If we are successfully populating Mars and mining the Asteroid belt, then it is a natural next step to start colonizing all the many moons of the outer planets, and building as many functioning bases as possible.
To begin we will need shielding on an extreme level, which will mean 100's if not 1000's of feet of rock etc......
Operational development will obviously be based on sending resources back to earth, and providing as needed materials to shield and fuel massive deep space interstellar colony ships.