You could always use another asteroid to deflect the one coming at you, like in this clip from futurama...
sorta in list of cost low to high 1) Solar collector 2) Satellites that provide ground based radar 3) GPS satellites that give better targeting...
Warp Gates, Gateways, Stargates, etc should be included. They were in TA but a balance for them could be high energy usages per mass sent and...
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