Juno completes third Jupiter flyby

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On December 11 Juno successfully completed its third close flyby of Jupiter.

They have released one quite spectacular image taken during the close approach. Expect more to follow soon.

Though they continue to say that they are still considering firing the spacecraft’s main engine to lower and shorten the orbit, I am getting the impression that they are increasingly leaning to leaving things as they are. While this longer orbit will produce larger gaps in their data of the gas giant’s atmosphere (53 days between close approaches versus 14 days), it will also allow them to tract changes over a much longer time period. Considering the risk of a catastrophic failure should they fire the questionable engine, this choice seems quite reasonable.



  • Alex

    Mr. Zimmerman: However, they run into problems with this 53-day orbit, because the sunshine/shadow conditions (solar cells) become more and more less advantageous compared to the original mission if mission time increases.

  • Jim Jakoubek

    Given the fact that firing the engine might end the mission, I have to agree that keeping the probe in a 53 day orbit does make sense. This situation has shades of the Mars Observer failure in the early 1990s.

    Even if it does mean that there will be less data from this mission, I’d think that eating half the pie is preferable to having it fall on the kitchen floor.

  • Steve Earle

    If it were me making the decision I would try and have my cake and eat it too…

    Keep the existing orbit for the period of time it takes to wring out a majority of the mission goals, or at least as many as possible with the 53 day orbit.

    Then go ahead and fire the engine. If it works, great, its a Win Win, if not then they will have still achieved a mostly successful mission.

    Not sure they have the necessary Cojones to do it that way, but we’ll see. Nothing ventured, nothing gained.

  • LocalFluff

    Alex, how does that work? Is it staying in Jupiter’s shadow longer now at apojove than it would have in the lower orbit, which also would’ve increased its inclination gradually? On the other hand, now there’s more time between the passages, so total energy per passage should be bigger.

    I bet they have planned this 53 day orbit from the beginning as a potential final orbit in case of a scenario like this, and can achieve the science goals with it.

    What about planetary protection? If the engine cannot fire, it cannot put crash Juno into Jupiter. if they really don’t want to risk it ending up on an icy moon, contaminating it biologically (which is really faaar fetched, but that is how they talk at NASA nowadays), then it would need to be cleaned away somehow in the future. Or is it set to finally end up on Jupiter anyway? The final low altitude image before the crash would’ve been nice to see. One would maybe see the altitude difference between different(ly colored) cloud layers.

  • Gealon

    Hmmmm. I don’t suppose the RCS jets have the same specific impulse as the main engine. IF they did, they could lower the orbit with them over the course of several passes. I’m unsure at this time if the RCS even uses the same fuel supply but I’m going to delve into those details in my off hours and perhaps come back with some insight into it tonight.

  • Alex

    Localfluff: It is not my own idea. I repeat only. The shadow “problem” is because the mission will now last much longer, the position of Juno’s orbital plane stays fixed in space, but Jupiter’s position relative to Sun is much different as first assumed for mission. Originally Juno would never fly into Jupiter’s shadow, but this now the case a the end of the longer mission as the project’s boss said.

  • Edward

    The shadow problem would depend upon the satellite’s batteries and their longevity, as well as the ability to turn off instruments and other systems as Juno passes through the shadow (cool word time: umbra).

    The solar array degeneration would eventually require the permanent or temporary shutting down of instruments. They could choose to cycle through instruments (temporary shut down) or those that have completed their tasks or have failed can be permanently turned off.

    You are probably right. Mission planning takes into account a variety of things from mission objectives to risks and their mitigation. Losing the main engine would be a risk, though they may have thought it a low probability.

    Also considered in mission planning is the degradation of the power supply, such as solar arrays. Generally, the end-of-life or end-of-mission power requirement drives the size of the power supply. Whenever mission extension is considered, the ability of the power supply to power the instruments and the craft is a consideration. If too many instruments have to be turned off anyway or the data that would be collected is not educational enough, the resources (e.g. Deep Space Network) may be better allocated to other missions. This is why we only occasionally hear from the Voyagers as they travel into interstellar space — reduced power and only occasional (not continuous) interesting data.

    Mission life may also depend upon attitude control, stationkeeping, or maneuvering propellant. This is one reason why Rosetta had a finite lifetime (another being that the comet would likely stop being interesting).

    Thank you for looking into this. It would be interesting to learn whether they have this option but are not yet talking about using it.

  • wayne

    Highly interesting comments by all. (I only know just-enough, to be dangerous.)

    Very sympathetic towards;
    -not flipping the pie onto the kitchen floor. (That paints such a picture!)
    -having my cake & eating it, as well. (Never call me late, for cake!)
    -disregarding any self imposed, biological-contamination restrictions, if they impact the options available right now, given the limitations presented. (environmental-malcontents, in Space.)
    -using RTG’s preferentially over solar-panels, for high-value, long-distance probes, such as this. (anti-nuclear malcontents, in Space.)

    Gealon– cool. (I can follow that thought, and appreciate your effort.)

    [and…Fig Newton’s were named after the City, and not the Scientist.]

  • Steve Earle

    Wayne said:
    “….-using RTG’s preferentially over solar-panels, for high-value, long-distance probes, such as this. (anti-nuclear malcontents, in Space.)…”

    Correct. Whose bright idea was it to send a probe to Jupiter using solar panels instead of RTGs????

    Was it purely political? Was it a cost saving measure? Was there a problem obtaining RTG’s?

    To go to all the time, money and effort to send a spacecraft that far and not optimize it’s power supply strikes me as foolish…

  • wayne

    Steve Earle–
    referencing the RTG’s; that has come up in past posts on Juno. Not sure of the official reasoning.
    To my mind– it was a politically driven decision. “No nukes in Space if we can get some Green Credits for being “environmentally aware.””
    -The Engineers then did what they could with solar-panels. To their credit alone, they made it work. I’m just not seeing it as the optimal solution, so far away.
    In my thinking, electricity is the last thing you want to worry about when orbiting Jupiter. (or anywhere, for that matter.) “You can always do something with heat & electricity, in Space!”
    –The whole “bio-contamination abatement efforts,” strike me as absurd as well. Anything that can survive Space & a re-entry into anywhere, deserves to take hold if it can manage it. (Our intellectual overlords are such All Seeing Mastermind’s, I must put on sunglasses to protect mine eyes from their blinding brilliance.)
    >It just goes to my suspicion that “politics” takes precedence over well thought out engineering at NASA. They not only lecture us constantly, they make us pay for their greeny experiments on top of it all. (No way 2 giant solar-arrays, were less-expensive & less-complicated, and more reliable in unanticipated situations, than going the RTG route, in my non professional opinion.)

    (This all is, amazing and fantastical, that goes without saying. I just want us to do our best.)

  • LocalFluff

    RTG was not an option since there does not exist enough Plutonium 238 on Earth. What exists is reserved for the 2020 Mars rover. But production is starting up again, at NASA’s insistence and cost:

    A Solar powered Saturn orbiter has been up for competition at NASA. There’s only 1% of Earth’s sunlight out there. Jupiter has 3½% to 4%. But electric power is not the problem for Juno now. Solar power is cheaper than RTG and can be scaled up, where there’s enough sunlight. Curiosity only has 1/6 of one horsepower electric effect with its RTG. Boeing say they are developing megawatt solar panels for communication satellites in GEO (about ten times what the ISS has).

  • Wayne

    Thanks for those tidbits.
    ( Dr. Wham–I like that, very appropriate for a man who studies nuke science!)

    I do recall– we (USA) stopped making Plutonium 238, for dubious political reasons, and was not aware how much we had stockpiled, if any.

    Putin still makes 238, (and never stopped,) does he not?

    I’m no engineer, but no-way those panels cost-less & are less-complicated to launch & deploy.
    (I would stand corrected.)
    >>I’d like to see the line-item Invoice for those panels.
    I’m seeing that Juno produces roughly 450 watts of power at Jupiter and the 3 panel-assemblies weigh 750 pounds.

    I haven’t forgotten this

  • Wayne

    Dr. Wham discusses resuming Plutonium 238 production

  • Gealon

    Update on the propulsion system. I turns out that using the RCS is not an option, in true NASA fashion, Juno was made more complicated then it has to be. The RCS jets use monopropellant while the main engine uses an entirely separate Bi-propellant system. Unless they choose to chance using the main engine again, Juno likely does not have the fuel available in the RCS system to bring it’s orbit down.

  • Edward

    Thanks for the update, Gealon. I appreciate the effort.

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