The Collaborative International Dictionary of English v.0.48:

blastoff \blast"off`\ n.
   the launching of a rocket, especially of a spacecraft, under
   its own power.

   Syn: rocket firing, rocket launching, shoot.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

blastoff
    n 1: the launching of a missile or spacecraft to a specified
         destination [syn: blastoff, shot]