There is some level of debate over whether Luke 24 records The Ascension of Jesus to the right hand of the Father (as in Acts 1) or whether Luke 24 records a pre-figuring of The Ascension in Acts 1. Advocates of the latter argue that the account in Luke only gives us an example of Jesus disappearing in the post-resurrection days. Simply, Jesus–after the resurrection–goes from heaven to earth continuously.
It appears, however, that the accounts are the same. The Ascension account in Luke marks the end of Christ’s earthly work (it is finished!) In this case, the Ascension is tied to the Resurrection, which is tied to His death. In Acts 1, the Ascension is mentioned again because it marks the beginning of a new work; the mission of the Church. The Church’s missiological task works on the basis of the Ascension and exaltation of the Son at the right hand of the Father (Psalm 110).