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NASA Space

NASA Has a Plan To Punch An Asteroid With a Spaceship To Protect Earth (vice.com) 116

Posted by BeauHD from the asteroid-redirection dept.
A new NASA mission, called the Double Asteroid Redirection Test (DART) mission due for launch this summer, aims to launch a spaceship that will directly punch an asteroid. Motherboard reports: The mission's target is an asteroid system called Didymos, which contains two space rocks that orbit each other. In late 2022, DART will forcefully impact the smaller asteroid in this system, a tiny moon called Dimorphos, so that scientists can assess the feasibility of knocking any space rocks that threaten Earth off course in the future. [...] DART will pioneer a subtler form of planetary defense, in which the trajectory of an asteroid is changed by a very small amount that becomes significant over time. Late next year, the mission will crash into Dimorphos at about seven kilometers per second. Shortly before the collision, the spacecraft will deploy a small satellite provided by the Italian Space Agency that is tasked with watching "the mess we make," [said Andy Rivkin, a planetary astronomer at the Johns Hopkins University Applied Physics Laboratory and the investigation team lead for DART].

Observations from the Italian satellite, as well as from powerful telescopes on Earth, will reveal just how much Dimorphos was affected by the crash. Rivkin and his colleagues expect the change in orbital speed to be small -- about one millimeter per second -- which would add up to a shortening of the orbital period by about 10 minutes. But even this very slight shift would be enough to redirect the trajectory of a hazardous asteroid that threatened Earth, provided scientists have a lead-time of a decade or two before the projected impact.
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NASA Has a Plan To Punch An Asteroid With a Spaceship To Protect Earth More

NASA Has a Plan To Punch An Asteroid With a Spaceship To Protect Earth

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  • Whatcould possibly go wrong (Score:5, Funny)

    by rossdee ( 243626 ) on Friday April 02, 2021 @02:19AM (#61227302)

    asteroid punches back

    • Re:Whatcould possibly go wrong (Score:5, Funny)

      by Admiral Krunch ( 6177530 ) on Friday April 02, 2021 @03:01AM (#61227350)
      Asteroids started it [astronomy.com]

    • Re:Whatcould possibly go wrong (Score:5, Interesting)

      by tinkerton ( 199273 ) on Friday April 02, 2021 @03:02AM (#61227354)

      Asteroid breaks in pieces so it can destroy many cities in one go. I recall that 50m piece is enough to destroy a city. So a 500m asteroid is good enough for 1000 cities.
      Gently pushing the asteroid out of the way is the way to go.

      • In order to gently push it out of the way you must slow down the "engine" then start it.
        This isn't great when the engine already moves at 7 km/s.

        They might try "pulverizing" the spaceship just before impact, so that most of it still hits the asteroid but any piece is small enough in order not to break the target into pieces (or large pieces from the target).

        • Re:Whatcould possibly go wrong (Score:4, Insightful)

          by tinkerton ( 199273 ) on Friday April 02, 2021 @04:37AM (#61227474)

          I read the article after my comment and it is clear NASA is aware of the challenges when avoiding collision with earth. They do want to keep the asteroid together. The actual experiment is about how rough they are allowed to be. If a piece with 10m diameter separates off that is no big deal. If one with 50m diameter breaks off it is a problem. The strength of the asteroid will be a factor. Some asteroids may act like a bag of sand, others like a big rock.
          So the general idea is to deviate an asteroid using a very long gentle push a long time in advance. But then asteroids are also rotating. You can't just stick a machine somewhere in its side which is good at throwing sand away very hard.

          • A large percentage of asteroids are carbonaceous chondrites, mostly ice. Im surprised the concept was not using focused lasers on the ice creating jets of evaporated water, thereby creating propulsion. Since the energy of a laser contains nearly no mass, the action/reaction force pair is side-stepped until the evaporation phase.

            • Re: (Score:2)

              by cusco ( 717999 )

              But asteroids rotate, many (most?) of them chaotically. Unless you're somehow able to stop its rotation first your jet is just going to spray vapor in random directions most of the time.

              • Re: (Score:2)

                by e3m4n ( 947977 )
                the spray is a result of a laser hit... so its always going to spray in the directional relation to the laser. So rotation should not matter.

                • Re: (Score:2)

                  by cusco ( 717999 )

                  This is ablation, not rebound or ricochet. My understanding (admittedly quite possibly wrong, and I'd love to learn otherwise) is that when ablation occurs the material ejected just moves outward in the path of least resistance away from the site of heating. If the laser hits a surface at a 45 degree angle the majority of the resulting plasma will be ejected from the point being heated in some other direction, and the impulse transmitted will be in the direction directly away from the surface rather than

                  • Its predictable though right? As far as angle of incident vs ejection.. if it werent a moving surface I would say that eventually you would be laser drilling a cone-like hole which would serve as a nozzle to focus the forces.

                    • Re: (Score:2)

                      by cusco ( 717999 )

                      It's only predictable if you have a single smooth homogeneous surface. Imagine your laser sweeping over the surface hitting a chunk of water ice, a piece of nickle-iron, some water ice, and then carbonaceous rock. Four different shock waves and four different plasma clouds, and the angle of each of them is likely to be different. I'm not optimistic about our ability to predict the results, at least not at this time.

                      I think young comets might be consistent enough inside for your rocket nozzle idea, if onl

              • How? You mean that if you blast one place on the asteroid with a laser beam, a random different potion of the asteroid will emit a jet?

            • Re: (Score:2)

              by mysidia ( 191772 )

              This is very boring.. trying to nudge asteroids by lasers a bit of a stretch - nuking it from orbit [nukeitfromorbit.com] would be much more exciting.

              Also, I suspect the heat output from deploying a thermonuclear device while colliding would be capable of evaporating a ton of ice much more quickly than a laser projected over some distance - to cause the jets "propelling" the mass, assuming there would be any solid mass left of the asteroid.

              • Re: (Score:2)

                by cusco ( 717999 )

                The Deep Impact spacecraft hit Comet Tempel with 100 kilo chunk of copper at 10 kilometers/second. Its kinetic energy was equivalent to 4.8 tons of TNT. A kinetic impact has the advantage of being able to control the directionality of the force imparted. The ablation resulting from a nearby thermonuclear blast would be less effective, since the shock wave and the force of the ejected plasma just travels opposite of the plane of the surface being ablated. Nuke it at a 45 degree angle from it's orbital di

              • You might want "exciting" from an asteroid defence. I'd prefer to concentrate on "effective". "Exciting and effective" might be fun, but only if you've already got "effective" done and dusted.

            • Since the energy of a laser contains nearly no mass

              Photons carry exactly zero mass. They do however, carry a small bit of momentum.

              • Re: (Score:2)

                by e3m4n ( 947977 )
                yes thats why i said nearly ... obviously for a solar sail to function, the photons would have to behave mass-like in some way. Momentum without mass is a puzzling concept in itself since the equation for momentum includes mass.

                • yes thats why i said nearly

                  Nearly isn’t zero, even for large values of zero.

                  Momentum without mass is a puzzling concept in itself since the equation for momentum includes mass.

                  That’s because your thinking of the Newtonian mass momentum equation(s). The photon momentum equation is planks constant/wavelength and you are missing a relativistic compensation term from your momentum equation if you need to be accurate at high relative speeds. From relativity and the speed of light, you can derive that frequency is like mass in intrinsic energy. In the 1930’s the Nobel prize was handed out for Compton scattering and

                  • Compton scattering is with subatomic particles. Like protons, but mostly neutrons, knocking electrons free of their nucleus. When photons do it we called it the Photoelectric effect.
                    • It’s specifically [wikipedia.org] photons scattering by transferring momentum to a charged particle, and in the case originally observed and in visible demonstrations, is strictly photons and electrons. The photoelectric effect [wikipedia.org] is when photons are emitted (or colloquially emitted or absorbed) by electrons changing energy states/shells.
                    • So question, how did they know it transferred momentum instead of absorbed the photon, excite to a higher state, and subsequently re-emit another, lesser, photon? The latter was the theory on how I got trained.
                    • You are conflating the photoelectric effect with Compton scattering. Put too simply it’s the photon reflecting off an electron whereas the photoelectric effect is absorption. The energy levels don’t fit, they are discrete and correlated with electron orbital energies in the photoelectric effect while much more analog with wide ranging possible outcomes in scattering.
                  • So without mass how do you explain red shifting of light when it comes in contact with gravity? Why does gravity affect a photon when it has no mass? Wasnt that Einsteins theory thst because light shifted red as it passed a planet, that it must have some immeasurable amount of mass?

                    • After Einstein made special relativity it was clear that you couldn't use the lorentz transform on gravitational forces. the speed should tell you how force transforms: the force between two objects moving fast next to each other transforms in the same way regardless of the nature of that force but for gravitational force that yielded no sensible answer.
                      So Einstein's solution was to make gravity 'nonforcelike' , to have the energy of an object change the geometry of space (it distorts the rubber sheet of sp

                    • So without mass how do you explain red shifting of light when it comes in contact with gravity?

                      Gravity emerges from curved spacetime, and spacetime curves wherever there is a concentration of energy (mass being a very concentrated form of energy). In curved spacetime, time slows down. This is what causes gravitational red shift. There is also another redshift, cosmological, which is caused by the metric expansion of space.

                      Why does gravity affect a photon when it has no mass?

                      Because the photon always follows the shortest path in spacetime, aka a geodesic, which is a straight line in free space. Curved spacetime causes geodesics to be curved in 3D space

                    • So whether a photon has mass or energy doesn't even matter when figuring out what the trajectory is.

                      I think this misses the point. Let’s use an infamous slashdot car analogy: I have a car, and it’s worth $500. Sweet ride. But I’m riding in a car, I don’t have the $500. Saying I’m riding around in $500 is obviously false and some kind of analogy.

                      The distinction is made because photons use a class of equations that specifically aren’t valid with mass and vice versa with the mass momentum equations.

                    • That is indeed a lousy analogy. The point was valid. It is a way of explaining that general relativity is a geometrical theory.

                    • Well, explaining it doesn’t matter when the equations are quite different isn’t very succinct.

              • Depends on what you mean by "mass" - in a way, you could argue they do have inertia (because they have momentum), and they interact with gravity (because gravity "bends" spacetime).

                They dont't have a mass at rest, but they do have a finite effective(*) mass while in motion.

                (*) pretty much like we claim that particles at relativistic speed become "heavier", up to infinite mass at speed of light. Which is not true, of course, it's just an effective variable that hides RT. /pedantic

          • The actual experiment is about how rough they are allowed to be.

            Which is likely to be a different answer for each of the first few dozen asteroids examined, until we've mapped out the parameter space. After that, we'll have a better understanding of the distribution of strengths.

            What we know from the small number of asteroids examined in any detail is that the strength varies from almost nothing ("rubble piles") to strong-enough to survive an impact that carves a crater approaching a quarter of the body's

            • I agree. I also imagine that any somewhat realistic scenario for intervention will consist of a long stage of probing, preparations and choices while the prediction of the trajectory becomes more accurate and they can figure out which way they should push.

              I wonder how a 'pile of rubble' impacts with the atmosphere. Much more energy will be dispersed before impact. For a large asteroid we still wouldn't like the result - how much of a shockwave can we handle - but I imagine the threshold for the mass to ge

              • I also imagine that any somewhat realistic scenario for intervention will consist of a long stage of probing, preparations and choices

                Which is how people like the B612 foundation have been talking about for - several decades if I recall. The general reaction from people has been ostrich imitations.

                I wonder how a 'pile of rubble' impacts with the atmosphere.

                I'm not sure that matters much. The kinetic energy of the impactor arrives within a couple of hundred km (horizontally) and 60-oddkm vertically. For any

        • Re: (Score:2)

          by hey! ( 33014 )

          A lot depends on how much delta-V you want to impart, and the further ahead from the time of impact you do nudge the asteroid, the less delta-v you need. If you're shooting the asteroid hours before it enters the Earth's atmosphere, like you would in a movie, then you'd have to worry about breaking it apart. But you could potentially nudge an asteroid into a less risky trajectory *years* before it comes close to Earth -- at least in the case of near Earth objects.

      • Didn't read TFA, but reading data in the comment... That math feels odd on first pass, by some order of magnitude, kind sir.

        • I read the article afterwards (*hm*) . Nasa is fully aware of the problems it creates when treating an asteroid in rude and uncourteous ways. The actual test they have in mind is how far they can push it and still keep things together. How much is too much.

          • "Keeping things together" is not necessarily desirable. If you manage to make a crater in the asteroid and the mass removed from the crater escapes, which is not very difficult due to low escape velocity, the escaped mass has a total momentum vector opposite to the momentum change you impart to the rest of the asteroid. Because of how kinetic energy and momentum work, it is in your interest to sever as much mass from the asteroid as you can and propel it away at just above the asteroid's escape velocity, be

            • It is desirable but I agree it is not necessarily on principle, just because some quick calculations show the strategy of lightening the rock is not realistic.

              If you take a 50m diameter rock (a supertanker) and sling it at 20km/2 into the atmosphere, it releases about 2 million TeraJoules or 500 megatonnes of TNT. (I hope I didn't miscount the zeroes here).
              Peeling off some of that matter reduces the impact but how much should it become until you feel safe and how long would it take?
              If you have a 500m diamet

              • It's not desirable because you can use slower-moving large mass split off the asteroid for *massively* more efficient propulsion of the rest of the asteroid. We're talking about several orders of magnitude more efficient here. The point is not to "peel away" some mass, the point is to change trajectory of the large body. If you split off, say, a 50m piece of your 500m asteroid and send it away at, say, 30m/s (which would be a meager speed for subsurface nuke detonation energy levels), you propel the rest by

                • Our posts crossed. I don't know why you want to split off a large mass. Because it can all move slower?

                  My additional point (and the initial one) would be that the amount of energy needed to displace the asteroid may be small in comparison with a healthy nuke but the challenge is to apply the energy in a controlled manner. As soon as bits start flying about you lose control.and large parts may end up headed straight for earth.

                  • It's very difficult to lose control over most of the mass, since even if it split it would recoalesce again, and the small ejected part doesn't matter - it won't amount to anything more than a year or two of cosmic dust and some bolides *even if* all of it hit Earth, which it won't.

              • So another quick calculation (again, the risk is I'm getting the number of zeroes wrong)
                If acceleration (time squared)/2 = 10000km(1e7m) and t is a year or about 100000s (1e5s)
                then a = 2e-3, you need a constant acceleration of .002m/s2.
                The speed achieved is then 200m/s. The energy you have pushed into that supertanker is then 50 kilotonnes of TNT.

                • 100000 s is about one day, not one year. And to get 0.002 m/s with a 500m asteroid, you'd need continuous Saturn-V-level thrust, so I'm not sure how you'd accomplish that.
                  • You would need Saturn V level thrust for short time periods. A Saturn V has say 7.6 million pounds of thrust at launch or 34 million Newtons force. Let’s say 1.6g/cc density (less for ice more for iron) and a 500m diameter sphere, or about 64 million cubic meters or 104 trillion kilos at the given density. That’s about 3.2 x10^-8 g. You wouldn’t need 200m/s delta unless the stone was comically close to earth. If it’s years out and it’s going to dead center strike you only

                    • Yes I'm awake now. since we have 360 times more time , square of that is 1e5 and the acceleration is 2e-8m/s2 instead of 2e-3m/s2.
                      the speed would be more like 1m/s then if you're a year out.

                    • Well, I substituted an average velocity inappropriately so it happens to everyone.

                  • Oh dear, I used 1e5s for time which is a year, not a day.
                    So times 360.
                    t**2 is then 1e5 larger and the acceleration can be 2e-8.

      • There's zero chance of 50m pieces of a 500m asteroid all hitting Earth. Hell, there's even zero chance of *most* of them hitting Earth. There really isn't any need to "gently push" anything, unless you're too close to Earth -- but if you're too close to Earth, it's probably too late for *any* pushing.

        • > 50m piece is enough to destroy a city. So a 500m asteroid is good enough for 1000 cities.

          > 500/50=10 not 1000

          You start with one 500 wide * 500 high * 500 deep.
          You divide it into pieces 50 wide * 50 high * 50 deep.

          That means it's divided 10 times width-wise, 10 times depth-wise, and 10 times height-wise = 1,000 times.

          Which reminds me of the reason it's easy to build a quadcopter that fits in your palm, yet large quadcopters don't work. Because making each dimension 10X larger makes the thing 1,000 la

      • If and only if all your cities are next to each other.

        • Hm, and only if you target the 1000 pieces very accurately.
          I can imagine that if the parts separate and drift apart they will move more slowly than if you actually try to propel them away.
          On the other hand I don't know about modelling the breaking up of asteroids with H-bombs but I do know that if you put H-bombs inside an asteroid the kinetic energy you can give to the parts you sling away can be very large, as opposed to exploding H-bombs in the vicinity of the asteroid, which heats up the surface and pro

          • So I can imagine that 'smashing up the asteroid with all the h-bombs you have'

            I can imagine "hitting the asteroid with all the H-bombs which you have" would result in the secret stash of reserve H-bombs being launched in a preemptive strike against the enemy. For all values of "your" and "enemy". I remember the Cold War and expecting to die from foreign nukes targeting the foreign nukes on the "unsinkable aircraft carrier" which we called "home". I don't have a high opinion of politicians who have armies an

            • I'm in two minds about this. First, it is a technical question with a potential disarmament side to it. An 'Orion' type project. Could it be possible to disperse the mass sufficiently. It is worth investigating.

              Secondly, you 'remember'? I am convinced we're in a cold war right now which can blow up at any moment, the more so because so many people are so confident they're safe.

              • I think the Russians have sufficiently neutralised the threat posed to them by the Americans. Getting their enemies to tear themselves apart is a lot cheaper than running a large military project.

    • Quoth Mike Tyson (Score:5, Funny)

      by n0nsensical ( 633430 ) on Friday April 02, 2021 @06:00AM (#61227532)
      Everyone has a plan til they get punched in the mouth
  • Why don't they test asteroid deflection by way of nuking it? To me this would seem a very sensible use of nuclear weapons. As of yet, we don't have any data whether what effect a nuclear explosion would have on an asteroid's trajectory.

    • Re:Nuke it (Score:4, Insightful)

      by Samantha Wright ( 1324923 ) on Friday April 02, 2021 @03:58AM (#61227430) Homepage Journal
      That's far more complicated than this plan. They don't even have to slow the rocket down!
      • Assuming you could fly a "cubesat train drill" ahead of the main probe, you might not have to slow down with a warhead either.

    • Re:Nuke it (Score:5, Informative)

      by Calinous ( 985536 ) on Friday April 02, 2021 @04:48AM (#61227486)

      Because a nuclear explosion would dissipate all of its energy in a sphere. In order to transfer more of that energy to the target, the nuke must explode as close as possible.
      Unfortunately, at 7 km/s closing speed the timing of the explosion is a bit tricky.
      You might try to slow down the missile from 7 km/s and "land" - in this case, let's say that half the energy of the nuke goes into the asteroid - as heat, radiation and momentum (i.e. added speed away from the explosion).
      The ideal solution would be to drill a small hole into the asteroid and explode the nuke inside it - it will give the highest momentum change to the remaining part (hopefully) or parts (more probably) of the asteroid.

    • Re:Nuke it (Score:5, Informative)

      by Alain Williams ( 2972 ) <addw@phcomp.co.uk> on Friday April 02, 2021 @06:46AM (#61227610) Homepage

      I suspect that the effects of blowing a nuke in a vacuum are very different from blowing it in an atmosphere. Without air to get caught up and be part of the blast all that hits the asteroid is the small mass of the nuke + radiation. So: not as effective as one would first think.

      • If you know the asteroid composition you can probably detonate the nuke at the right distance to evaporate material from the suface to give a push. Of course that will be very different for a ice surface asteroid than for an iron one. I'm not convince the risks of shattering are that bad since the great majority of the fragments will be moving at a significant speed and not impact the earth.

        • If you know the asteroid composition

          For an asteroid that might hit us in 50 years, that's not a big problem. For one that might hit us next year, that is a very big "if"

      • The heat can ablate the surface, giving rise to a hopefully fairly uniform and even thrust across the entire exposed side to the blast. That’s going to be where most of the momentum change comes from.

        • Re: (Score:2)

          by cusco ( 717999 )

          The shock wave from ablation and thrust from the resulting plasma cloud travel opposite to the plane of the surface being ablated, not the direction the heat is coming from. They also vary dramatically depending on the material being ablated, a chunk of nickle-iron is going to react considerably differently than a piece of nitrogen ice. Unless you have a fairly smooth surface of fairly uniform material (which describes almost nothing in space) the result turns out to be pretty much unpredictable.

          • Casabah howitzer. A gift from project Orion, a method of making a shaped charge nuke that channels the energy into a cone of tungsten plasma and thus achieves diffused kinetic/thermal energy transfer. We have the technology. We have had the technology since the 60s.

    • Re:Nuke it (Score:4, Funny)

      by Kokuyo ( 549451 ) on Friday April 02, 2021 @06:54AM (#61227632) Journal

      Frankly science be damned, I'd just like to see that happening for the fun of it :D.

  • Pilot selection for the mission has narrowed... (Score:5, Funny)

    by h33t l4x0r ( 4107715 ) on Friday April 02, 2021 @04:02AM (#61227432)
    To Bruce Willis and Ben Affleck.

  • NASA... (Score:3)

    by dave-man ( 119245 ) on Friday April 02, 2021 @05:13AM (#61227498)

    ...has been watching too many science fiction movies and not reading enough classic science fiction novels and novellas. Get Hollywood out of the scenario development.

    • Re: (Score:1)

      by Anonymous Coward

      Kinetic energy planetary defense systems are a common theme in not only Hollywood, but in literature as well.

  • There is an easier solution... (Score:5, Funny)

    by Skiron ( 735617 ) on Friday April 02, 2021 @05:39AM (#61227522)
    ... just get SpaceX to land on it.

  • Less about momentum transfer (Score:3)

    by JoeRobe ( 207552 ) on Friday April 02, 2021 @07:30AM (#61227728) Homepage

    This seems to me to be less about momentum transfer and more about what such an impact would do to the structure of the asteroid. The physics of the momentum transfer verges on trivial if the asteroid stays intact after impact. But if the asteroid breaks up after impact, or releases trapped gases, or kicks off tons (literally) of dust in an unexpected way, things get more complicated.

    I think there's really fun science to be had from the Italian spacecraft, since this will be essentially excavating the asteroid, albeit in a violent way. There could be interesting new information about crater formation, and how "cohesive" the internal structure of this asteroid really is.

    • Re: (Score:3)

      by cusco ( 717999 )

      It will be interesting to see the difference between the asteroid and the result of the Deep Impact comet intercept mission.

      https://en.wikipedia.org/wiki/... [wikipedia.org]

      The Impactor's payload, dubbed the "Cratering Mass", was 100% copper, with a weight of 100 kg.[12] Including this cratering mass, copper formed 49% of total mass of the Impactor (with aluminium at 24% of the total mass);[13] this was to minimize interference with scientific measurements. Since copper was not expected to be found on a comet, scientists c

    • This seems to me to be less about momentum transfer and more about what such an impact would do to the structure of the asteroid.

      It's about momentum transfer. They're expecting something like an 0.5mm/second change in velocity of the moonlet after impact. That'll change the period at which it orbits around the asteroid and we'll be able to measure that.

  • *ba-dum TISS*

    Favorite punch line of the week, right there. :)

  • >DART will forcefully impact the smaller asteroid
    >DART will pioneer a subtler form of planetary defense
    >the mission will crash into Dimorphos at about seven kilometers per second

    At 7km/s I'm going with forceful, not subtle.

    • Re: (Score:2)

      by cusco ( 717999 )

      At the scales of mass it's more like a dragonfly colliding with a human walking across the yard. You might slow down 0.5 mm/second (the desired result of the experiment) but you probably wouldn't consider the impact "forceful" unless it hit you in the eye. For the dragonfly (or DART) it's a bit more impactful (pun intended).

  • Can we just ram the mormon space ship into eros and call it a day?

  • While momentum transfer is bound to work, I don't think you can depend on an asteroid holding together against a strong shock. It would be much better to use a low impact landing, and then keep running the rocket engine to do the momentum transfer. And even if they get this to work on one asteroid, that doesn't prove anything about all the rest. Some asteroids are expected to be degenerate comet heads that have evaporated all their gases. In that case the asteroid is basically a ruble-pile, and if you g

  • ..please, please, PLEASE make it shaped like a giant fist!

    Oh, and these guys MUST have grown up watching Tranzor Z and totally stole the idea.

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