There's at least one adventure where the PCs have to deal with a world killer asteroid bearing down on the planet and one of the potential twists is that it's being guided by another ship...
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Kurt Feltenberger
kurt@thepaw.org/kfeltenberger@yahoo.com
“Before today, I was scared to live, after today, I'm scared I'm not living enough." - Me
I just checked the only asteroid impact scenario I could think of William H Keith Jrs' "Critical Vector" from JTAS 20 and the idea of the asteroid being guided by someone else does not appear in it, one wonders how many other 'Armageddon' like scenarios there are?