Titanium armor is our first crack at putting up defenses against mass drivers. Mass drivers are basically space-based bullets. That's an oversimplification since mass drivers are shot using a Hyperdrive assisted gun, so we are talking very, very fast bullets.
The only defense we have come up with so far is good old fashioned armor. Bullets go right through shields with only a modest impact and anti-missile defenses can only slow mass drivers down a bit. Armor is our best bet against the deadly mass driver weapons.