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Cassini's Saturn Mission Goes Out in a Blaze of Glory

235 points by okket 9y ago

luckyt 9y ago
> 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?
- dottrap 9y ago
  They are worried Earth microbes on the satellite might eventually be confused for life on the moon.
- pavel_lishin 9y ago
  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.
  - nsxwolf 9y ago
    Shouldn't we expect life on Enceladus to be different enough to tell the difference?
    - sosuke 9y ago
      I'd say when we can ensure no contamination there isn't any reason not to ensure no contamination. What if it turned out that the DNA found was similar to ours? Now think of the difference in chances if we'd dropped Cassini on the surface or if we hadn't.
    - pavel_lishin 9y ago
      > Shouldn't we expect life on Enceladus to be different enough to tell the difference? We should likely have as few expectations as possible. The discovery of an entirely different form of life on Enceladus would be as incredible as the discovery that life on Enceladus uses the same DNA building blocks as we do.
  - ekianjo 9y ago
    > We may never know, we can't know what native Enceladus life was like, or if it even existed! To be fair we don't even know if life on Earth is native to it in the first place or not...
    - Cthulhu_ 9y ago
      True, in fact I think a dominant theory is that life came from Somewhere Else, hitching a ride on an asteroid. Another one is that it formed around the volcanic vents in the ocean.
      - Retric 9y ago
        Solar wind makes live seeding from outside the solar system significantly less likely. It's possible, but considered far less likely than you might think. On the other hand life going from Earth to Mars/other moons etc is expected.
    - adrianN 9y ago
      Finding life on Saturn's moons that looks eerily related to life on Earth would provide some weight to panspermia theories. But only if we could be sure that we didn't bring it there ourselves.
  - FuNe 9y ago
    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 9y ago
      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 9y ago
        Titan is actually larger than Mercury. Just something I learned yesterday while reading Cassini posts. It really puts the size of Saturn into perspective.
        dmoy 9y ago
        Mercury is also real damn small. Just a tiny bit bigger than Earth's moon.
        FreeFull 9y ago
        Titan is larger, but also significantly less dense. Mercury is more massive than Titan.
        craftyguy 9y ago
        Mercury is pretty much just a leftover iron core
    - delibes 9y ago
      Gas giants are a much less obvious place for native life to evolve, at least from our understanding of life. Enceladus appears to have liquid water, which makes it much more likely (still slim). That said, Arthur C Clarke included giant city-sized lifeforms floating in the clouds of Jupiter in his 2001, 2010, 2061 series. And Isaac Asimov wrote "Victory Unintentional" in the robots series.
  - mcbits 9y ago
    It seems pretty unlikely that Earth life could accidentally seed any moon of Saturn, and extremely unlikely that it could out-compete life that's been adapting to that environment for eons. As in, even less likely than Earth's surface bacteria hitching a ride on probes down to volcanic vents on Earth and out-competing the life there. Maybe it would find a small niche to fill. No matter how careful we are, if we do find life on another planetary body, genetically similar enough to be confused with present-day Earth life, the assumption should be that it is from Earth and there had been no other life. Unfortunately it leaves "are we alone?" unanswered, but it answers "can life exist beyond Earth?"
    - ceejayoz 9y ago
      Cassini has an RTG, so a crash into something like Encaladus could potentially create a nice warm little oasis for Earth bacteria to live in. A few decades and some on the fringes of this oasis might adapt - there's believed to be liquid water there. Don't have to out-compete if there's nothing there, and being similar to Earth life wouldn't let us rule it out - rocks from asteroid impacts are known to have travelled between Earth and Mars, so it's not outrageous for one to have travelled between Earth and Saturn.
      - mcbits 9y ago
        If we find life on Enceladus that looks just like Earth life, the null hypothesis is that it came from Earth. That won't change, whether we crash a probe there or not. Finding extant life anywhere beyond Earth would still be a paradigm-shattering discovery, even if we must assume it arrived from Earth on a probe or ejecta. The probe we send to test for life must, of course, be completely sterile to ensure it's not detecting its own hitchhikers.
        ceejayoz 9y ago
        > If we find life on Enceladus that looks just like Earth life, the null hypothesis is that it came from Earth. Sure, and ruling that out is easier if we can say for certain we didn't crash an old space probe nearby.
  - Robotbeat 9y ago
    "no idea" and "impossible" is a stretch of the truth. Hyperbole. There are lots of tools in the biologist's shed for this sort of thing, and we know how to use them (think of all the field work done anywhere on Earth, such as Antarctica... if the task of sorting life was impossible, we should defund all of that immediately). We have an idea. It just makes it harder in the extremely remote chance that it crashes in such a way that it could contaminate an icy moon and have any passengers start growing wildly. Personally, I think that, fundamentally and cosmically, the whole point of Gaia producing a species which can send probes to other planets is contamination. We're Gaia's reproductive system.
- MikeFez 9y ago
  >contaminating a place where we might someday search for life Should it have crashed into a moon that we later find life on (especially should the life be remarkably similar to that here on earth), whose to say we didn't send it there via Cassini in the first place? Avoiding this problem entirely seems to be the best bet, also allowing them to collect atmospheric data from Saturn on the way out.
  - pvaldes 9y ago
    In some cases we could still estimate a probable answer. Biologists can separate two cryptic species of living beings placed into an species complex, just taking a look to its DNA. The mutation rate among two isolated bacteria from earth and saturn would be noticeable. Unless we discover an active saturnian's nano-turism to pass the holidays on earth's oceans, the only reasonable answer to explain two identical or almost identical bacteria in both planets is a contamination event.
- nickhalfasleep 9y ago
  Cassini's mission profile was to do progressively more dangerous activities as the time allowed. Nearing propellant exhaustion, they investigated close to the rings and the planet's upper atmosphere before destruction. Contamination prevention was only a part of the decision.
- celias 9y ago
  "All solar systems missions are subject to constraints designed to minimize the unintentional impacts of Mars and, when applicable, the contamination of icy satellites such as Europa, Enceladus, and Ganymede." [1], also see [2] "The Huygens probe which landed on Titan was not sterilized as the chances of finding life were considered insignificant. From further investigations it is evident that chances for life on Titan are higher than initially thought. Although forward contamination in this case is still considered unlikely, it reinforces the need to ensure we protect extra-terrestrial chances of life." [3], also see the second page of [4] [1] https://planetaryprotection.nasa.gov/requirements https://planetaryprotection.nasa.gov/requirements [2] https://saturn-archive.jpl.nasa.gov/faq/FAQHuygens/ https://saturn-archive.jpl.nasa.gov/faq/FAQHuygens/ [3] http://www.spacesafetymagazine.com/space-exploration/extraterrestrial-life/cassini-huygens-preventing-biological-contamination/ http://www.spacesafetymagazine.com/space-exploration/extrate... [4] http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens/No_bugs_please_this_is_a_clean_planet http://www.esa.int/Our_Activities/Space_Science/Cassini-Huyg...
adventured 9y ago
"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 9y ago
  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 9y ago
    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.
    - ygra 9y ago
      There's also a difference between a space probe, built once and having a mission that spans years or decades, and a rocket that gets built more often and operates only in Earth orbit (especially the first stage has to worry far less about radiation flipping bits). This isn't solely a difference between NASA and SpaceX, but also a difference in mission requirements.
ccozan 9y ago
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
- rhcom2 9y ago
  > Insulating gold-colored blankets will char and break off first, followed by Cassini's antenna, 30-foot-long magnetometer boom, and other loose or fragile parts. Carbon blocks full of plutonium-238 fuel will last the longest. > "It will basically disintegrate ... long before we hit any real surface of Saturn," Webster said. http://www.businessinsider.com/time-cassini-will-be-destroyed-timeline-2017-9 http://www.businessinsider.com/time-cassini-will-be-destroye... Sounds like an explosive goodbye ;)
- nsxwolf 9y ago
  I'm not seeing a "Grand Finale". Did it move?
  - jonkiddy 9y ago
    Blue dropdown menu on the left side under the main graphic.
- ygra 9y ago
  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 9y ago
    >75,000 MPH at atmosphere contact.
herodotus 9y ago
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?
- ccozan 9y ago
  Found this[1] answer. Basically, each of them is watching/controlling a small part or a subsystem of a such mission. Some organisational overhead is possible ( dunno, chief scientist, mission director/assistant, etc ). [1] http://www.slate.com/blogs/quora/2014/05/25/how_do_nasa_s_mission_control_centers_operate.html http://www.slate.com/blogs/quora/2014/05/25/how_do_nasa_s_mi...
- sosuke 9y ago
  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-for_the_public/2015/06/control-room-lhc-physics-restart-2015.jpg http://home.cern/sites/home.web.cern.ch/files/image/update-f... http://today.slac.stanford.edu/images/2008/lhc-control-room3-lg.jpg http://today.slac.stanford.edu/images/2008/lhc-control-room3... There are a lot of moving parts
  - digikata 9y ago
    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 9y ago
      You're absolutely right I was flippant with the open office remark.
dmix 9y ago
> "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.
- clarkmoody 9y ago
  If you know the thrust of the engine, then you can calculate the mass of the spacecraft based on how the orbit changes given a certain engine burn. I assume the dry mass of the craft is known to high certainty, so (almost) everything else is propellant.
  - deleted 9y ago
    [deleted]
- pjc50 9y ago
  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.
  - dmix 9y ago
    True, they probably didn't need to solve the problem of directly measuring fuel in low gravity, given the thousands of other problems they needed to solve. Apparently this is a common problem with satellites as well: > “Traditional gauging methods tend to have wider error bands as the tank empties" > Measuring how much fuel remains in an operating spacecraft has been a matter of educated guesswork. It is calculated either by book-keeping – estimating the fuel used on every thruster burn – or using a pressure sensor to estimate from headspace gas pressure how much liquid fuel is left. Unfortunately, book-keeping can be as much as 10% too high or too low, while the gas method consistently overestimates fuel reserves. https://www.newscientist.com/article/dn11254-new-spacecraft-fuel-gauge-may-reduce-space-junk/ https://www.newscientist.com/article/dn11254-new-spacecraft-...
cletusw 9y ago
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 9y ago
  That was incredible. Really moving :'(
ctdonath 9y ago
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-20090223034855816.jpg?w=700 https://10middletonp.files.wordpress.com/2015/09/watchmen-20...
- dpq 9y ago
  They definitely did, at least in the JPL 360deg stream (can't say if the commentary was identical across all locations, but probably not).
rficcaglia 9y ago
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!
HillaryBriss 9y ago
> "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 9y ago
  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.
jachee 9y ago
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.
- TheOtherHobbes 9y ago
  Amazing mission. But I expect some of us (probably not me) will get to see it close-up for ourselves.
- kafkaesq 9y ago
  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.
jra_samba 9y ago
Anyone remember the anti-nuclear protests trying to stop Cassini from launching ? https://www.youtube.com/watch?v=X_S3pvt2PvY https://www.youtube.com/watch?v=X_S3pvt2PvY I do. Anti-science savages who would have prevented one of the greatest achievements of the human race. It's why I no longer think of Michio Kaku as anything but a bad joke. He should have known better.
ionwake 9y ago
What is the time latency between taking a photo and transmitting the complete data for it?

235 points by okket 9y ago

> 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?

dottrap 9y ago
They are worried Earth microbes on the satellite might eventually be confused for life on the moon.
pavel_lishin 9y ago
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.
- nsxwolf 9y ago
  Shouldn't we expect life on Enceladus to be different enough to tell the difference?
  - sosuke 9y ago
    I'd say when we can ensure no contamination there isn't any reason not to ensure no contamination. What if it turned out that the DNA found was similar to ours? Now think of the difference in chances if we'd dropped Cassini on the surface or if we hadn't.
  - pavel_lishin 9y ago
    > Shouldn't we expect life on Enceladus to be different enough to tell the difference? We should likely have as few expectations as possible. The discovery of an entirely different form of life on Enceladus would be as incredible as the discovery that life on Enceladus uses the same DNA building blocks as we do.
- ekianjo 9y ago
  > We may never know, we can't know what native Enceladus life was like, or if it even existed! To be fair we don't even know if life on Earth is native to it in the first place or not...
  - Cthulhu_ 9y ago
    True, in fact I think a dominant theory is that life came from Somewhere Else, hitching a ride on an asteroid. Another one is that it formed around the volcanic vents in the ocean.
    - Retric 9y ago
      Solar wind makes live seeding from outside the solar system significantly less likely. It's possible, but considered far less likely than you might think. On the other hand life going from Earth to Mars/other moons etc is expected.
  - adrianN 9y ago
    Finding life on Saturn's moons that looks eerily related to life on Earth would provide some weight to panspermia theories. But only if we could be sure that we didn't bring it there ourselves.
- FuNe 9y ago
  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 9y ago
    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 9y ago
      Titan is actually larger than Mercury. Just something I learned yesterday while reading Cassini posts. It really puts the size of Saturn into perspective.
      - dmoy 9y ago
        Mercury is also real damn small. Just a tiny bit bigger than Earth's moon.
      - FreeFull 9y ago
        Titan is larger, but also significantly less dense. Mercury is more massive than Titan.
        craftyguy 9y ago
        Mercury is pretty much just a leftover iron core
  - delibes 9y ago
    Gas giants are a much less obvious place for native life to evolve, at least from our understanding of life. Enceladus appears to have liquid water, which makes it much more likely (still slim). That said, Arthur C Clarke included giant city-sized lifeforms floating in the clouds of Jupiter in his 2001, 2010, 2061 series. And Isaac Asimov wrote "Victory Unintentional" in the robots series.
- mcbits 9y ago
  It seems pretty unlikely that Earth life could accidentally seed any moon of Saturn, and extremely unlikely that it could out-compete life that's been adapting to that environment for eons. As in, even less likely than Earth's surface bacteria hitching a ride on probes down to volcanic vents on Earth and out-competing the life there. Maybe it would find a small niche to fill. No matter how careful we are, if we do find life on another planetary body, genetically similar enough to be confused with present-day Earth life, the assumption should be that it is from Earth and there had been no other life. Unfortunately it leaves "are we alone?" unanswered, but it answers "can life exist beyond Earth?"
  - ceejayoz 9y ago
    Cassini has an RTG, so a crash into something like Encaladus could potentially create a nice warm little oasis for Earth bacteria to live in. A few decades and some on the fringes of this oasis might adapt - there's believed to be liquid water there. Don't have to out-compete if there's nothing there, and being similar to Earth life wouldn't let us rule it out - rocks from asteroid impacts are known to have travelled between Earth and Mars, so it's not outrageous for one to have travelled between Earth and Saturn.
    - mcbits 9y ago
      If we find life on Enceladus that looks just like Earth life, the null hypothesis is that it came from Earth. That won't change, whether we crash a probe there or not. Finding extant life anywhere beyond Earth would still be a paradigm-shattering discovery, even if we must assume it arrived from Earth on a probe or ejecta. The probe we send to test for life must, of course, be completely sterile to ensure it's not detecting its own hitchhikers.
      - ceejayoz 9y ago
        > If we find life on Enceladus that looks just like Earth life, the null hypothesis is that it came from Earth. Sure, and ruling that out is easier if we can say for certain we didn't crash an old space probe nearby.
- Robotbeat 9y ago
  "no idea" and "impossible" is a stretch of the truth. Hyperbole. There are lots of tools in the biologist's shed for this sort of thing, and we know how to use them (think of all the field work done anywhere on Earth, such as Antarctica... if the task of sorting life was impossible, we should defund all of that immediately). We have an idea. It just makes it harder in the extremely remote chance that it crashes in such a way that it could contaminate an icy moon and have any passengers start growing wildly. Personally, I think that, fundamentally and cosmically, the whole point of Gaia producing a species which can send probes to other planets is contamination. We're Gaia's reproductive system.
MikeFez 9y ago
>contaminating a place where we might someday search for life Should it have crashed into a moon that we later find life on (especially should the life be remarkably similar to that here on earth), whose to say we didn't send it there via Cassini in the first place? Avoiding this problem entirely seems to be the best bet, also allowing them to collect atmospheric data from Saturn on the way out.
- pvaldes 9y ago
  In some cases we could still estimate a probable answer. Biologists can separate two cryptic species of living beings placed into an species complex, just taking a look to its DNA. The mutation rate among two isolated bacteria from earth and saturn would be noticeable. Unless we discover an active saturnian's nano-turism to pass the holidays on earth's oceans, the only reasonable answer to explain two identical or almost identical bacteria in both planets is a contamination event.
nickhalfasleep 9y ago
Cassini's mission profile was to do progressively more dangerous activities as the time allowed. Nearing propellant exhaustion, they investigated close to the rings and the planet's upper atmosphere before destruction. Contamination prevention was only a part of the decision.
celias 9y ago
"All solar systems missions are subject to constraints designed to minimize the unintentional impacts of Mars and, when applicable, the contamination of icy satellites such as Europa, Enceladus, and Ganymede." [1], also see [2] "The Huygens probe which landed on Titan was not sterilized as the chances of finding life were considered insignificant. From further investigations it is evident that chances for life on Titan are higher than initially thought. Although forward contamination in this case is still considered unlikely, it reinforces the need to ensure we protect extra-terrestrial chances of life." [3], also see the second page of [4] [1] https://planetaryprotection.nasa.gov/requirements https://planetaryprotection.nasa.gov/requirements [2] https://saturn-archive.jpl.nasa.gov/faq/FAQHuygens/ https://saturn-archive.jpl.nasa.gov/faq/FAQHuygens/ [3] http://www.spacesafetymagazine.com/space-exploration/extraterrestrial-life/cassini-huygens-preventing-biological-contamination/ http://www.spacesafetymagazine.com/space-exploration/extrate... [4] http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens/No_bugs_please_this_is_a_clean_planet http://www.esa.int/Our_Activities/Space_Science/Cassini-Huyg...

adventured 9y ago

"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 9y ago
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 9y ago
  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.
  - ygra 9y ago
    There's also a difference between a space probe, built once and having a mission that spans years or decades, and a rocket that gets built more often and operates only in Earth orbit (especially the first stage has to worry far less about radiation flipping bits). This isn't solely a difference between NASA and SpaceX, but also a difference in mission requirements.

ccozan 9y ago

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

rhcom2 9y ago
> Insulating gold-colored blankets will char and break off first, followed by Cassini's antenna, 30-foot-long magnetometer boom, and other loose or fragile parts. Carbon blocks full of plutonium-238 fuel will last the longest. > "It will basically disintegrate ... long before we hit any real surface of Saturn," Webster said. http://www.businessinsider.com/time-cassini-will-be-destroyed-timeline-2017-9 http://www.businessinsider.com/time-cassini-will-be-destroye... Sounds like an explosive goodbye ;)
nsxwolf 9y ago
I'm not seeing a "Grand Finale". Did it move?
- jonkiddy 9y ago
  Blue dropdown menu on the left side under the main graphic.
ygra 9y ago
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 9y ago
  >75,000 MPH at atmosphere contact.

herodotus 9y ago

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?

ccozan 9y ago
Found this[1] answer. Basically, each of them is watching/controlling a small part or a subsystem of a such mission. Some organisational overhead is possible ( dunno, chief scientist, mission director/assistant, etc ). [1] http://www.slate.com/blogs/quora/2014/05/25/how_do_nasa_s_mission_control_centers_operate.html http://www.slate.com/blogs/quora/2014/05/25/how_do_nasa_s_mi...
sosuke 9y ago
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-for_the_public/2015/06/control-room-lhc-physics-restart-2015.jpg http://home.cern/sites/home.web.cern.ch/files/image/update-f... http://today.slac.stanford.edu/images/2008/lhc-control-room3-lg.jpg http://today.slac.stanford.edu/images/2008/lhc-control-room3... There are a lot of moving parts
- digikata 9y ago
  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 9y ago
    You're absolutely right I was flippant with the open office remark.

dmix 9y ago

> "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.

clarkmoody 9y ago
If you know the thrust of the engine, then you can calculate the mass of the spacecraft based on how the orbit changes given a certain engine burn. I assume the dry mass of the craft is known to high certainty, so (almost) everything else is propellant.
- deleted 9y ago
  [deleted]
pjc50 9y ago
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.
- dmix 9y ago
  True, they probably didn't need to solve the problem of directly measuring fuel in low gravity, given the thousands of other problems they needed to solve. Apparently this is a common problem with satellites as well: > “Traditional gauging methods tend to have wider error bands as the tank empties" > Measuring how much fuel remains in an operating spacecraft has been a matter of educated guesswork. It is calculated either by book-keeping – estimating the fuel used on every thruster burn – or using a pressure sensor to estimate from headspace gas pressure how much liquid fuel is left. Unfortunately, book-keeping can be as much as 10% too high or too low, while the gas method consistently overestimates fuel reserves. https://www.newscientist.com/article/dn11254-new-spacecraft-fuel-gauge-may-reduce-space-junk/ https://www.newscientist.com/article/dn11254-new-spacecraft-...

cletusw 9y ago

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 9y ago
That was incredible. Really moving :'(

ctdonath 9y ago

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

dpq 9y ago
They definitely did, at least in the JPL 360deg stream (can't say if the commentary was identical across all locations, but probably not).

rficcaglia 9y ago

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!

HillaryBriss 9y ago

> "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 9y ago
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.

jachee 9y ago

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.

TheOtherHobbes 9y ago
Amazing mission. But I expect some of us (probably not me) will get to see it close-up for ourselves.
kafkaesq 9y ago
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.

jra_samba 9y ago

Anyone remember the anti-nuclear protests trying to stop Cassini from launching ? https://www.youtube.com/watch?v=X_S3pvt2PvY https://www.youtube.com/watch?v=X_S3pvt2PvY I do. Anti-science savages who would have prevented one of the greatest achievements of the human race. It's why I no longer think of Michio Kaku as anything but a bad joke. He should have known better.

ionwake 9y ago

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