"It is now known that any prolonged human presence deeper in space would need to be behind a shield of the effective strength of two feet of lead, which would weigh 400 tonnes for a small capsule."<p>Uhm, the first thing that comes to my mind - regardless of whether this black hole propulsion might actually work - is the amount of lead we have available. Just building the spaceship seems to be just as much a problem as accelerating it..