need help on a movie
 

I'm remembering a movie from the 80's, where 5 kids (elementry students) build a spaceship that miraculously works, and they fly to space, and there is a little green martian in their ship too. Appreciate any help.

EXPLORERS! it has ethan hawke and river phoenix in it...I used to love that movie as a child...haven thtought about it in a long time though.

http://www.imdb.com/title/tt0089114/