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.

[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.