
Cassini's Saturn Mission Goes Out in a Blaze of Glory - okket
http://www.npr.org/sections/thetwo-way/2017/09/15/550709214/cassinis-saturn-mission-goes-out-in-a-blaze-of-glory
======
adventured
"It's 13-year mission to explore the strange world of Saturn went on nearly a
decade longer than planned."

Another testament to NASA's approach of relying on extremely well tested,
older technology.

When I was younger I didn't entirely agree with that approach (imagining what
could be done with the latest & greatest camera tech etc etc). Having lived
long enough to see a few of these very extended duration missions, has
entirely put me in the corner of agreeing with their approach.

This is also why it's ok, more often than not, that NASA missions cost so much
(a more frequent criticism these days). 20 years in space; 13 engaged in a
highly functional, active mission; truly incredible.

~~~
mikeash
Don't they use the latest and greatest tech that has been made spaceworthy?
It's not just a matter of whether it's been tested a lot. Off-the-shelf
electronics just won't work for these things, because they're not sufficiently
hardened against radiation. From what I can dig up, it looks like Cassini uses
20-30MHz 16-bit CPUs, which is really not bad at all for a probe whose design
started around the early 1990s.

~~~
pilom
NASA does things this way but SpaceX explicitly does not. Rather than using 1
space hardened part, SpaceX usually uses 3 non-space hardened parts
(processor, memory, bus, etc) that all do exactly the same calculations
simultaneously and then compare every single answer and ignore it when one out
of 3 parts disagree. This allows them to be both cheaper and much less power
hungry because they operate at least 2 process nodes smaller than NASA
hardware. I've seen data that says that while each individual processor will
experience space related errors quite often, the whole 3 part voting system is
at least as accurate as the way NASA does it.

~~~
branchan
It's not a SpaceX-only scheme, nor is it novel technology. It's got a long
history in fighter jets, as well as modern passenger planes for example
(Boeing 777).

Triple Mode Redundancy:
[https://en.wikipedia.org/wiki/Triple_modular_redundancy](https://en.wikipedia.org/wiki/Triple_modular_redundancy)

Also, the longest life span SpaceX has ever really needed is maybe the Dragon,
which is a month-long mission. Cassini has been in space for 20 years. Very
different design requirements.

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ccozan
Linking my comment to a sister submission [1]:

Final Images ( choose Grand Finale )

[https://saturn.jpl.nasa.gov/galleries/images/](https://saturn.jpl.nasa.gov/galleries/images/)

I wonder if it got destroyed or just lost the signal due to the atmosphere.
Amazing times to live.

[1]
[https://news.ycombinator.com/item?id=15256753](https://news.ycombinator.com/item?id=15256753)

~~~
ygra
Considering the final speed of the probe I don't think there's any likelihood
of not breaking and burning up. The whole end of its mission was designed to
do exactly that.

~~~
ctdonath
>75,000 MPH at atmosphere contact.

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ctdonath
Watching final coverage, I didn't notice anyone mention that the crash
actually happened an hour earlier - speed of light being what it is, the
signal being watched taking around an hour to arrive. Spent some time trying
to grok the dichotomy while waiting for "signal lost".

[https://10middletonp.files.wordpress.com/2015/09/watchmen-20...](https://10middletonp.files.wordpress.com/2015/09/watchmen-20090223034855816.jpg?w=700)

~~~
dpq
They definitely did, at least in the JPL 360deg stream (can't say if the
commentary was identical across all locations, but probably not).

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herodotus
Pictures from these kind of NASA events always show rows and rows of people
sitting at computer screens. I have always wondered why there are so many of
them, and what they are doing. Obviously there is a lot of work to be done to
process the data that is received, but why so many real-time people? Is it
just organizational bloat?

~~~
sosuke
They were ahead of the curve with the open office plan. I always assumed each
person was responsible for paying attention to or watching some specific
system or stream of data to alert any possible issue.

I'd also be fine with everyone just showing up because they worked hard and
long on the project.

Look at the CERN control room shots too
[http://home.cern/sites/home.web.cern.ch/files/image/update-f...](http://home.cern/sites/home.web.cern.ch/files/image/update-
for_the_public/2015/06/control-room-lhc-physics-restart-2015.jpg)
[http://today.slac.stanford.edu/images/2008/lhc-control-
room3...](http://today.slac.stanford.edu/images/2008/lhc-control-room3-lg.jpg)

There are a lot of moving parts

~~~
digikata
A nitpick would be that open office is probably pretty great for mission
control/control rooms where some complex event is being coordinated as it
unfolds in real time. But I don't think NASA engineers necessarily develop in
such settings.

~~~
sosuke
You're absolutely right I was flippant with the open office remark.

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rficcaglia
It was rewarding to have made a contribution, however small, to Cassini. I
can't believe that beautiful object I last saw in the clean bay all those
years ago (decked out with a jack-o-lantern face for Halloween) is gone. Good
bye Cassini!

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cletusw
Don't miss NASA's incredible CG video of what this was like:
[https://www.youtube.com/watch?v=xrGAQCq9BMU](https://www.youtube.com/watch?v=xrGAQCq9BMU)

~~~
tombh
That was incredible. Really moving :'(

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jachee
I'm truly sad that Cassini's gone; more than I thought I'd be.

I didn't fully realize until today that I'd been keeping an eye on it for
roughly 1/4 of my life.

~~~
kafkaesq
It isn't "gone", by any stretch.

Its images and the research directions it spawned will live on far longer than
anything most of us will hope to every be able to bring into the world, or
otherwise accomplish.

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luckyt
> Scientists [were] worried that when [Cassini] loses power, it could crash
> into a pristine moon, contaminating a place where we might someday search
> for life

Why is this so bad? Moons are pretty big compared to spacecraft, why are they
so worried about the environmental damage of a single spacecraft weighing a
few tons?

~~~
pavel_lishin
Think fifty years in the future. The Herschel probe lands on Enceladus, armed
with instruments that can sample the water and test it for presence of
biological life. A hit! A world-changing discovery, we've detected DNA!

...but wait, hang on a second, check the records. Isn't this really close to
where we predict that Cassini crash-landed after it ran out of fuel and
contact was lost in 2023? Shit. Shit shit shit. We have no idea whether this
DNA is actually from the oceans of Enceladus, or if it's from a hardy bacteria
that hitched a ride on Cassini all the way from Earth, and thrived in the
oceans of Enceladus.

If it's thriving in Enceladus, it might be out-competing the life that's
already there. We may never know, we _can 't_ know what native Enceladus life
was like, or if it even existed!

They're not worried about knocking down some space-trees; they're worried
about it being impossible to assess scientific results with accuracy.

~~~
FuNe
Why not worrying about the same thing about Saturn though? The best thing
would be to slingshot Cassini in outer space like Voyagers but I guess they
wouldn't have this option here.

~~~
crispyambulance
The moons of Saturn are small even compared to the earth. One could expect far
more "wreckage" to survive the entry to a moon.

Getting into Saturn, however, is vastly different. Casssini has broken up into
many smallish, white-hot pieces only to eventually merge into clouds of
ammonia at -200C that are blowing at extreme velocities. Further down, there
are clouds of water at 0C and then metallic liquid hydrogen. Perhaps pieces
could end up there or on the rocky core? Saturn is a weird place.

How much worse than an autoclave is entry to Saturn?

~~~
Pigo
Titan is actually larger than Mercury. Just something I learned yesterday
while reading Cassini posts. It really puts the size of Saturn into
perspective.

~~~
FreeFull
Titan is larger, but also significantly less dense. Mercury is more massive
than Titan.

~~~
craftyguy
Mercury is pretty much just a leftover iron core

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dmix
> "We don't have a gas gauge. It would be really nice if we did," Molly
> Bittner, a systems engineer at JPL who has worked on Cassini for the past
> four years, tells NPR. Instead, mission controllers had to estimate the
> amount of fuel used by each maneuver. And there had been lots of maneuvers
> since 2004.

Does anyone know why they couldn't have a way to measure the amount of fuel
left? This seems like a relatively easy engineering problem from a non-expert
perspective.

~~~
pjc50
The conventional method is a float valve, which obviously doesn't work in
space. Putting a sensor in the tank also involves drilling a hole, which
compromises its strength. I think the simple answer is that they didn't _need_
it, so they left it out and relied on highly accurate predictions of fuel
usage.

~~~
bashinator
There's not actually gas, or a tank. Most space probes like this are powered
by radioactive decay of a plutonium core.

~~~
jakebasile
That's used to generate electricity. The spacecraft still use propellant when
they need to generate thrust.

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ionwake
What is the time latency between taking a photo and transmitting the complete
data for it?

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HillaryBriss
> _" Congratulations to you all," Maize announced to applause. "It's been an
> incredible mission, incredible spacecraft, and you're all an incredible
> team."_

And one final note: we have just about run out of budget on this, so back at
your desks you'll each find a security guard and an empty, commemorative JPL
cardboard box and if you can just fill that by 4 pm and ...

~~~
greglindahl
JPL actually does a pretty good job of taking care of their employees, with
many projects in action at once.

I went to grad school with a JPL employee who was getting her master's degree
in astronomy during the cruise part of Voyager 2's flight between Uranus and
Neptune.

