The easy part of the flight (flight!) has been successful!
/dps
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.
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!
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 UPSÂ -6.67C
Spacecraft bus 9.44C
Cold Side
Mirrors -57.22C
ISIMÂ Â Â -153.33C
<URL:https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.html?units=metric>
Le Dec/30/2021 à 00:40, Snidely a écrit :
Hot Side
Sunshield UPSÂ -6.67C
Spacecraft bus 9.44C
Cold Side
Mirrors -57.22C
ISIMÂ Â Â -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.
Hot Side
Sunshield UPSÂ 27.78C
Spacecraft bus 8.33C
Cold Side
Mirrors -45.00C
ISIMÂ Â Â -145.00C
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.
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.
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 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?
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.
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.
The easy part of the flight (flight!) has been successful!
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)?
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).
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).
You can start with looking up a Hohmann transfer orbit.
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.
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?)
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.
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.
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.
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.
The easy part of the flight (flight!) has been successful!
/dps
The easy part of the flight (flight!) has been successful!
/dps
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
The easy part of the flight (flight!) has been successful!
/dps
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