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 http://ciclops.org/news/looking_ahead.php?js=1 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 http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/44315/1/13-2872_A1b.pdf 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.
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.
Some links to information and movies:
Animated video about Cassini's Grand Finale https://youtu.be/xrGAQCq9BMUhttps://youtu.be/xrGAQCq9BMU
Information and links from JPL http://saturn.jpl.nasa.gov/grandfinalehttp://saturn.jpl.nasa.gov/grandfinale
First dive Wednesday April 26th.
Less than 150,000 miles out now.
Fingers crossed!
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 https://twitter.com/CassiniSaturn no earlier than ~midnight PT April 26 (3am ET, 7am UTC April 27)"
Carrier?
https://eyes.nasa.gov/dsn/dsn.html
Downlink started!
Awesome.
Great news!
Images--see Twitter https://twitter.com/CassiniSaturn
Excuse my ignorance, but this hurricane is the one at the North Pole, right?
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.
Yeah, here's a https://twitter.com/BeckePhysics/status/857561648495828992 of the north pole cloud structure.
I made a gif of the dive!
http://i.imgur.com/i6uMzG2.gifv
Nice colours in this recent view (RGB stack from W00107043, W00107044 and W00107045)
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!
Not sure if this has been posted, but this movie puts the images in context nicely:
https://www.youtube.com/watch?v=9LBLCgCYy0I
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
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:
Interesting brightness changes on the limb. Is this Saturnian twilight modulated by ring shadows?
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/images/raw/casJPGFullS99/N00281060.jpg
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.
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.
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.
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.
https://flic.kr/p/UPviDrhttps://flic.kr/p/UPviDr by https://www.flickr.com/photos/10795027@N08/, on Flickr
Breathtaking stuff! The definitive image of a backlit Saturn.
Very nice work.
Thanks Jase!
The other version of the mosaic (sans annotations) is actually presented 'upside-down', which is just an aesthetic choice:
https://flic.kr/p/UzdMSWhttps://flic.kr/p/UzdMSW
Cassini survived a close brush by the D ring, no word yet on whether it encountered much in the way of particle impacts.
https://spaceflightnow.com/2017/05/30/cassini-survives-closest-brush-with-saturns-inner-ring/
I made a video homage to the Cassini Mission:
https://vimeo.com/217370907
No new posts for two whole months? Where is everybody? :-o
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.
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.
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
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.
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.
EOM press event schedule https://saturn.jpl.nasa.gov/news/3104/nasa-announces-cassini-end-of-mission-activities/
A bit of surprise astrophotography from Cassini: http://saturnraw.jpl.nasa.gov/multimedia/images/raw/casJPGFullS101/N00287662.jpg
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.
Outstanding! Good hunting.
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 https://www.nasa.gov/press-release/nasa-announces-cassini-end-of-mission-media-activities
I assume most of us members of unmanned space flight will be watching.
Enhanced version of the cluster:
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.
Enhanced version of the cluster
Cassini also imaged Neptune and Triton back in August:
I realize that the only piece oh human hardware left in the Saturnian system will be Huygens on Titan...
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.
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.
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!
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).
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.
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/
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.
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
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
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.
Interior to Dione's orbital distance now.
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.
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.
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.
I'm not crying, you're crying!
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!)
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.
The final mosaic of Saturn is being downlinked. Here's a little part of it:
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
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
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.
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.
Looks like the final raws are down, showing the final target....
(and a final Captain's Log from Carolyn Porco: http://ciclops.org/)
Thank you and farewell, Cassini.
You will be missed.
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.
From Jonathan McDowell @planet4589 (via @elakdawalla)
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.
A truly awesome mission! This is humanity at its finest!
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/sets/72157686616794044/
Rob
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.
The plutonium fuel pellets in their aeroshells were believed to be the most 'survivable' hardware on board.
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.
According to a thread started by Jonathan McDowell @planet4589, again via @elakdawalla:
"There is still one piece of Cassini still in orbit around Saturn: the neutral mass spectrometer cover was ejected just after orbit insertion."
https://twitter.com/planet4589/status/908667423166955520
Edit: Jinxed by Doug.
Even if Cassini had descended gently past atmospheric entry, there's no part of it that would survive as the craft descends into Saturn's atmosphere which, like Jupiter's, is essentially bottomless and which will eventually, at sufficient depth, turn titanium into vapor and/or gas. This was the fate of the Galileo Probe, and would certainly be the fate of any such similar descent into Saturn.
The precise sequence of destruction with atmospheric entry might be a complex, unsolved, or even unsolvable research problem. Ablation would occur, part of the design of a heat shield, but inevitably a process also with some of Cassini's innards, which weren't designed for surviving entry. It seems like a complex fluid dynamic problem. When Skylab reentered Earth's atmosphere, nobody could have predicted which chunks survived to hit Australia. How a highly complex structure comes apart under stress cannot be predictable without (or even with) destructive testing.
So I'm not sure if we'll ever know which parts of Cassini lasted till when, but it's a sure thing that it's all gas or vapor now.
By the way, I was possibly imaging Saturn at the time the plunge was beginning. I was shooting an all-sky photo to capture the Milky Way, and Saturn was a dot somewhere in the field of view, unless a tree happened to block it. I'll definitely shoot a glimpse upwards tonight, as I did last night, and contemplate the mighty Cassini that was and is no more.
I'm just, like, all *sniffle sniffle* I love Cassini and all the work it's done for us. Enormously huge hats off to the engineers, scientists, and mission contol members who did all this.
Cassini's Grand Finale is especially bittersweet for me as it comes the day before my birthday. Thank you for all the great images, great revelations, and great science!
Followed the charmed mission since listening to the launch on the radio in '97. Sad to see it go but it's been one hell of a ride. I remember the first 7 years of the journey to Saturn being painfully long, though the past 10 or so of its presence there have now gone by terrifyingly fast. The Huygens landing remains the pinnacle of planetary science excitement for me, and I fear its fantastic wonder may never be equaled in my lifetime. Even though I post like once every 3 years now, glad to see this site still going, albeit not nearly with the level of activity of its heyday 8 years or so ago. I do not see many missions in progress or on the horizon having nearly the level of grandeur of our now largely complete initial survey of the solar system, but will stop by here from time to time nonetheless and hope to see that things are still marching along. till then...
In reference to past missions, and what we've lived through, it is perhaps obvious but must be stated in respect to the greatness of this board and those who run it…
The first big mission I was old enough to remember was Viking. And Viking was a masterpiece – four craft exploring the heck out of the most interesting planet and one really can't imagine the technology of the time doing it any better.
But my main source of Viking info was National Geographic and "year books" that supplemented encyclopedias. Occasionally, something would make the print or TV news, but the information cycle for me was more typically one year. Then a book summarizing the main mission might make it into my hands. Viking happened "while" I was alive and waiting for the results, but it wasn't all that different from reading about something that had happened in the 18th century. There was a before and an after, but no during. Likewise Pioneer Venus and Voyager at Jupiter. By the time of Voyager at Saturn, I was subscribed to publications that shortened the news cycle considerably, but it was rarely under a week.
In sharp contrast to that, I remember chatting live here about the first ISS pictures of Titan and manipulating them in Photoshop and having the real sense that I might be seeing something before anyone else ever had… and if I weren't first, I was certainly no more than minutes behind whoever was. Then, when Huygens arrived, a day when I shamelessly did no work at work, the fact that the first image was one of drainage channels in the headlands – unbelievable! And the descent more or less happened here in real time (plus some speed-of-light, downlink, etc. delay), with commentary (and sometimes it's well that interested amateurs are game to speculate more than a publishing scientist should). Viking happened in my lifetime, but Cassini and Huygens happened and were experienced here. And for the life that this provides the flow of information, I am tremendously grateful.
Cassini has been an awesome mission that I have been following closely since several years before (!) it was launched. I remember the launch back in 1997 as if it was yesterday and ditto for SOI, the Huygens landing and various other events and mission highlights.
I have mixed feelings about how the missions ended. I really like missions to end like Messenger and Venus Express, i.e. to keep going until the fuel is completely exhausted. On the other hand, ending the mission with an atmospheric entry yields valuable data that could not have been obtained by completely spending all of the fuel.
Ranking planetary missions by success is very difficult (and highly subjective) but it is my opinion that the Cassini-Huygens mission is the second most successful planetary mission ever flown; closely behind Voyager.
Congratulations to everyone on the Cassini team for bringing such a marvelous and inspiring mission to the public!
I wouldn't rank missions. Each mission returns data and is a success that stands on its own. And each mission serves as a basis or a foundation for future missions.
--Bill
.
Many thanks to the science and engineering teams that designed, delivered and kept this mission running so well for so long.
Cassini-Huygens was truly a mission of discovery. Cassini's Jupiter flyby delivered the full promise that Galileo could have provided, and then the Saturn primary mission yielded exhilarating exploration, including the early Phoebe encounter, Saturn orbit insertion, Huygens landing on Titan, radar and VIMS imaging of the Titan surface, Enceladus geysers, the Iapetus equatorial mountain ridge, and the Grand Finale Juno-like investigation of the giant planet, just to name a few.
While we all knew this day would come, it is a bittersweet passing onto a different, post-Cassini era.
The last 13 years have been amazing - it's been a great honour to be alive to witness them - and I'm sure there are many more discoveries lurking in the archived Cassini data. My heartfelt thanks to everyone who worked on the mission. May future exploration efforts do its memory justice.
As an archivist, history buff and a fan of vintage electronics, I'm mainly interested in the older missions, i.e. anything that carried a vidicon and a tape recorder and became one of the first couple spacecraft to encounter a specific planet or moon. As a 23 year old, I never got to experience any of them in real time (besides Voyager's interstellar journey), which saddens me. However, when I read recollections such as JRehling's - that for the public during the '70s, there was often just a before and an after, with no live experience like you'd get with a '60s Apollo mission - I am brought back to stark reality.
Cassini though? Cassini felt like an idealized version of those formative missions, and that has caused me to grow very fond of it and regard it as one of my favorite modern missions. It was like being able to follow, in real time, a Mariner or a Voyager that lasted a really long time, never chronically malfunctioned, and had a perfect suite of instruments, including some successors to Voyager hardware (like RPWS). Every flyby of a moon and every revolution in general felt like an event - like a Mariner or Voyager flyby. Having access to stuff like NASA's Eyes and being able to see the raw images as they came down really enhanced that "event" feeling. I think Cassini is as much of a successor to those old missions as New Horizons is.
All things must come to an end, though, and this was the perfect ending. The death plunge kept it from slowly dying and then becoming paper weight in a derelict orbit - it performed flawlessly until the very end, it became a part of Saturn in the process, and some interesting atmospheric science will probably come out of it. Many, many thanks and congratulations to all the champs on the Cassini team, and like others, I am very grateful for their openness to the public that allowed us to experience the mission as it happened. I hope someday we'll get to see a successor to this magnificent machine at Uranus or Neptune.
It may have been mentioned already, but Cassini's entry marks the point when all five classical planets have been directly touched by humanity. I wonder what the ancient astronomers would think.
The Prop team wanted to perform a "burn to depletion" all the way until the end of the mission, but that was vetoed years ago. The logic at the time was that it wasn't worth the risk to the INMS plunge science to perform the engineering test. There was also some nebulous concern about instrument contamination. If you burn to depletion then you will run out of either fuel first or oxidizer first and whichever one is left will then vent unburned as a cold gas thruster. There was some concern that the unburned fuel or oxidizer might coat or contaminate the science instruments.
There were a whole bunch of engineering tests that were seriously and jokingly suggested: jettisoning the ME cover to test if the unused pyros still functioned, performing a burn with the unused backup Main Engine, etc
Some calendrical bits of trivia that I find jarring: Cassini was launched only 11 months after the launch of Mars Global Surveyor, three years after the end of Magellan, and less than 2 years after the arrival of Galileo at Jupiter. The first pair is perhaps most significant, because Cassini was, in some estimations, the last hurrah for big "Battlestar Galactica" missions and MGS was an early exemplar in the faster, better, cheaper (FBC) paradigm that the failure of Mars Observer, a sort of Cassini-for-Mars, ushered in.
I can't help but think of how unfortunate it was that all of Cassini-Huygens' discoveries came too late for Carl Sagan to enjoy them. The initial reconnoissance of the solar system's major worlds was nearly complete when he died in 1996, but when one thinks of Titan and Pluto, it feels as though the solar system kept much of the best for last.
This juncture might be a time to remember that extended mission concepts once proposed for Cassini included going into Titan orbit or leaving Saturn orbit and journeying to Uranus. It sounded like the first was infeasible and the second simply unwise.
Yep, I remember the idea of Cassini ending up in Titan orbit from both a Stephen Baxter novel, and some speculation on how it could be accomplished in this very forum, circa 2004! ( http://www.unmannedspaceflight.com/index.php?showtopic=559 ). I still do wonder how plausible the main antenna as a heat shield would be...
I don't think the Uranus option ever made much sense. It would have cost a lot of Saturn science and created a huge and risky delay before arrival at Uranus. If anything, it was more of an impressive statement of possibilities.
Of course, in some alternate reality, alternate versions of us in 2029 will say, "Wow, if Cassini hadn't been sent to Uranus, we never would have known about _______!"
During the finale coverage, one member of the team (I forgot who) said that another possible alternative for disposal would have been an orbit far beyond both Enceladus and Titan. It may have been possible, but all the good science is of course in the centre of the system, so they decided to follow the science.
Sure, a few flybys of the irregular moons would have be good, along with plasma and dust science, but they balanced that against the ring and atmosphere science (we'll see what is recovered from the final dive)
See slide 19 here: http://www.lpi.usra.edu/opag/march_08_meeting/presentations/spilker.pdf
gif anim of the parting https://saturn.jpl.nasa.gov/raw_images/426408/ from September 13
My pictorial tribute to our dear and departed robotic friend ....
https://flic.kr/p/YyAFcE
https://flic.kr/p/YyAFcE by https://www.flickr.com/photos/10795027@N08/, on Flickr
The CICLOPS team version of the final mosaic: http://ciclops.org/view/8631/A-Farewell-to-Saturn
Farewell...
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