The Grand Finale, Proximal orbits Options

[jasedm]

With a month to go before the F-ring orbits commence, I thought it would be good to open a discussion about what exactly to expect, and the challenges and risks associated with the final months of Cassini's mission.

The final phase has been described as a mission in itself - one that might have attracted funding if it were stand-alone rather than one planned for the end of an already phenomenally successful enterprise.

We will no doubt continue to get regular updates at ciclops a resource which has been invaluable to followers of the mission, and which have provided a brilliant insight into upcoming science activities during each orbit, since early 2007 (Thanks Jason).
I'm hoping too that perhaps Emily may post one of her excellent articles on the TPS blog that give more of an inside track on the science that is planned for the final months.

To summarise, the F-ring orbits commence on November 30th and comprise 20 orbits of the spacecraft with periapses just a few thousand kilometres outside the F-ring - this will allow the opportunity to image the dynamism of the F-ring as never before, as well as (imaging opportunities willing) our best views of the rings and ring-moons - Atlas, Pan, Daphnis, Pandora, Epimetheus and Janus (Prometheus has already had it's closeup) There may be opportunities to get images of some of the known ring clumps (S/2004/S6 if still extant) and/or the known propellers/clumps in the outer A-ring such as S/2009/S1 and Bleriot/Earhart. The rings are simply gigantic though, and many of the orbits of the ring-embedded moons are chaotic so probably I'm hoping for a bit too much.

From what I can gather, there seems to be less risk with the F-ring orbits than with the proximal orbits as Cassini has sampled this environment to a degree already, and I believe it is intrinsically less dusty than the D-ring, and with relatively low radiation exposure to Cassini.

The 23 proximal orbits commence on 23rd April next year following the penultimate Titan flyby, and will thread between the inner rings and Saturn's cloud tops. This is slated as the opportunity to pin down Saturn's rotation, measure the mass of the rings and obtain unparalleled data on Saturn's atmosphere. This is where the spirits of adventure and exploration reach their zenith, as the environment between the rings and the planet is not fully understood.

The attached article gives an insight into the enormous planning challenges that these orbits present. It's fairly technical, but in summary:

The dust and radiation hazards present unknown risks to not only Cassini's science instruments but also the ability of the spacecraft to maintain it's optimal orientation whilst preventing any safing events.
As I understand it, it's not possible to prevent the glare of Saturn's atmosphere and rings blinding the sun sensor and star trackers, as they are located on the HGA which is facing forward to minimise risk of damage to the science instruments, so it's planned to command Cassini to 'suspend' star identification for 5 hours either side of each periapsis - thus flying blind during the 'hairy' part of the orbit.
Mission controllers also have to deal with the not-fully constrained effects of aeroheating during periapses which may affect the instruments, and there is also a risk of safing due to radiation constrained within Saturn's magnetic field.
The article states that the first proximal orbits will 'test the water' as regards the environment in that region, with periapse being lower on the final five orbits.

It seems that many of the 'safing' protocols/thresholds will be relaxed during periapses, hopefully preventing Cassini entering safe mode - perhaps one of the worst-case scenarios - each orbit at this stage is only seven days, which doesn't allow a huge amount of time to upload new commands should that happen.

I can only marvel at the technical brilliance of people involved in Cassini-Huygens and all they do, and have no doubt the final months of the mission will be a fitting end to this generation's exploration of Saturn.

[alan]

Cassini has just passed the last periapse of its F-ring orbits, in 2 1/2 days its last targeted Titan encounter will shift Cassini onto proximal orbits.

[Floyd]

Some links to information and movies:

Animated video about Cassini's Grand Finale https://youtu.be/xrGAQCq9BMU

Information and links from JPL http://saturn.jpl.nasa.gov/grandfinale

First dive Wednesday April 26th.

[MahFL]

Less than 150,000 miles out now.

[jasedm]

Fingers crossed!

[craigmcg]

5:19 am EDT

[Floyd]

I trust that Cassini has successfully made it, but our first chance to know for sure is about 20 hours out. From a recent tweet:

"Stay tuned! Earth's first opportunity to regain contact with @CassiniSaturn no earlier than ~midnight PT April 26 (3am ET, 7am UTC April 27)"

[Ames]

Carrier?
https://eyes.nasa.gov/dsn/dsn.html

[Explorer1]

Downlink started!

[MahFL]

Awesome.

[jasedm]

Great news!

[Floyd]

Images--see Twitter LINK

[B Bernatchez]

Excuse my ignorance, but this hurricane is the one at the North Pole, right?

[JRehling]

Saturn's north pole – and those of its satellites – are now in full sunlight nearing mid summer. The south poles are in the dark now, but were in late summer when Cassini arrived.

[SigurRosFan]

Yeah, here's a first amateur panorama of the north pole cloud structure.

[wildespace]

Excuse my ignorance, but this hurricane is the one at the North Pole, right?

Yes.

The south pole is currently in the shadows (saturnian winter) and looks like this:

[Guest_avisolo_*]

I made a gif of the dive!
http://i.imgur.com/i6uMzG2.gifv

[wildespace]

Nice colours in this recent view (RGB stack from W00107043, W00107044 and W00107045)



Although I'm not quite sure what we're looking at here. Night side of Saturn with some inner rings?

[Astroboy]

Enceladus spraying away on April 27. Reminds me a lot of the Io volcano footage from Voyager 2.



EDIT: I didn't realize there would be more to this observation! D'oh!

[MichaelJWP]

Not sure if this has been posted, but this movie puts the images in context nicely:

NASA: Cassini's First Fantastic Dive Past Saturn

[Phil Stooke]

Wildespace said, just above:

"Nice colours in this recent view (RGB stack from W00107043, W00107044 and W00107045)

Although I'm not quite sure what we're looking at here. Night side of Saturn with some inner rings?"


I think probably the outer rings, E at the top and G in the middle in forward-scattered light, with the limb of Saturn below, and a long exposure.

Phil

[Ian R]

We're looking at the south pole of Saturn (currently in mid-winter darkness), and the G and E rings. In the background is a star field which straddles the Orion / Taurus border:



http://nova.astrometry.net/user_images/1609771#original

[scalbers]

Interesting brightness changes on the limb. Is this Saturnian twilight modulated by ring shadows?

[ngunn]

With much of the attention on Saturn and the rings, Titan has decided to put on an extra special clouds performance: https://saturnraw.jpl.nasa.gov/multimedia/i...9/N00281060.jpg

[tanjent]

The background writeup for the cloud picture.
https://saturn.jpl.nasa.gov/resources/7673/
It's good to know that the spacecraft is still able to monitor events at Titan, even with no more close passes scheduled.

[JRehling]

Interesting brightness changes on the limb. Is this Saturnian twilight modulated by ring shadows?

The rings do indeed partially block sunlight from reaching the southern border of what would otherwise be the southern boundary of daylight / seasonal darkness. This is suggested by current telescope views of Saturn as seen from Earth and I just confirmed it with the Solar System Simulator's view of Saturn as seen from the Sun. The SSS view of Saturn as seen from below (attached) shows a U-shape, which matches your intuition. Cassini is seeing the tips of the U in a twilight time of day.

Thank goodness for the simulator, because it would take pages of trigonometry to work that out from first principles.

An interesting consequence is that an observer at the right latitude in Saturn's clouds would see two periods of daylight during this season – morning and afternoon – with a couple hours of "night" during the solar eclipse-by-the-rings around noon.

Attached thumbnail(s)

 

[scalbers]

Thanks JRehling for that informative discussion with the simulated view. In that I can note an inner U and an outer U. Perhaps we're seeing more of the inner U in the Cassini image, and this U is from the sunlight coming through the Cassini division? The center of the limb is thus shadowed by the A ring and the limb edges (in the image) show sunlight coming through the Cassini division.

As seen from the Sun (and Earth) the outer edge of the A ring thus completely misses the planet while the Cassini Division continues to intersect the planetary ellipsoid. We are really close to the widest open possible with the summer solstice coming up May 24. It then follows that light passing through the Cassini Division would never hit the terminator point nearest the pole.

[JRehling]

I puzzled over the geometry for a while, trying to simulate, in Photoshop, what the planet looks like behind the rings when it occurred to me that the summer and winter geometries are similar, and the parts of the rings that do and don't cast a shadow on the winter pole are exactly symmetrical with the parts of the rings that do and don't have the planet's shadow cast on them on the summer pole. I've attached an image of Saturn that I took on April 15, which is close to the current situation.

The inner edge of the A ring is slightly in the planet's shadow behind the north pole, but the outer edge is not, so the same situation will apply in the south, where it's harder to visualize what's going on. The Cassini Division will paint a curvy stripe of light on the planet near the winter pole, and that's the inner "U" in the view from below.

Attached thumbnail(s)

 

[Ian R]

Soon .....

[jasedm]

Nice image from 1st May - Sirius (bleaching out dozens of pixels in the camera) just about to be occulted by the F-ring.

I love the little bonus of Pandora photobombing the shot just to the left.

Still a mission full of unexpected delights.

[Ian R]

Cassini Grand Finale Saturn Portrait (Annotated Version) (April 13, 2017) by Ian Regan, on Flickr

[jasedm]

Breathtaking stuff! The definitive image of a backlit Saturn.

Very nice work.

[Ian R]

Thanks Jase!

The other version of the mosaic (sans annotations) is actually presented 'upside-down', which is just an aesthetic choice:


Cassini's 'Grand Finale' Saturn Portrait (April 13, 2017)

[Holder of the Tw...]

Cassini survived a close brush by the D ring, no word yet on whether it encountered much in the way of particle impacts.

Spaceflight Now article

[Guest_avisolo_*]

I made a video homage to the Cassini Mission:
https://vimeo.com/217370907

[wildespace]

No new posts for two whole months? Where is everybody? :-o

[Phil Stooke]

Too much other stuff going on! But I feel your pain so how about this?

Two images of Dione taken on August 1st, as part of a long sequence of Dione and Enceladus shots. The right image shows a very narrow sunlit crescent at bottom, and a much wider area lit by sunlight reflected off Saturn. Bear in mind that sunlight on Saturn is about 1 percent of its intensity at Earth, so the night side of Dione is illuminated by a weak light source. The left image is a long exposure shot of the same view, where even the very faint illumination at the 'limb'* of the Saturn-illuminated area is overexposed. The bright disk is surrounded by a fuzzy halo. Normally I would associate that with light from the overexposed region scattered in the camera optics.

But... but... the unilluminated crescent of Dione appears to be silhouetted against that scattered light. I'm trying to think of a way for that to happen without some of the light being scattered by a faint cloud of material around and behind Dione. No luck so far. So is this a real 'haze' around the moon? I don't know.

Phil

EDIT: * I mean, of course, the limb as seen from Saturn, the terminator of Saturnshine as seen from the spacecraft.

[ngunn]

I noticed this and assumed that Dione was orbiting within a very diffuse 'atmosphere' similar to Enceladus within the E-ring. Not knowing if this was to be expected I didn't remark on it, but maybe this is a new observation.

(By the way, we are all still here!)

On another subject, the recent images of Titan's lakes and seas have been superb and I hope some of our imagers will work their magic with those.

[john_s]

I noticed that too. One other possibility is that it's a double reflection: sunlight scattered off the sunlit side of Dione and then off ambient E-ring particles close enough to Dione to be illuminated by it, but not necessarily concentrated near Dione. But that would require the backscattered illumination of the E-ring particles by Dione-light to be comparable to the forward-scattered sunlight from the same particles, which may not make sense.

John

[ynyralmaen]

Depending on the path between Cassini and Dione through the E ring, maybe this fuzzy halo is due to forward scattering of the light from Dione by E ring grains that were between the moon and spacecraft?

Alternatively, Dione does have a tenuous exosphere which could be considered a potential cause, but I suspect that it'd be surprising for it to be this bright. The falloff in brightness could be compared to the expected scale length of the exosphere. I can't see any hint of a shadow being cast opposite to the narrow sunlit crescent, which I think may be expected if the halo is due to material, either gaseous or particulate, concentrated around Dione itself.

[jasedm]

No new posts for two whole months? Where is everybody? :-o

I think we're all used to seeing and discussing spectacular images, and this last phase of the mission focuses more on fields and particles, rather than the ISS.
Not that there aren't some fantastic images of the rings coming down, but I think Cassini's cameras are not able to take close-up un-smeared images of the cloud-tops in the way that Juno can, and in any case, other instruments are 'prime' at closest approach.

[fredk]

But that would require the backscattered illumination of the E-ring particles by Dione-light to be comparable to the forward-scattered sunlight from the same particles

Why do you say that? Do we know what the intensity of the forward-scattered sunlight is? Do you think there's a background glow away from Dione that's due to forward-scattered sunlight? Wouldn't it be hard to tell if such a background was due instead to backscattered light from the E ring?

The glow appears to me to be consistent with backscattered illumination of E-ring material from the sunlit side of Dione, which would be directed away from the camera and slightly towards the 7 o'clock direction. Forward scattering of the light from Dione by E-ring grains that were between the moon and spacecraft seems unlikely since the dark crescent is much darker than the adjacent glow.

[GS_Brazil]

No new posts for two whole months? Where is everybody? :-o

And how about this image:



I personally think this is one of the most amazing images of the ring I've ever seen.
If I'm interpreting the image well this is similar to these roofing sheets:

[ynyralmaen]

The glow appears to me to be consistent with backscattered illumination of E-ring material from the sunlit side of Dione, which would be directed away from the camera and slightly towards the 7 o'clock direction. Forward scattering of the light from Dione by E-ring grains that were between the moon and spacecraft seems unlikely since the dark crescent is much darker than the adjacent glow.

I was thinking that as the thin crescent as seen from Cassini is fully sunlit, it may be that there are more forward-scattering particles between the sunlit crescent and Cassini that there are relatively near Dione to backscatter sunlight from the daylit side as a whole. Forward scattering around the bright crescent could also explain the apparent enhanced brightness around the 7 o'clock position.

However, your point about the unilluminated portion of Dione being darker than the surrounding glow is a very good one, so yes, the source must be at least partially behind the moon.

[jasedm]

I personally think this is one of the most amazing images of the ring I've ever seen.
If I'm interpreting the image well this is similar to these roofing sheets:

Given that the rings are reckoned to be only a few hundred metres (a kilometre perhaps) thick, my guess is that this is an optical illusion. The rings are very open currently (around 27 degrees with respect to the earth) and I'd be surprised if shadows would be cast at this angle of incidence. Different if this image had been taken around equinox of course.

Nevertheless amazingly intricate and beautiful.

[Steve G]

No new posts for two whole months? Where is everybody? :-o

Alas, the forum gurus are stranded on Mars!

[rlorenz]

No new posts for two whole months? Where is everybody? :-o

Yes, lots going on. But here's something to think about - a long shot, but skilled video astronomers and/or spectroscopists might give it a go,
and the bigger aperture the better

https://arxiv.org/abs/1708.05036

The Cassini spacecraft will enter Saturn's atmosphere on 15th September 2017. This event may be visible from Earth
as a 'meteor' flash, and entry dynamics simulations and results from observation of
spacecraft entries at Earth are summarized to develop expectations for astronomical observability

[nprev]

Interesting. I don't suppose there's a ghost of a chance of getting HST time for this? Wouldn't require a long observation period, but of course the instrument's time is booked years in advance.

[Explorer1]

EOM press event schedule https://saturn.jpl.nasa.gov/news/3104/nasa-...ion-activities/

[wildespace]

A bit of surprise astrophotography from Cassini: http://saturnraw.jpl.nasa.gov/multimedia/i...1/N00287662.jpg



Any idea what this object is?

P.S. It turns out to be part of a lovely panorama of the sky:



Full-size: http://ibb.co/cYz7E5
http://www.flickr.com/photos/wildespace/36792380385

Images have also been taken in IR, GR, and BL wavelengths, so I'll trust someone will create a nice, clean colour image.

[alan]

If that is the Large Magellanic Cloud in the second image, the first might be the cluster 30 Doradus at the center of the Tarantula Nebula.

[wildespace]

If that is the Large Magellanic Cloud in the second image, the first might be the cluster 30 Doradus at the center of the Tarantula Nebula.

Yep, you're right, the panorama is that of the LMC.

[rlorenz]

Interesting. I don't suppose there's a ghost of a chance of getting HST time for this? Wouldn't require a long observation period, but of course the instrument's time is booked years in advance.

We were awarded HST time - it remains to be seen if the timing will work (HST has to be on the right side of the Earth during the entry, and ideally not in the South Atlantic Anomaly, etc.) and if the event is bright enough.

I was actually awarded HST time to observe the Huygens entry, but the STIS instrument failed between when I was awarded an orbit, and when the observation was to be implemented, so it didnt happen. There were a couple of groundbased efforts, but nothing was detected. Cassini is a rather more energetic entry, though

[nprev]

Outstanding! Good hunting.

[Floyd]

Information on the live Cassini Finale on NASA TV is now up.

Wednesday September 13, 1:00pm EDT, News Conference on Cassini's Final Mission Activities.

Friday September 15, 7:00-9:30am EDT, Cassini Grand Finale

Both with be available at https://www.nasa.gov/live

The web page with Cassini Grand Finale information is at this link

I assume most of us members of unmanned space flight will be watching.

[alan]

Enhanced version of the cluster:



Image of Tarantula Nebula from http://eso.org/public/images/eso0005a/ rotated counterclockwise

[nprev]

Sadly, I'll be working the job that pays my bills during EOM. But I think that it's not too early to express my profound admiration of and gratitude to each and every person who made this epic mission happen.

And I do mean 'epic' in the literal sense. Throughout recorded history there have been very few voyages of exploration that are even remotely comparable to that of Cassini-Huygens in terms of audacity, scope, and discovery. There's no need to recount the revelations here, not on this Forum, but suffice to say that we have all been privileged indeed to witness what Cassini has revealed.

It's been a humbling and joyous journey in every way. Deepest thanks to those who made it happen.

[jasedm]

Enhanced version of the cluster

Cassini also imaged Neptune and Triton back in August:

Attached thumbnail(s)

 

[JRehling]

And I do mean 'epic' in the literal sense. Throughout recorded history there have been very few voyages of exploration that are even remotely comparable to that of Cassini-Huygens in terms of audacity, scope, and discovery.

There's some part of my consciousness that can't help but compare Cassini to Galileo, which was itself wonderful but, unforgettably, handicapped. Cassini's operations and its machinery were as close to flawless as a mission of this duration could be. From its arrival at Saturn till now, I've always thought of it as "an ace" and that's nothing but the accomplishment of all those people scattered far and wide who helped plan, construct, and operate the finest spacecraft that the outer solar system's ever seen.

[climber]

I realize that the only piece oh human hardware left in the Saturnian system will be Huygens on Titan...

[jasedm]

Cassini receives its final gravitational tug/nudge from Titan in a couple of hours time with its now irreversible consequence.

What an incredible piece of engineering. Almost flawless performance for twenty years.

The outer solar system is going to seem very distant again.

[MatthewK]

I feel a bit self-conscious posting this because I lack the processing capabilities on such rich display across this forum.
Anyway, I want to say thanks to all the dedicated image tweakers for their wonderful work, which adds so much to the mission.
And I wanted to float an idea - one the last raw image has been received, I assume there will be just shy of 400 000 of them.
I've seen some evocative movies made by using the raws as frames, which I think is really compelling because the greyscale grittiness and radiation flecks make it look like a mysterious relic. (e.g. https://www.youtube.com/watch?v=OGCWA6o8LE4) But one thing which frustrates me is the strict sequential presentation so that wide angle and narrow angle images are intercut, sometimes in alternating frames, making a flashing mess, and the brightness levels jolting up and down. I know they are raw images - the latter aspect bothers me less.
What I'd like to propose is if it's possible to compile all of the RAWs into a movie, that the wide angle and narrow angle camera images (presumably separable by metadata) be presented side by side in a 2:1 overall aspect ratio. And whichever side is not being updated would just stay on the most recent image from that camera. That and a basic black point correction (lowest pixel value goes to 0, or 5, or something like that) might reduce the flashing while retaining the magic.
If anyone can point me at software I could use to do it myself, I'd be very glad to try!
Anyway - just an idea. If someone wants to use or adapt it, please do.

[bobik]

But here's something to think about - a long shot, but skilled video astronomers and/or spectroscopists might give it a go,
and the bigger aperture the better

https://arxiv.org/abs/1708.05036

Any new info? Will there be a ground-based observation campaign with large (>1m) telescopes involved?

[JRehling]

The outer solar system is going to seem very distant again.

I have an outsized personal affection for Pioneer 11's flyby of Saturn. The planets from Mercury to Jupiter had all been visited at least once by 1974, but it took 4.5 more years for Saturn to get its first visit, and the images perhaps didn't do a lot for science, but it seemed like a huge jump in the reach of human exploration, with distances now measured in billions, more than doubling the last big jump. It lasted only a short time, but the pictures made magazine covers. It also hammered home that the U.S. had long since left the Soviets in the dust for this sort of thing. The strange, haunting images with the rings bizarrely different from any telescope photos planted the flag of humanity at a new, distant outpost. I don't think Voyager 2's flybys of Uranus and Neptune captured the public in the same way, perhaps because those names have never been so prominent in the public imagination; New Horizon's Pluto flyby was perhaps similar in cultural impact, making a distant world temporarily a star in the Hollywood sense. And then Pioneer 11 flew on, giving us the image of a crescent Saturn as it took the long road out of town to infinity.

Cassini, though, really has been an outpost since 2004, one of the most flawless performers in the history of robotic space exploration. The laypublic has appreciated this; Huygens is the subject of a Washington Post article even today. Perhaps the best gauge of Cassini's impact will be the vacancy it leaves. In a world where technological progress is rapid, Cassini like a few exploration programs before it is a hard act to top. It's a dare to the future to try to surpass it. It may, like Apollo, not be replaced anytime soon by anything comparable.

[propguy]

Friday AM will be a very sad day for me. I started my work on interplanetary missions back in 1993 working Cassini propulsion at good old Martin Marietta (now LM). Back then a 7 year cruise to JOI seemed like forever. Now it seems like a distant memory. Having had the fortune to work 13 interplanetary mission over the years (3 currently; Juno ops, InSight ATLO, and Lucy design) I still have lots of pride and fond memories of Cassini. More than 1/2 of what I know about propulsion design and analysis I learned on Cassini (we had budget to actually look into the why of things). Doing a very long orbit insertion burn a billion miles from home was quite a challenge, but it went flawlessly. Will hopefully get together with some of the old (now mostly retired) prop team members Thursday or Friday night to raise a glass or two and hopefully meet with the old JPL prop folks next week in LA. Godspeed Cassini!

[Tom Tamlyn]

Has anyone found an archive of today's Cassini press conference?

The Cassini twitter account mentions a replay, https://twitter.com/CassiniSaturn/status/908106974616633344, but that seems to have been a once only replay, not an archive. Myy old standby, space-multimedia.nl.eu.org, seems to be gone (years ago, in fact).

[Explorer1]

Has anyone found an archive of today's Cassini press conference?

The Cassini twitter account mentions a replay, https://twitter.com/CassiniSaturn/status/908106974616633344, but that seems to have been a once only replay, not an archive. Myy old standby, space-multimedia.nl.eu.org, seems to be gone (years ago, in fact).

Here https://www.youtube.com/watch?v=gs-dscW95PE

Almost all the press conferences are archived on Youtube, but they don't have things older than a certain date (I wish I could watch the orbit insertion coverage, or the Huygens landing, again!)

[Tom Tamlyn]

Thanks very much.

May I ask how you found it? I spent more time than I care to admit this evening trying a variety of google searches with Cassini, press conference, and youtube among the search terms, and did not turn up this video. In fact just now I googled the title of the video you linked to, "NASA Previews Saturn Mission End (news briefing)," and the video did not show up. The searches returned videos of press conferences from previous months, many articles about the end of mission, articles _about_ today's press conference, and now inactive sites that carried the press conference live, but not the video in your link.

Almost all the press conferences are archived on Youtube, but they don't have things older than a certain date (I wish I could watch the orbit insertion coverage, or the Huygens landing, again!)

So do I. Maybe some private archives exist whose owners could be coaxed into sharing.

[Superstring]

In my view, Cassini is a defining mission for the post-Voyager generation (those of us who grew up after that epic tour). I had to write an ode to this spacecraft:

http://mannmetrics.com/an-ode-to-cassini/

[Explorer1]

Thanks very much.
May I ask how you found it?

I am subscribed to both the NASA and JPL Youtube pages, so anything new will pop up in my feed.

By the way, thanks for the link, superstring, you took the words right out of my mouth (plus I think we're nearly the same age!)

[climber]

Speaking of age etc... Doug started UNMSF a few days after Spirit & Oppy landed on Mars but a mere 4 months before Cassini arrived at Saturn. I guess she performed the first important event (arrival/landing/flyby/launch) (can I say Peanuts event?) of an interplanetary spacecraft we enjoyed together. So long old friend.

[djellison]

Cassini is why I took the old mer.rlproject.com URL and turned it into UMSF. And we all know how the story goes from there

[Phil Stooke]

I was born before Sputnik, and though I was not really paying attention until 1968, I have pretty much seen it all. For me, Voyager takes the planetary (i.e. non-lunar) prize... there will never be another Voyager until we get a probe to another solar system. But Cassini must be a close second. The sheer variety of things it has seen, mostly for the first time, is amazing. Not that I don't appreciate all the other missions!

Phil

[stevesliva]

A Neptune orbiter would be pretty sweet in the same way. Arrival could be as soon as 2042. That is only 25 years from now.

[jasedm]

I was born before Sputnik, and though I was not really paying attention until 1968, I have pretty much seen it all. For me, Voyager takes the planetary (i.e. non-lunar) prize... there will never be another Voyager until we get a probe to another solar system. But Cassini must be a close second. The sheer variety of things it has seen, mostly for the first time, is amazing. Not that I don't appreciate all the other missions!

Phil

I was born in 1967, and started to notice in 1980 with the Voyager 1 Saturn flyby and the airing of Carl Sagan's 'Cosmos' that year.
I agree Phil that Voyager takes the laurels, with Cassini/Huygens a close second. I couldn't have dreamed of a more comprehensive reconnaissance of the Saturn system when the mission launched.

[jasedm]

Interior to Dione's orbital distance now.

[belleraphon1]

Born in 1953. A time when public could still wonder about lichens on Mars and swamps or oceans on Venus. I became aware with Mariner 4 at Mars in 1965.
What a journey through a wonderland of worlds have we seen in the 50 some years since. VOYAGER gave us the introduction. CASSINI sealed the wonder at Saturn.
I will never forget the moments of discovery throughout the Saturn system, from methane storms at Titan's south pole seen in 2004, to the weird walnut shape of Iapetus on new years eve 2005.
Geysers on Enceladus, red streaks on icy moons.... mysteries to be further explored in the future. And through it all this forum UMSF. Thank you to the CASSINI team. Thank you to
UMSF for a ride with folks who love what I love.

[MahFL]

Hi all. Watching here. My name is on Cassini . My night shift finishes at 6 am so I'll stop up and watch the end. ( I work from home ).

PS I had a cloud free view of the Total Solar Eclipse, was awesome.

[elakdawalla]

Images for the final wide angle mosaic are coming down now. I hope there are some folks here who'll work on assembling it. Looks like they shot 3 different versions, one each exposed for Saturn and the rings (RGB) and one (clear filter only) for the G ring, for a real HDR mosaic.

[Astroboy]

I'm not crying, you're crying!

[Explorer1]

And with that, I realize that tomorrow morning will be tougher than I thought... this mission has been there for basically half my life. Many of you others grew up with the Voyagers, Vikings, Galileo, and others, and I will have future missions to see, perhaps back to Saturn, Titan and Enceladus, but Cassini truly bridged the generations (in so many ways!)

[tedstryk]

I became old enough to kind of understand at the very end of the old era (1989, Voyager's last encounter and the Soviet planetary program's last gasp with Phobos-2), and Cassini and CRAF (it's twin, which NASA pulled out of and evolved into Rosetta) were at the time, along with a Pluto mission, the distant dreams on the horizon. Rosetta has ended, New Horizons, which I've had the privilege to be a part of, has been by Pluto, and tomorrow Cassini ends. Honestly, I feel strangely displaced.

[wildespace]

The final mosaic of Saturn is being downlinked. Here's a little part of it:


NASA/JPL-Caltech/SSI/Maksim Kakitsev

Gonna be another stunning backlit view of Saturn!

[JRehling]

These are the days of miracle and wonder
This is the long distance call
The way the camera follows us in slo-mo
The way we look to us all

The way we look to a distant constellation
That's dying in a corner of the sky
These are the days of miracle and wonder
And don't cry baby, don't cry
Don't cry

-Paul Simon

[climber]

Don't know why, but I wake up this morning with a song already in my head that goes like this:

This is the end,
Hold your breath and count to ten,
..........
Let the sky fall....
-Adele

[jch]

And how can a probe die better than facing alien worlds,
for the knowledge of its creators, and the future of next probes?

I would like to say "Thank you!" to everyone involved in this mission. Thank you - for what you did for me in last so many years.

[nprev]

To die like a meteor in a blaze of glory, gracing an alien sky after a long life of discovery and wonder, is somehow fitting, even poetic.

Thank you.

[Explorer1]

Looks like the final raws are down, showing the final target....
(and a final Captain's Log from Carolyn Porco: http://ciclops.org/)

[ugordan]

Thank you and farewell, Cassini.

You will be missed.

[paxdan]

Thank you to the Team who built and flew the craft, and thank you to Cassini for showing us the wonders of the solar system.

[Tom Tamlyn]

From Jonathan McDowell @planet4589 (via @elakdawalla)

"I'm going to call this the end of mission. Project Manager off the net."
Cassini lasted about 40 seconds longer than expected!

https://twitter.com/elakdawalla/status/908663073010941953

[mchan]

Many great moments of first looks at images on UMSF. Many great images to go back to and relive those moments. Thanks NASA Cassini Team, Doug for starting this forum, and UMSF members who monitor the image feeds and post their processed versions of the images.

I started following this forum during the Huygens descent image downloads. Good to see posts from a few of the folks here in the early days of the mission. It has been a most enjoyable journey.

[Ron Hobbs]

A truly awesome mission! This is humanity at its finest!

[Roby72]

From Jonathan McDowell @planet4589 (via @elakdawalla)



https://twitter.com/elakdawalla/status/908663073010941953

I think this belongs to the transmission in S-Band...data relay was on the X-Band, which was out a few seconds earlier, but still longer than expected.

Rob

[Roby72]

Here is a nice flickr picture set what happend in the control room in the last hours (and during last days press con too)

https://www.flickr.com/photos/nasahqphoto/s...57686616794044/

Rob

[xflare]

Is there any component of Cassini that could have survived the entry? Weird to think that there might be a tiny piece of Cassini still falling deeper and deeper through the atmosphere now. Also. with Huygens sitting on the surface of Titan for near eternity, destroying Cassini for planetary protection purposes seems.....odd.

[tasp]

The plutonium fuel pellets in their aeroshells were believed to be the most 'survivable' hardware on board.

[Keatah]

Also. with Huygens sitting on the surface of Titan for near eternity, destroying Cassini for planetary protection purposes seems.....odd.

Titan isn't likely to have life. So it falls into a Category II mission.
https://saturn-archive.jpl.nasa.gov/faq/FAQHuygens/#q3

But when they discovered Enceladus' warm oceans they had to come up with something, hence the crash into Saturn.

[craigmcg]

Is there any component of Cassini that could have survived the entry? Weird to think that there might be a tiny piece of Cassini still falling deeper and deeper through the atmosphere now. Also. with Huygens sitting on the surface of Titan for near eternity, destroying Cassini for planetary protection purposes seems.....odd.

That question was asked at the press conference on Wednesday, and the answer was no, but as noted above the shell protecting the radioactive pieces was designed to survived potential problems during the launch, and so it would probably last the longest.

[Tom Tamlyn]

Still no chance of survival. Cassini was moving at 123,000 km/hr relative to Saturn, and that's just too fast. The higher melting temperatures of the plutonium and its iridium aeroshell gave those components at most an additional minute or so of existence before their component atoms mixed with Saturn's atmosphere.

I can't locate the best of the articles that I read about this recently (it noted, for instance, that it's more accurate to describe Cassini as melting rather than burning up, because there's no oxygen in Saturn's atmosphere), but the following passage contains discussion from a late August press briefing.

Julie Webster, the manager of Cassini's spacecraft-operations team at JPL, said during the call that the probe would heat up to nearly 500 degrees Celsius "within seconds" of its instruments breaking off and losing contact with Earth.

"We'll reach the aluminum melting point within about 20 seconds," she said. "The iridium will be the last thing to melt, and it will go about 30 seconds after the aluminum."

As the iridium shells melt away, the plutonium inside will sprinkle across Saturn like a radioactive shooting star. However, this won't necessarily make a bigger flash.

"It's just going to melt," [Earl] Maize [Cassini Program Manager] said. "It is going to be so hot at Saturn that it will quickly dissipate ... I think any possibility of it escaping is nil."

http://www.businessinsider.com/cassini-sat...-burn-up-2017-8

One aspect of this that surprised me is how very tenuous Saturn's atmosphere is at the altitude where Cassini disintegrated. One article -- again, I can't locate it now -- said that the atmospheric pressure was equivalent to that of the environment of the International Space Station, or what would pass for a pretty good vacuum in a lab on the earth. The ISS does need to boost its orbit periodically against atmospheric drag, but its orbital velocity is much less than Cassini's entry velocity (34 km/second versus 7.6 km/second, if my math is correct). And of course the pressure that Cassini experienced was increasing rapidly.