Design problem # 1 - find a cable/net strong enough not to snap (impossible?)
Design problem # 2 - find a way to connect the cable/net to the ship so that it doesn’t tear out (impossible?)
#3 - find a way to keep the ship from falling apart when suddenly accelerated by 50,000 mph in an instant*
#4 - if there’s a crew - keep them from being turned to mush when they hit the back wall
#5 - etc.
An interesting idea, but remember that comets/asteroids can be a few miles across & travelling at incredible speeds (near the Earth anyway). That’s a LOT of momentum to catch.
Oncle Bière made a good point about the comets coma & tail being a problem to get around/through.
The net seems impossible given the size of a comet/asteroid. The harpoon would have to be able to latch on well enough to pull a massive ship (not easy to sink a harpoon into rock or ice).
- Of course, this assumes near-zero velocity compared to the comet/asteroid. I suppose you could have some closer relative velocity so it would be more of a velocity boost effect instead of a from-zero acceleration. But gravity assists (slingshots) by planets & moons seem more elegant & feasible.