It was single file seating (not side by side). You could sit with one person in a seat, or two people could share the seat, with the smaller person sitting between the larger person's legs. Kind of like how you'd ride a two-person waterslide. There were grab handles in the inside walls of the car.

Whether you can sit "next" to someone on Space Mountain depends entirely on which Disney park you are visiting, as the ride vehicles are fundamentally different. At Walt Disney World (Magic Kingdom), the answer is no; the rockets feature single-file seating where each passenger has their own individual seat in a row of three. You sit in front of or behind your companions, but never side-by-side. However, at Disneyland (California), Disneyland Paris, and Hong Kong Disneyland, the answer is yes. These versions use vehicles where two passengers sit side-by-side in each row. For 2026 travelers, this is a major distinction for families with small children who might be nervous; if you want to hold your child's hand during the "blast off," you'll want to ride the California or Paris versions. The Magic Kingdom version, while more "classic" in its bumpy, single-file descent, offers a more solitary and intense feeling of flying through the dark, whereas the side-by-side versions are generally considered more "social" and technologically smooth.