back to article After eight years, NASA's Dawn probe brings Ceres into closest focus

More than a thousand times farther from Earth than the moon, farther even than the Sun, an extraordinary extraterrestrial expedition is taking place. NASA’s Dawn spacecraft is exploring dwarf planet Ceres, which orbits the Sun between Mars and Jupiter. The probe has just reached the closest point it ever will, and is now …

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  1. RIBrsiq
    Go

    I feel very conflicted about living in this period of history.

    On the one hand, awesome stuff like this.

    But on the other hand, anthropogenic global climate change.

    On a related sidenote: sci-fi loving types would do well, I think, to take a look at SyFy's (Sigh-Fy, amirite...?) "The Expanse". The book is naturally better, so far. But considering it's TV, it's not that bad.

    1. frank ly

      I'm admiring and liking The Expanse so far but haven't read the books. (It's not strictly off-topic since Ceres has been colonised in these stories.)

      1. Anonymous Coward
        Anonymous Coward

        Ceres has been colonised

        Gravity on Ceres is 3% of Earth's.

        Sneeze and you'd spend half the afternoon in a suborbital trajectory.

        1. RIBrsiq

          Re: Ceres has been colonised

          "Gravity on Ceres is 3% of Earth's".

          The Expanse's Ceres has apparently somehow been spun to create artificial gravity. So more of a really large space station than a planetoid.

          I am hoping the book(s) -- which I started to read after seeing the series, BTW -- will explain how this could be achieved without scattering the thing to dust. Considering the relative accuracy of the physics so far (I didn't do the math. But I didn't get the urge to bang my head on the nearest solid surface in frustration, either), I am hopeful.

          1. Anonymous Coward
            Anonymous Coward

            Re: Ceres has been colonised

            I've read them and from what I can recall they reference Ceres being spun up as one of mankinds major engineering achievements and refer to a long slow process, more of a side note, but I agree their approach to the physics and explanations aren't bad and well ahead of a lot of stuff.

            1. RIBrsiq

              Re: Ceres has been colonised

              "they reference Ceres being spun up as one of mankinds major engineering achievements and refer to a long slow process".

              Ah! I see... Please excuse me while I find the nearest solid surface I can bang my head against.

              I already came across that bit and was hoping for more.

              The problem I see is that regardless of how slowly and carefully you do it, if you spin up something like Ceres with enough angular velocity to create a radially outward acceleration that would exceed its own gravitational acceleration, then it will fly apart. Probably long before you got to that point, in fact. After all, it's essentially just a pile of rubble held together by gravity.

          2. JeffyPoooh
            Pint

            Re: Ceres has been colonised

            "The Expanse's Ceres has apparently somehow been spun to create artificial gravity..."

            E=mc²

            How many million rotations per second is required to create gravity from kinetic energy?

            1. RIBrsiq

              Re: Ceres has been colonised

              "E=mc²"

              Huh...? You're completely on the wrong track, I am afraid.

              Think radial acceleration outwards due to rotation.

              1. JeffyPoooh
                Pint

                Re: Ceres has been colonised

                Ceres is hollow and they're standing on the ceiling?

                1. JaffaMan

                  Re: Ceres has been colonised

                  It's been hollowed out as part of the mining (with large chunks accelerated off to create the spin), and yes they're effectively standing on the ceiling.

                  I too wondered how Ceres hasn't just flown apart given its new spin...?

                  1. Martin Budden Silver badge

                    Re: Ceres has been colonised

                    Probably held together with gaffa tape. Works for backyard cricket balls.

        2. W Donelson

          Re: Ceres has been colonised

          Wrong. Gravity is strong enough to prevent people from "jumping into orbit"

          1. Mikel

            Re: Ceres has been colonised

            Wrong. What keeps people from jumping into orbit is that there is no ellipse trajectory that doesn't intersect the jumping off point. For simple jumping the paths are escape velocity or impact. To achieve orbit you have to add a horizontal thrust of some sort.

    2. John Sanders
      Thumb Down

      Please

      ""But on the other hand, anthropogenic global climate change.""

      Keep the pseudoscience out of this, you are runining the moment.

      1. RIBrsiq
        Facepalm

        Re: Please

        "Keep the pseudoscience out of this, you are runining the moment".

        I am extremely sorry if I offended your religious beliefs. But you might do well to grab an actual scientific text on the subject, between prayer meetings.

        Also, it's spelt "ruining"...

      2. tgm

        Re: Please

        "Keep the pseudoscience out of this, you are runining the moment."

        Ahh, so NASA ruined the NASA moment?

        Interesting.

    3. Anonymous Coward
      Anonymous Coward

      Yes, awesome stuff mixed with weird cult like global warming hysteria. When will humans grow up?

    4. Qwertius

      'I feel very conflicted about living in this period of history."

      Really ? That's probably how the Dinosaurs felt.

      One the one hand .... lots of stuff to eat.

      But on the other hand Meteor - and extinction.

      Life sucks.

  2. banalyzer
    Thumb Up

    Applause

    Much more of this please Reg, some one closely involved with the project who can describe what they do with an eloquence and enthusiasm that gets us to read the entire article.

    Well done to everybody on the Dawn project, you are all indeed deserving of the accolade boffin

  3. Anonymous Coward
    Anonymous Coward

    "But the ship will remain in orbit around Ceres as surely as the moon remains in orbit around Earth and Earth remains in orbit around the sun"

    So after we finish littering our gravitational sphere with scrap, we start doing it to other worlds

    Won't the interstellar travellers see us as the "Pikey's" of an inhabited solar system?

    1. Anonymous Coward
      Anonymous Coward

      If it weren't for Assyrian, Indus Valley, Meso-American, Chinese and Egyptian 'pikeys' we would know a lot less about our ancient past than we actually do.

      What's worrying is not so much that we've left a lot of stuff in orbit around Earth; it's that some irresponsible idiots in both China and the US deliberately created large debris fields that threaten near-Earth orbits, and that it wasn't mandated early on that any entity lofting a sattelite into Earth orbit should have built in the means or otherwise have doable plans and the ability to de-orbit it safely too.

      Fingers crossed someone comes up with a solution to the current mess up there before kessler Syndrome starts biting too hard, its already at a worrisome point.

      1. RIBrsiq

        "Fingers crossed someone comes up with a solution to the current mess up there before kessler Syndrome starts biting too hard, its already at a worrisome point".

        Look t it this way: this future solution will certainly require significant technological, if not scientific, advancement. Challenges present opportunities to advance. Even those challenges that we ourselves needlessly create.

      2. JCitizen
        Boffin

        Elon Musk...

        we already have part of the answer to the space debris - the returnable rocket. Now we will see what Space X does with the 2nd stage of the Falcon system. The DSCOVR mission will be the 1st time a Falcon 2nd stage left earth orbit - sounds like the safest plan ever! Eject them into the Sun!

        1. eldakka

          Re: Elon Musk...

          "we already have part of the answer to the space debris - the returnable rocket. "

          The returning of the first stage has nothing to do with space debris. Prior to this (and Bezos' earlier equivalent - but much smaller scale, sorta like getting the scooter to come back vs the Heavy Truck of Space X) feat, the first stage did not become space debris. It became ocean (or in the case of Russia/Soviets Siberian) debris. The first stage of a multi-stage to orbit rocket would never reach space. It would splash down in the Atlantic Ocean and (mostly) break up and sink to the ocean floor.

    2. Anonymous Coward
      Anonymous Coward

      "...after we finish littering our gravitational sphere with scrap, we start..."

      Yeah, we certainly don't want to litter the -> Asteroid Belt <- with any debris.

      LOL

      1. RIBrsiq
        Happy

        Re: "...after we finish littering our gravitational sphere with scrap, we start..."

        "Yeah, we certainly don't want to litter the -> Asteroid Belt <- with any debris".

        Let me guess: your idea of what an asteroid belt looks like comes from Star Wars, yes...?

        1. Anonymous Coward
          Anonymous Coward

          Re: "...after we finish littering our gravitational sphere with scrap, we start..."

          RIBetc. "your idea of what an asteroid belt looks like comes from Star Wars, yes...?"

          Same logic applies to the man-made debris.

          Unless you're worried that we'll be leaving A LOT of space junk.

    3. allthecoolshortnamesweretaken

      "Oh, won't somebody think of the dwarf planets!"

      Seriously - I think the interstellar travellers will be thrilled, excited and very happy to find such an artefact. Assuming they are explorers and not the equivalent of drunken teenagers on a road trip in daddy's car.

      1. Neil Barnes Silver badge
        Alien

        They won't need to be interstellar... once we're all over the asteroid belt, as we should be, early spacecraft (like this) are going to turn up from time to time. And there have *always* been well-heeled collectors...

        1. Michael Wojcik Silver badge

          once we're all over the asteroid belt, as we should be, early spacecraft (like this) are going to turn up from time to time

          Presumably those times will be pretty far apart, since 1) there aren't likely to have been a whole lot of said "early spacecraft", and 2) the asteroid belt, is, um, a fairly large place. Quite a few of "us" could be "all over" the asteroid belt and miss a lot of stuff (and not be particularly easy to find ourselves); there are around a million asteroids with a diameter of a kilometer or more.

          Of course, the belt is mostly full of nothing, which presumably makes anything that's something easier to find. But I'd think little probe spacecraft will either be pretty straightforward to find because they're still broadcasting a strong signal, or pretty damn hard to find because they aren't.

          This site estimates the volume of the belt at around 6x1023km3. (Or a bit less than a mole of cubic kilometers, in one of those completely irrelevant coincidences.)

  4. Anonymous Coward
    Anonymous Coward

    Ion engines

    Actually rocket engines in general are more efficient than the IC engines in cars, otherwise in Randall Munroe's words, you will not go to space today. Although car engines can be as much as 35-40% of the Carnot efficiency, all the added mass means that, in terms of moving the human payload, the average US car efficiency is about 0.5% and the average European/Far Eastern car is around 1% (these figures from an article in Scientific American.)

    Real ion engines are very low thrust, which makes sense if you think about the electric charge that would need to be transferred to create a TIE fighter. As the ions come out the back at speed, they have to recombine with an electron supply so the spacecraft stays overall neutral. I haven't calculated the current necessary for a TIE fighter (perhaps I will if I can summon up the enthusiasm) but solar panels won't cut it; it's going to be on board nuclear or fusion reactor order of magnitude. Perhaps in that galaxy very long ago and very far away the laws of physics were different.

    1. Anonymous Coward
      Anonymous Coward

      Re: Ion engines - OK, TIE fighters.

      Let's assume a mass around 10t and a maximum required acceleration of 8g. No air in space so this has to come entirely from propulsion. To give 8g to a 10t mass requires about 800kN. The peak power is thus 0.5 * 80 * 800 000 or approx. 32MW.

      Thrust is roughly equal to flow rate * exhaust velocity. 90 000mph in the example is roughly 40kM/s in real units, so to get 800kN we need to output 20kg/s of gas. That actually isn't too bad.

      The atomic weight of xenon is about 131 so 20kg is very roughly 1/6th of a mole. That means that the charge transferred per second is 1/6th of a Faraday or approx. 16000A, and for a perfectly efficient ion engine this would involve a PD of about 2kV.

      Ion engines have been built with higher velocities than those in the article, so at 4 times the velocity we might get that down to 5kg/s, 4000A and 8kV.

      The gen4energy proposed portable nuclear reactor produces about 25MWe so it is in the ballpark, but all I can find about the weight is that it is "under 50t". Unfortunately the ancillary equipment is an awful lot bigger than that. One major problem with a TIE fighter is going to be cooling.

      tl;dr is that to make it work we need a way of removing an awful lot of mass and heat.

      1. Chris 244
        FAIL

        Mole of Xenon

        "The atomic weight of xenon is about 131 so 20kg is very roughly 1/6th of a mole."

        You might want to double-check that. You're off by an order of magnitude or three.

        1. Brewster's Angle Grinder Silver badge

          Re: Mole of Xenon

          "To give 8g to a 10t mass requires about 800kN. The peak power is thus 0.5 * 80 * 800 000 or approx. 32MW."

          I don't understand that equation. Power has dimensions of m2⋅kg⋅s-3 But your equation seems to be "dimensionless constant (0.5) × acceleration (80m⋅s-2) × force (800,000 m⋅kg⋅s-2) = 32×106 m2⋅kg⋅s-4" making the "units" MW/s.

          I accept that an acceleration of 80m⋅s-2 produces a change in velocity of 80m/s in unit time (v=u+at). So, if and only if, the ship's velocity was initially 0, then a 10Mg ship has gained 32MJ of kinetic energy in unit time (via ½mv2). (And note it gains 96MJ in the second second.)

          However this neglects the energy given to the propellent. We know the change in momentum of the ship in unit time is 800kNs (Δp=FΔt); conservation of momentum requires the propellant be given the same momentum. I agree that 20kg at 40km/s produces 800kNs of momentum (p=mv) so the kinetic energy given to the propellent, via ½mv2, is a whopping 0.5*20*40E3*40E3 = 16GJ

          So your power plant needs O(16GJ). And a loss of 20kg/s is non trivial: in one minute you've lost over 1Mg of your 10Mg ship.

          The corrector's law says I will have gone horribly wrong somewhore.

      2. imanidiot Silver badge

        Re: Ion engines - OK, TIE fighters.

        You do have a convenient gas flow leaving the spacecraft available for cooling though.

      3. Brewster's Angle Grinder Silver badge
        Joke

        Re: Ion engines - OK, TIE fighters.

        "tl;dr is that to make it work we need a way of removing an awful lot of mass and heat."

        How do you think the energy weapons work? It has to fire them to keep cool.

      4. Anonymous Coward
        Pint

        Re: Ion engines - OK, TIE fighters.

        @ Voyna i Mor

        Reading your post made my head hurt.

        A Pint because I need a few...

      5. Mikel

        Re: Ion engines - OK, TIE fighters.

        The VASIMR engine appears to be the champ for specific impulse and thrust to weight, yes. And yes, at 200KW you are probably going to need a fusion power plant. And at that point, why not just use the bare fusion for thrust and skip the energy conversion losses, the heating and so forth?

        We have a ways to go, but we will solve this star travel problem eventually now that it's "finder's keepers for as long as you can maintain possession" for everything off of Earth. As if it wasn't always that way down here too.

        To the people who would call me a "space nutter": a homeless disowned 18 year old refugee from South Africa grew up, challenged your preconceptions, and just took ownership of all the world's space launch business by inventing something you said wasn't worthwhile - a reusable rocket. Now he's got a dozen launches scheduled in the next year that are already paid for, and he gets to keep all those rockets for free! Remember that to the buyer a proven rocket is $80M with of critical delivery. To the manufacturer it's $8000 worth of scrap metal, some plant, some IP, and some labor. And the plant and IP is paid for. And that kid? Why? He wants to go to Mars, personally, and the $3B he got for inventing PayPal wasn't enough to get him there without smashing your despair meme.

        Lockheed Martin thinks they have Fusion sorted, and are developing the commercial product. Unless they've been smoking dope, we're on our way. And these are the people who invented the SR71.

        The rest of the world, on notice that this is actually possible, is now on a nation-state funded race to compete because apparently all the money on Earth ain't a grain of sand on the beach of the Cosmos.

        1. JeffyPoooh
          Pint

          Re: Ion engines - OK, TIE fighters.

          Mikel "The VASIMR engine appears to be the champ for....thrust to weight..."

          I'm pretty that it's not 'the champ' in thrust to weight, as the thrust is so tiny. Ion engines make very poor 1st stage boosters for this reason.

          "Lockheed Martin thinks they have Fusion sorted."

          LM made the obviously-BS claims that a 100MW fusion plant could "fit on the back of a truck." That sound-bite claim sets off all sorts of alarm bells. Just the plumbing to move 100MW of heat, the steam plumbing, turbine, cooling towers, generators, switch yard, control systems, canteen, offices, ...must be a pretty big truck.

          Not to mention the radiation alarm bells because their "truck" is spewing neutrons due to lack of shielding.

          Obvious BS.

  5. JeffyPoooh
    Pint

    Comparisons in decreasing order?

    "More than a thousand times farther from Earth than the moon, ..."

    Roughly 245,000 miles x 1000 = 245 million miles. Okay.

    "...farther even than the sun..."

    Roughly 93 million miles. ...Huh? That's LESS than the first phrase.

    Bad style to have such comparisons (of vastness) in decreasing order by magnitude.

    1. JeffyPoooh
      Pint

      Re: Comparisons in decreasing order?

      Downvote?

      So this is okay? "More than a thousand times farther from Earth than the moon, farther even than the sun, even further (amazingly) than the chemist down the street; astoundingly this is further away than your kitchen (in case we've not established that already). More than a foot, more than an inch, and - OMG yes! - more than a millimeter..."

      It's fundamentally-incorrect Writing 101.

      1. Stevie

        Re:So this is okay?

        If you work for the Fluff Writers of Goons Wonkshop it is.

        Also okay for Spinal Tap lyrics.

      2. Brewster's Angle Grinder Silver badge

        Re: Comparisons in decreasing order?

        You're probably right, but I downvoted you for using non-SI units. I know the earth-moon distance and the AU off the top of my head in metres (384km and 0.150Tm). I haven't a clue what they are in miles.

        Note: I would have also accepted AU, parsecs, and lunar or terrestrial radii.

        1. JeffyPoooh
          Pint

          Re: Comparisons in decreasing order?

          "...using non-SI units."

          I'm old enough that we had material presented in Imperial, cgs, MKS and SI. I never did like cgs.

          Would you have accepted Smoots?

          1. Brewster's Angle Grinder Silver badge

            Comedy downvotes

            "I'm old enough that we had material presented in Imperial, cgs, MKS and SI. I never did like cgs."

            Astronomers haven't outgrown cgs. My reaction on first encountering an erg was priceless. "What the FUCK is an erg?!" ;) It's not as if the distances, masses or energies need to be magnified.

            I still cook in ounces and pints. So if there's a serious point---and there wasn't---it's picking the right unit for the field. Converting light years to parsecs can be done roughly by multiplying by three; converting miles to km is horrible.

            1. Michael Wojcik Silver badge

              Re: Comedy downvotes

              Converting light years to parsecs can be done roughly by multiplying by three; converting miles to km is horrible.

              Divide by 6, multiply by 10. Really not that bad, particularly since the former can be reduced to "divide by 2 then divide by 3" and the latter is just adding one to the exponent. It doesn't strike me as "horrible" compared to the times-three approximation for parsecs-to-light-years.

              1. swm

                Re: Comedy downvotes

                What's the difficulty? Miles and Kilometers are in the golden ratio.

                1. JeffyPoooh
                  Pint

                  Re: Comedy downvotes

                  swm pointed out "Miles and Kilometers are in the golden ratio."

                  Nice. Accurate to about 0.5%. I never noticed that factoid in my entire life. Thank you.

                  So you just extract the square root of 5 (in your head), subtract 1, and divide by 2, then multiply miles to get km. Or inverse (which is +1) as needed.

                  (The definition is 2.54 cm *exactly* = 3 barleycorns, then of course 8 furlongs to get the precise mile-km conversion factor.)

      3. Glen 1
        Alien

        Re: Comparisons in decreasing order?

        "It's fundamentally-incorrect Writing 101."

        Ignoring that the moon is closer than the sun, (yes, I know 20 times the distance isn't)

        I'll refer to a better writer than I...

        "Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space."

        Edit: You do seem to be channeling DNA with the chemist reference. This is The Reg, not The Times. Next you'll be banishing the hard-won title Boffin.

        1. JeffyPoooh
          Pint

          Re: Comparisons in decreasing order?

          "... channeling DNA with the chemist reference..."

          Intentional. Of course.

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