NASA looking at 'hitchhiking' across solar system on speeding comets(cnet.com)
cnet.com
NASA looking at 'hitchhiking' across solar system on speeding comets
http://www.cnet.com/uk/news/nasa-looking-at-hitchhiking-across-solar-system-on-speeding-comets/
But lunar orbit insertion requires a delta-v of only 2km/s. Maybe one day, on the far side of the moon there will be a great magnetic hook that space ships will shoot their harpoon at in order to quickly insert into moon's orbit.