Commercial space missions, colonies on Mars and finding a way for the tourists of the future to book round-trip flights to the Moon were among the out-of-this-world ideas being discussed by brainiacs yesterday at a Massachusetts Institute of Technology forum aimed at helping private companies get a foothold in what could be a budding multibillion dollar economy. The university’s second annual New Space Age Conference focused on getting out in front of the space race of the new millennium, which is being fueled by private companies looking to create and expand a brand new commercial market for space travel.