Cassini’s mission ends

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Enceladus as seen by Cassini two days before mission end

After a seven year journey and thirteen years in orbit around Saturn, Cassini’s mission ended early this morning with a dive into Saturn’s atmosphere.

The image above, cropped to show here, is actually one from a short movie, showing Enceladus setting behind the horizon of Saturn. The images were taking two days ago, but provide a fitting image for the mission’s end.

Some of the best images from the dive, including Cassini’s last image, can be found here.

While most of the press will rightly wax eloquent about the magnificence of this mission, my focus remains on what will come next. We no longer have any way to observe what is happening on Saturn. We are blind. We should not be.



  • wodun

    my focus remains on what will come next

    I don’t know if the orbital mechanics would work out, so this would need to be adjusted for launch seasons. I always thought we should be building classes of satellites rather than one offs. Then we should be launching them on a regular schedule to visit all the planets. Considering long travel times, there would eventually always be something going on. Some of the satellites could be sent on Voyager type of journeys and others could be slow boats for prolonged observation.

    Something like this will never happen because there are so many voices competing for government money and each one wants to do some worthy, but one off, mission that will never be repeated. We likely wont get any sustained observation of any planet until people want to move there or open up a robotic water mine.

  • Edward

    wodun wrote: “I always thought we should be building classes of satellites rather than one offs.

    If by “classes of satellites” you mean several of the same design, that sounds like it could save money on design effort. Unfortunately, different destinations have different science requirements.

    For instance, the missions and requirements were very different for the Huygens probe into Titan’s atmosphere, the Galileo into probe into Jupiter, the Philae probe to comet 67P, and the various probes into Venus’s atmosphere.

    Different instruments are needed for different planets, asteroids, and comets. Followup probes often require new instruments in order to answer the questions raised by the previous probe. Different amounts of propellant are needed for different destinations, so propellant tanks need to be different in size. For instance, getting into orbit around Jupiter takes more delta V than getting into orbit around comet 67P, Ceres, Vesta, or Pluto.
    NASA did a flyby of Pluto, because it would take too much propellant for New Horizons to slow down into orbit.

    As technologies improve, it is nice to include updated, more modern instrumentation, thrusters, electronics, and structural materials. For instance, the Dawn spacecraft provided flight experience that proved that ion propulsion works well for travel around the solar system.

    Repeating exploration missions is not as useful as it may seem. For the most part, all we would get is more of the same information. Even Cassini changed her orbit several times in order to obtain different information from different perspectives.

    When Louis and Clark performed their expedition, no one thought that there was a need for a repeated expedition. Additional exploration and expansion into the western continent was done differently than a Louis and Clark type of expedition.

    As mpthompson noted, it would be nice for the next Saturn probe to be able to have close encounters (rendezvous) with the particles and rocks that make up the many rings. It would be nice to go there and do that, but it may be less productive if we have a generic, standard probe rather than a probe that is designed specifically for this exploration.

    wodun wrote: “We likely wont get any sustained observation of any planet until people want to move there or open up a robotic water mine.

    True. This is what is happening with Mars. After Apollo, NASA and much of the world looked toward Mars as the next destination for mankind, so the spacefaring nations sent far fewer probes to the Moon and began to send multiple probes to Mars, eventually maintaining sustained observation of that planet.

    When Dr. Alan Binder’s probe, Lunar Prospector, found evidence of large amounts of water at the Moon’s poles, there was sudden renewed enthusiasm for more lunar probes and for manned return to the Moon.

  • wodun

    different destinations have different science requirements.

    You sacrifice some specialization to gain commonality. Of course landing on Venus will require a different type of vehicle than landing on Titan. Observing either for long periods of time would not. Observation satellites could also help enable those other planetary specific missions.

    But let’s take your desire for hyper specialization. Here again, rather than one offs, it would be beneficial to build more at once. Why would we send just one probe to the surface of Venus? Why not send ten? Any desired changes in design could be fixed to the next run. And why wouldn’t we want missions to the surface of Venus supported from standardized satellites from above rather than yet another one off?

    The problem is that if you suggest sending ten landers, the scientists will think they all have to be unique.

    I am not sure how you can say that observing isn’t as beneficial as it seems because the recent flybys barely gave us any information. Even with longer programs like Cassini, there is so much that goes unstudied. Even our own planet presents us with mysteries despite how much it is observed.

    There are any number of solutions for propellant that don’t require radically different satellites. For one, you could build the standard one beefy enough for destinations further out/in and not min/max for everything in between. Another solution to special missions are modules launched from a mother, like cube sats or other devices.

    There is so much to be learned through what we are currently capable of and there are endless questions that require a specialized approach. Always focusing on the hyper specialization can be a detriment. What comes after landing a boat on Titan? Some other mission that doesn’t build off the last or support future missions.

  • Edward

    wodun suggested: “You sacrifice some specialization to gain commonality.

    When you only get an occasional satellite for each planet, sacrificing the specialization is not the first choice of the scientists who are interested in studying it. In fact, if you sacrifice the knowledge gained for a small reduction in cost, there will quickly become a point where the savings are not worth the missed knowledge. It is as obvious as the requirement for different probes for landing on Titan, Jupiter, Mars, or Venus.

    wodun asked: “Here again, rather than one offs, it would be beneficial to build more at once. Why would we send just one probe to the surface of Venus? Why not send ten?

    The Soviets Union sent several Venusian atmospheric probes with their Venera spacecraft. But is it cost effective to send ten identical probes that will return virtually identical atmospheric data when one or two identical probes will do the job? If we are going to send ten probes, then why not have them each be unique so that we get ten times as much knowledge from the very limited funds that we have?

    When we spend too much money on exploring one planet, then another planet(s) does not get explored. If we had sent ten Cassini type probes to Saturn, then how many other probes would not have been built to explore Jupiter, Pluto, Mars, Vesta, and Ceres? If only Cassini spacecraft had been built then it would have been too heavy to send to Pluto. If only Cassini spacecraft had been built, then we would be getting different data about Jupiter than from the more modern Juno satellite’s instrumentation?

    wodun asked: “you could build the standard one beefy enough for destinations further out/in and not min/max for everything in between.

    Then all that extra mass would limit the data returned. wodun complains about the limited data received from the New Horizons flyby of Pluto, but Dr. Alan Stern’s team explicitly chose more instrumentation over a heavier transmitter, preferring more data over the longer time required to transmit all that data.

    This is why the desire for “hyper specialization.” The whole purpose of the probe is to return data, not to save a couple of bucks. The scientists want the right tool for the right job. They don’t want to be limited with only a hammer to pound in a screw, and they don’t want a screwdriver where a file is necessary. This is a virtue, not a detriment.

    wodun wrote: “Another solution to special missions are modules launched from a mother, like cube sats or other devices.

    I made that point with mpthompson in reply to his comment. So far, cubesats are still being developed. So far, very few have propulsion systems. In the future, I hope that we have a lot of daughter probes that complement a mother probe, but that is different from standardization, because we would still want the right probe for each exploration. Each cubesat would be specialized for its specific mission, and that violates wodun’s thesis. Or we could just make a bunch of cheap, identical student cubesats to study the planets. That should be a big savings.

  • Edward

    Another way to look at the downsides of “hyper specialization” is that if someone decided that all of our space based telescopes would be Hubble telescopes then we wouldn’t have had COBE to give us a map of the cosmic microwave background radiation. We wouldn’t have had space based x-ray observatories, such as Chandra, to prove that black holes exist or that there is at least one black hole at the center of most galaxies.

    Financially, on a $500 million mission (probe, launch, operations costs) we may be able to save $50 million in “hyper specialization” design costs. However, if we only get 75% of the data that we want because we standardized our probes rather than “hyper specialize” then we were penny wise but pound foolish, because we now have to send 1.3 missions and spend $600 million to get the same data as the $1/2 billion mission. Rather than saving 10% we spend an extra 20%.

    Or if we standardize on the largest probe, then a mission that could have cost $500 million might cost $750 million (larger probe than necessary, larger launch vehicle than would have been necessary for the smaller, lighter probe).

  • Edward

    Sorry, the downside is of standardization, not specialization.

    (Where is my proofreader when I need one?)

  • Steve Earle

    I’ve always liked the idea of sending twin spacecraft on any long term mission: Two Pioneers, Two Voyagers, Two Vikings, Two Mars Rovers…. One-offs may be hyper specialized but they also put all of the “eggs” in one basket.

  • Edward

    Steve Earle,
    The idea of a backup probe has merit, especially when a technology is new and unproved. Another reason for duo probes is to explore two regions simultaneously. The lunar probes Ebb and Flow were necessary as a pair because the mapping required two spacecraft in order for their separation to be measured.

    However, any time that there is a second probe rather than a single probe, another probe to somewhere else is not funded. NASA is not like our welfare programs (paying people to be unproductive), for which funding automatically expands to fit the political expediency of the moment. NASA gets limited funding and thus requires priorities to assure wise and fruitful use of that limited funding. This is why there is only one Curiosity rover; the funding that could have built a second one was used for another probe(s), perhaps Juno.

    This is why I am so upset that tens of billions of dollars are being spent on SLS; it has no mission or goal and if only one probe uses it (to Europa), then that was a terribly expensive probe — especially since other existing rockets could launch that probe. It is nice to have heavy lift capability, but if that capability is not used to good effect, then it was neither a wise nor a fruitful use of limited funding.

    We could have used the money that is (mis)spent on SLS to design, build, launch, and operate another probe to Saturn and have tens of billions of dollars left over for even more science missions.

  • Steve Earle

    IIRC wasn’t the basic design of Curiosity supposed to be used again for several future RTG powered Rovers, not just one? I seem to recall that it was designed to have interchangeable experiments on the same chassis, which would (in theory) greatly reduce the price of follow-on missions.

    And yes, the existence of Twins has indeed meant that we could get twice the “bang for the buck”. Pioneers 10 and 11 went in different directions, as did the two Voyagers (after a mid-mission change). The two Vikings, and the two MERs were able to explore different parts of Mars.

    We are seeing one of the benefits to “Twinning” missions right now. If we had only sent the Spirit rover, the mission and science would have ended several years ago, but luckily we still have Opportunity. I only hope we don’t wish we had sent a twin with Curiosity if some Spirit-type mishap should happen to it.

    And as far as funding goes, I do get that all missions have to compete for limited dollars, but I have always been a fan of the Haddon Aerospace Co’s Motto:
    “The first rule of Government contracts is why build just one when you can build two at twice the price….” ;-)

    Contact: “Why Build One?”

  • Steve Earle: The next Martian rover, targeted for 2020 launch, is essentially using the same design as Curiosity, and some of the equipment built during the first rovers construction.

  • Steve Earle

    Oops, lets try that again:

    Contact: “Why Build One?”

    I was in another FB debate about George Soros earlier with someone who denied that Soros had ever willingly worked for/with the Nazi’s and still had that Youtube link on my clipboard…..

    I wish this board had an edit feature :-)

  • Steve Earle

    That’s great news Mr Z. is it still on target for that date? And did they solve the RTG supply problem?

  • wayne

    at one of the Cassini press conferences last week, the question of RTG’s & future supply, did come up during a Q&A.
    They currently have a certain amount of material on hand right now (which I do not recall) for the near term, and agreements for re-starting a production-line have been inked and I believe, are in process.

  • Edward

    Spirit and Opportunity come under the new and unproved technology category. Before them, we had Sojourner, which didn’t travel far from its lander. Its main purpose was to demonstrate that we could succeed with rovers on Mars. JPL was surprised with the difficulty that they had with the terrain that Spirit encountered, and learned to avoid that type of terrain, even with Curiosity’s larger wheels. Spirit and Opportunity proved the technology was ready for long distance exploration, independent of a Martian home base.

  • Steve Earle

    Thanks Wayne, I was under the impression that they had used the last available RTG’s already and had no timeline for any new ones.
    And by what I’ve read here (and heard from Mr Z on the JB podcast!), not only does NASA need a reliable source of RTG fuel, it also needs a new source for Rover wheels…… hopefully changing the wheels does not trigger a need to completely redesign the Curiosity Class rover chassis.

  • wayne

    RTG’s definitely came up in one of the 2 big press-conferences they had last week. I remember it, because I was surprised at the positive answer.

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