Dunno, there's helpful photons traveling from distant points through out stellar neighborhood and to any possible observer. We are already making 3D gravitatio

Dunno, there's helpful photons traveling from distant points through out stellar neighborhood and to any possible observer. We are already making 3D gravitation maps of our neighborhood. Also who says there's not some minor navigational control, much like today's smart bombs. Even minor corrections made well ahead of time could greatly help the aim. Not to mention if you are slinging probes into other solar systems you likely could send 1000x into each one, so if a few miss, not big deal.