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Everything I know about orbital mechanics I know from Kerbal Space Program, so this may be a dumb question.

Using (possibly wrong) math, it looks like that even for the lowest delta-v (to Earth) objects we know about, with existing chemical rockets we probably couldn't bring back a fragment bigger than a few tons, at least within a reasonable number of orbits. But with a nuclear rocket, it might not only be possible, but pretty easy.

After playing KSP, I got this very off the wall idea, that Chelyabinsk - possibly a piece of (86039) 1999 NC43 - could have been a weapons test. It came from the direction of the sun, which is exactly what I'd do if I wanted to throw a rock at someone.

You could argue that it would be more efficient, in terms of spent energy, if you just launched a nuke directly. But kinetic bombardment has two major advantages: 1. no fallout, 2. total deniability.

What is the current consensus about the feasibility of such a weapon? At what point, if ever, should we worry about this?

PJ7
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    "...even for the lowest delta-v objects we know about..." I don't understand; what is a low delta-v object? Maneuver's may have delta-v, but as far as I know, objects don't have delta-v. Is there another way to word this? For the sake of future readers, it would be better to change the wording than to just answer in comments. Thanks! – uhoh Feb 26 '18 at 16:51
  • I still don't really understand what "the lowest delta-v (to Earth) objects" are. Also, what does your theory about Chelyabinsk have to do with the question stated in the title? Are you asking if naturally occurring near Earth objects could be weaponized using Earth-based spacecraft by altering their trajectory? Is that the delta-v you are referring to? The problem here would be that "practical" would be an opinion. One answer could argue that "yes" it is practical, another could argue that "no" it's not practical, and there would be no clear "correct" answer. They'd be primarily opinion-based – uhoh Feb 26 '18 at 23:35
  • As an engineer myself, I disagree that practicality is merely a matter of opinion... I intended this question for someone familiar both with the design of rockets and orbital mechanics.

    https://www.google.com/search?q=low+delta+v

     – PJ7 Feb 27 '18 at 23:19
  • and which of those should we read? Please explain the term in your question.- for those familiar with orbital mechanics delta-v has a different meaning to the one used by astronomers when talking about low delta-v NEOs. Also note that KSP's NERVA ISP is (iirc) very overpowered –  Feb 27 '18 at 23:27
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    They planned to push over 10,000 tons into interplanetary orbit with Project Orion back in the 60's, which was cancelled due to treaty and not feasibility. Maybe this is a bad question. I'm fishing for a reason not to worry, and I don't think I'm going to get one. – PJ7 Feb 28 '18 at 01:30
  • @PJ7 it's an interesting topic for sure, and I think your intent is to explore the question in a serious and logical manner. Since SE is open to an extremely wide variety of users and not just engineers, it's necessary to tip-toe more carefully around questions that could result in primarily opinion-based answers, even if an engineering team might reach a more unanimous conclusion. If there's a way to adjust this question so that it asks for calculable quantities, that might help. For example, propose a NEO with similar Keplerian elements similar to Earth's and ask what kind of Δv could... – uhoh Feb 28 '18 at 05:11
  • @PJ7 ...result in its reentry in a safe way in an uninhabited location, purely hypothetically, in order to access it's rare-earth metals or for scientific study blah blah blah... with appropriate disclaimers about it not needing to be economically feasible etc. Or not ;-) As a cautionary example for reference, you can see how poorly received my earnestly asked (and still compelling in my opinion) PrankSat question has been so far! – uhoh Feb 28 '18 at 05:15

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