50:33 2022
    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.

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  • From JF Mezei@21:1/5 to Snidely on Tue Jan 11 12:59:09 2022
    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.

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  • From Alain Fournier@21:1/5 to JF Mezei on Tue Jan 11 19:42:42 2022
    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

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  • From Snidely@21:1/5 to All on Tue Jan 11 20:44:58 2022
    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

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  • From Alain Fournier@21:1/5 to Snidely on Thu Mar 17 11:00:21 2022
    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

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  • From Alain Fournier@21:1/5 to Snidely on Mon May 2 19:45:50 2022
    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

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  • From Snidely@21:1/5 to All on Tue May 3 02:03:46 2022
    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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