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From: Martin Brown <'''newspam'''@nonad.co.uk>
Newsgroups: sci.electronics.design
Subject: Re: Earth-grazing asteroids as a military resource
Date: Wed, 5 Mar 2025 10:02:17 +0000
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On 04/03/2025 22:59, TTman wrote:
> On 04/03/2025 02:02, Bill Sloman wrote:
>> The latest New Scientist talks about asteroid 2024 YR4 being 
>> downgraded from a 1 in 32 chance of hitting Earth (the 17th February 
>> estimate) to a one in 25,000 chance on the 24th February.
>>
>> It's some where between 40 and 90 metres in diameter. Presumably there 
>> are more smaller asteroids (which will be harder to see).
>>
>> Eventually some military clown is going to get the idea finding a few 
>> of them and sending up stick-on ion drives, so that the earth-grazing 
>> orbits can be shifted into earth-impacting orbits.
>>
>> A couple of them hitting Russian occupied-areas of the Ukraine would 
>> upset Putin no end.
>>
> 
> Excellent suggestion.! Needs some clever maths calcs though...

Timing is everything in orbital dynamics.

The Earth is moving along it's orbit at 30km/s and the impactor is 
similar or possibly faster depending on its orbital parameters. IOW just 
a couple of minutes difference between a direct hit and a miss.

Its actually better than that since glancing impacts will skim off the 
upper atmosphere like a stone does off off a pond. And only iron or 
stone ones coming in at relatively steep angles get to reach the ground. 
Many are loose aggregates of ice and pebbles that disintegrate on entry.

One of those peppered part of France with stones just after their Royal 
Academy had declared conclusively that "Nothing ever falls from the sky"

https://en.wikipedia.org/wiki/L%27Aigle_(meteorite)

https://en.wikipedia.org/wiki/Jean-Baptiste_Biot#Meteorites

Earth also spins at 1000 mph at the equator which further complicates 
timing if you want to hit an actual specific coordinate on the globe.

Modern NEO surveys get most of the potential impactors in plenty of 
time. The ones that can sneak up on us tend to be dirty sooty black 
comet residues but even they can't hide from thermal infrared.

There is of course a catalogue of such objects:

https://theskylive.com/near-earth-objects

NASA's official site is broken at the moment.


-- 
Martin Brown