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NASA holds media briefings ahead of Juno's arrival at Jupiter Monday

By Marc Boucher
NASA Watch
June 30, 2016
Filed under ,
NASA holds media briefings ahead of Juno's arrival at Jupiter Monday

Watch: Media Briefing – The Science of Juno’s Mission to Jupiter
During a news briefing from NASA’s Jet Propulsion Laboratory in Pasadena, California the science team involved with the Juno mission to Jupiter talked about the scientific goals of the mission.
This Fourth of July, the solar-powered Juno spacecraft will arrive at our solar system’s most massive planet after an almost five-year journey. Once in Jupiter’s orbit, the spacecraft will circle the Jovian world 37 times during 20 months, skimming to within 3,100 miles (5,000 kilometers) above the cloud tops. This is the first time a spacecraft will orbit the poles of Jupiter, providing new answers to ongoing mysteries about the planet’s core, composition and magnetic fields.

Marc’s note: NASA and Apple Music collaborated on short film, Visions of Harmony. The film and original music is available from the link in the tweet below on iTunes. It’s worth watching.

SpaceRef co-founder, entrepreneur, writer, podcaster, nature lover and deep thinker.

24 responses to “NASA holds media briefings ahead of Juno's arrival at Jupiter Monday”

  1. Daniel Woodard says:
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    Juno is an interesting mission to be sure, but solar panels don’t provide much power when the Sun is less than 5% as bright as it is on Earth. A small reactor like that designed for JIMO would be game-changing for both instruments and electric propulsion.

    • Tritium3H says:
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      Absolutely agree, Daniel. Our nation’s strategic nuclear infrastructure has been allowed to “decay” (pun intended) to a state in which the maintenance of a credible deterrent and state of readiness is at risk. This applies to not only to the weapons and delivery systems, but the human talent and resources necessary for design, testing, maintenance, staffing (etc.) of the active elements…as well as the stewardship of the national strategic stockpile. The production of PU-238 is an indirect casualty of this Nation’s deterioration of capabilities.

      Fortunately, the DOE has recognized the urgent need for new production of PU-238. ORNL is in proof-of-concept / pilot stage fuel production…with plans for ramping up to full-scale production levels by 2023.

      • Daniel Woodard says:
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        I agree, however I would point out that the JIMO reactor design used enriched uranium, not plutonium. Uranium is already produced in essentially unlimited quantities for the Navy’s fleet of nuclear-powered subs and surface ships, and in the unlikely event of a release, uranium is far less hazardous.

        • Tritium3H says:
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          Hi Daniel. JIMO was a completely different kettle of fish. The reason the cancelled JIMO spacecraft would have used enriched uranium is due to the fact that it would have employed nuclear electric propulsion (NEP), and thus required a bona-fide nuclear fission reactor and a Brayton cycle generator for power conversion. We are talking about almost a quarter megawatt of power.

          The proposed JIMO reactor involved a significant mass penalty, including much more intensive shielding requirements as well as heat dissipation system. Additionally, the cost for the design / development of the miniature nuclear reactor was considerable, and would have introduced significant novelty and mission risk. The JIMO mission was canceled in large part due to the cost and complexity of the fission reactor and power converter system, which would have required multiple launches and in-orbit assembly.

          Yes, the JIMO mission would have been amazing…and ultimately we require a high power density nuclear reactor to support long-endurance spacecraft propulsion for manned exploration and deep space missions.

          • Daniel Woodard says:
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            Wait a minute – JIMO was cancelled because it would have required development of challenging new technology that would have enabled spectacular new missions… isn’t that NASA’s job? Or am I missing something?

          • Tritium3H says:
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            Lol, you pretty much nailed it.

          • fcrary says:
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            As someone who was following it carefully for professional reasons, it was canceled because (1) the development costs would have been over $10 billion, and NASA didn’t have the money, (2) the only identified mission to use the technology didn’t justify the cost (although you could debate the wisdom of this criteria), and (3) electric propulsion would take months, if not years, to go from LEO to Earth escape. How those issues were weighted, and if there were others, I don’t know. But those were the main ones discussed at the time.

          • Daniel Woodard says:
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            Why couldn’t the launch vehicle take JIMO to Earth escape? With a total thrust of ~10 newtons, why would it take years with the Hall thrusters? Was there some reason NASA could not come up with more than one (1) potential mission for a spacecraft with a quarter megawatt of power at any distance from the Sun? What about Titan orbiting high-resolution imaging radar, orbiters of Saturn, Uranus, Neptune, Pluto, Triton, explorers of the Kuiper belt? What about energy for human exploration?

            Is nuclear power too dangerous for manned vehicles? Someone should tell the Navy.

            Development cost is a separate and important question. JIMO was twice the cost of a Nimitz-class nuclear carrier over three hundred meters in length. Why was it so expensive? NASA has had programs that have stayed on budget, programs that have gone vastly over budget, and programs for which no credible estimate of total cost has even been released. More accurate prediction of program cost and ways to reduce cost are critical needs, with or without JIMO.

          • fcrary says:
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            I’m splitting this into three replies, since you asked too many questions to answer without a excessively long reply.

            Let’s see, someone else made me dig up the Prometheus project final report (982-R120461, dated October 1, 2005), so let’s see if it helps.

            The wet mass of JIMO, with margin and uncertainty is given as 35,102 kg (26,681 kg CBE.) We do not have a launch vehicle which can take that mass to Earth escape velocity. The project considered various launch options, which included developing an enhanced version of existing launch vehicles or a heavy lift launch vehicle (as well as on-orbit assembly or fueling.) A heavy lift launch vehicle would allow a launch to escape velocity.

            With existing vehicles, going from LEO to escape takes a delta-v of about 7.5 km/s (for a slow spiral, the delta-v is close to the difference in circular orbital velocities.) Appallingly, the report does not give the electric propulsion system’s thrust. (If fact, a word-search for Newton and “N” as a single word turned up nothing but someone’s initials and things like events N and N-1. At least “pound” didn’t turn up anything either.) From the power and specific impulse, I get about 5-7 N, but let’s use your 20 N. 7.5 km/s, 20 N, 35,000 kg. That’s 6e-4 m/s^2 and 13 ks (152 days).

          • fcrary says:
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            As for other missions, I’m afraid NASA is working within a system that involves identifying science goals and questions, specifying the measurements required, and developing a system (spacecraft) which can satisfy those requirements _without_ spending resources on anything beyond those requirements. If you think 0.5 meter resolution global imaging is required, you can’t say, “but 0.1 meter resolution would be nice.” The current system doesn’t really have a place for it.

            When you talk about “potential mission for a spacecraft with a quarter megawatt of power… Titan orbiting high-resolution imaging radar, orbiters of Saturn, Uranus, Neptune, Pluto, Triton, explorers of the Kuiper belt?” you would have to show that this could not be done without a Prometheus-sized nuclear power system. That was, by the way, the standard applied to Discovery missions in the one call allowing the use of RTGs: They had to show that there wasn’t any other way to do the job. You can do Titan radar mappers with RTGs (or ASRGs). You can also do outer planet orbiters and Kuiper belt missions without a couple hundred kW. Maybe you could do a better one with a couple hundred kW (actually, no maybe about that.) But can you (or could anyone) show what improvements would be enabled? In practice, no. When I said there was only one identified mission, I meant one that was really under serious consideration and could answer those questions.

            Use of the Prometheus system for human spaceflight, they talked about it, but not in detail. It’s hard to justify very expensive technology development when there isn’t a funded user on the horizon. They couldn’t say human missions to the Moon or Mars _would_ need this sort of technology, so they couldn’t prove that these benefits _would_ pan out.

          • fcrary says:
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            As for the development cost, the final report put it at $21 billion. The report contained mind-numbingly lengthy details on how this was estimated. In fact, probably more information on management structure, cost modeling, etc. was given than on the engineering details. Unfortunately, I’ve seen that before, and it’s a symptom of made-up numbers. If the numbers can’t really be justified or even accurately estimated, there is a strong tendency to describe the methodology in detail and show how precise it is (although that says nothing about how accurate it is.) Saying, “I calculated the number according to the following, highly detailed process” sounds much better than saying, “I just made it up.” But it doesn’t mean the result is any better than an educated guess.

          • fcrary says:
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            Nuclear electric propulsion does not require a reactor. It needs a high specific power (power per kilogram of power source.) Other than that, you can plug the electric propulsion in to just about anything. A conventional RTG wouldn’t do, since it’s too massive for the power it produces. But more efficient energy conversion (e.g. a heat engine like the ASRG designs) might change that. At least, it might be competitive with solar, if you are far enough from the Sun. I don’t think I’ve seen anyone check those numbers. But it’s a fairly simple calculation.

          • fcrary says:
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            Simple enough to do over breakfast, so I’ll answer my own question. Solar power is about 130 W/kg at 1 AU. The ASRG would have been 4 W/kg and JIMO’s reactor (in the 200 kW version described in the final report) would have been 13-25 W/kg, depending on whether you use their current best estimate or include their uncertainty and margin. So ASRGs would be better than solar outside 5.7 AU, and a JIMO-like reactor would be outside 2.3 to 3.2 AU.

          • Daniel Woodard says:
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            Apparently the Juno solar array has a total mass of 341Kg and produces 405 watts at Jupiter, for about 1.19W/Kg. Of course it may still be the best choice for this mission, but for SEP the mass would cut into delta V capability.
            http://www.nasa.gov/mission

          • fcrary says:
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            My notes are from before launch, but the say 103 kg. for the arrays and 490 W (at beginning of life). I assume you got the 341 kg by converting the “750 pounds” in the press release. My notes could be the mass per array (for a pre-launch estimate of 309 kg, which is close to your number.) I’ll double check. But, more importantly, I did normalize to 1 AU, so that’s a factor of 5.2^2 or 27.04. Assuming 341 kg and 490 W, the break-even points would be 9.4 and 3.8-5.3 AU.

            (And, yes, I know Juno’s arrays don’t produce 13 kW at 1 AU. They weren’t designed for full power at 1 AU, but a solar array with similar performance could be designed.)

          • Michael Spencer says:
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            I hope your toast didn’t get cold…

    • Michael Spencer says:
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      I wondered about that as well; I suppose the instrumentation has made huge advances to require so little energy.

      • fcrary says:
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        Actually, the Juno instruments aren’t atypically low power. Some types of instruments use more power than other types, and the mission simply calls for instruments which aren’t power hogs. Radars tend to use a huge amount of power; an energetic particle sensors, plasma wave instruments and magnetometers don’t use much at all.

        In addition, transmitting data to Earth tends to be a big user of a planetary spacecraft’s power. The requirements for Juno only call for high-resolution (and therefor high data volume) measurements around periapsis. There is plenty of time to downlink the data during the rest of the orbit. So lower transmission power is possible and keeps down the overall needs.

    • fcrary says:
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      I’m not so sure about that. While more power is good for the instruments, you can have too much of a good thing. JIMO at 100 kW, was very overpowered for the available payload mass. It would actually have run into serious thermal complications (the reactor they envisioned did not run well at lower powers, and getting rid of 100 kW when you don’t need it isn’t easy.)

      You definitely want enough power that instrument (and other) electronics don’t have to be power-minimizing, custom designs. Being able to throw power at problems like cooling detectors would be very nice. It would also make the spacecraft more operable by reducing Sun-on-radiator constraints. Having more power for the radio lets you transmit at a higher rate for a given antenna size. I’m also a fan of electric propulsion (as long as I can turn off the reactor when I don’t need the power.) But going from the current 500-750 W spacecraft to 100,000 W is probably not necessary. Except for electric propulsion, radar and some other active experiments, I’m not sure if a planetary mission could make good use of more than 10 kW. Not unless you are increasing available payload and the number of instruments by a couple orders of magnitude.

      • Daniel Woodard says:
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        Earth observation is about to bury us in terabytes of data every day from imaging alone. Maybe because of the current data rate constraints for planetary spacecraft we are closing our minds to the possibilities that would exist if those constraints were lifted.

        • fcrary says:
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          One problem with terabytes of data is paying someone to look at all of it. Even for planetary missions, most of the data doesn’t get much more than a glance. There is a tendency to skim over all of it to look for interesting things, and then focus on those interesting things.

          In any case, taking advantage of that sort of data volume would involve new and different instruments, and ones which would probably require additional resources like mass. That’s not a bad idea, but it would take more than providing power. If you could also reduce launch costs by an order of magnitude, this would start getting very interesting.

          Current instruments could probably make good use of an order of magnitude more data. But beyond that, the I think benefits would be marginal. You’d also get cost savings from the operational simplicity of never having to carefully manage every megabit.

  2. Dewey Vanderhoff says:
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    I’d love to view the JUNO short film made by NASA in collaboration with Apple Music referred to here by Marc , but the minimum requirement for watching is iTunes version 12.2
    No Go for me. Is there an alternative version outside the Apple walled garden in the real world ?

    • Marc Boucher says:
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      Not that I’m aware of.

    • Michael Spencer says:
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      The ill-tempered among us would be enjoying this piece of schadenfreude, having long-suffered as Mac users in a Windows world. Certainly not yours truly.

      [iTunes runs on Windows and Linux machines, I’d point out].