Doraemon: Nobita no Uchuu Kaitakushi(1981)

Doraemon: Nobita no Uchuu Kaitakushi

Nobita has been having a weird dream about a boy named Roppel and his strange companion Chami traveling in space. By a twist of fate, he met them in person where it turns out that they are real and that they were being pursued in space, causing their space vehicle to malfunction, connecting the space vehicle itself with Nobita's room. They journeyed to Roppel's planet and amidst their enjoyment, Nobita and Doraemon pledged to help Roppel's planet free from their oppressors.

(Source: Anime News Network)