# Redirecting asteroids on an impact course by momentum transfer **URL:** \ **Category:** Factual Questions\ **Created:** [December 17, 2017, 4:53pm UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718 "2017-12-17T16:53:54Z")\ **Posts on this page:** 20\ **Page:** 4
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [December 20, 2017, 3:28am UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/61 "2017-12-20T03:28:45Z")
> [@joema](#): > > There is no question a guidance and imaging probe would make things easier, and that would probably be done. However I don’t think it’s absolutely necessary. No I was really thinking it would be more about accelerating the speed at which you could make decisions. Interplanetary probes and their research programmes run at a very slow measured pace. Here we want to be able to work out exactly where a nuke must be placed and do it very quickly - having already launched the nukes right behind the guidance and imaging probe. Given we have no good idea of the shape, rotation or composition of the asteroid, faffing about once the nukes arrive working out what to do is going to lose a lot of time. > [@](#): > > Actually they could not be dropped anywhere – that would require a reentry vehicle with the associated heavy aeroshell and frictional thermal protection. When the vehicle is headed directly away from earth at 36,000 mph, every gram counts, so you’d never waste so much mass accelerating a useless atmospheric heat shield to the outer solar system. Yeah, although you would need to trust the other nations that the nuke they launched, and just so happened didn’t use, and is still up there, didn’t just happen to also have a re-entry vehicle. OTOH, you don’t absolutely need a re-entry vehicle. That is just the most efficient way of breaking - using the atmosphere. If you have a nice amount of fuel remaining in your system you can decelerate with that, and the nuke can just fall through the atmosphere with only trivial heating. Virgin Galactic doesn’t need a heat shield. ---
**Author:** ![SamuelA](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@SamuelA](https://boards.straightdope.com/u/SamuelA)\ **Post date:** [December 20, 2017, 3:32am UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/62 "2017-12-20T03:32:57Z")
> [@running\_coach](#): > > How the hell do you make a atomic bomb go off in one direction? You don’t have to. You just have some tungsten on the side facing the asteroid. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [December 20, 2017, 3:40am UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/63 "2017-12-20T03:40:40Z")
> [@running\_coach](#): > > How the hell do you make a atomic bomb go off in one direction? You can’t. Sadly you just take the hit that half the energy has basically vanished into space. Inside the nuke things are as weird as one can imagine, and there are asymmetries in boosted and thermonuclear weapons. You have the notion of neutron reflectors and various other ways of modifying the physics to guide the process. However these things last nanoseconds before they turn into superheated plasma, and I very much doubt there is any sort of asymmetry in the energy of the fireball once it gets much more than a metre in diameter. Maybe selective asymmetry in the tampers will yield some difference in the nature of radiation in different directions. As I noted earlier you probably want to favour gamma radiation over neutrons to carry the energy to avoid useless deep heating of the rock and favour maximum energy going into vaporising the surface rock. OTOH, I don’t know enough (like nothing really) about the relative energy deposition that would occur and is needed. Just seems like it would be a reasonable thing to do. We have a vast body of knowledge about the effects of nukes and such things as cratering and energy balances - many many tests before the bans came in. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [December 20, 2017, 11:48am UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/64 "2017-12-20T11:48:37Z")
> [@Francis\_Vaughan](#): > > You can’t. Sadly you just take the hit that half the energy has basically vanished into space. What about [shooting muskmelons](http://toughsf.blogspot.com/2016/06/the-nuclear-spear-casaba-howitzer.html) at the target? ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [December 20, 2017, 12:26pm UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/65 "2017-12-20T12:26:01Z")
Any chance we could win the game, at least with enough advance notice, using a billiard shot? Instead of trying to deflect the 5km asteroid, just find a much smaller asteroid already on a near-collision course with the big asteroid, and deflect the small asteroid enough to nudge it into a deflecting collision with the larger threat. ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [December 20, 2017, 12:28pm UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/66 "2017-12-20T12:28:05Z")
> [@septimus](#): > > Any chance we could win the game, at least with enough advance notice, using a billiard shot? Instead of trying to deflect the 5km asteroid, just find a much smaller asteroid already on a near-collision course with the big asteroid, and deflect the small asteroid enough to nudge it into a deflecting collision with the larger threat. You mean like using a moped to divert a semi? 😃 ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [December 20, 2017, 12:46pm UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/67 "2017-12-20T12:46:47Z")
> [@septimus](#): > > Any chance we could win the game, at least with enough advance notice, using a billiard shot? Instead of trying to deflect the 5km asteroid, just find a much smaller asteroid already on a near-collision course with the big asteroid, and deflect the small asteroid enough to nudge it into a deflecting collision with the larger threat. What if we use one guy on a trolley? ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [December 20, 2017, 4:34pm UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/68 "2017-12-20T16:34:38Z")
> [@running\_coach](#): > > You mean like using a moped to divert a semi? 😃 If you can get it to collide at all, the momentum transfer will be _huge_. Obviously time until Earth collision will be a major factor in determining what impulse is needed, but the impulse would be much greater than thrusting on the big asteroid itself. _ **Remember that you’d be exploiting the smaller asteroid’s existing momentum** _ — the human-provided impulse would be to redirect the small asteroid, not to increase its energy. ---
**Author:** ![Marvin\_the\_Martian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/marvin_the_martian/32/2898_2.png) [@Marvin\_the\_Martian](https://boards.straightdope.com/u/Marvin_the_Martian)\ **Post date:** [December 20, 2017, 4:46pm UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/69 "2017-12-20T16:46:57Z")
> [@septimus](#): > > …just find a much smaller asteroid already on a near-collision course with the big asteroid… The odds against this seem extremely high. ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [December 21, 2017, 4:13am UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/70 "2017-12-21T04:13:06Z")
> [@Marvin\_the\_Martian](#): > > The odds against this seem extremely high. Much more correct than #66 or #67. 😃 Thank you. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [December 21, 2017, 6:02am UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/71 "2017-12-21T06:02:12Z")
If it’s a nuclear explosion nearby, then as mentioned, the main impact is high-energy particles, photons and neutrons, some vaporised bomb components. Causing a collision using another high-energy rock is simpler, but then how do we give that rock the necessary momentum and direction. It seems to me the most effective diversionary tactic is to bury the nuke inside the asteroid deep enough (shallow enough) so it blows a substantial chunk of the asteroid off. preferably this would be from the side - or some fancy orbital math to determine which direction course change diverts the asteroid from collision course the most. It could be that speeding it up or slowing it down would work better. The only worry is where that chunk blown off ends up, but a few of those apartment-block sized meteors is preferable to a KT event. The only problem is - how many of these bombs do you have to set off to effectively change the course of the asteroid? A sphere say, 20m on a side, about the size of the recent Russian meteor vs. a 10km sphere, a ratio of 20^3 vs 10,000^3 - that chunk would have to fly off at one helluva velocity to divert the asteroid very much. Or, we need that huge fleet of heavy launch vehicles at the ready. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [December 21, 2017, 8:46am UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/72 "2017-12-21T08:46:16Z")
> [@joema](#): > > Others like Lutetia are probably not “rubble piles”: [21 Lutetia - Wikipedia](https://en.wikipedia.org/wiki/21_Lutetia) Lutetia is unusual in that it probably formed in the inner solar system, perhaps from the Lunar formation event. So it is more solid, and drier, than most. We probably don’t have to worry about the big objects, anyway; it is smaller objects, around 100 metres or less, that could cause a credible threat. These often tumble so fast and erratically that they have negative gravity on their surface at times, so they are likely to be single objects not rubble piles. Nukes would probably work for these solid objects, though I’d prefer to use gravity tugs if they could be made to work. ---
**Author:** ![Tripler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripler/32/21807_2.png) [@Tripler](https://boards.straightdope.com/u/Tripler)\ **Post date:** [December 25, 2017, 3:43am UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/73 "2017-12-25T03:43:25Z")
**SamuelA** , not a slight, nor an insult; but is English your native tongue? Tripler I ask to help determine what you mean. ---
**Author:** ![SamuelA](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@SamuelA](https://boards.straightdope.com/u/SamuelA)\ **Post date:** [December 25, 2017, 7:03am UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/74 "2017-12-25T07:03:21Z")
> [@Tripler](#): > > **SamuelA** , not a slight, nor an insult; but is English your native tongue? > > Tripler > I ask to help determine what you mean. Tripler, not a slight or an insult, but do you have a college degree? When Stranger wrote his little post, the main topic was about an effect that doesn’t physically matter. This was apparent in the original post. Every poster in this thread who actually passed physics 1 has confirmed this. The only ones arguing against me…like you…just try to twist the words around or make personal attacks. ---
**Author:** ![needscoffee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/needscoffee/32/1076_2.png) [@needscoffee](https://boards.straightdope.com/u/needscoffee)\ **Post date:** [December 25, 2017, 10:05am UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/75 "2017-12-25T10:05:10Z")
> [@SamuelA](#): > > And this analysis is wrong. That’s why I posted this in General Questions. You’ve made the same fundamental physics error that Stranger has. > > There are 2 effects here. > > a. You set the nuke off near a homogenous patch of asteroid material. \ People who use “homogenous” instead of the correct term “homogeneous” really get my goat. Has he ever actually had a science class? ---
**Author:** ![Tripler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripler/32/21807_2.png) [@Tripler](https://boards.straightdope.com/u/Tripler)\ **Post date:** [December 25, 2017, 1:51pm UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/76 "2017-12-25T13:51:52Z")
**SamuelA** , I was not making a personal attack, I was asking a question that you have yet to answer as is your style. I have already answered yours. But if you want to turn my question into an attack on your logic, by all means let me know and I will let loose facts upon you. Tripler Your posts are disjointed, and if English is not your first language, it would help me understand where your argument is coming from. ---
**Author:** ![SamuelA](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@SamuelA](https://boards.straightdope.com/u/SamuelA)\ **Post date:** [December 25, 2017, 10:14pm UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/77 "2017-12-25T22:14:36Z")
> [@needscoffee](#): > > People who use “homogenous” instead of the correct term “homogeneous” really get my goat. Has he ever actually had a science class? Lol. You obviously didn’t pay attention in yours to the topics about weighting of evidence. I neglected to type an e lol. ---
**Author:** ![Morgenstern](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@Morgenstern](https://boards.straightdope.com/u/Morgenstern)\ **Post date:** [December 25, 2017, 10:28pm UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/78 "2017-12-25T22:28:26Z")
> [@SamuelA](#): > > … > Every poster in this thread who actually passed physics 1 has confirmed this. The only ones arguing against me…like you…just try to twist the words around or make personal attacks. Seriously, I haven’t been keeping score. Are there actually posters in this thread agreeing with you? ---
**Author:** ![Tripler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripler/32/21807_2.png) [@Tripler](https://boards.straightdope.com/u/Tripler)\ **Post date:** [December 25, 2017, 11:18pm UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/79 "2017-12-25T23:18:44Z")
**SamuelA** , I’m going to ask a very direct question; prepare yourself. What are your credentials? Are you an Engineer? Are you a Physicist? What is your background and technical basis to make some of these assertions? Tripler Go ahead kid. ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [December 25, 2017, 11:25pm UTC](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718/80 "2017-12-25T23:25:21Z")
> [@Tripler](#): > > **SamuelA** , I’m going to ask a very direct question; prepare yourself. > > What are your credentials? Are you an Engineer? Are you a Physicist? What is your background and technical basis to make some of these assertions? > > Tripler > Go ahead kid. It’s going to be some version of “book-larnin” isn’t the full extent of human knowledge. [Previous page](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718.md?page=3) [Next page](https://boards.straightdope.com/t/redirecting-asteroids-on-an-impact-course-by-momentum-transfer/804718.md?page=5)