My brother and I are going crazy trying to figure out the name of what we're sure was an 80's film. We vaguely remember it involves three kids (american) constructing a rocket with parts including a faiground waltzer car which they later use to travel into space. Sad I know but can anyone help?

Explorer

Had three american boys who built a rocket ship
Amazon.com: Explorers: Video: Ethan Hawke,River Phoenix,Bobby Fite,Bradley Gregg,Georg Olden,Chance Schwass,Amanda Peterson,Danny Nucci,Jason Presson,Dana Ivey,Taliesin Jaffe,James Cromwell,Brooke Bundy,Tricia Bartholome,Eric Luke,Robert Picardo,Kare