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D3ATHfromAB0V3x t1_iqx1mes wrote

Serious question: Why not just nuke it? A direct impact of a nuke on an asteroid the size of didymorphus/didymos would surely disintegrate or severely break it down and cause nothing more than a meteor shower. And the explosion would alter its path too.

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Brusion t1_iqx2q6z wrote

A nuke in space would do less than you think. A nuke itself doesn't cause much impulse in a vacuum. It has inconsequential mass by itself, it just releases an immense amount of energy.

On Earth, we see a giant blast wave from a nuke. This is because it heats up matter(the atmosphere and ground around it), and that matter expands very quickly.

In a vacuum, you don't get that. It would heat up one side of the asteroid, which do to outgassing could alter it's course, and there is photon pressure. It's certainly been discussed. But I think at this point, especially with falling costs of mass to orbit, and kinetic impactor is a more viable option.

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HikeEveryMountain t1_iqx5syg wrote

And you can always do a series of kinetic impactors for increased power, like a train of StarLink satellites, slowly but systematically smashing it off course

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Apostastrophe t1_iqx8m93 wrote

With the advent of a super heavy launch vehicle that can be refilled in orbit like Starship, we could also just make a gravity tractor.

A fully expendable, fully refilled SS could get a beast of a gravity tractor out there.

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thxpk t1_iqxxvwy wrote

Not true, simulations already show it would be very effective

https://www.nytimes.com/2021/10/18/science/asteroid-nuclear-bomb.html

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Brusion t1_iqy42h0 wrote

I never said it wouldn't be effective. I am saying there is no shockwave from a nuke in space. That it doesn't behave like people might think.

I literally said in my post the ways it would affect an asteroid's motion.

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WhalesVirginia t1_iqz45t0 wrote

You would absolutely sink a nuke to the right depth so that it does have maximum impulse.

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jawshoeaw t1_iqyq4wx wrote

Right you would have to tunnel into the middle of it

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karlzhao314 t1_iqz59ih wrote

No you wouldn't. The most realistic option for a nuclear avoidance strategy is to use a surface standoff detonation some tens or hundreds of meters above the surface.

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ItsMyImPulse t1_iqxoao9 wrote

That is absolutely a great thought. People are responding to you saying that it's not the solution, but I had a discussion with someone working on DART who is a co-author of the paper this post is about. A nuke provides the greatest amount of energy per mass that can be delivered to an asteroid, so it absolutely is a 100% feasible option for planetary protection.

The largest issue with the nuke is the timing. DART impacted going roughly 6 kilometers per second. This means that a nuke would need to be timed within a few milliseconds of impact so it would be able to transfer energy to the asteroid without wasting it, but needs to be detonated before impact as the speed is so extreme if the spacecraft impacted the asteroid first the nuke would be destroyed without detonating.

Detonating a nuke in space is actually rather trivial though, the largest issue is navigating and guiding a spacecraft to the asteroid. DART was able to locate Didymos over a month out, but only was able to see Dimorphos a few hours before impact. Didymos is nearly 1,000 meters in diameter, Dimorphos is about 170 meters while the asteroids we are actually worried about are closer to 50 meters. Since they are smaller than we can detect from Earth, we would likely only discover it possibly weeks or months before impact, whereas something much larger would be discovered years earlier.

I have heard from people who worked on DART, that a potential DART-2 mission is a dry-run of nuking an asteroid without the actual nuke onboard, so that the design would already be finished if we discovered an asteroid with limited time before impacting Earth. That way they could re-build from existing designs, add the nuke and launch considerably faster in the case of an emergency.

Breaking it into multiple pieces/re-directing it both end up going together, at some point of pushing it you're going to break it up anyway because of the force required. One concern of breaking it up is that if it still impacted Earth, while it would be less likely to kill us all, it would have a high likelyhood of damaging many of our satellites in orbit. In 2014 a comet nearly hit Mars, and all the satellites (since there are not many around Mars) navigated to be on the opposite side of the planet to where it was likely to hit. Earth satellites wouldn't realistically have the same ability.

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arcaeris t1_ir06laf wrote

I want to add to this, we currently today can’t even reliably shoot a missile to blow up another missile in the way you’re describing, by detonating it next to the attacking missile. It’s much, much easier to calculate the incoming attack missile trajectory and fire a defense missile to slam into it head on to destroy it. If the US can’t do this with things going much slower, that are much smaller, with a controlled trajectory, and like a million times closer, there’s no way we can do it in space yet.

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Fortune090 t1_iqx3ecy wrote

Why go all the way to nuking it if we can confirm crashing into at high speeds is an effective solution? A lot easier to plot a direct collision course than it is to time an explosion and/or make sure the device actually explodes on time.

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D3ATHfromAB0V3x t1_iqx52ni wrote

I'm not arguing about the validity of the impactor. It's probably the best solution we have at the moment. I'm just curious why we would rather move it slightly off course than destroy it and never worry about it again.

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led76 t1_iqx678l wrote

I think the idea is that an extinction-level asteroid might be bigger than this one, so destroying may not be an option.

Also, nudging it out of the way of earth takes far less energy. And if you blow it up big chunks of it could still cause immense damage. They don’t have to be big. Enough pebble-sized meteorites in succession could heat up the atmosphere enough to kill off a lot of things.

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crazyjkass t1_ir1szrc wrote

The probability that an extinction-sized asteroid will hit in the next 100 years are infinitesimally small. We already mapped out all the large asteroids in the solar system. NASA is actually worried about asteroids big enough to vaporize one city, because they're so numerous and hard to see.

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sumelar t1_iqxs9jk wrote

Because if those high speeds aren't enough, what's your next plan?

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WhalesVirginia t1_iqz4lb0 wrote

Crashing into a body requires affecting it's path further in advance because we only have such big rockets that can only add so much dV.

Energy density of a nuke is way higher than rocket fuel of equivalent mass.

Precisely timing a device is trivial in the grand scheme of thrust vector control, orbital navigation, and all of the other control systems operating the device. Like sure it's hard, but an extra PCB, sensor system, and software isn't going to exactly break the bank.

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karlzhao314 t1_iqz66lv wrote

Every answer telling you some supposed reason about why this is infeasible or ineffective is wrong. NASA and related, credible parties have conducted studies and generally conclude that a nuclear device is one of the most effective strategies we have of asteroid avoidance. The catch is that it would not be used in the manner you describe to "disintegrate" an asteroid - rather, it would most likely be detonated in a surface standoff detonation and use the vaporized surface as ejecta to propel the asteroid in the opposite direction.

https://web.archive.org/web/20160303220543/http://www.nasa.gov/pdf/171331main_NEO_report_march07.pdf

In the case of a large and/or imminent threat, this would likely be one of our only options. No other feasible strategy, whether kinetic impactor or gravity tractor, is capable of transferring so much energy to an asteroid in such a short amount of time. DART and the gravity tractor approach are both similarly mature technologies, but they require either for us to see the threat years in advance or for the threat to be very small - possibly both. A nuclear device is capable of redirecting a much larger asteroid with a much shorter notice.

There are technical challenges to address, yes, but relatively minor ones especially given the level of spaceflight technology we've already had for decades.

The obstacles right now are geopolitical, not technical. The Outer Space Treaty bans the use of nuclear weapons in space. That means we can't even test it. The DART II mission that /u/ItsMyImPulse mentioned would certainly be interesting, though - a dry run to confirm our technical ability to pull off a mission like this would do a lot for our preparedness in case we ever do need to actually do it, without violating the treaty.

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jcmidmo t1_iqxkxbe wrote

There's a treaty that says we can not use nukes in space.

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AWildDragon t1_iqz75w5 wrote

That treaty would go out if the window if it was determined that nuking an asteroid would stop it from impacting a populated area.

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D3ATHfromAB0V3x t1_iqxmmhl wrote

So the ludicrous, yet slightly feasible, method of terraforming mars is off the table?

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jawshoeaw t1_iqyq0tf wrote

I did some rough calculations of how much energy the DART craft had and it was about 1/1000 of the atomic bomb over Hiroshima. 1/1000 doesn’t sound like much but this was just an initial try. And that’s still equivalent to 15 tons of TNT. Not bad. The problem with a nuke is you can’t just slam it in, you first have to slow down, match speeds , then land and tunnel into the middle of it . Maybe all doable but dang .

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Steeve_Perry t1_iqzep4k wrote

Because a nuke would blast in all directions, losing most of the energy to space. Smacking into it at 14,000 mph directs almost all the energy directly into the asteroid. Much more effective.

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