The Grand Finale, Proximal orbits Options

[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.

[djellison]

Is there any component of Cassini that could have survived the entry?

Possibly the INMS cover that was jettisoned after SOI many many years ago

[Tom Tamlyn]

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.

This post has been edited by Tom Tamlyn: Sep 15 2017, 06:02 PM

[JRehling]

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.

[wildespace]

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!

[deglr6328]

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...