back to article Juno probe has tech trouble, cancels orbital re-adjustment

The Juno probe orbiting Juipter has some trouble with its propulsion feed system and plans for the craft's stay at the gas giant are therefore being revisited. "Telemetry indicates that two helium check valves that play an important role in the firing of the spacecraft's main engine did not operate as expected during a command …

  1. JeffyPoooh
    Pint

    "...so it could concentrate..."

    "...Juno would have shut down all scientific instruments so it could concentrate on entering its new orbit."

    I'm not convinced that "so it could concentrate" is the best description of the reasons why the scientific instruments are commanded Off during burns.

    1. Destroy All Monsters Silver badge

      Re: "...so it could concentrate..."

      Menace it with no dessert and see what happens.

    2. Anonymous Coward
      Anonymous Coward

      Re: "...so it could concentrate..."

      Engineering explanation coming up, read at your own risk ....

      The main control computers used on Juno (and in fact on a lot of space missions) are pretty slow when compared to, for example, your smartphone. They are often based on processor technology that is 15+ years out-of-date; this is basically due to the very long lead-times associated with the development of a deep space mission, coupled with their use of rad-hardened designs that have been proven on previous missions (one thing that deep-space mission designers do not like to do, and that is use the latest gee-whizz technology on their core systems.

      So when Juno fires up its main engine, all of sudden the main control systems have to start monitoring a whole bunch of sensors to make sure that everything is going according to plan. For example the system will be monitoring the star trackers to make sure that Juno is not moving off the expected thrust axis - if it does then the AOCS will be commanded to get the spacecraft back on track. Similarly the fuel tanks, fuel lines and the engines themselves will be carefully monitored to make sure that everything stays nominal. This all has to be done very frequently since any thing going wrong will become serious (possibly mission-fatal) really fast!

      In order to ensure that the control systems do not overload, it is standard practice in such a situation to shut down anything that is not essential, including all of the science instruments. This ensures that the control system is not having to handle non-critical data streams, and hence minimises the risk associated with the main engine burn.

      A further reason for shutting the science instruments down is that they are pretty much useless when the main engine is running - the vibration induced in Juno's superstructure will ruin just about any attempt to gain useful science with anything apart from the magnetometers, and those will be useful due to the engine exhaust planning havoc with the local magnetic field.

      1. RIBrsiq

        Re: "...so it could concentrate..."

        Thanks for the succinct explanation, I enjoyed reading it.

        That said, I suspect JeffyPoooh's objection was to the anthropomorphising of a non-sentient space probe, and not questioning the need of shutting down the science instruments for the manoeuvre. But I could be mistaken.

        Also: please forgive me, Juno! I don't mean to hurt your feelings you beautiful, beautiful probe, you!

      2. Mystic Megabyte

        Re: "...so it could concentrate..."

        >> it is standard practice in such a situation to shut down anything that is not essential

        So much like a Volvo driver changing direction :(

      3. DropBear
        Facepalm

        Re: "...so it could concentrate..."

        ...so, astrocomputing-wise, we're still at the LEM's "1202 alarm" level...? *sigh* great...

      4. JeffyPoooh
        Pint

        Re: "...so it could concentrate..."

        ANH "Engineering explanation coming up, read at your own risk ...."

        You forget to mention that things on Juno are hard mounted. So during burns, when the rocket is aligned along the direction of travel for orbital adjustment, other systems are thus misaligned.

        During burns, the solar panels are misaligned from the Sun. So there's a power shortage. The science gear needs to be turned off because of this. All goes back to the lack of RTG material.

        Also, during burns, the big dish is pointed off into space. So there's no way to send back large volumes of data anyway. They rely on simple low gain antennas and tones.

        These are the two primary (direct) reasons.

        Your explanation was a stretch to justify the 'concentrate'. It's not wrong as such, but you omitted the two primary reasons.

        1. Anonymous Coward
          Anonymous Coward

          Re: "...so it could concentrate..."

          Granted and noted. I was mostly giving a general reason for doing this, not something that is Juno-specific. In fact Juno is pretty much an exceptional case in itself since no-one has tried to send a mission to the outer planets before that has been powered by anything other than RTGs. Not certain how often a Juno-like design is likely to be reused unless solar array efficiency improves significantly (although the shortage of Pu for the RTGs is an ongoing issue).

          However saying that it could have been possible to build Juno with solar array fittings that allowed it to keep them aligned with the Sun; my understanding is that that was the original intention, but it got dropped to save mass (and budget) and was replaced by more fixed mounts.

      5. Anonymous Coward
        Anonymous Coward

        Re: "...so it could concentrate..."

        I should add that a good example of an overloaded control system due to a failure to switch off non-critical systems occurred during the descent of the Lunar Module for the Apollo 11 mission.

        1. JeffyPoooh
          Pint

          Re: "...so it could concentrate..."

          ANH, on 1201 / 1202 alarms.

          An excellent example. Full points and a bonus. :-)

  2. imanidiot Silver badge
    Joke

    Stuck valves are easy

    Just send someone out there to hit the valves with a 2 pound lump hammer. That should clear it up!

    1. Anonymous Coward
      Go

      Re: Stuck valves are easy

      As long as you are up there, maybe just give it a shove into the correct orbit, and check the fluids.

    2. DropBear
      Trollface

      Re: Stuck valves are easy

      Yeah, and if that doesn't work? Stir the oxygen tanks...?

  3. Anonymous Coward
    Anonymous Coward

    Tight fit

    "The valves should have opened in a few seconds, but it took several minutes."

    Those aren't valves, they're sphincters.

  4. Tromos
    Joke

    Still using valves?

    I would have thought it would all be at least transistors by now.

    1. JeffyPoooh
      Pint

      Re: Still using valves?

      Tromos on 'valves' vs transistors.

      Hmmm...

      They should double-check the trade-offs, what with being surrounded by a hard vacuum and all.

      No glass bottles required...

      Somebody should at least send a bottle-less vacuum tube up as an experiment. Just to try.

  5. allthecoolshortnamesweretaken

    Wolowitz, if the telemetry shows that the valves are sticky with meat loaf residue, there'll be trouble. Understand? Trouble.

  6. airshod

    Monolith

    "All these worlds are yours, except Europa. Attempt no landing there. Use them together. Use them in peace."

    We've been asked to "move along"...

  7. phuzz Silver badge
    Alien

    I'm not saying it was aliens

    But it was probably aliens.

  8. DCFusor

    I do a bit of work with some things that can make fairly large amounts of radiation (fusion reactor - I'm easy to find on youtube etc).

    I find the same thing as the space guys do. The older tech is a lot less likely to become upset by a stray high energy particle than the newer stuff. And it's getting harder to find as well. The tinier a transistor or dram cell becomes, the fewer knocked-out electrons it takes to mess it up, more or less. Things that the old CMOS wouldn't even notice with its 15v logic levels and large geometries are devastating to .8 volt supply logic, for example. This is no joke, and the particles I deal with are a lot less energetic than your average cosmic ray, or the radiation a spacecraft gets a lot more of than we on earth (as our magnetic field, due to its rather large size, shields us somewhat).

    Yes, you can tell in my lab. An older machine sitting right next to the fusion core survives, yet a newer Intel small geometry machine at twice or three times the distance with similar (good) EMI shielding just crashes right off when things get "hot".

    You'd think they could nevertheless design code that could handle doing it all at once if there was a good reason, but I see above that yeah, when an engine is running, there's not so much point anyway, so might as well shut things down...assuming that doesn't risk them not coming up or taking a huge long time to get stable again (thermal and other drifts).

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