This is in the correct ballpark. But 0.9c is crazy fast. [Expanse spoiler alert]
I love how they use this mechanic for storytelling in "The Expanse". The rebels of the belt threaten earth by slinging rocks at it at really high speed. Seems a very realistic way of interplanetary war. Why not bend some fast moving rocks to your enemy?
I don't know if it's been the first time in fiction where that concept was described but in Heinleins "The Moon is a harsh Mistress" this was what the Moon Colonists did.
I love how they use this mechanic for storytelling in "The Expanse". The rebels of the belt threaten earth by slinging rocks at it at really high speed. Seems a very realistic way of interplanetary war. Why not bend some fast moving rocks to your enemy?