Doraemon Movie 29: Shin Nobita no Uchuu Kaitakushi

A dimensional passage opens beneath Nobita's room and connects it to the spacecraft of Ropple and Chammy. The young travelers come from Koya Koya, a low-gravity planet where Nobita's ordinary strength makes him seem heroic, but a mining corporation is driving the settlers from their homes to seize a valuable mineral.

Nobita and Doraemon use the hidden doorway to visit their new friends, unaware that shifting dimensions could close it permanently. When the corporation prepares to destroy the settlement, they must cross space one final time and defend a world whose people have nowhere else to go.