These all happen in the Saturday Supercade TV show. To read about other interactions in that show see Saturday Supercade links.
September 08, 1984
TV shows based on both series, called respectively Q*bert and Space Ace, were produced and aired together in the second season of Saturday Supercade. Additionally, since Q*bert aired right before Space Ace, the show also featured transition bumpers between the two, showing characters from both series meeting each other. Specifically in this case it shows Q*bert floating on his disk and unespectedly getting hit by Space Ace's spaceship with him and Kimberly on board. Q*bert ends up sitting on the ship with his nose flattened. Space Ace then opens the ship's glass and picks Q*bert's disk while he pulls out his nose. He then gets back on his disk and waves his hand as they fly away in space. (see the clip here: )
Ruby-Spears was licensed by the games' respective companies (Gottlieb and Cinematronics) to produce their cartoons. Once they got the license for both series there was nothing preventing them to make characters from both series appear together.