The DART mission to nudge an asteroid

Peartree

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So what was the purpose? Was there a chance they'd hit the moon, they'd make measurements, and then say, "Well dang, I did NOT expect that to happen?"

As others have noted, yes, there was, and is, a very good chance of that happening. As I recall, the two relatively recent sample return missions, which most closely approximate what NASA was doing with DART (but not crashing), both (actually three) had exactly that happen. The first Hayabusa mission failed and had to try again, and both Hayabusa2 and OSIRIS-REx had unexpected things happen because of the makeup of the regolith, gravity variations, and other things. So yes, while we understand the math, there are still a great many things that we do not understand well and, more frighteningly, our limited experience tells us that there are still more things that we don't even know that we don't know. Yes, we understand the math that we know, but there remain unknowns in the mathematics that we still don't know, which implies that we really don't know the math as well as we *think* we know the math.

A
nd, when the day comes that we need to do this to save the planet (or half of it), we had better understand it VERY well and get it right the first time.
 

ThirstyBarbarian

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One thing we might find out is that inside this asteroid lives a colony of hostile aliens who are going to come swarming out of the crater like a bunch of angry hornets and make a beeline straight to Earth to annihilate us!
 

aerostadt

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Correct. In fact all people should not be satisfied with simulations alone. Refer to my signature below.
Yes, the data should be interesting. Using classical Newtonian mechanics would be relatively straightforward and very accurate, if there were no such thing as energy losses from the collision. However, material will be blown away into new orbits, some material will eventually fall back onto the moon, some energy will be converted into heat, light, and gases, etc., etc. How well a colliding man-made probe alters an asteroid orbit will depend on the make up of the asteroid.
 

Funkworks

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Yes, the data should be interesting. Using classical Newtonian mechanics would be relatively straightforward and very accurate, if there were no such thing as energy losses from the collision. However, material will be blown away into new orbits, some material will eventually fall back onto the moon, some energy will be converted into heat, light, and gases, etc., etc. How well a colliding man-made probe alters an asteroid orbit will depend on the make up of the asteroid.
There's also the angle. Like hitting a cue ball, the moon's new motion depends on the exact point of impact, so there's an angle at play that affects what the new orbit now looks like. Energy could also be lost in the moon's rotation. Does it rotate differently now? (how did it rotate before?). But unlike a cue ball, the moon is not spherical, so there's no easy calculation here. Can it be approximated as a sphere? Maybe, but some may want more accuracy. The ejected mass though is probably the most exotic thing. Where else do we see a cloud of dust and rocks being knocked off and split into a part that leaves, one part that orbits (maybe) and one part that falls back? Wild, wild stuff.
 
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aerostadt

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There's also the angle. Like hitting a cue ball, the moon's new motion depends on the exact point of impact, so there's an angle at play that affects what the new orbit now looks. Energy could also be lost in the moon's rotation. Does it rotate differently now? (how did it rotate before?). But unlike a cue ball, the moon is not spherical, so there's no easy calculation here. Can it be approximated as a sphere? Maybe, but some may want more accuracy. The ejected mass though is probably the most exotic thing. Where else do we see a cloud of dust and rocks being knocked off and split into a part that leaves, one part that orbits (I guess?) and one part that falls back? Wild, wild, wild stuff.
Good points! Also, some asteroids will be rubble piles, others will be more solid, some may contain ices. How does a probe go through a rubble pile?
 

Funkworks

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Good points! Also, some asteroids will be rubble piles, others will be more solid, some may contain ices. How does a probe go through a rubble pile?
Above a certain size, gravity should cause the rubble at the core to be solid (and when much bigger, liquid because of heat). I think they can calculate what size (what mass) that is and determine whether the probe (having a known mass and speed) would go through or not. Anyway, with the data they collected here, there's a whole bunch of stuff to figure out and validate. Knowing what mass and speed should a "missile-probe" have may be the most important thing - matching that to whatever thing it's aimed at to cause a desired deviation. Thinking about this makes me doubt this will be the last. I suspect they already have candidates for more targets.

Just found this:
 

Marc_G

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Is there a good site showing the latest images from the Italian cubesat as they come in over the next couple weeks?

I've been here:

But it hasn't been updated in days.
 

mh9162013

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To build off what @Mushtang has brought up, I slightly question the wisdom of this mission.

Ok, let's assume Mushtang is right and this mission wasn't very useful...or at the very least, its funding could have been better spent doing something else. Well, in that case, this is a dumb mission.

Now let's assume Musthang is wrong because, as many of you have already mentioned, it'll tell us things we don't know. But that increase in knowledge implies our understanding of the mission is incomplete. And that means that the mission could have consequences we don't understand. And if the impact could produce results we don't understand, it also means it can product results we don't expect. And we don't expect this impact to lead to some other hunk of rock getting slightly modified in its trajectory/orbit so that it's now headed toward earth when it previously wasn't, right? RIGHT?

In other words, the DART mission is the flapping of butteryfly wings which will start a chain of events that leads to a hurricane. Unlikely? Highly, but many of you just admitted the purpose of this mission is to see real world results and not rely on just "the math." And this implies there are things about this mission we can't predict with 100% accuracy. QED: we can't predict with 100% accuracy that hitting the asteroid won't be the start of a more serious problem later on (like an asteroid eventully getting nudged into a direct path for earth).
 

OverTheTop

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In other words, the DART mission is the flapping of butteryfly wings which will start a chain of events that leads to a hurricane.
No. The target was chosen so there is no chance of this happening. It was also chosen so they could get the best measurements on the perturbation of the orbit of the target.

There are a lot of nuances in dealing with asteriods for planetary defense. I have a good book which goes into a lot of this, even though it is a book mainly on orbital mechanics. A couple of chapters are dedicated to missions like DART and planetary protection. They will learn lots from this mission, some expected and some not. Knowledge gained could save humanity, so it is a worthwhile endeavour. This is not what a planet-saving mission would look like, but it will guide future choices.
 

Marc_G

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To build off what @Mushtang has brought up, I slightly question the wisdom of this mission.

Ok, let's assume Mushtang is right and this mission wasn't very useful...or at the very least, its funding could have been better spent doing something else. Well, in that case, this is a dumb mission.

Now let's assume Musthang is wrong because, as many of you have already mentioned, it'll tell us things we don't know. But that increase in knowledge implies our understanding of the mission is incomplete. And that means that the mission could have consequences we don't understand. And if the impact could produce results we don't understand, it also means it can product results we don't expect. And we don't expect this impact to lead to some other hunk of rock getting slightly modified in its trajectory/orbit so that it's now headed toward earth when it previously wasn't, right? RIGHT?

In other words, the DART mission is the flapping of butteryfly wings which will start a chain of events that leads to a hurricane. Unlikely? Highly, but many of you just admitted the purpose of this mission is to see real world results and not rely on just "the math." And this implies there are things about this mission we can't predict with 100% accuracy. QED: we can't predict with 100% accuracy that hitting the asteroid won't be the start of a more serious problem later on (like an asteroid eventully getting nudged into a direct path for earth).

By this logic I should also worry that by flushing my toilet I'm somehow going to end the world.

The impact target was specifically chosen as being both easily observed for orbital changes and for the fact that its orbit is extremely safe and small nudges won't make it a threat. Even if some fragments did head toward earth they would be small enough to not be a threat.

No experiment -or action- is completely without some risk, but this impact experiment is as safe as things get.
 

mh9162013

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By this logic I should also worry that by flushing my toilet I'm somehow going to end the world.
That's different, because practically speaking, you have no other choice. Sure, you can use an outhouse or w/e instead, but that's not a reasonable alternative solution. It's not like NASA/JPL/ESA have too much money and can't spend it fast enough for missions and/or research. There are so many other quality and needed mission proposals that are begging for funding.
 

mh9162013

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No. The target was chosen so there is no chance of this happening. It was also chosen so they could get the best measurements on the perturbation of the orbit of the target.

There are a lot of nuances in dealing with asteriods for planetary defense. I have a good book which goes into a lot of this, even though it is a book mainly on orbital mechanics. A couple of chapters are dedicated to missions like DART and planetary protection. They will learn lots from this mission, some expected and some not. Knowledge gained could save humanity, so it is a worthwhile endeavour. This is not what a planet-saving mission would look like, but it will guide future choices.

You can't have it both ways. You can't say, "we need to do this mission b/c simulations and math can't tell us exactly what happens if we hit the asteroid. But we know with 100% certainty that nothing bad will happen from the mission."

To be clear, I'm pretty sure that we won't get a hurricane from the butterly flying through the air. And I'm pretty sure we'll learn a lot of useful stuff from this mission. But I think it's foolish to not admit that there's a chance that this mission has the small potential to lead to a very bad unxpected circumstance.

This reminds me of vaccines, seatbelts and airbags. Yes, they're super duper helpful and benefit many more lives than they harm. But to act like they're 100% safe, 100% of the time in 100% of circumstances is wrong.
 

CalebJ

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You can't have it both ways. You can't say, "we need to do this mission b/c simulations and math can't tell us exactly what happens if we hit the asteroid. But we know with 100% certainty that nothing bad will happen from the mission."

To be clear, I'm pretty sure that we won't get a hurricane from the butterly flying through the air. And I'm pretty sure we'll learn a lot of useful stuff from this mission. But I think it's foolish to not admit that there's a chance that this mission has the small potential to lead to a very bad unxpected circumstance.

This reminds me of vaccines, seatbelts and airbags. Yes, they're super duper helpful and benefit many more lives than they harm. But to act like they're 100% safe, 100% of the time in 100% of circumstances is wrong.
That's a weird series of conclusions to jump through...

Just because we don't know precisely what the outcome of this mission will be absolutely does not mean we don't know what range of things it could include.

Take hurricane path prediction as an example. Several days out, we can plot a projection of where it will be as time progresses.
1664457521021.png
From the starting point at 11pm on Fri in the image, it's a narrow geographic distribution. By 8am on Sunday, that range has at least doubled. Projecting out to 8pm on Wednesday, it's a very broad diameter projection. But we still know with high confidence that it will be within that range and not make landfall in Louisiana.

Much like that, we have a very clear comprehension that bumping the asteroid in the DART mission won't somehow redirect it to Earth. But observing the changes in a real world test gives us a lot of data to refine our modeling for the future.
 

Marc_G

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Well, for my part, I'm quite comfortable with the cost/benefit/risk ratios of this mission. As with any mission involving a rocket launch, almost all the risk to anyone on Earth was during the manufacture, testing, and launch of the booster. Once the mission left orbit, the risk was over.
 

mh9162013

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Much like that, we have a very clear comprehension that bumping the asteroid in the DART mission won't somehow redirect it to Earth
Of course! That's the easy part. But if we nudge the asteroid a small bit, it might have an effect on an asteroid it passes within within several hundred miles of a few years from now. Then that asteroid (#2) now has a slightly different orbit/movement around the sun/Jupiter/asteroid #3. Now, asteroid #3's movements are now modified so that in 50 years, it collides with asteroid #4. This results in asteroid #4 turning into asteroids #5-15. And one of othose new asteroids ends up having a trajectory that intersects with Earth's orbit 75 years from now.

Far fetched? Sure! But are you telling me that the mission planners looked at every single one of those possibilities and concluded that wouldn't happen? I doubt it. For one thing, they don't have the time or money. But more importantly, they can't calculate a domino effect when they aren't even sure how many dominoes there are, let alone how big they are, what their mass is and what their orbits are.

My whole point isn't that the above will happen. My whole point is that the above is possible under the laws of orbital mechanics as we understand them because we don't fully understand 100% what will happen when we hit that asteroid and what objects are floating in and around the asteroid we hit.
 

mh9162013

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Well, for my part, I'm quite comfortable with the cost/benefit/risk ratios of this mission. As with any mission involving a rocket launch, almost all the risk to anyone on Earth was during the manufacture, testing, and launch of the booster. Once the mission left orbit, the risk was over.
I'm not disputing the above. I'm just calling out people who say, "we need this mission b/c there's so much we can learn from it b/c our simulations are incomplete." But at the same time, they're saying, "our simulations show that there's a 0% chance hitting the asteroid will lead to another rock hitting earth."
 

Peartree

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I'm not disputing the above. I'm just calling out people who say, "we need this mission b/c there's so much we can learn from it b/c our simulations are incomplete." But at the same time, they're saying, "our simulations show that there's a 0% chance hitting the asteroid will lead to another rock hitting earth."
I think you're putting words in their mouths. I'm pretty certain that no one said, "our simulations show that there's a 0% chance hitting the asteroid will lead to another rock hitting earth." What they said was that they had a high level of confidence that this particular asteroid would not be deflected into an orbit that would intersect with earth. Is it possible that this asteroid would be deflected into another, that would bump into another and then gravitationally influence yet another that would drift into an earth-intersecting orbit? Well... I suppose that... theoretically, it's possible. But the chances are really, and I mean infinitesimally, small. And even then, the likelihood is that it would take thousands, tens of thousands, or hundreds of thousands of years for such a sequence of events to play out. Recall that when Elon Musk launched a Tesla towards Mars, people asked if its orbit would ever intersect with earth, and the answer was that someone had calculated its orbit for the next several thousand years and it would not. But again, we know that there are many undiscovered and uncataloged chunks of stuff out there, so... in theory... it might still be possible. But again, space is really, really, really big and empty so even those theoretical collisions and gravitational influences, are going to take a very, very long time. Frankly, the odds are better that humans will kill themselves off long before that happens.
 

Mushtang

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Ok, let's assume Mushtang is right and this mission wasn't very useful
Wait a damn minute, don't put words into my mouth that I never said.

I was asking for clarification of the mission because I didn't understand what information could be gained, I never said that I believed the mission wasn't useful.

Not knowing what something means doesn't equate to believing the thing shouldn't be.

I've gotten a lot of good answers to my question and I have more, but I now see that additional information gained by the experiment will be valuable for future situations beyond just being able to hit an asteroid.
 

mh9162013

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Wait a damn minute, don't put words into my mouth that I never said.

I was asking for clarification of the mission because I didn't understand what information could be gained, I never said that I believed the mission wasn't useful.

Not knowing what something means doesn't equate to believing the thing shouldn't be.

I've gotten a lot of good answers to my question and I have more, but I now see that additional information gained by the experiment will be valuable for future situations beyond just being able to hit an asteroid.
I stand corrected.
 
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