NASA looking at 'hitchhiking' across solar system on speeding comets

If my harpoon allows me to accelerate/decelerate at 10g for 1 minute, I'd gain 5.9km/s. This requires a tether that's 176km long. That would be a pretty long tether; that can take a lot of weight.

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.